The evolution of borneol repellency in culicine mosquitoes

Insects have developed remarkable adaptations to effectively interact with plant secondary metabolites and utilize them as cues to identify suitable hosts. Consequently, humans have used aromatic plants for centuries to repel mosquitoes. The repellent effects of plant volatile compounds are mediated through olfactory structures present in the antennae, and maxillary palps of mosquitoes. Mosquito maxillary palps contain capitate-peg sensilla, which house three olfactory sensory neurons, of which two are mainly tuned to either carbon dioxide or octenol - two animal host odorants. However, the third neuron, which expresses the OR49 receptor, has remained without a known ecologically-relevant odorant since its initial discovery. In this study, we used odorant mixtures and terpenoid-rich Cannabis essential oils to investigate the activation of OR49. Our results demonstrate that two monoterpenoids, borneol and camphor, selectively activate OR49, and OR9-expressing neurons, as well as the MD3 glomerulus in the antennal lobe. We confirm that borneol repels female mosquitoes, and knocking out the gene encoding the OR49 receptor suppresses the response of the corresponding olfactory sensory neuron. Importantly, this molecular mechanism of action is conserved across culicine mosquito species, underscoring its significance in their olfactory systems.

Large scale systemic control short-circuits pathogen transmission by interrupting the sand rat (Psammomys obesus)-to-sand fly (Phlebotomus papatasi) Leishmania major transmission cycle

Systemic control uses the vertebrate hosts of zoonotic pathogens as "Trojan horses," killing blood-feeding female vectors and short-circuiting host-to-vector pathogen transmission. Previous studies focused only on the effect of systemic control on vector abundance at small spatial scales. None were conducted at a spatial scale relevant for vector control and none on the effect of systemic control on pathogen transmission rates. We tested the application of systemic control, using Fipronil-impregnated rodent baits, in reducing Leishmania major (Kinetoplastida: Trypanosomatidae; Yakimoff & Schokhor, 1914) infection levels within the vector, Phlebotomus papatasi (Diptera: Psychodidae; Scopoli, 1786) population, at the town-scale. We provided Fipronil-impregnated food-baits to all Psammomys obesus (Mammalia:Muridae; Cretzschmar, 1828), the main L. major reservoir, burrows along the southern perimeter of the town of Yeruham, Israel, and compared sand fly abundance and infection levels with a non-treated control area. We found a significant and substantial treatment effect on L. major infection levels in the female sand fly population. Sand fly abundance was not affected. Our results demonstrate, for the first time, the potential of systemic control in reducing pathogen transmission rates at a large, epidemiologically relevant, spatial scale.

A next-generation (DNA) sequencing (NGS)-based method for identifying the sources of sugar meals in mosquito vectors of West Nile virus in Israel

Mosquitoes of the genus Culex comprise important vectors of pathogenic arboviruses in our region, including West Nile and Rift Valley Fever viruses. To improve our understanding of the epidemiology and transmission dynamics of arboviruses, we need to study the behavior and ecology of their vectors. The feeding patterns of the vector mosquitoes can be very useful in determining how and where to focus control efforts. For example, determining the preferred blood hosts of the females can assist in the implementation of potentially efficacious strategies for focused control of mosquito females. Determining the plants from which both sexes derive their sugar meals can comprise the initial step towards the formulation of efficient lures for trapping mosquitoes. In the past, plant meal identification was based mainly on chemical detection of fructose and microscopical observations of cellulose particles in mosquito guts. More recent studies have utilized DNA barcoding capable of identifying plant food sources. In the current study, we identify multiple plant species from which large numbers of mosquitoes obtained their sugar meals in one experimental procedure. We employed next generation DNA sequencing to sequence the chloroplast specific plant genes atpB and rbcL.

Effects of larval rearing substrates on some life-table parameters of Lutzomyia longipalpis sand flies

Sand flies are the insects responsible for transmitting Leishmania parasites, the causative agents of leishmaniasis in humans. However, the effects of sand fly breeding sites on their biology and ecology remain poorly understood. Herein, we studied how larval nutrition associated with putative breeding sites of the sand fly Lutzomyia longipalpis affects their oviposition, development, microbiome, and susceptibility to Leishmania by rearing L. longipalpis on substrates collected from an endemic area for leishmaniasis in Brazil. The results showed that female L. longipalpis select the oviposition site based on its potential to promote larval maturation and while composting cashew leaf litter hindered the development, larvae reared on chicken feces developed rapidly. Typical gut microbial profiles were found in larvae reared upon cashew leaf litter. Adult females from larvae reared on substrate collected in chicken coops were infected with Leishmania infantum, indicating that they were highly susceptible to the parasite. In conclusion, the larval breeding sites can exert an important role in the epidemiology of leishmaniasis.

Sand flies are the insect vectors involved in the transmission of many pathogens, however, the transmission of parasites to humans leading to visceral leishmaniasis is currently the most critical threat caused by this insect. Despite the importance of the vector, many aspects of the biology of sand flies are poorly understood, especially their breeding sites. This study was designed to evaluate the oviposition, life span, microbiome, and parasite infections in the main species of sand fly responsible for visceral leishmaniasis in America. Insects were reared on substrates collected from different putative habitats of sand flies in an endemic area for the disease in Brazil. The results showed that female vectors selected an oviposition site depending on the potential offered to their offspring. Furthermore, the development of immature stages varied according to the type of substrate evaluated, with cashew leaves litter delaying larval development, while chicken shelter promoted larval development. The challenge of females emerging from chicken shelter substrate with the parasite indicates that insects reared in such an environment could successfully sustain the infection. These results suggest that the type of breeding site can affect insect biology as well as the epidemiology of the disease.

Ecology of Leishmaniasis in an urbanized landscape: Relationship of sand fly densities, and Leishmania tropica infection rates with reservoir host colonies

Urbanization may influence the transmission of leishmaniasis, which is as a serious public health issue in Palestine. Semi urban environments can provide suitable habitats for the reservoir host species and the vector sand flies to create favorable condition for disease transmission. This study was aimed to evaluating the effect of distance from hyrax (reservoir host) colonies on sand fly (vector) abundance and its relationship to Leishmania infection within a semi urban landscape. In the Aleskan neighborhood the town of Tubas, sand flies were collected in July and September of 2016. Five trapping transects were set running from a rocky area containing hyrax dwelling habitats into an area of inhabited houses. 1051 Phlebotomus sand flies from 9 species were captured. The numbers of Phlebotomus sergenti, the vector species, correlated negatively with the distance from hyrax. Infected, blood engorged female sand flies were captured closer to hyrax colonies than infected, non-fed females. The risk of disease transmission to humans increased with a high density of reservoirs, closer proximity of reservoir hosts, and high densities of sand flies near houses. These results must be taken into account when implementing future interventions to reduce CL in urban environments.

The spatial and temporal distribution, species composition, and host preference of phlebotomine sand flies in the Bethlehem District of Palestine

In the Palestinian West Bank, leishmaniasis is emerging as a serious public health issue with incidence increasing over time, especially in the western and the northern parts. This study was aimed to evaluating the effect of altitude on sand fly density, temporal and spatial distribution, species composition, and host preference within and between three villages in the Bethlehem District. The three villages occur along an elevation cline, ranging from the disease-free area of Kisan (KIS; 732-782 m ASL), down to the endemic areas of Arab Ar-Rashaiyda (AAR; 522-568 m ASL), and Al'Azazma (AZA; 473-510 m ASL) in the Bethlehem District (southeastern West Bank). Sand flies were trapped monthly from May through October in 2013 in traps located north, south, east, and west of each village. The abundance of sand flies differed among the three villages, with Arab Ar-Rashaiyda (AAR) > Al 'Azazma (AZA) >Kisan (KIS). The sex ratio was even in AAR and AZA, and female biased in KIS. Both male and female Phlebotomus sand fly densities varied with elevation, with greatest densities found at intermediate elevations (AAR). Elevation correlated negatively with the proportion of blood-fed Phlebotomus females. Male Phlebotomus species composition differed among sites, with all the species found in this study present in AZA, while some species were absent from AAR and KIS. The host blood species engorged by P. sergenti were grouped in four categories: human (45.5%), livestock (25%), avian (19.9%), and dog (9.6%). This study provided information about the spatial and temporal distribution, age and species composition, and host preference of sand fly vectors that influence disease transmission. This information will allow us to better target sand flies, to control the disease, and to monitor risk prone areas.

Development of a next generation DNA sequencing-based multi detection assay for detecting and identifying Leishmania parasites, blood sources, plant meals and intestinal microbiome in phlebotomine sand flies

Leishmaniasis is a disease caused by Leishmania parasites transmitted by phlebotomine sand flies (Diptera: Psychodidae). Human infections with different Leishmania species cause characteristic clinical manifestations; cutaneous or visceral leishmaniasis. Here we describe the development and application of a Miseq Next GenerationSequencing (NGS)-based Multi Detection Assay (MDA) designed to characterize metagenomics parameters pertinent to the sand fly vectors which may affect their vectorial capacity for Leishmania. For this purpose, we developed a MDA by which, DNA fragments were amplified through polymerase chain reactions (PCR) and then sequenced by MiSeq/NGS. PCR amplification was achieved using some published and some new primers designed specifically for identifying Leishmania spp. (ITS1), sand fly spp. (cytochrome oxidase I), vertebrate blood (Cytochrome b), plant DNA ribulose-1,5-bisphosphate carboxylase large subunit gene (rbcL), and prokaryotic micobiome (16 s rRNA). This MDA/NGS analysis was performed on two species of wild-caught sand flies that transmit different Leishmania spp. in two ecologically distinct, but geographically neighboring locations. The results were analyzed to identify, quantitate and correlate the measured parameters in order to assess their putative importance in the transmission dynamics of leishmaniasis.

A molecular analysis of sand fly blood meals in a visceral leishmaniasis endemic region of northwestern Ethiopia reveals a complex host-vector system

Background

Visceral leishmaniasis (VL, or “kala-azar”) is a major cause of disability and death, especially in East Africa. Its vectors, sand flies (Diptera: Psychodidae: Phlebotominae), are poorly controlled and guarded against in these regions, owing in part to a lack of understanding about their feeding behavior.

Methods

A total of 746 freshly fed female sand flies were collected in five population centers in Kafta Humera (northwestern Ethiopia), where VL is endemic. Flies were collected from habitats that ranged from inside houses to open fields, using light traps and sticky traps. Sources of sand fly blood meals were identified using enzyme-linked immunosorbent assays (ELISA) and DNA amplification with reverse-line blot analysis (PCR-RLB); 632 specimens were screened using ELISA, 408 of which had identifiable blood meals, and 114 were screened using PCR-RLB, 53 of which yielded identifications. Fly species determinations were based on morphology, and those specimens subjected to PCR-RLB were also screened for Leishmania parasites using conventional PCR to amplify the nuclear marker ITS1 (internal transcribed spacer 1) with Leishmania-specific primers.

Results

More than three-fourths of all sand flies collected were Phlebotomus orientalis, and the remaining portion was comprised of nine other species. Nearly two-thirds of P. orientalis specimens were collected at village peripheries. The most common blood source for all flies was donkey (33.9% of all identifications), followed by cow (24.2%), human (17.6%), dog (11.8%), and goat or sheep (8.6%); mixtures of blood meals from different sources were found in 28.2% of all flies screened. Unidentified blood meals, presumably from wildlife, not domestic animals, were significantly higher in farm fields. Leishmania parasites were not detected in any of the 114 flies screened, not surprising given an expected infection rate of 1–5 out of 1,000. Meals that included a mixture of human and cow blood were significantly more frequent relative to all cow meals than human blood meals were to non-cow meals, suggesting a zoopotentiative interaction between cows and humans in this system.

Conclusions

Habitat and host preferences of sand fly vectors in Kafta Humera confirmed the finding of previous reports that the main vector in the region, Phlebotomus orientalis, is a highly opportunistic feeder that prefers large animals and is most commonly found at village peripheries. These results were similar to those of a previous study conducted in a nearby region (Tahtay Adiabo), except for the role of cattle on the prevalence of human blood meals. Preliminary examinations of blood meal data from different settings point to the need for additional surveys and field experiments to understand the role of livestock on biting risks.

Human antibody reaction against recombinant salivary proteins of Phlebotomus orientalis in Eastern Africa

Background

Phlebotomus orientalis is a vector of Leishmania donovani, the causative agent of life threatening visceral leishmaniasis spread in Eastern Africa. During blood-feeding, sand fly females salivate into the skin of the host. Sand fly saliva contains a large variety of proteins, some of which elicit specific antibody responses in the bitten hosts. To evaluate the exposure to sand fly bites in human populations from disease endemic areas, we tested the antibody reactions of volunteers' sera against recombinant P. orientalis salivary antigens.

Methodology/Principal findings

Recombinant proteins derived from sequence data on P. orientalis secreted salivary proteins, were produced using either bacterial (five proteins) or mammalian (four proteins) expression systems and tested as antigens applicable for detection of anti-P. orientalis IgG in human sera. Using these recombinant proteins, human sera from Sudan and Ethiopia, countries endemic for visceral leishmaniasis, were screened by ELISA and immunoblotting to identify the potential markers of exposure to P. orientalis bites. Two recombinant proteins; mAG5 and mYEL1, were identified as the most promising antigens showing high correlation coefficients as well as good specificity in comparison to the whole sand fly salivary gland homogenate. Combination of both proteins led to a further increase of correlation coefficients as well as both positive and negative predictive values of P. orientalis exposure.

Conclusions/Significance

This is the first report of screening human sera for anti-P. orientalis antibodies using recombinant salivary proteins. The recombinant salivary proteins mYEL1 and mAG5 proved to be valid antigens for screening human sera from both Sudan and Ethiopia for exposure to P. orientalis bites. The utilization of equal amounts of these two proteins significantly increased the capability to detect anti-P. orientalis antibody responses.

Hosts repeatedly bitten by phlebotomine sand flies develop species-specific antibody responses against certain sand fly salivary antigens. Salivary gland homogenate (SGH) is frequently used to evaluate the levels of this antibody response in host. However, SGH is less suitable for large-scale studies, since obtaining sufficient numbers of salivary glands is labor intensive and requires expertise in dissection. To replace SGH as antigen to screen for exposure to sand fly bites, specific recombinant salivary antigens were utilized. Our study assessed the human antibody reactions against recombinant salivary proteins of Phlebotomus orientalis. This sand fly species is a vector of Leishmania donovani, the causative agent of severe visceral leishmaniasis in Eastern Africa. To identify valid markers of exposure to P. orientalis in humans, we screened for anti-P. orientalis antibody responses in serum samples from individuals residing in Sudan and Ethiopia. We tested nine recombinant salivary antigens and found a combination of yellow-related protein (mYEL1) and antigen 5-related protein (mAG5) the best marker of exposure, accurately correlating with the levels of exposure to P. orientalis bites as determined using SGH. Thus the combination mYEL1+ mAG5 can comprise a useful epidemiological tool to determine levels of exposure to P. orientalis in populations living in endemic areas of Eastern Africa, which could help in monitoring the distribution of P. orientalis and therefore assessing suitable anti-vector campaigns.

A fine scale eco-epidemiological study on endemic visceral leishmaniasis in north ethiopian villages

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We conducted fine-scale eco-epidemiological analyses of factors associated with visceral leishmaniasis transmission.

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The population densities of Phlebotomus orientalis, the vector, were negatively correlated with distance from vertisols.

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Sero-positivity to Ph. orientalis saliva, was found in people living close to vertisol areas.

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Apparent clustering of infections indicates that transmission occurs around houses located close to vertisols.

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Our data suggest that asymptomatic individuals serve as reservoir hosts for anthroponotic transmission inside villages.

Visceral Leishmaniasis (VL) is a disseminated protozoan infection caused by Leishmania donovani that affects almost half a million people annually. In Northern Ethiopia, VL is common in migrant agricultural laborers returning from the lowland sesame fields of Metema and Humera. Recent VL foci have emerged in resident rural populations near the town. In the current study, we evaluate multilevel entomological, epidemiological and ecological factors associated with infection and disease through fine-scale eco-epidemiological analyses in three villages. Satellite images showed that villages constructed in or close to vertisols, were likely to become endemic for VL. Vertisols or black-cotton soil, are characterized by high contents of smectitic clay minerals, which swell when hydrated and shrink upon desiccation, causing extensive deep cracking during the dry season. The population densities of Phlebotomus orientalis, the vector, were negatively correlated with distance from vertisols and persons living close to vertisols were more likely to be bitten by sand flies, as evidenced by sero-positivity to Ph. orientalis saliva. Apparent (albeit non-significant) clustering of VL cases and abundant asymptomatic infections close to vertisols, suggest anthroponotic transmission around houses located close to vertisols. Comparable rates of male and female volunteers, mostly under 15 years of age, were infected with L. donovani but a significantly higher proportion of males succumbed to VL indicating a physiological gender-linked male susceptibility. Our data suggest that the abundant infected persons with high parasitemias who remain asymptomatic, may serve as reservoir hosts for anthroponotic transmission inside villages. Only limited insights on the transmission dynamics of L. donovani were gained by the study of environmental factors such as presence of animals, house structure and vegetation cover.

Studies on the behaviour and control of phlebotomine sandflies using experimental houses

Programmes for the control of phlebotomine sandflies (Diptera: Psychodidae), the vectors of leishmaniases, mainly target adults because larval breeding sites are generally unknown or inaccessible. To determine how blood-questing sandfly females enter homes and to develop means for their control, an experimental house (EH) was constructed in a village endemic for cutaneous leishmaniasis. Initially, carbon dioxide (CO₂ )-baited suction traps were installed inside the EH to attract and capture sandflies. For other experiments, the windows of the EH were fitted with CO₂ -baited window entrance traps (WETs) that allow each window to be considered as a separate unit. The majority of captures inside the EH and in WETs consisted of Phlebotomus sergenti, a species that enters inhabited houses relatively infrequently. Analyses of collections in WETs and in sticky traps on external walls showed that sandflies entered windows having landed previously on the wall below or either side of the window. Shelves constructed below windows significantly reduced the numbers of sandflies that entered both the EH and inhabited houses. The lining of internal walls with insecticide-impregnated fabric significantly increased mortality rates of sandflies captured inside the EH. To reduce the biting burden imposed by phlebotomine sandflies, several control measures must be integrated and sustained.

Genome wide comparison of Ethiopian Leishmania donovani strains reveals differences potentially related to parasite survival

Leishmania donovani is the main cause of visceral leishmaniasis (VL) in East Africa. Differences between northern Ethiopia/Sudan (NE) and southern Ethiopia (SE) in ecology, vectors, and patient sensitivity to drug treatment have been described, however the relationship between differences in parasite genotype between these two foci and phenotype is unknown. Whole genomic sequencing (WGS) was carried out for 41 L. donovani strains and clones from VL and VL/HIV co-infected patients in NE (n = 28) and SE (n = 13). Chromosome aneuploidy was observed in all parasites examined with each isolate exhibiting a unique karyotype. Differences in chromosome ploidy or karyotype were not correlated with the geographic origin of the parasites. However, correlation between single nucleotide polymorphism (SNP) and geographic origin was seen for 38/41 isolates, separating the NE and SE parasites into two large groups. SNP restricted to NE and SE groups were associated with genes involved in viability and parasite resistance to drugs. Unique copy number variation (CNV) were also associated with NE and SE parasites, respectively. One striking example is the folate transporter (FT) family genes (LdBPK_100390, LdBPK_100400 and LdBPK_100410) on chromosome 10 that are single copy in all 13 SE isolates, but either double copy or higher in 39/41 NE isolates (copy number 2-4). High copy number (= 4) was also found for one Sudanese strain examined. This was confirmed by quantitative polymerase chain reaction for LdBPK_100400, the L. donovani FT1 transporter homolog. Good correlation (p = 0.005) between FT copy number and resistance to methotrexate (0.5 mg/ml MTX) was also observed with the haploid SE strains examined showing higher viability than the NE strains at this concentration. Our results emphasize the advantages of whole genome analysis to shed light on vital parasite processes in Leishmania.

Diversity and altitudinal distribution of phlebotomine sand flies (Diptera: Psychodidae) in visceral leishmaniasis endemic areas of northwest Ethiopia

BACKGROUND

The Leishmaniases are caused by the protozoan parasites of the genus Leishmania and are transmitted to humans by the bite of infected female phlebotomine sand flies. Both visceral and cutaneous leishmaniases are widely distributed in different parts of Ethiopia. The aim of this study was to determine the diversity and altitudinal distribution of phlebotomine sand flies from Kafta Humera to Gondar town in northwest Ethiopia.

METHODS

Seven localities were selected with distinct altitudinal variations between 550m above sea level (m a.s.l) and 2300m a.s.l. In each locality, sand flies were collected using standard CDC light traps and sticky traps during the active sand fly season from December 2012 to May 2013. Shannon-Weiner species diversity index and Jaccard's coefficient were used to estimate species diversity and similarity between altitudes and localities, respectively.

RESULTS

A total of 89,044 sand flies (41,798 males and 47, 246 females) were collected from the seven localities/towns throughout the study period. Twenty-two species belonging to 11 species in the genus Phlebotomus and 11 species in the genus Sergentomyia were documented. Of these, Sergentomyia clydei (25.87%), S. schwetzi (25.21%), S. africana (24.65%), S. bedfordi (8.89%), Phlebotomus orientalis (6.43%), and S. antennata (4.8%) were the most prevalent species. The remaining 10 Phlebotomus species and six Sergentomyia were less frequent catches. In CDC light trap and sticky trap, higher species diversity and richness for both male and female sand flies was observed at low altitude ranging from 550 to 699m a.s.l in Adebay village in Kafta Humera district whereas low species richness and high evenness of both sexes were also observed in an altitude 1950-2300m a.s.l.

CONCLUSION

The results revealed that the presence of leishmaniasis vectors such as P. orientalis, P. longipes, P. papatasi, and P. duboscqi in different altitudes in northwest Ethiopia. P. orientalis a vector of L. donovani, occurred between altitude 500-1100m a.s.l, the area could be at high risk of VL. P. longipes a vector of L. aethiopica, was recorded in the highland area in Tikil-Dingay and Gondar town, implicating the possibility of CL transmission. Hence, further investigation into vector competence in relation to leishmaniasis (VL and CL) in the region is very vital.

Comparative study on the nocturnal activity of phlebotomine sand flies in a highland and lowland foci of visceral leishmaniasis in north-western Ethiopia with special reference to Phlebotomus orientalis

BACKGROUND

Leishmania donovani, the causative agent of visceral leishmaniasis (VL), is most probably vectored by Phlebotomus orientalis in north-western Ethiopia. The aim of this study was to determine and compare the nocturnal activity patterns of Ph. orientalis in VL endemic foci of Libo-Kemkem (highland) and Metema (lowland) districts of north-western Ethiopia.

METHODS

Sampling of sand flies was conducted bimonthly from January-May 2012 in the highland and from March-June 2013 in the lowland. Sand flies were sampled using two CDC light traps placed in compounds occupied by both cattle and humans. Sampling of sand flies started at 18:00 h and ended at 06:00 h. Every hour, a cage was replaced by another cage.

RESULTS

In total, 9479 nocturnally active sand flies were collected from both study areas. Six Phlebotomus species (Ph. orientalis, Ph. duboscqi, Ph. papatasi, Ph. bergeroti, Ph. rodhaini and Ph. martini) and several Sergentomyia spp. were identified. In both areas, of the six Phlebotomus spp., Ph. orientalis was the preponderate. In the highland, the hourly activity pattern of Ph. orientalis females was higher before midnight with a peak in density between 22:00-23:00 h, whereas in the lowland after midnight between 03:00-04:00 h.

CONCLUSIONS

The present study showed that Ph. orientalis females exhibited different nocturnal activity patterns with a peak in the early part of the night in the highland and in the latter part of the night in the lowland areas. As the risk of acquiring L. donovani infections vary in the two areas, appropriate control strategies should be developed according to the activity of Ph. orientalis in the respective areas.

Minimally invasive microbiopsies: a novel sampling method for identifying asymptomatic, potentially infectious carriers of Leishmania donovani

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Microbiopsy devices were designed to assess the infectiousness of asymptomatic Leishmania donovani carriers.

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The microbiopsy devices sample both skin tissues and blood, as do pool-feeding phlebotomine sand flies.

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Devices were tested on human volunteers in Ethiopia and proven effective, surpassing the sensitivity of finger-pricks.

Visceral leishmaniasis (VL) is a potentially lethal, sand fly-borne disease caused by protozoan parasites belonging to the Leishmania donovani species complex. There are several adequate methods for diagnosing VL, but the majority of infected individuals remain asymptomatic, comprising potential parasite reservoirs for transmission of the disease. The gold standard for assessing host infectiousness to biting vector insects is xenodiagnosis (i.e. scoring infection rates among insectary-reared insects that had fed on humans suspected of being infected). However, when it comes to sand flies and leishmaniasis, xenodiagnosis is an intricate operation burdened by logistical hurdles and ethical concerns that prevent its effective application for mass screening of widely dispersed communities, particularly in rural regions of underdeveloped countries. Minimally invasive microbiopsy (MB) devices were designed to penetrate the skin to a depth of ∼200 µm and absorb blood as well as skin cell lysates, mimicking the mode by which phlebotomine sand flies acquire blood meals, as well as their composition. MBs taken from 137 of 262 volunteers, living in endemic VL foci in Ethiopia, detected Leishmania parasites that could potentially be imbibed by feeding sand flies. Although the volume of MBs was 10-fold smaller than finger-prick blood samples, Leishmania DNA detection rates from MBs were significantly higher, implying that skin, more often than blood, was the source of parasites. Volunteers with histories of VL were almost as likely as healthy volunteers to test positive by MBs (southern Ethiopian focus: 95% CI: 0.35–2.59, P = 1.0. northern Ethiopian focus 0.87: 95% CI: 0.22–3.76, P = 1), suggesting the importance of asymptomatic patients as reservoirs of L. donovani. Minimally invasive, painless MBs should be considered for reliably and efficiently evaluating both L. donovani infection rates among large numbers of asymptomatic carriers and their infectiousness to blood-feeding sand flies.

Studies on sand fly fauna and ecological analysis of Phlebotomus orientalis in the highland and lowland foci of kala-azar in northwestern Ethiopia

BACKGROUND

Visceral leishmaniasis (VL) also known as kala-azar is a growing health problem in Ethiopia with an estimated annual VL incidence between 3700 and 7400. The disease is mainly endemic in northwestern parts of the country. The aim of the current study was to determine the sand fly fauna and ecology of Phlebotomus orientalis in two endemic and ecologically distinct areas of northwestern Ethiopia.

METHODS

Sand flies were collected using CDC light traps, sticky traps and pyrethrum spray catches from peri-domestic, mixed forest, farm field and indoor habitats from both Libo-Kemkem (May 2011-April 2012) and Metema (October 2012-September 2013) districts.

RESULTS

A total of 51,411 sand fly specimens were collected and identified (10,776 from highland and 40, 635 from the lowland areas). Seven species were found in the highland area: two Phlebotomus spp. (P. orientalis and P. rodhaini) and five Sergentomyia species. Whereas 19 species were found in the lowland area: six Phlebotomus (P. orientalis, P. rodhaini, P. bergeroti, P. duboscqi, P. papatasi and P. martini) and 13 Sergentomyia species. Of the Phlebotomus spp., P. orientalis was the predominant species in both the highland (99.9%) and lowland (93.7%) areas. Indoor collections using pyrethrum spray catches and sticky traps indicated that P. orientalis has a strong exophilic and exophagic behaviors in both districts. In both areas, this species showed seasonal occurrence and showing abundance during the dry months (March-May/June) of the year and increasing in numbers till the rain season, when numbers dropped dramatically. Mean density of P. orientalis in the two areas had positive and significant correlation with mean temperature in light trap collections (P<0.05). However, mean density of P. orientalis in the two areas in sticky trap collections had positive and insignificant association with the temperature (P>0.05). Regarding the rainfall pattern, density of P. orientalis had negative and statistically insignificant correlation (for light trap collections for both areas) and significant correlation (for sticky trap collections for lowland area).

CONCLUSIONS

The current study indicated the variation in sand fly fauna between the highland and lowland districts, wherein, P. orientalis was found to be the most abundant Phlebotomus species. The study also determined that P. orientalis exhibits distinct seasonality, where its abundance increases during the dry season and disappears when the rainy period starts in both study areas. This entomological observation on the bionomics of P. orientalis provides significant evidence for considering vector control or preventive measures in the areas studied.

Coinfection of Leishmania guyanensis and Human Immunodeficiency Virus-Acquired Immune Deficiency Syndrome: Report of a Case of Disseminated Cutaneous Leishmaniasis in Ecuador

AbstractReported herein is the first case of Leishmania-human immunodeficiency virus (HIV) coinfection in Ecuador. In Ecuador, HIV infections overlap endemic areas of leishmaniasis. Immunosuppression is a well-established risk factor for developing severe disease. This is a severe case of a 32-year-old man presenting with disseminated pleomorphic ulcers, papules, and cutaneous plaque-like lesions over his whole body. Numerous amastigotes were observed in both skin scrapings and biopsies. The sequence of the cytochrome b gene confirmed the presence of Leishmania guyanensis. The patient was treated but failed to respond to meglumine antimoniate and amphotericin B. Six months later, the patient died due to bacterial septic shock.

Habitat preference and seasonal dynamics of Phlebotomus orientalis in urban and semi-urban areas of kala-azar endemic district of Kafta Humera, northwest Ethiopia

Visceral leishmaniasis is a significant public health problem in northwest Ethiopia, particularly in Kafta Humera district. The study was designed to determine the species composition and population dynamics of sand flies in five villages representing urban and semi-urban areas of Kafta Humera district namely, Setit Humera, Mykadra, Rawyan, Bereket and Adebay. Sand flies were collected for two to three nights monthly from May 2011 to April 2012 using CDC light-traps and sticky traps. Traps were placed in villages, at periphery of villages and farm fields. Sticky traps were also used for sampling indoor active sand flies. In total, 13,097 sand fly specimens of eight Phlebotomus species and 91,949 Sergentomyia specimens were collected. Among the Phlebotomus, P. orientalis was the predominant species (58.1%) followed by P. papatasi (29.6%), P. lesleyae (5.6%), P. bergeroti (3.8%), P. duboscqi (2.1%), P. alexandri (0.4%), P. heischi (0.2%) and P. rodhaini (0.2%). Significantly, higher number of P. orientalis was caught in Adebay village and the least in Setit Humera town. Seasonal abundance of P. orientalis increased during the dry season (January-May) and dropped drastically in the wet season (late June-September). Significant positive correlation was found between monthly abundance of P. orientalis and the monthly average air and surface soil temperature, while a negative correlation was found with monthly average rainfall and relative humidity. Higher number of P. orientalis was collected outdoors, especially in the farm fields followed by periphery of villages. Thus, various observations strongly suggested P. orientalis to be the principal vector in the study areas, where farm lands and periphery of villages were identified as the most risky habitats, whereas the indoors were the least ones. Appropriate control methods should be designed and implemented according to the knowledge of P. orientalis habitat preferences and seasonal dynamics in the district.

Optimization of loop-mediated isothermal amplification (LAMP) assays for the detection of Leishmania DNA in human blood samples

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Three systems of loop-mediated isothermal amplification (LAMP) were developed for diagnosing leishmaniasis.

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The green nucleic acid stain, SYTO-16 was adapted for monitoring the reactions in real-time.

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The LAMP assays proved highly sensitive detecting >100Fg DNA/reaction.

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Leishmania DNA was detected in a significant number of asymptomatic individuals living in endemic areas.

Visceral leishmaniasis (VL), one of the most important neglected tropical diseases, is caused by Leishmania donovani eukaryotic protozoan parasite of the genus Leishmania, the disease is prevalent mainly in the Indian sub-continent, East Africa and Brazil. VL can be diagnosed by PCR amplifying ITS1 and/or kDNA genes. The current study involved the optimization of Loop-mediated isothermal amplification (LAMP) for the detection of Leishmania DNA in human blood or tissue samples. Three LAMP systems were developed; in two of those the primers were designed based on shared regions of the ITS1 gene among different Leishmania species, while the primers for the third LAMP system were derived from a newly identified repeated region in the Leishmania genome. The LAMP tests were shown to be sufficiently sensitive to detect 0.1 pg of DNA from most Leishmania species. The green nucleic acid stain SYTO16, was used here for the first time to allow real-time monitoring of LAMP amplification. The advantage of real time-LAMP using SYTO 16 over end-point LAMP product detection is discussed. The efficacy of the real time-LAMP tests for detecting Leishmania DNA in dried blood samples from volunteers living in endemic areas, was compared with that of qRT-kDNA PCR.

Recombinant Salivary Proteins of Phlebotomus orientalis are Suitable Antigens to Measure Exposure of Domestic Animals to Sand Fly Bites

Background

Certain salivary proteins of phlebotomine sand flies injected into the host skin during blood-feeding are highly antigenic and elicit strong antibody-mediated immune responses in repeatedly-exposed hosts. These antibodies can be measured by enzyme-linked immuno sorbent assays (ELISAs) using salivary gland homogenates (SGHs) as the source of antigens and serve as a markers for exposure to biting sand flies. Large-scale screening for anti-sand fly saliva antibodies requires replacement of SGH with recombinant salivary proteins. In East Africa, Phlebotomus orientalis is the main vector of Leishmania donovani, a trypanosomatid parasite causing visceral leishmaniasis. We tested recombinant salivary proteins derived from Ph. orientalis saliva to study exposure of domestic animals to this sand fly species.

Methodology/Principal Findings

Antigenic salivary proteins from Ph. orientalis were identified by immunoblot and mass spectrometry. Recombinant apyrase rPorSP15, yellow-related protein rPorSP24, ParSP25-like protein rPorSP65, D7-related protein rPorSP67, and antigen 5-related protein rPorSP76 were tested using ELISA with sera of domestic animals from L. donovani foci in Ethiopia where Ph. orientalis is present. Our results highlighted recombinant yellow-related protein rPorSP24 as the most promising antigen, displaying a high positive correlation coefficient as well as good sensitivity and specificity when compared to SGH. This recombinant protein was the most suitable one for testing sera of dogs, sheep, and goats. In addition, a different antigen, rPorSP65 was found efficacious for testing canine sera.

Conclusions/Significance

Recombinant salivary proteins of Ph. orientalis, specifically rPorSP24, were shown to successfully substitute SGH in serological experiments to measure exposure of domestic animals to Ph. orientalis, the vector of L. donovani. The results suggest that rPorSP24 might be a suitable antigen for detecting anti-Ph. orientalis antibody-mediated reactions also in other host species.

The sand fly Phlebotomus orientalis is the main vector of Leishmania donovani, the causative agent of visceral leishmaniasis in East Africa. During bloodfeeding, sand flies inject saliva into the host skin and repeated bites result in a specific antibody response in the bitten hosts. Antibody responses are directed against sand fly salivary proteins and the levels of these antibodies reflect the intensity of exposure to biting sand flies. The antibody reactions can be measured using salivary gland homogenates (SGHs), but for large-scale testing its use is impractical because of the amount of work required to obtain sufficient quantities of SGH. Recombinant proteins prepared based on the antigens in the sand fly saliva can substitute whole SGH in large-scale studies. We tested five recombinant proteins from Ph. orientalis saliva expressed in Escherichia coli and demonstrated that the yellow-related protein rPorSP24 can replace the SGH in estimating exposure to sand flies of dogs, goats, and sheep in Ethiopia. Immune reactions to vector saliva in endemic areas, provides useful information on levels of exposure and, thereby, on the effectiveness of vector control programs.

Zoonotic disease in a peripheral population: persistence and transmission of Leishmania major in a putative sink-source system in the Negev Highlands, Israel

Populations at the edge of their geographic distributions are referred to as peripheral populations. Very little attention has been given to this topic in the context of persistence of infectious disease in natural populations. In this study, we examined this question using zoonotic cutaneous leishmaniasis (ZCL) caused by Leishmania major in the Negev Desert of Israel as a model system. Here, we suggest that the regional persistence of Phlebotomus papatasi populations and L. major transmission in the Sede Boqer region could be explained through processes akin to sink-source and/or mainland-island metapopulation dynamics. Given its potentially enzootically superior ecological conditions, we hypothesize that the Zin Valley ecotope constitutes the "mainland" or the "source" patch for the Sede Boqer area where L. major transmission is persistent and resistant to local extinctions (die-outs) whereas the local sand fly populations on the Zin Plateau ("island patch" or "sink patch") are more prone to local extinctions. Between 2007 and 2008, we trapped sand flies and sand rats in the two areas and compared sand fly abundance and L. major infection prevalence in both. In both 2007 and 2008, sand fly abundance was high and continuous in the Zin Wadi but low and discontinuous in the Zin Plateau. Infection prevalence of sand rats was significantly higher in the Wadi (13%) compared with the Zin Plateau (3%). Minimum infection rate in sand flies did not differ significantly between the two areas. Overall, our results are consistent with the premise that the Zin Valley population is relatively robust in terms of L. major transmission, whereas transmission is potentially more tenuous in the plateau. Understanding the biotic and abiotic processes enabling the persistence of L. major and other vector-borne diseases in peripheral disease foci is important for predicting the effect of anthropogenic land use and climate change.

Natural infection of bats with Leishmania in Ethiopia

The leishmaniases, a group of diseases with a worldwide-distribution, are caused by different species of Leishmania parasites. Both cutaneous and visceral leishmaniasis remain important public health problems in Ethiopia. Epidemiological cycles of these protozoans involve various sand fly (Diptera: Psychodidae) vectors and mammalian hosts, including humans. In recent years, Leishmania infections in bats have been reported in the New World countries endemic to leishmaniasis. The aim of this study was to survey natural Leishmania infection in bats collected from various regions of Ethiopia. Total DNA was isolated from spleens of 163 bats belonging to 23 species and 18 genera. Leishmania infection was detected by real-time (RT) PCR targeting a kinetoplast (k) DNA and internal transcribed spacer one (ITS1) gene of the parasite. Detection was confirmed by sequencing of the PCR products. Leishmania kDNA was detected in eight (4.9%) bats; four of them had been captured in the Aba-Roba and Awash-Methara regions that are endemic for leishmaniasis, while the other four specimens originated from non-endemic localities of Metu, Bedele and Masha. Leishmania isolates from two bats were confirmed by ITS1 PCR to be Leishmania tropica and Leishmania major, isolated from two individual bats, Cardioderma cor and Nycteris hispida, respectively. These results represent the first confirmed observation of natural infection of bats with the Old World Leishmania. Hence, bats should be considered putative hosts of Leishmania spp. affecting humans with a significant role in the transmission.

Exposure to Leishmania spp. and sand flies in domestic animals in northwestern Ethiopia

Background

Human visceral leishmaniasis caused by Leishmania donovani is considered an anthroponosis; however, Leishmania-infected animals have been increasingly reported in L. donovani foci, and the role of these animals as reservoirs for human L. donovani infection remains unclear.

Methods

We conducted a study of domestic animals (goats, sheep, cows, dogs, and donkeys) in three L. donovani foci in northwestern Ethiopia. Domestic animals were screened for Leishmania DNA and for anti-L. donovani IgG. Serum anti-sand fly saliva antibodies were used as a marker of exposure to the vector sand fly, Phlebotomus orientalis.

Results

Of 546 animals tested, 32 (5.9 %) were positive for Leishmania DNA, with positive animals identified among all species studied. Sequencing indicated that the animals were infected with parasites of the L. donovani complex but could not distinguish between L. infantum and L. donovani. A total of 18.9 % of the animals were seropositive for anti-L. donovani IgG, and 23.1 % of the animals were seropositive for anti-P. orientalis saliva IgG, with the highest seroprevalence observed in dogs and sheep. A positive correlation was found between anti-P. orientalis saliva and anti-L. donovani IgGs in cows, goats, and sheep.

Conclusions

The detection of L. donovani complex DNA in the blood of domestic animals, the reported seroprevalence to the L. donovani antigen, and the widespread exposure to sand fly saliva among domestic animals indicate that they are frequently exposed to Leishmania infection and are likely to participate in the epidemiology of Leishmania infection, either as potential blood sources for sand flies or possibly as parasite hosts.

Electronic supplementary material

The online version of this article (doi:10.1186/s13071-015-0976-1) contains supplementary material, which is available to authorized users.

Estimation of infection prevalence and sensitivity in a stratified two-stage sampling design employing highly specific diagnostic tests when there is no gold standard

In this work, we describe a two-stage sampling design to estimate the infection prevalence in a population. In the first stage, an imperfect diagnostic test was performed on a random sample of the population. In the second stage, a different imperfect test was performed in a stratified random sample of the first sample. To estimate infection prevalence, we assumed conditional independence between the diagnostic tests and develop method of moments estimators based on expectations of the proportions of people with positive and negative results on both tests that are functions of the tests' sensitivity, specificity, and the infection prevalence. A closed-form solution of the estimating equations was obtained assuming a specificity of 100% for both tests. We applied our method to estimate the infection prevalence of visceral leishmaniasis according to two quantitative polymerase chain reaction tests performed on blood samples taken from 4756 patients in northern Ethiopia. The sensitivities of the tests were also estimated, as well as the standard errors of all estimates, using a parametric bootstrap. We also examined the impact of departures from our assumptions of 100% specificity and conditional independence on the estimated prevalence.

Host-feeding preference of Phlebotomus orientalis (Diptera: Psychodidae) in an endemic focus of visceral leishmaniasis in northern Ethiopia

Background

Blood-feeding behavior studies are important for estimating the efficiency of pathogen transmission and assessing the relative human disease risk. However, in Ethiopia and other parts of East Africa there are large remaining gaps in identifying the feeding habits of Phlebotomus orientalis, the vector of Leishmania donovani. The aim of the study was to determine the blood feeding patterns of P. orientalis in Tahtay Adiyabo district, northern Ethiopia.

Methods

For bloodmeal analysis, sandflies were collected from three different villages of Tahtay Adiyabo district using CDC light traps, sticky traps, and pyrethrum spray catches. Bloodmeal of engorged female sandflies was identified using cytochrome (cyt) b-PCR and reverse-line blotting (RLB) and enzyme linked immunosorbent assay (ELISA) assays.

Results

Most (637/641) of the females analyzed were P. orientalis. Successful identification of the host from bloodmeals was achieved in 83.03 and 92.1 % using cyt b PCR-RLB and ELISA, respectively. Bloodmeal analysis of P. orientalis females revealed that they have a range of hosts with predominant preference to bovines followed by donkey, human, goat, sheep, dog, and camel.

Conclusion

Results obtained from bloodmeal analyses demonstrate that the feeding preference of P. orientalis is mainly zoophilic, which could vary depending on the availability of hosts.

Detection of Leishmania donovani and L. tropica in Ethiopian wild rodents

Human visceral (VL, also known as Kala-azar) and cutaneous (CL) leishmaniasis are important infectious diseases affecting countries in East Africa that remain endemic in several regions of Ethiopia. The transmission and epidemiology of the disease is complicated due to the complex life cycle of the parasites and the involvement of various Leishmania spp., sand fly vectors, and reservoir animals besides human hosts. Particularly in East Africa, the role of animals as reservoirs for human VL remains unclear. Isolation of Leishmania donovani parasites from naturally infected rodents has been reported in several endemic countries; however, the status of rodents as reservoirs in Ethiopia remains unclear. Here, we demonstrated natural Leishmania infections in rodents. Animals were trapped in 41 localities of endemic and non-endemic areas in eight geographical regions of Ethiopia and DNA was isolated from spleens of 586 rodents belonging to 21 genera and 38 species. Leishmania infection was evaluated by real-time PCR of kinetoplast (k)DNA and confirmed by sequencing of the PCR products. Subsequently, parasite species identification was confirmed by PCR and DNA sequencing of the 18S ribosomal RNA internal transcribed spacer one (ITS1) gene. Out of fifty (8.2%) rodent specimens positive for Leishmania kDNA-PCR and sequencing, 10 were subsequently identified by sequencing of the ITS1 showing that five belonged to the L. donovani complex and five to L. tropica. Forty nine kDNA-positive rodents were found in the endemic localities of southern and eastern Ethiopia while only one was identified from northwestern Ethiopia. Moreover, all the ten ITS1-positive rodents were captured in areas where human leishmaniasis cases have been reported and potential sand fly vectors occur. Our findings suggest the eco-epidemiological importance of rodents in these foci of leishmaniasis and indicate that rodents are likely to play a role in the transmission of leishmaniasis in Ethiopia, possibly as reservoir hosts.

Species composition of phlebotomine sand flies and bionomics of Phlebotomus orientalis (Diptera: Psychodidae) in an endemic focus of visceral leishmaniasis in Tahtay Adiyabo district, Northern Ethiopia

Background

Visceral leishmaniasis (VL) is a neglected tropical disease, which is strongly associated with poverty. VL caused by Leishmania donovani and transmitted by Phlebotomus orientalis is endemic in various remote areas of north and north-west Ethiopia. The present study was designed to determine the sand fly fauna and bionomics of P. orientalis in the VL endemic focus of Tahtay Adiyabo district.

Methods

Sand flies were collected using CDC light traps (n = 602), sticky traps (n = 9,350) and indoor pyrethrum spray catches (n = 578 house visits) from indoor, peri-domestic and agricultural field habitats between May 2011 to April 2012. All sand fly specimens collected were identified to species level and counted.

Results

In total, 100,772 sand fly specimens, belonging to 25 sand fly species (nine Phlebotomus and sixteen Sergentomyia) were collected and identified. S. africana and P. orientalis made up 59.1% and 23.5% of the collected sand flies, respectively. As it could be determined from the proportion of collections from outdoor (peri-domestic and agricultural fields) and indoor locations, P. orientalis appears to exhibit increased exophilic behavior. The outdoor to indoor index was 79:1 on m² of sticky traps. Mean density of P. orientalis caught was significantly higher on horizontally placed sticky traps (mean = 60 ± 14.56/m²/night) than vertically deployed sticky traps (12 ± 3.57/m²/night). The highest abundance of P. orientalis occurred between March and April. Through July to September, there was a sharp decline in abundance of P. orientalis population. Regarding climatic variables, P. orientalis density in light traps and on sticky traps showed a significant positive and negative association with temperature and relative humidity, respectively. However, non-significant negative correlation was observed with rainfall pattern.

Conclusions

Overall, P. orientalis was found to be the most abundant Phlebotomus species, showing marked seasonal abundance that mainly peaks during the dry season (March to April). Likewise, the people in the area usually sleep in compounds during these months that potentially expose them to a high risk of peri-domestic VL transmission.

Host choice of Phlebotomus orientalis (Diptera: Psychodidae) in animal baited experiments: a field study in Tahtay Adiyabo district, northern Ethiopia

Background

Host choice and feeding success of sand fly vectors of visceral leishmaniasis (VL) are important factors in understanding the epidemiology and for developing efficient control strategies. The aim of the present study was to determine the host preference of Phlebotomus orientalis in the VL focus of Tahtay Adiyabo district, northern Ethiopia.

Methods

Two separate experiments were conducted testing attraction of P. orientalis to humans, domestic animals, and small wild animals. The host choice of P. orientalis and other sand fly species was assessed using tent traps baited with seven different animals (human, cow, sheep, goat, donkey, dog and chicken) and a blank control. Baited traps were rotated every night in a Latin square design for two consecutive full rounds totaling 16 trap-nights. The second set of experiments tested attraction to small wild animals including; ground squirrel (Xerus rutilus), hare (Lepus sp.), gerbil (Tatera robusta) and spiny mouse (Acomys cahirinus). Animals were caged in standard rodent traps or cylindrical wire-mesh cages. The bait animals were placed in agricultural field and the attracted sand flies were collected using unlit CDC traps for 10 trapping nights. Sand fly specimens collected from each of the experiments were identified to species level and counted.

Results

Significant difference (P < 0.05) was observed in the attraction and feeding rate of P. orientalis to different baits. In the first experiment, cow-baited tent traps attracted the highest mean number of P. orientalis (mean = 510 flies). The engorgement rate of P. orientalis on donkey was the highest followed by cow, and much lower on goat, sheep, dog and chicken. In the case of smaller wild animals, more numbers of P. orientalis females were attracted to squirrels followed by hares, gerbils and the spiny rat. However, the engorgement rates for P. orientalis in the smaller animals were very low (1.08%) compared with larger domestic animals (30.53%).

Conclusion

The tendency of female P. orientalis to engorge in large numbers on certain species of domestic as well as wild animals strongly indicated that the species is primarily zoophilic in its host preference with feeding habits that may vary depending on the availability of hosts.

Nocturnal periodicity of Phlebotomus (Larroussius) orientalis (Diptera: Psychodidae) in an endemic focus of visceral leishmaniasis in Northern Ethiopia

BACKGROUND

Phlebotomus orientalis is the major vector of the intramacrophage protozoa, Leishmania donovani, the etiological agent of visceral leishmaniasis (VL) in northern Ethiopia and Sudan. The objective of this study was to determine the nocturnal periodicity of P. orientalis in the VL endemic focus of Tahtay Adiyabo district, northern Ethiopia.

METHODS

Sandflies were collected using CDC light traps by changing collecting bags at an hourly interval from dusk to dawn for six months (January-June 2013) from outdoors (i.e. peri-domestic and agricultural fields). Sandfly specimens collected in the study were identified to species level and counted.

RESULTS

In total, 21,716 nocturnally active sandfly specimens, which belong to two genera (i.e., Phlebotomus and Sergentomyia) were collected and identified. In the collection, P. orientalis, the dominant species in the genus Phlebotomus, constituted 33.79% while Sergentomyia spp. comprised 65.44%. Analysis of data showed that activity of P. orientalis females increased from 18:00 to 24:00 hours, with a peak after midnight (24:00-03:00 hrs). Likewise, activity of parous P. orientalis females was found to be unimodal, peaking at 24-01:00 hrs.

CONCLUSION

P. orientalis females had marked nocturnal activity, which peak after midnight. Similarly, the epidemiologically dangerous parous females generally were more active after midnight. Therefore, humans are at risk of L. donovani infections through the bite of P. orientalis possibly between midnight and dawn.

Xenodiagnosis of Leishmania donovani in BALB/c mice using Phlebotomus orientalis: a new laboratory model

Background

In areas endemic for visceral leishmaniasis (VL), the majority of infected hosts remain asymptomatic but potentially infectious to biting sand flies. Their infectiousness for sand fly vectors is crucial for the transmission of the disease and can be quantified only by xenodiagnosis. However, in the case of human hosts, xenodiagnosis can be problematic for ethical and logistic reasons. The BALB/c mouse model described in this paper was designed to enable xenodiagnostic studies on VL hosts circumventing the need for human volunteers, it permits xenodiagnosis using the same individual host repeatedly, over several months.

Methods

BALB/c mice were intradermally inoculated in the ear pinnae with Leishmania donovani, primarily metacyclic stages isolated from the thoracic midguts of experimentally-infected Phlebotomus orientalis females. Naïve sand flies were allowed to feed on anaesthetized mice in 1-3-weeks- interval, firstly on the site of inoculation of L. donovani (weeks 2–8 post infection, p.i.), later on the whole body of mice (weeks 9 – 15 p.i.). Infections of sand flies were evaluated microscopically or by PCR analysis.

Results

Although infected mice did not show any signs of disease, 19% (N = 876) of the P. orientalis females that fed at the site of inoculation, became infected. The majority of L. donovani-positive females (76%) had heavy infections with their stomodeal valves colonized by attached parasites. Inoculated mouse ears remained infective for sand flies until week 15 p.i. Females feeding on other parts of the body remained negative with exception of two groups feeding on contralateral ears by week 12 p.i. On week 15, however, these two mice returned negative at xenodiagnosis of the contralateral ears. In sacrificed mice, the highest parasite numbers were found in inoculated ears and their draining lymph nodes. Infections were detected also in the spleen, liver, blood and rarely in the contralateral ear.

Conclusions

The study showed that BALB/c mice harbored parasites in sufficient numbers to promote heavy infections in P. orientalis and thus comprised a suitable laboratory model for xenodiagnoses of L. donovani. Parasites persisted in the inoculation site and were found transmissible for months to sand flies biting on the same site.

Recent advances in phlebotomine sand fly research related to leishmaniasis control

Phlebotomine sand flies are the subject of much research because of the role of their females as the only proven natural vectors of Leishmania species, the parasitic protozoans that are the causative agents of the neglected tropical disease leishmaniasis. Activity in this field was highlighted by the eighth International Symposium on Phlebotomine Sand flies (ISOPS) held in September 2014, which prompted this review focusing on vector control. Topics reviewed include: Taxonomy and phylogenetics, Vector competence, Genetics, genomics and transcriptomics, Eco-epidemiology, and Vector control. Research on sand flies as leishmaniasis vectors has revealed a diverse array of zoonotic and anthroponotic transmission cycles, mostly in subtropical and tropical regions of Africa, Asia and Latin America, but also in Mediterranean Europe. The challenge is to progress beyond descriptive eco-epidemiology, in order to separate vectors of biomedical importance from the sand fly species that are competent vectors but lack the vectorial capacity to cause much human disease. Transmission modelling is required to identify the vectors that are a public health priority, the ones that must be controlled as part of the integrated control of leishmaniasis. Effective modelling of transmission will require the use of entomological indices more precise than those usually reported in the leishmaniasis literature.

Sero-prevalence of Leishmania donovani infection in labour migrants and entomological risk factors in extra-domestic habitats of Kafta-Humera lowlands - kala-azar endemic areas in the northwest Ethiopia

Background

Visceral leishmaniasis (VL) or kala-azar cases in seasonal labour migrants from highland areas are addressed to travel history to the Metema–Humera lowlands, northwestern Ethiopia. Factors that affect the incidence of VL in extra-domestic habitats were not evaluated. The aim of this study was to evaluate sero-prevalence of Leishmania donovani infection in randomly selected labour migrant workers and entomological risk factors which might affect the incidence of kala-azar.

Methods

Sero-prevalence of L. donovani infection in labour migrants was obtained from Direct Agglutination Test (DAT) using blood samples. Logistic regression analysis was used to correlate the possible risk factors with L. donovani infection. The season for L. donovani infection or Phlebotomus orientalis bite was estimated from the study of population dynamic of P. orientalis in areas where the blood was sampled.

Result

A total of 7, 443 P. orientalis (1,748 female and 5,695 male) were collected from agricultural fields and thickets of Acacia seyal using 461 CDC light traps. The highest mean number of P. orientalis/trap in the thickets of A. seyal and agricultural fields were 46.9 and 43.9 in March and April respectively. The mean P. orientalis/trap for November – May dry season in agricultural fields (11.39) and thickets of A. seyal (25.30) were higher compared to 0.66 in fields and 3.92 in thickets during June – August weeding season. Of the total 359 labour migrants screened using DAT, 45 (12.5%) were DAT-positive (≥1:800) for L. donovani infections. Very high titers (1:12800) were found in 3 (0.8%) individuals who had the risk of kala-azar development. Statistically significant p-values and odd ratio (OR) for staying in the areas both in the weeding and harvesting seasons (p = 0.035; OR = 2.83) and sleeping in the agricultural fields (p = 0.01; OR = 15.096) were positively correlated with L. donovani infection. Night harvest (p = 0.028; OR = 0.133) and knowledge about sign or symptoms (p = 0.042; OR = 0.383) were negatively associated with this infection.

Conclusions

Sleeping in open agricultural fields was related with L. donovani infections in labour migrants during June-August weeding season.

The influence of moonlight and lunar periodicity on the efficacy of CDC light trap in sampling Phlebotomus (Larroussius) orientalis Parrot, 1936 and other Phlebotomus sandflies (Diptera: Psychodidae) in Ethiopia

BACKGROUND

Phlebotomus orientalis is the main sandfly vector of visceral leishmaniasis in the north and northwest of Ethiopia. CDC light traps and sticky traps are commonly used for monitoring sandfly populations. However, their trapping efficiency is greatly influenced by various environmental factors including moonlight and lunar periodicity. In view of that, the current study assessed the effect of moonlight and lunar periodicity on the performance of light traps in collecting P. orientalis.

METHODS

Trapping of P. orientalis and other Phlebotomus spp. was conducted for 7 months between December 2012 and June 2013 using CDC light traps and sticky traps from peri-domestic and agricultural fields. Throughout the trapping periods, collections of sandfly specimens were carried out for 4 nights per month, totaling 28 trapping nights that coincided with the four lunar phases (viz., first quarter, third quarter, new and full moon) distributed in each month.

RESULTS

In total, 13,533 sandflies of eight Phlebotomus species (P. orientalis, P. bergeroti, P. rodhaini, P. duboscqi, P. papatasi, P. martini, P. lesleyae and P. heischi) were recorded. The predominant species was P. orientalis in both trapping sites and by both methods of collection in all lunar phases. A significant difference (P < 0.05) was observed in the mean numbers of P. orientalis and other Phlebotomus spp. caught by CDC light traps among the four lunar phases. The highest mean number (231.13 ± 36.27 flies/trap/night) of P. orientalis was collected during the new moon phases, when the moonlight is absent. Fewer sandflies were attracted to light traps during a full moon. However, the number of P. orientalis and the other Phlebotomus spp. from sticky traps did not differ in their density among the four lunar phases (P = 0.122).

CONCLUSION

Results of the current study demonstrated that the attraction and trapping efficiency of CDC light traps is largely influenced by the presence moonlight, especially during a full moon. Therefore, sampling of sandflies using light traps to estimate population density and other epidemiological studies in the field should take the effect of moonlight and lunar periodicity into account on the trapping efficacy of light traps.

Nocturnal activities and host preferences of Phlebotomus orientalis in extra-domestic habitats of Kafta-Humera lowlands, Kala-azar endemic, Northwest Ethiopia

Background

Phlebotomus orientalis feeds on a variety of wild and domestic animals and transmits Leishmania donovani from hitherto unknown reservoir hosts to humans in extra-domestic habitats in the Metema - Humera lowlands. The aim of this study was to determine the nocturnal activities of P. orientalis and its preferred blood meal hosts.

Methods

Collections of Phlebotomus orientalis were made by using CDC light traps to determine the density as P. orientalis/hour CDC trap and preference to rodents by using Turner’s traps in agricultural fields, animal shelters and thickets of Acacia seyal in Baeker site-1 and Gelanzeraf site-2. The blood meal sources were detected by Reverse Line Blot (RLB) of cytochrome b polymerase chain reaction (PCR) amplification in August, 2012 from collections of sand flies in thickets of A. seyal (March 2011) and dense mixed forest (July 2011) in Baeker site 1. RLB PCR involved first amplification of animal specific sequences of cytochrome b using PCR techniques. Then the amplified sequence was hybridized with 11 species-specific probes for domestic animals adsorbed on nitrocellulose membrane for calorimetric color detection.

Results

A total of 6,083 P. orientalis (2,702 males and 3,381 females) were collected at hourly intervals using 22 CDC traps from January to May 2013. The peak activities of P. orientalis were at 1.00 a.m (134.0 ± 7.21) near animal shelters, 3.00 a.m (66.33 ± 46.40) in agricultural fields and 21:00 pm (40.6 ± 30.06) in thickets of A. seyal. This species was not attracted to the different species of rodents in trials carried out in March and April 2013. RLB PCR identified 7 human (28%), 9 mixed (human and cattle) (36%) and 2 cattle (8%) blood meals while 7 were unknown (28%).

Conclusion

Female P. orientalis can bite humans in extra-domestic habitats of Kafta-Humera lowlands at any hour of the night with peak biting after midnight.

Characterization of breeding sites of Phlebotomus orientalis - the vector of visceral leishmaniasis in northwestern Ethiopia

We studied breeding sites of Phlebotomus orientalis (Diptera: Psychodidae) the vector of visceral leishmaniasis in northern Ethiopia. Although numbers were rather small, 165 sand flies were captured emerging from vertisol cracks. The most productive breeding sites were cracked vertisols, dry river banks and close to trees. No sand flies were caught emerging from sandy clay loam soils in peri-domestic habitats but a few were captured emerging from gaps in a stone wall. Abiotic parameters in vertisols close to trees and in open field from which P. orientalis had emerged, were compared. Soil pH was slightly alkaline and salinity was low. Organic matter contents were similar in both sites. Temperatures and RH remained relatively stable near trees from the end of the rainy season through mid dry season, yet fluctuated markedly at the shallower depth in the open field. During the rainy season, cracks in the soil were sealed resulting in significant lowering of the oxygen concentrations near the tree. Gravimetric water content of soil near trees was lower than open field at shallow depth but similar deeper down. We conclude that ambient conditions suitable for sand fly larvae at shallow depths (45cm) are restricted to areas close to trees. However, deeper in vertisols (90cm) suitable conditions are apparently maintained throughout the dry season even in open fallow fields.

Quantifying the contribution of hosts with different parasite concentrations to the transmission of visceral leishmaniasis in Ethiopia

Background

An important factor influencing the transmission dynamics of vector-borne diseases is the contribution of hosts with different parasitemia (no. of parasites per ml of blood) to the infected vector population. Today, estimation of this contribution is often impractical since it relies exclusively on limited-scale xenodiagnostic or artificial feeding experiments (i.e., measuring the proportion of vectors that become infected after feeding on infected blood/host).

Methodology

We developed a novel mechanistic model that facilitates the quantification of the contribution of hosts with different parasitemias to the infection of the vectors from data on the distribution of these parasitemias within the host population. We applied the model to an ample data set of Leishmania donovani carriers, the causative agent of visceral leishmaniasis in Ethiopia.

Results

Calculations facilitated by the model quantified the host parasitemias that are mostly responsible for the infection of vector, the sand fly Phlebotomus orientalis. Our findings indicate that a 3.2% of the most infected people were responsible for the infection of between 53% and 79% (mean – 62%) of the infected sand fly vector population.

Significance

Our modeling framework can easily be extended to facilitate the calculation of the contribution of other host groups (such as different host species, hosts with different ages) to the infected vector population. Identifying the hosts that contribute most towards infection of the vectors is crucial for understanding the transmission dynamics, and planning targeted intervention policy of visceral leishmaniasis as well as other vector borne infectious diseases (e.g., West Nile Fever).

An important factor influencing the transmission dynamics of vector-borne diseases is the contribution of hosts with different parasitemia (no. of parasites per ml of blood) to the infected vector population. In this study we developed a novel mechanistic model that facilitates the quantification of this contribution and applied it to an ample data set of people infected with visceral leishmaniasis in Ethiopia. Among vector borne diseases, visceral leishmaniasis is the second most important killer after malaria. It is caused by infection with Leishmania parasites with most cases (∼90%) occurring in the Indian sub-continent, East Africa, and South America. The disease is transmitted between people and other mammalian hosts by blood-sucking sand flies. Our findings indicate that a 3.2% of the most infected people were responsible for the infection of about 65% of the infected sand fly vector population. Identifying the hosts that contribute most towards infection of the vectors is crucial for understanding the transmission dynamics, and planning targeted intervention policy of visceral leishmaniasis, as well as other vector borne infectious diseases (e.g., Dengue, West Nile Fever).

Risk factors of visceral leishmaniasis: a case control study in north-western Ethiopia

Background

Visceral leishmaniasis (VL, also called ‘’kala-azar”), is a life threatening neglected tropical infectious disease which mainly affects the poorest of the poor. VL is prevalent in Ethiopia particularly in the northwest of the country. Understanding the risk factors of VL infection helps in its prevention and control. The aim of the present study was to identify the factors associated with VL.

Methods

A case–control study was carried out during the period of January-July 2013 in northwest Ethiopia. Cases and controls were diagnosed using clinical presentation, the rk39 rapid diagnostic test and Direct Agglutination Test (DAT). A total of 283 (84.8% males versus 15.2% females) participants were interviewed. 90 cases and 193 controls were involved, matched by age, sex and geographical location with a ratio of 1:2 (case: controls). Univariate and backward multivariate conditional logistic regression were used to identify risk factors of VL.

Results

Elevated odds of VL was associated with goat ownership (OR = 6.4; 95%: confidence interval [Cl]: 1.5-28.4), living in houses with cracked wall (OR = 6.4; 95% Cl: 1.6-25.6), increased family size (OR = 1.3; 95% Cl: 1.0-1.8) and the number of days spent in the farm field (OR = 1.1; 95% Cl: 1.0-1.2). However, daily individual activities around the home and farm fields, mainly sleeping on a bed (OR = 0.2; 95%: Cl 0.03-0.9), sleeping outside the house under a bed net (OR = 0.1; 95% Cl: 0.02-0.36)] and smoking plant parts in the house during the night time (OR = 0.1; 95% Cl: 0.01-0.6) were associated with decreased odds of being VL case.

Conclusion

Our findings showed that use of bed net and smoke could be helpful for the prevention of VL in the area particularly among individuals who spend most of their time in the farm. VL control effort could be focused on improving housing conditions, such as sealing cracks and crevices inside and outside houses. Further research is warranted to elucidate the role of goats in the transmission of L. donovani, assess the impact of bed nets and the role of the traditional practice of smoking plants.

Sergentomyia spp.: breeding sites in vertisols and peri-domestic habitats in North West Ethiopia

Sand flies belonging to the genus Sergentomyia Franca & Parrot, 1920, are hematophagous insects feeding mostly on reptiles and birds, but some species feed also on mammals including humans. Sergentomyia spp. frequently comprise the vast majority of sand flies trapped along with Phlebotomus spp., the vectors of mammalian leishmaniasis. Within the framework of a project on the ecology and transmission of visceral leishmaniasis in Ethiopia, putative breeding sites of phlebotomine sand flies were studied. Large horizontal sticky traps (LHSTs) covered with sand fly-proof mesh were deployed over cracked vertisol and related habitats for up to 3 nights, and emerging sand flies were collected daily. Emergence traps (ETs) were also adapted to sample other putative breeding sites including tree trunks, termite mounds, rock piles and vertical river banks. Productive breeding sites were identified in the trunks and roots systems of trees, vertisol fields, cracks and burrows in vertisol dry river banks and termite mounds. Emerging flies were also collected form a stone wall and a rock pile situated inside a village. Significantly more Sergentomyia spp. were trapped in vertisols by ETs deployed over root system than in open fields. Similarly, more sand flies emerged from cracks in the vertisol in fallow Sorghum than in fallow sesame fields. Productive breeding sites were characterized by stable micro-climatic conditions. Species composition of emerging sand flies varied with habitat, season and geographical location.

Population dynamics and habitat preferences of Phlebotomus orientalis in extra-domestic habitats of Kafta Humera lowlands--kala azar endemic areas in Northwest Ethiopia

Background

Kafta Humera lowlands are endemic for kala-azar (visceral leishmaniasis). These lowlands are characterized by black clay soil which is used for growing sesame, sorghum and cotton for commercial purposes.

The aim of this study was to determine seasonal dynamics and habitat preferences of Phlebotomus orientalis, the vector of kala-azar, in extra-domestic habitats of Kafta Humera lowlands.

Methods

CDC-light Trap [CDC-LT] and Sticky paper Trap [ST] were used to collect sand flies from different habitats before species identification by their morphological characteristics using appropriate keys. Data summarized and analyzed included: species, sex, density, habitats, type of trap used and date (month).

Results

A total of 389,207 sand flies using CDC-LT (n = 955) and ST (n = 5551) were collected from May 17, 2011 to June 6, 2012. The highest Mean Monthly Density (MMD) of P. orientalis trapped by CDC-LT was found in thickets of Acacia seyal in March (64.11 ± 75.87). The corresponding highest MMD of P. orientalis trapped by STs was found in April (58.69 ± 85.20) in agricultural field. No P. orientalis were caught in September using CDC traps and July-October using sticky traps. The overall MMD of P. orientalis trapped by CDC-LT was 15. 78 ± 28.93 (n = 320) in agricultural field, 19.37 ± 36.42 (n = 255) in thickets of A. seyal, and 3.81 ± 6.45 (n = 380) in dense mixed forest. Similar habitats in different localities did not show statistically significant difference for the MMD of P. orientalis trapped by CDC-LT (p = 0.117) and ST (p = 0.134).

Conclusion

Agricultural fields and thickets of A. seyal habitats, which exhibit extensive soil cracks and fissures, as opposed to dense mixed forests, serve as preferred breeding sites for P. orientalis.

Comparative analysis of salivary gland transcriptomes of Phlebotomus orientalis sand flies from endemic and non-endemic foci of visceral leishmaniasis

Background

In East Africa, Phlebotomus orientalis serves as the main vector of Leishmania donovani, the causative agent of visceral leishmaniasis (VL). Phlebotomus orientalis is present at two distant localities in Ethiopia; Addis Zemen where VL is endemic and Melka Werer where transmission of VL does not occur. To find out whether the difference in epidemiology of VL is due to distant compositions of P. orientalis saliva we established colonies from Addis Zemen and Melka Werer, analyzed and compared the transcriptomes, proteomes and enzymatic activity of the salivary glands.

Methodology/Principal Findings

Two cDNA libraries were constructed from the female salivary glands of P. orientalis from Addis Zemen and Melka Werer. Clones of each P. orientalis library were randomly selected, sequenced and analyzed. In P. orientalis transcriptomes, we identified members of 13 main protein families. Phylogenetic analysis and multiple sequence alignments were performed to evaluate differences between the P. orientalis colonies and to show the relationship with other sand fly species from the subgenus Larroussius. To further compare both colonies, we investigated the humoral antigenicity and cross-reactivity of the salivary proteins and the activity of salivary apyrase and hyaluronidase.

Conclusions

This is the first report of the salivary components of P. orientalis, an important vector sand fly. Our study expanded the knowledge of salivary gland compounds of sand fly species in the subgenus Larroussius. Based on the phylogenetic analysis, we showed that P. orientalis is closely related to Phlebotomus tobbi and Phlebotomus perniciosus, whereas Phlebotomus ariasi is evolutionarily more distinct species. We also demonstrated that there is no significant difference between the transcriptomes, proteomes or enzymatic properties of the salivary components of Addis Zemen (endemic area) and Melka Werer (non-endemic area) P. orientalis colonies. Thus, the different epidemiology of VL in these Ethiopian foci cannot be attributed to the salivary gland composition.

Phlebotomus orientalis is the vector of visceral leishmaniasis (VL) caused by Leishmania donovani in Northeast Africa. Immunization with sand fly saliva or with individual salivary proteins has been shown to protect against leishmaniasis in different hosts, warranting the intensive study of salivary proteins of sand fly vectors. In our study, we characterize the salivary compounds of P. orientalis, thereby broadening the repertoire of salivary proteins of sand fly species belonging to the subgenus Larroussius. In order to find out whether there is any connection between the composition of P. orientalis saliva and the epidemiology of VL in two distinct Ethiopian foci, Addis Zemen and Melka Werer, we studied the transcriptomes, proteomes, enzymatic activities, and the main salivary antigens in two P. orientalis colonies originating from these areas. We did not detect any significant difference between the saliva of female sand flies originating in Addis Zemen (endemic area) and Melka Werer (non-endemic area). Therefore, the different epidemiology of VL in these Ethiopian foci cannot be related to the distant salivary gland protein composition. Identifying the sand fly salivary gland compounds will be useful for future research focused on characterizing suitable salivary proteins as potential anti-Leishmania vaccine candidates.

Attraction of Ethiopian phlebotomine sand flies (Diptera: Psychodidae) to light and sugar-yeast mixtures (CO(2))

BACKGROUND

Visceral leishmaniasis (VL) known as Kala-Azar is a serious systemic disease caused by Leishmania donovani parasites (Trypanosomatidae: Kinetoplastida). The disease is prevalent in the Indian Sub-continent, East Africa and Brazil. In Africa, the worst affected regions are in Sudan, with an estimated 15,000-20,000 cases annually and Ethiopia with 5,000-7,000 cases a year. The main vector of VL in Sudan and Northern Ethiopia is Phlebotomus orientalis, a sand fly frequently found in association with Acacia spp and Balanite spp woodlands.

METHODS

To optimize sampling of sand flies for epidemiological studies in remote areas we tested different means of attraction. Miniature suction traps employing 2AA batteries (3 V) were deployed in the up-draft orientation and baited with chemical light-sticks (Red, Yellow and Green), or bakers' yeast in sugar solution (emitting CO2 and perhaps other attractants). These traps were compared with standard CDC incandescent light traps employing 6 V batteries. Trials were conducted during two consecutive years at different localities around Sheraro, a town in West Tigray, Northern Ethiopia.

RESULTS

The sand fly species composition was similar but not identical in the different locations tested with different Sergentomyia spp. predominating. Phlebotomus spp. comprised less than 1% of the catches during the first year trials (November - December 2011) but increased markedly during the second year trials performed later in the dry season at the height of the sand fly season in February 2012. Although there did not appear to be a species bias towards different light wave-lengths, fermenting yeast in sugar solution attracted relatively more Phlebotomus spp. and Sergentomyia schwetzi.

CONCLUSIONS

Although the standard 6 V CDC incandescent light traps captured more sand flies, light-weight (~350 g) 3 V suction traps baited with chemical light-sticks were shown to be effective means of monitoring sand flies. Such traps operated without light and baited with yeast in sugar solution caught relatively more Phlebotomus spp.

Theileria infection in domestic ruminants in northern Ethiopia

Piroplasmosis caused by different tick-borne hemoprotozoan parasites of the genera Theileria and Babesia is among the most economically important infections of domestic ruminants in sub-Saharan Africa. A survey for piroplasm infection was conducted in three locations in Northern Ethiopia. Of 525 domestic ruminants surveyed, 80% of the cattle, 94% of the sheep and 2% of the goats were positive for different Theileria spp. based on PCR of blood followed by DNA sequencing. Sheep had a significantly higher rate of infection compared with cattle (P<0.0003) and both sheep and cattle had higher rates of infection compared to goats (P<0.0001). Four species of Theileria were detected in cattle: T. velifera, T. mutans, T. orientalis complex and T. annulata with infection rates of 66, 8, 4, and 2%, respectively. This is the first report of T. annulata, the cause of Tropical Theileriosis in Ethiopia. Of the two Theileria spp. detected in small ruminants, T. ovis was highly prevalent (92%) in sheep and rare in goats (1.5%) whereas T. seperata was infrequent in sheep (2%) and rare in goats (0.4%). None of the animals were positive for Babesia spp.; however, Sarcocystis capracanis and S. tenella were detected in one goat and a sheep, respectively. The widespread distribution of Theileria spp. among cattle in northern Ethiopia including the virulent T. annulata and more mildly pathogenic T. mutans and T. orientalis, and the high infection rate in sheep with the usually sub-clinical T. ovis indicate extensive exposure to ticks and transmission of piroplasms with an important economic impact.

Sergentomyia schwetzi is not a competent vector for Leishmania donovani and other Leishmania species pathogenic to humans

BACKGROUND

Sand fly species of the genus Sergentomyia are proven vectors of reptilian Leishmania that are non-pathogenic to humans. However, a consideration of the role of Sergentomyia spp. in the circulation of mammalian leishmaniasis appears repeatedly in the literature and the possibility of Leishmania transmission to humans remains unclear. Here we studied the susceptibility of colonized Sergentomyia schwetzi to Leishmania donovani and two other Leishmania species pathogenic to humans: L. infantum and L. major.

METHODS

Females of laboratory-reared S. schwetzi were infected by cultured Leishmania spp. by feeding through a chicken membrane, dissected at different time intervals post bloodmeal and examined by light microscopy for the abundance and location of infections.

RESULTS

All three Leishmania species produced heavy late stage infections in Lutzomyia longipalpis or Phlebotomus duboscqi sand flies used as positive controls. In contrast, none of them completed their developmental cycle in Sergentomyia females; Leishmania promastigotes developed within the bloodmeal enclosed by the peritrophic matrix (PM) but were defecated together with the blood remnants, failing to establish a midgut infection. In S. schwetzi, the PM persisted significantly longer than in L. longipalpis and it was degraded almost simultaneously with defecation. Therefore, Leishmania transformation from procyclic to long nectomonad forms was delayed and parasites did not attach to the midgut epithelium.

CONCLUSIONS

Sergentomyia schwetzi is refractory to human Leishmania species and the data indicate that the crucial aspect of the refractoriness is the relative timing of defecation versus PM degradation.

Attraction of phlebotomine sand flies to baited and non-baited horizontal surfaces

Female phlebotomine sand flies (Diptera: Psychodidae) transmit leishmaniasis as they engorge on vertebrate blood required for egg production. Phlebotomus (Phlebotomus) papatasi (Scopoli, 1786), the vector of Leishmania major (Yakimoff & Schokhor, 1914), the causative agent of cutaneous leishmaniasis (CL) were not attracted to large horizontal sticky traps (LHSTs) unless these were baited with CO2 derived from dry ice or from fermenting sugar/yeast mixture (SYM). Attraction of P. papatasi males by CO2 may indicate their tendency to mate on or near the blood-host. Male P. (Larroussius) orientalis (Parrot, 1936), the vector of visceral leishmaniasis (VL) in Ethiopia, were collected on LHSTs in large numbers. Although the number of females remained low, augmentation with SYM, increased the number of females by 800% while the number of males increased by only about 40%. Apparently, male P. orientalis utilize the horizontal surfaces for forming mating swarms. P. (Paraphlebotomus) sergenti (Parrot, 1917), is the vector of CL caused by Leishmania tropica. Although approximately twice as many P. sergenti males were caught on LHSTs as females, it appears that LHSTs were attractive to both sexes. Use of SYM baits is potentially useful for monitoring phlebotomine sand flies in places where dry ice is unobtainable or prohibitively expensive. LHSTs can provide an inexpensive alternative to CDC traps for monitoring some species of sand flies. Unfortunately, the numbers of female sand flies, crucial for estimating transmission of Leishmania, is usually low on LHSTs.

Phlebotomus orientalis sand flies from two geographically distant Ethiopian localities: biology, genetic analyses and susceptibility to Leishmania donovani

BACKGROUND

Phlebotomus orientalis Parrot (Diptera: Psychodidae) is the main vector of visceral leishmaniasis (VL) caused by Leishmania donovani in East Africa. Here we report on life cycle parameters and susceptibility to L. donovani of two P. orientalis colonies originating from different sites in Ethiopia: a non-endemic site in the lowlands - Melka Werer (MW), and an endemic focus of human VL in the highlands - Addis Zemen (AZ).

METHODOLOGY/PRINCIPAL FINDINGS

Marked differences in life-cycle parameters between the two colonies included distinct requirements for larval food and humidity during pupation. However, analyses using Random Amplified Polymorphic DNA (RAPD) PCR and DNA sequencing of cytB and COI mitochondrial genes did not reveal any genetic differences. F1 hybrids developed successfully with higher fecundity than the parental colonies. Susceptibility of P. orientalis to L. donovani was studied by experimental infections. Even the lowest infective dose tested (2×10(3) per ml) was sufficient for successful establishment of L. donovani infections in about 50% of the P. orientalis females. Using higher infective doses, the infection rates were around 90% for both colonies. Leishmania development in P. orientalis was fast, the presence of metacyclic promastigotes in the thoracic midgut and the colonization of the stomodeal valve by haptomonads were recorded in most P. orientalis females by day five post-blood feeding.

CONCLUSIONS

Both MW and AZ colonies of P. orientalis were highly susceptible to Ethiopian L. donovani strains. As the average volume of blood-meals taken by P. orientalis females are about 0.7 µl, the infective dose at the lowest concentration was one or two L. donovani promastigotes per sand fly blood-meal. The development of L. donovani was similar in both P. orientalis colonies; hence, the absence of visceral leishmaniasis in non-endemic area Melka Werer cannot be attributed to different susceptibility of local P. orientalis populations to L. donovani.

Evaluation of PCR procedures for detecting and quantifying Leishmania donovani DNA in large numbers of dried human blood samples from a visceral leishmaniasis focus in Northern Ethiopia

Background

Visceral Leishmaniasis (VL) is a disseminated protozoan infection caused by Leishmania donovani parasites which affects almost half a million persons annually. Most of these are from the Indian sub-continent, East Africa and Brazil. Our study was designed to elucidate the role of symptomatic and asymptomatic Leishmania donovani infected persons in the epidemiology of VL in Northern Ethiopia.

Methods

The efficacy of quantitative real-time kinetoplast DNA/PCR (qRT-kDNA PCR) for detecting Leishmania donovani in dried-blood samples was assessed in volunteers living in an endemic focus.

Results

Of 4,757 samples, 680 (14.3%) were found positive for Leishmania k-DNA but most of those (69%) had less than 10 parasites/ml of blood. Samples were re-tested using identical protocols and only 59.3% of the samples with 10 parasite/ml or less were qRT-kDNA PCR positive the second time. Furthermore, 10.8% of the PCR negative samples were positive in the second test. Most samples with higher parasitemias remained positive upon re-examination (55/59 =93%). We also compared three different methods for DNA preparation. Phenol-chloroform was more efficient than sodium hydroxide or potassium acetate. DNA sequencing of ITS1 PCR products showed that 20/22 samples were Leishmania donovani while two had ITS1 sequences homologous to Leishmania major.

Conclusions

Although qRT-kDNA PCR is a highly sensitive test, the dependability of low positives remains questionable. It is crucial to correlate between PCR parasitemia and infectivity to sand flies. While optimal sensitivity is achieved by targeting k-DNA, it is important to validate the causative species of VL by DNA sequencing.

Breeding sites of Phlebotomus sergenti, the sand fly vector of cutaneous leishmaniasis in the Judean Desert

Phlebotomine sand flies transmit Leishmania, phlebo-viruses and Bartonella to humans. A prominent gap in our knowledge of sand fly biology remains the ecology of their immature stages. Sand flies, unlike mosquitoes do not breed in water and only small numbers of larvae have been recovered from diverse habitats that provide stable temperatures, high humidity and decaying organic matter. We describe studies designed to identify and characterize sand fly breeding habitats in a Judean Desert focus of cutaneous leishmaniasis. To detect breeding habitats we constructed emergence traps comprising sand fly-proof netting covering defined areas or cave openings. Large size horizontal sticky traps within the confined spaces were used to trap the sand flies. Newly eclosed male sand flies were identified based on their un-rotated genitalia. Cumulative results show that Phlebotomus sergenti the vector of Leishmania tropica rests and breeds inside caves that are also home to rock hyraxes (the reservoir hosts of L. tropica) and several rodent species. Emerging sand flies were also trapped outside covered caves, probably arriving from other caves or from smaller, concealed cracks in the rocky ledges close by. Man-made support walls constructed with large boulders were also identified as breeding habitats for Ph. sergenti albeit less important than caves. Soil samples obtained from caves and burrows were rich in organic matter and salt content. In this study we developed and put into practice a generalized experimental scheme for identifying sand fly breeding habitats and for assessing the quantities of flies that emerge from them. An improved understanding of sand fly larval ecology should facilitate the implementation of effective control strategies of sand fly vectors of Leishmania.

Sand flies are small blood sucking flies that transmit Leishmania, the etiologic agent of leishmaniasis - a prevalent disease over large areas of the World. Unlike mosquitoes, sand flies do not breed in water. Their larvae develop in humid habitats containing decaying organic matter (e.g. habitats such as burrows, tree holes and caves). However, in most cases, larval breeding habitats are unknown and larvae remain inaccessible to control efforts. In this paper we identified the breeding sites of an important sand fly vector of cutaneous leishmaniasis by using emergence traps to collect adult sand flies exiting caves and cracks. We identified young male sand flies (less than 24 hours old) by examining their external sex organs. The data collected enabled us to determine that sand flies were breeding primarily inside caves and in adjacent cracks but also in man-made support walls constructed with large boulders. These findings will be useful for applying more effective sand fly and leishmaniasis control measures.

Identification of bloodmeals in wild caught blood fed Phlebotomus argentipes (Diptera: Psychodidae) using cytochrome b PCR and reverse line blotting in Bihar, India

Identification of the source of bloodmeals in vectors plays an important role in epidemiological studies by determining the host preferences of wild sand flies in natural habitat. The anthropophilic index is a crucial component in human leishmaniasis. Bloodmeal analysis can identify the reservoir hosts of vector borne diseases. The amplification of the mitochondrial cytochrome b gene, followed by reverse line blot analysis, helps to identify the bloodmeal ingested by the wild caught sand flies. In the current study, blood fed sand flies were collected from three different villages in Bihar, India, by using Centers for Disease Control mini traps with incandescent light. Traps were placed in five different sites in the villages. Whole genome DNA was extracted from the blood fed sand flies and was amplified for the cytochrome b region, followed by reverse line blot analysis. In total, 442 blood fed sand flies were analyzed out of which 288 (65%) were positive to cytochrome b polymerase chain reaction. Humans, cattle, buffalo, and goats were the major bloodmeals identified, followed by chickens. In some of the blood fed sand flies, multiple bloodmeals were identified. In the current study, sand flies mostly fed on humans, followed by cattle, buffalo, and goats. In this regard, it is necessary to also consider cattle, buffalo, and goats when addressing vector control in Bihar, India.