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

Demographic characteristics and prevalence of asymptomatic Leishmania donovani infection in migrant workers working in an endemic area in Northwest Ethiopia

Introduction

Visceral leishmaniasis (VL), a neglected tropical disease that causes substantial morbidity and mortality, is a serious health problem in Ethiopia. Infections are caused by Leishmania (L.) donovani parasites. Most individuals remain asymptomatic, but some develop VL, which is generally fatal if not treated. We identified the area of Metema-Humera in Northwest Ethiopia as a setting in which we could follow migrant workers when they arrived in an endemic area. The demographic characteristics of this population and factors associated with their risk of asymptomatic infection are poorly characterised.

Methods

We divided our cohort into individuals who visited this area for the first time (first comers, FC) and those who had already been in this area (repeat comers, RC). We followed them from the beginning (Time 1, T1) to the end of the agricultural season (Time 2, T2), performing tests for sand fly bite exposure (anti-sand fly saliva antibody ELISA) and serology for Leishmania infection (rK39 rapid diagnostic test and the direct agglutination test) at each time point and collecting information on risk factors for infection.

Results

Our results show that most migrant workers come from non-endemic areas, are male, young (median age of 20 years) and are farmers or students. At T1, >80% of them had been already exposed to sand fly bites, as shown by the presence of anti-saliva antibodies. However, due to seasonality of sand flies there was no difference in exposure between FC and RC, or between T1 and T2. The serology data showed that at T1, but not at T2, a significantly higher proportion of RC were asymptomatic. Furthermore, 28.6% of FC became asymptomatic between T1 and T2. Over the duration of this study, one FC and one RC developed VL. In multivariable logistic regression of asymptomatic infection at T1, only age and the number of visits to Metema/Humera were significantly associated with asymptomatic infection.

Conclusion

A better understanding of the dynamics of parasite transmission and the risk factors associated with the development of asymptomatic infections and potentially VL will be essential for the development of new strategies to prevent leishmaniasis.

Cutaneous leishmaniasis in Kutaber District, Ethiopia: Prevalence, sand fly fauna and community knowledge, attitude and practices

Background

Cutaneous leishmaniasis (CL) affects 25% of the population living in the highlands of Ethiopia. CL intervention has not decreased the number of leishmaniasis patients. A cross-sectional study was conducted to determine CL prevalence, community's knowledge, attitude and practices (KAP), and the sand fly fauna in Kutaber district, northeast Ethiopia.

Methods

A retrospective, community-based cross-sectional study was conducted in Boru Meda Hospital from December 2014-March 2021 to study CL prevalence of Kutaber district. A Pre-tested, well-structured questionnaire was used to collect data on the participants' socio-demographic characteristics, KAP towards CL and knowledge about sand fly vectors. Chi-square test and logistic regression analysis were used in the study, and data were analyzed using SPSS version 23 (p < 0.05).

Results

A total of 10,002 (14.02%), of which 71,325 samples were confirmed as positive for CL. The infection rate of CL in females (7.1%) was a little bit higher than males (7.0%). More cases were recorded among 15-29 age category. The study also revealed that 77.1% of the respondents had poor knowledge about CL treatment, prevention, clinical presentation and disease transmission. Farmers tended to have poorer knowledge about sand flies than non-workers and students (32.7 vs. 35 and 44.1%; P = 0.049). Housewives had poorer knowledge about sand flies than farmers and workers (22.2 vs. 32.7 and 33.3%; P = 0.023). Phlebotomus longipes comprised the highest composition (80%) of the sand fly species identified in Kutaber district.

Conclusions

The data showed that the community had poor knowledge about CL, vector, and transmission mode. CL preventive measures were prevalent, implying the need to raise CL awareness. Phlebotomus longipes was identified as the most dominant sand fly species which accounted for CL. The findings can be used in developing an effective control strategy to reduce CL transmission in the study area and elsewhere in Ethiopia.

Non-target effects of chemical malaria vector control on other biological and mechanical infectious disease vectors

Public health insecticides play a crucial role in malaria control and elimination programmes. Many other arthropods, including mechanical and biological vectors of infectious diseases, have similar indoor feeding or resting behaviours, or both, as malaria mosquitoes, and could be exposed to the same insecticides. In this Personal View, we show that little is known about the insecticide susceptibility status and the extent of exposure to malaria interventions of other arthropod species. We highlight that there is an urgent need to better understand the selection pressure for insecticide resistance in those vectors, to ensure current and future active ingredients remain effective in targeting a broad range of arthropod species, allowing us to prevent and control future outbreaks of infectious diseases other than malaria.

Sero-prevalence of visceral leishmaniasis and its associated factors among asymptomatic individuals visiting Denan health center, southeastern Ethiopia

BACKGROUND

In the Somali region of Ethiopia, visceral leishmaniasis (VL) is a public health concern. However, VL epidemiology and sand fly vectors have not been well studied in various areas of the regional state, including Denan district. Therefore, this study was conducted to determine the sero-prevalence, associated factors, and distribution of sand fly vectors of VL in Denan district, south-eastern Ethiopia.

METHODS

A facility-based cross-sectional study was conducted from April to September 2021 among VL patients with classic signs and symptoms visiting Denan Health Center in south-eastern Ethiopia. Using a convenience sampling method, 187 blood samples were collected from individuals who visited Denan Health Center during the study period. Blood samples were subjected to Direct Agglutination Test for the detection of antibodies to VL. A pre-tested structured questionnaire was also used to gather information on risk factors and other characteristics of knowledge and attitude assessment. Sand flies were also collected from indoor, peri-domestic, mixed forest, and termite mounds using light and sticky traps to determine the fauna and abundance.

RESULTS

The overall sero-prevalence rate was 9.63% (18/187). The sero-prevalence was significantly associated with outdoor sleeping (OR = 2.82), the presence of damp floors (OR = 7.76), and sleeping outdoor near animals (OR = 3.22). Around 53.48% of the study participants had previously heard about VL. Study participants practiced different VL control methods, including bed nets (42%), insecticide spraying (32%), smoking plant parts (14%), and environmental cleaning (8%). In total, 823 sand fly specimens, comprising 12 species in two genera (Phlebotomus and Sergentomyia), were trapped and identified. The most abundant species was Sergentomyia clydei (50.18%), followed by Phlebotomus orientalis (11.42%). Also, a higher proportion of P. orientalis was found in termite mounds (65.43%), followed by mixed forest (37.8%) and peri-domestic (20.83%) habitats.

CONCLUSION

The study demonstrated a 9.63% sero-positivity of VL and a remarkable gap in knowledge, attitude, and practices towards VL. P. orientalis was also detected, which could be a probable vector in this area. Thus, public education should be prioritized to improve the community's awareness of VL and its public health impact. In addition, detailed epidemiological and entomological studies are recommended.

Case Report: FDG-PET/CT findings in co-infection of visceral leishmaniasis and chronic hepatitis B

Visceral leishmaniasis is an opportunistic infection in immunocompromised patients. Herein, we report a case of an adult male patient with a persistent fever of unknown origin, along with chronic hepatitis B. The patient underwent bone marrow aspiration twice, which revealed hemophagocytosis. Abdomen enhanced CT revealed splenomegaly with a persistent strengthening of multiple nodules, and hemangiomas were diagnosed. A subsequent 18-fluoro-deoxyglucose (18F-FDG) PET/CT scan, which was implemented to search for the reason for the fever, showed diffuse splenic disease uptake, and splenic lymphoma was considered as the diagnosis. His clinical symptoms improved after receiving hemophagocytic lymphohistiocytosis (HLH) chemotherapy. However, the patient was readmitted for fever again only 2 months later. Splenectomy surgery is performed to confirm the diagnosis and classification of lymphoma. Visceral leishmaniasis was eventually diagnosed in a spleen specimen and the third bone marrow biopsy. He received treatment with lipid amphotericin B and remained recurrence-free for 1 year. In this paper, we aim to provide detailed information that will help further our understanding of the clinical symptoms and radiographic findings of visceral leishmaniasis.

Phlebotomine sandflies (Diptera: Psychodidae) of Ethiopia

Phlebotomine sandflies have a long history of association with humans, which makes them the only proven natural vectors of Leishmania species, the parasitic protozoans that cause leishmaniases in humans and animals. In Ethiopia, the three forms of leishmaniases, viz., visceral, dermal and mucocutaneous are endemic in different parts of the country. Since the first report of phlebotomine sandflies in Ethiopia in 1936, the distribution of different species and their role in the transmission of leishmaniases have been extensively studied. The objective of this review was to summarize the patchy information and give an updated list of phlebotomine sandfly species in Ethiopia and their known geographical distribution in the country. Peer-reviewed literature search was conducted using online databases. All articles published which focus on distribution and medical importance of Phlebotomus and Sergentomyia species of Ethiopia starting from 1936 up to 2022 were reviewed. Until July 2022, 65 phlebotomine sandfly species have been reported, belonging to the genus Phlebotomus and Sergentomyia. The genus Phlebotomus in Ethiopia is represented by six subgenera such as Adlerius, Anaphlebotomus, Larroussius, Paraphlebotomus Phlebotomus and Synphlebotomus, whereas the genus Sergentomyia is represented by six subgenera, namely Grassomyia, Parrotomyia, Parvidens, Rondanomyia, Sergentomyia, and Sintonius.

Climate Change and Environmental Influence on Prevalence of Visceral Leishmaniasis in West Pokot County, Kenya

Kala-azar is a parasitic disease caused by Leishmania species transmitted by sand fly. In Kenya, kala-azar is endemic in thirty subcounties spread over in eleven counties in the arid zones. Climate change-influenced seasonal weather variability and environmental alterations remain important determinants of many vector-borne diseases. The present study focused on climate change and environmental influence on kala-azar in West Pokot. A descriptive cross-sectional and retrospective research design was adapted. Study area was purposively selected. Locations were randomly selected, and households were systematically selected. Three hundred sixty-three household questionnaires, eleven key informant interviews, and five focus group discussions were undertaken. Secondary data were obtained from Kacheliba subcounty hospital records. Statistical Package for the Social Sciences version 24 was used to analyze quantitative data while qualitative data were analyzed to establish connection for interpretation. Kala-azar cases have been on the rise on aggregate and surge towards the end of dry season and just after the rains. Significant environmental factors included the presence of seasonal rain water pathways and rock piles around houses (AOR = 4.7; 95% CI = (2.3-9.6), $p<0.05$ ), presence of acacia trees in and around homesteads (AOR = 8.5; 95% CI = (2.5-28.6), $p<0.05$ ), presence of anthills around the homesteads (AOR = 5.2; 95% CI = (1.2-23.4), $p<0.05$ ), and presence of animal shed within compound (AOR = 2.8; 95% CI = (0.96-8), $p<0.05$ ). Climate change-induced seasonal weather variability, increased temperature and reduced precipitation as well as environmental alterations influence kala-azar occurrence in West Pokot. Community sensitization on disease prevalence, clearing of vector predilection sites, and improving community environmental risk perception are imperative to promote prevention.

Community deployment of a synthetic pheromone of the sand fly Lutzomyia longipalpis co-located with insecticide reduces vector abundance in treated and neighbouring untreated houses: Implications for control of Leishmania infantum

Background

The rising incidence of visceral leishmaniasis due to Leishmania infantum requires novel methods to control transmission by the sand fly vector. Indoor residual spraying of insecticide (IRS) against these largely exophilic / exophagic vectors may not be the most effective method. A synthetic copy of the male sex-aggregation pheromone of the key vector species Lutzomyia longipalpis in the Americas, was co-located with residual pyrethroid insecticide, and tested for its effects on vector abundance, hence potential transmission, in a Brazilian community study.

Methods

Houses within eight defined semi-urban blocks in an endemic municipality in Brazil were randomised to synthetic pheromone + insecticide or to placebo treatments. A similar number of houses located >100m from each block were placebo treated and considered as “True Controls” (thus, analysed as three trial arms). Insecticide was sprayed on a 2.6m² surface area of the property boundary or outbuilding wall, co-located within one metre of 50mg synthetic pheromone in controlled-release dispensers. Vector numbers captured in nearby CDC light traps were recorded at monthly intervals over 3 months post intervention. Recruited sentinel houses under True Control and pheromone + insecticide treatments were similarly monitored at 7–9 day intervals. The intervention effects were estimated by mixed effects negative binomial models compared to the True Control group.

Results

Dose-response field assays using 50mg of the synthetic pheromone captured a mean 4.8 (95% C.L.: 3.91, 5.80) to 6.3 (95% C.L.: 3.24, 12.11) times more vectors (female Lu. longipalpis) than using 10mg of synthetic pheromone. The intervention reduced household female vector abundance by 59% (C.L.: 48.7, 66.7%) (IRR = 0.41) estimated by the cross-sectional community study, and by 70% (C.L.: 56.7%, 78.8%) estimated by the longitudinal sentinel study. Similar reductions in male Lu. longipalpis were observed. Beneficial spill-over intervention effects were also observed at nearby untreated households with a mean reduction of 24% (95% C.L.: 0.050%, 39.8%) in female vectors. The spill-over effect in untreated houses was 44% (95% C.L.: 29.7%, 56.1%) as effective as the intervention in pheromone-treated houses. Ownership of chickens increased the intervention effects in both treated and untreated houses, attributed to the suspected synergistic attraction of the synthetic pheromone and chicken kairomones. The variation in IRR between study blocks was not associated with inter-household distances, household densities, or coverage (proportion of total households treated).

Conclusions

The study confirms the entomological efficacy of the lure-and-kill method to reduce the abundance of this important sand fly vector in treated and untreated homesteads. The outcomes were achieved by low coverage and using only 1–2% of the quantity of insecticide as normally required for IRS, indicating the potential cost-effectiveness of this method. Implications for programmatic deployment of this vector control method are discussed.

The predominant sand fly vector of the intracellular parasite Leishmania infantum, that causes human and canine visceral leishmaniasis in the Americas, is Lutzomyia longipalpis. Vector control tools to reduce transmission are needed. A sex-aggregation pheromone released by male Lu. longipalpis attracts female conspecifics which facilitates blood-feeding and transmission. This study, conducted in Brazil, quantifies the effects of community deployment of a synthetic version of the sex-aggregation pheromone, in a controlled-release dispenser, and co-located with lethal insecticide applied to a small area of the household compound or outbuilding wall. 50mg synthetic pheromone dispensers were used since they attracted substantially more vectors than 10mg dispensers. Deploying this novel lure-and-kill method to houses in eight replicate study blocks in two suburban endemic areas, demonstrated that it reduces vector numbers at both pheromone + insecticide treated houses, and neighbouring untreated houses. The presence of chickens (a known additional attraction to blood-seeking female Lu. longipalpis) increased the beneficial effects of the intervention. The method used only 1–2% of the quantity of insecticide necessary for IRS for an average sized house. The results demonstrate the efficacy and potential cost-effectiveness of this novel lure-and-kill control method.

Outdoor Residual Insecticide Spraying (ODRS), a New Approach for the Control of the Exophilic Vectors of Human Visceral Leishmaniasis: Phlebotomus orientalis in East Africa

Visceral Leishmaniasis (VL) due to Leishmania donovani is a neglected protozoan parasitic disease in humans, which is usually fatal if untreated. Phlebotomus orientalis, the predominant VL vector in East Africa, is a highly exophilic/exophagic species that poses a major challenge to current Integrated Vector Management (IVM). Here we report results of pilot studies conducted in rural villages in Gedarif state, Sudan, to evaluate outdoor residual spraying of 20mg active ingredient (a.i.) /m² deltamethrin insecticide applied to the characteristic household compound boundary reed fence and to the outside of household buildings (Outdoor Residual Insecticide Spraying, ODRS), and as an alternative, spraying restricted to the boundary fence only (Restricted Outdoor Residual Insecticide Spraying, RODRS). Four to six clusters of 20 households were assigned to insecticide treatments or control in three experiments. Changes in sand fly numbers were monitored over 2,033 trap-nights over 43–76 days follow-up in four sentinel houses per cluster relative to unsprayed control clusters. Sand fly numbers were monitored by sticky traps placed on the ground on the inside (“outdoor”) and the outside (“peridomestic”) of the boundary fence, and by CDC light traps suspended outdoors in the household compound. The effects of ODRS on sand fly numbers inside sleeping huts were monitored by insecticide knockdown. After a single application, ODRS reduced P. orientalis abundance by 83%-99% in outdoor and peridomestic trap locations. ODRS also reduced numbers of P. orientalis found resting inside sleeping huts. RODRS reduced outdoor and peridomestic P. orientalis by 60%-88%. By direct comparison, RODRS was 58%-100% as effective as ODRS depending on the trapping method. These impacts were immediate on intervention and persisted during follow-up, representing a large fraction of the P. orientalis activity season. Relative costs of ODRS and RODRS delivery were $5.76 and $3.48 per household, respectively. The study demonstrates the feasibility and high entomological efficacy of ODRS and RODRS, and the expected low costs relative to current IVM practises. These methods represent novel sand fly vector control tools against predominantly exophilic/exophagic sand fly vectors, aimed to lower VL burdens in Sudan, with potential application in other endemic regions in East Africa.

Phlebotomus orientalis is the predominant vector of visceral leishmaniasis (VL, kala azar) in Sudan and other countries of East Africa, where the disease causes high morbidity and mortality. This sylvatic sand fly species is abundant in wild habitats characterized by presence of black cotton soil and vegetation dominated by Balanites aegyptiaca and/or Acacia seyal trees. In villages, the vector bites people in the household yard and in nearby peri-domestic locations, exhibiting limited indoor resting behaviour. The marked exophagic and exophilic behaviours of P. orientalis represent a profound challenge for VL control by excluding indoor residual spraying of insecticides (IRS) and compromising the efficacy of insecticide-impregnated bednets (ITNs). In this study, we evaluated the entomological efficacy of residual pyrethroid applied outdoors to household boundary fences and the exterior walls of household huts (outdoor residual insecticide spraying, ODRS), to reduce the abundance of P. orientalis inside and outside houses. We also evaluated the entomological impact of a restricted outdoor residual insecticide spraying (RODRS), whereby insecticide was applied only to the boundary fence. The study was carried out in June 2016-June 2017 in Jebel-Algana and Umsalala villages, Gedarif state, eastern Sudan, which are highly endemic for VL. The results showed that a single ODRS application of 20mg a.i. /m² 2.8% deltamethrin provided average reductions of 83%-99% in outdoor and peridomestic P. orientalis sand fly numbers relative to unsprayed control clusters. RODRS reduced outdoor and peridomestic P. orientalis by 60%-88%. The average cost of ODRS and RODRS per household were $5.76 and $3.48, respectively. The costs of these community-based control measures were substantially lower than the costs of LLINs, which is the only evidence-based tool used to protect against VL in the area. Future studies should evaluate the impact of ODRS/RODRS transmission of VL incidence in endemic villages and in seasonal agricultural farms.

High-resolution habitat suitability model for Phlebotomus pedifer, the vector of cutaneous leishmaniasis in southwestern Ethiopia

BACKGROUND

Phlebotomus pedifer is the vector for Leishmania aethiopica causing cutaneous leishmaniasis (CL) in southwestern Ethiopia. Previous research on the transmission dynamics of CL resulted in recommendations for vector control. In order to target these interventions towards affected areas, a comprehensive understanding of the spatial distribution of P. pedifer at high spatial resolution is required. Therefore, this study determined the environmental predictors that facilitate the distribution of P. pedifer and created a map indicating the areas where conditions are suitable for survival of the vector in southwestern Ethiopia with high spatial resolution.

METHODS

Phlebotomus pedifer presence points were collected during two entomological surveys. Climate, vegetation and topographic variables were assembled. Climate variables were interpolated with variables derived from high-resolution digital elevation models to generate topoclimatic layers representing the climate conditions in the highlands. A Maximum Entropy model was run with the presence points, predicting variables and background points, which were selected based on a bias file.

RESULTS

Phlebotomus pedifer was the only captured Phlebotomus species in the study area and was collected at altitudes ranging between 1685 and 2892 m. Model projections indicated areas with suitable conditions in a 'belt' surrounding the high mountain peaks. Model performance was high, with train and test AUC values being 0.93 and 0.90, respectively. A multivariate environmental similarity surface (MESS) analysis showed that the model projection was only slightly extrapolated for some of the variables. The mean annual temperature was the environmental variable, which contributed most to the model predictions (60.0%) followed by the seasonality in rainfall (13.2%). Variables representing steep slopes showed very low importance to model predictions.

CONCLUSIONS

Our findings indicate that the suitable habitats for P. pedifer correspond well with the altitudes at which CL was reported previously, but the predictions are more widely distributed, in contrast with the description of CL to occur in particular foci. Moreover, we confirm that vector distribution is driven by climate factors, suggesting inclusion of topoclimate in sand fly distribution models. Overall, our model provides a map with a high spatial resolution that can be used to target sand fly control measures in southwestern Ethiopia.

Sand Fly (Diptera: Psychodidae) Species Diversity, Habitat Preferences, and Ecological Aspects of Distribution in Bajaur District, Khyber Pakhtunkhwa, Pakistan

The species composition, distribution, and bionomics of sand flies was investigated from January to December 2017 in four tehsils (20 villages) of district Bajaur (formally Bajaur agency), Khyber Pakhtunkhwa, Pakistan. In total, 4,173 adult specimens comprising of seven species of Phlebotomus (Diptera: Psychodidae) and three species of Sergentomyia (Diptera: Psychodidae) were collected by oral aspirator, insecticide spray, and sticky traps from June to October. Highest numbers of flies were collected indoors in July and August when relative humidity and temperature were highest. Phlebotomus sergenti Parrot (Diptera: Psychodidae) was the most abundant species from all the collection sites, making approximately 70% of the total capture. Combined dwellings and chicken cages harbored the highest number of adult and immature flies (unrotated external genitalia). Abundance of P. sergenti had a significant (P ≤ 0.05) positive correlation with monthly average temperature, relative humidity, and average rainfall in indoor collections. On the other hand, P. papatasi Scopoli displayed similar correlation in the indoor and nighttime collections. Both the species were apparently abundant in the elevation range ≤ 419 m above sea level and on rangelands. Phlebotomus papatasi, however, also occurred on agricultural lands. The number of cutaneous leishmaniasis (CL) cases did not significantly correlate with the abundance of sand fly vectors across the villages surveyed. The results reported herein can serve as a baseline for an all-extensive future work in Bajaur. Our investigations will benefit the public health experts and medical entomologists for improved control and surveillance vectors of leishmaniasis.

Understanding sand fly sampling methods: sticky traps are attraction-based and not interceptive sampling tools of Phlebotomus orientalis

BACKGROUND

Sticky traps are generally viewed as interceptive sand fly sampling methods; although no previous experimental evidence has supported this assumption. In this study, we tested this assumption experimentally for Phlebotomus orientalis, the principal vector of visceral leishmaniasis in East Africa, and propose an explanation for the highly male-biased collection of sticky traps.

METHODS

A number of field experiments were carried out in March-June 2016-2019, in Gedarif state, eastern Sudan. In the first experiment, we compared numbers of P. orientalis caught on sticky traps made of black, red, transparent, white, yellow, green and blue A4 size papers set simultaneously at different lunar light conditions. In the second and third experiments, we compared numbers of P. orientalis captured on sticky traps placed side-by-side horizontally or vertically on the ground, or horizontally on a 15 cm height stool. We also witnessed mating behaviour of sand flies following their landing on un-sticky papers placed on the ground.

RESULTS

Phlebotomus orientalis showed significant attraction to white, yellow and transparent traps, with negligible numbers caught on the black and the red traps. Similarly, significantly higher numbers of P. orientalis were attracted to the horizontal traps, resulting in an 8-fold increase in sand fly trapping efficacy as compared to the vertical traps. Placing the traps on the stools resulted in significant reduction in this attraction. In contrast to the sticky traps that captured only very few females; we found that when male sand flies land on un-sticky white paper they successfully lure females and copulate with them.

CONCLUSIONS

We demonstrate that, for P. orientalis, sticky traps are more attractant-based than interception-based sampling tools. Further, our findings support the notion that males of this sand fly species likely utilize the bright surface of the trap papers to perform mating rituals that attract the females for copulation. However, pre-mature death in the sticky oil hampers the completion of these rituals, and thus results in failure to attract the females. These findings inform our understanding of P. orientalis behaviour and have important implications for optimization of sticky trap design for vector surveillance purposes.

Nutrition, malnutrition, and leishmaniasis

Leishmaniasis is a vector-borne infectious disease with a long history of infecting humans and other animals. It is a known emerging or resurging disease. The host nutritional state has an indispensable role in defense against pathogens. The host defense system disorganization as a result of undernutrition is responsible for asymptomatic infections and even severe diseases. Host susceptibility and pathophysiologic severity to infection can be aggravated owing to undernourishment in a number of pathways, and infection also may aggravate preexisting poor nutrition or further increase host susceptibility. This study suggests that there may be some relationship between malnutrition and the endemicity of the parasite. The susceptibility to and severity of leishmanial infection can be altered by the body weight and serum levels of micronutrients. Nutrition not only affects the vulnerability of the host but also may affect the desire of sandfly to bite a specific host. Apart from host defense mechanism, nutritional stress also greatly influences vector competence and host-seeking behavior, especially during larvae development. The host and sandfly vector nutritional states could also influence the evolution of the parasite. It is essential to elucidate the roles that diets and nutrition play in the leishmanial life cycle. The aim of this article is to review the influences of nutrition and diets on the host susceptibility and severity of infection, preemptive and therapeutic strategy feedback, parasite evolution, and vector competence.

Epidemiology of visceral leishmaniasis in Shebelle Zone of Somali Region, eastern Ethiopia

Background

Visceral leishmaniasis (VL), a vector-borne disease caused by species of the L.donovani complex, has (re)-emerged in Ethiopia during the last two decades and is currently of increasing public health concern. However, very little is known about VL epidemiology in the Somali Region of Ethiopia. The aim of this study was to provide detailed epidemiological information on seroprevalence, associated factors and incriminated vectors of VL in Shebelle Zone and Ethiopian Somali Region in general.

Methods

A cross-sectional epidemiological study was conducted between March and May 2016 in Gode and Adadle districts of Shebelle Zone, Ethiopian Somali Region. Two-stage semi-random sampling was applied for selecting study participants for the field survey. The study included structured questionnaire interviews, serological assays (rK39-immunochromatographic test), ELISA and entomological surveys.

Results

From a total of 361 participants, 57 (15.8%) were seropositive for VL including 46 (12.7%) rK39 positive and 11 (3.0%) positive by both rK39 and ELISA. VL seroprevalence was higher (P < 0.001) in Adadle (31.1%) compared to Gode (12.7%) district. The VL seroprevalence rate was higher in females than in males [rK39 (17.2 vs 14.0%) and ELISA (3.4 vs 2.5%)]. Children under the 15 years of age were the most highly affected group [rK39 (20.4%) and ELISA (4.4%)]. Increased VL risk was associated with presence of termite hills, study district, outdoor sleeping, Acacia trees and domestic animals [odds ratio (95% confidence interval): 12.58 (5.911–26.763), 5.40 (2.90–10.07), 5.31 (2.283–12.364), 2.37 (1.1190–4.728) and 0.199 (0.097–0.410), respectively]. The entomological survey identified 74 Phlebotomus [P. (Larroussius) orientalis (52/74), P. (Anaphlebotomus) rodhaini (14/74), P. (Paraphlebotomus) sergenti (8/74)] and 11 Sergentomyia sand flies. The average frequency of P. orientalis (3.06 ± 0.66) collected by all traps per night was higher than that of other species. The average frequency of total and specific (P. orientalis) female sand flies was higher in Adadle (1.89 ± 0.423 vs 1.11 ± 0.309) than in Gode (0.62 ± 0.324 vs 0.38 ± 0.183) district. The highest mean numbers of total (8 ± 1.5) and P. orientalis (6 ± 0.913) sand flies were collected in termite hills.

Conclusions

The present findings revealed potential new VL-transmission foci in the study districts. Therefore, the need for parasitological and molecular characterization of the parasite in humans and vector sand flies is of paramount importance to confirm transmission.

Electronic supplementary material

The online version of this article (10.1186/s13071-019-3452-5) contains supplementary material, which is available to authorized users.

Zoonotic impact and epidemiological changes of leishmaniasis in Ethiopia

Leishmaniasis is one of the growing public health challenges in Ethiopia and estimated over 7,000 and 50,000 new cases of visceral leishmaniasis (VL) and cutaneous leishmaniasis (CL) per year, respectively. The aim of the review is to address zoonotic impact and epidemiological changes of leishmaniasis in Ethiopia. VL is caused by L. donovani and it is endemic in many parts of the country with one third of the country’s landmass is highly suitable for VL. CL is principally caused by L. aethiopica. CL is endemic and widespread in the highland of Ethiopia. Northern lowland foci are Humera and Metema plains in the Tigray and Amhara regional states constitute the main VL endemic areas in the country, contributing over 60% of the total burden. The southern foci are the south-western savannah, and the south-eastern semi-arid lowlands which account for approximately 20 % of the total VL burden in Ethiopia. Leishmaniasis is a serious zoonotic disease in Ethiopia with more reservoir hosts maintaining the disease. Dogs and hyraxes are the main reservoir hosts for visceral and cutaneous leishmaniasis in the country, respectively. Epidemiological changes of leishmaniasis may relate to environmental changes and expansion of mega projects such as irrigations and sugar cane factories, knowledge and socio-economic factors, development of new settlements, migration of peoples and HIV/AIDS co-infection. Expansions of mega projects such as sugar factories and irrigations are suitable for reproduction of stray dogs, rodents, wild canids and vectors. VL is one of the major challenges to prevent and control in the endemic areas of the country. Therefore, new research should be imperative, especially in the mega projects to design strategic control and prevention methods.

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

•

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

•

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

•

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

•

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

•

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.

Distribution and Seasonal Activity of Phlebotominae Sand Flies in Yazd and Its Outskirts, Center of Iran

Background

Phlebotominae sand flies are the main vectors of leishmaniasis and some other diseases.

Materials and Methods

Using sticky traps, sand flies were collected fortnightly from outdoors and indoors areas of selected sites.

Results

A total of 2032 specimens (498 in the city and 1534 in the outskirts of Yazd) belonging to 11 species were collected. The activity of sand flies started in early-April and ended in mid-November. There were two peaks of activity in the end of April and mid-September. Phlebotomus sergenti and P. papatasi were the most abundant species in the city and outskirts of Yazd city, respectively. Other species were P. salehi, P. ansarii, P. kazerouni, P. caucasicus, P. andrejevi, P. alexandri, P. mongolensis, Sergentomyia sintoni, and S. palestinensis.

Conclusion

In comparison to some other parts of Iran, the extended period between two peaks suggests that the larvae to adult development of sand fly were delayed by the higher temperature of the summer months in Yazd province.

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.

Performance comparison of CareStart™ HRP2/pLDH combo rapid malaria test with light microscopy in north-western Tigray, Ethiopia: a cross-sectional study

BACKGROUND

Rapid diagnostic tests (RDTs) are alternative methods for microscopy in the diagnosis of malaria in resource limited settings. Among commercially available RDTs, CareStart™ Malaria test was found to show reliable results. This study evaluated the performance of CareStart™ Malaria Combo test kit in Northwestern Tigray in Ethiopia.

METHODS

Blood samples were collected from 320 malaria-suspected patients at Mayani Hospital in Northwestern Tigray from December 2015 to March 2016. All blood samples were examined using both light microscopy and CareStart™ Malaria HRP2/pLDH Combo Test kit. Statistical analyses were performed using SPSS version 20.

RESULTS

The overall parasite positivity using light microscopy and CareStart™ RDT was 41 (12.8%) and 43 (13.4%), respectively. The sensitivity and specificity of CareStart™ RDT, regardless of species, were found to be 95.4 and 99.3%, respectively. Furthermore, the sensitivity of CareStart™ RDT for Plasmodium falciparum or mixed infection and non-falciparum malaria parasites was 94.4 and 85.0%, respectively while the specificity was found to be 98.9 and 99.7%, respectively. The agreement between the two test methods was "excellent" with a kappa value of 0.92.

CONCLUSION

CareStart™ RDT has very good sensitivity and specificity for malaria diagnosis. The test kit also has an excellent agreement with light microscopy. It is therefore useful in resource-limited areas where microscopy is not available.

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.

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.

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.

Amazonian Triatomine Biodiversity and the Transmission of Chagas Disease in French Guiana: In Medio Stat Sanitas

The effects of biodiversity on the transmission of infectious diseases now stand as a cornerstone of many public health policies. The upper Amazonia and Guyana shield are hot-spots of biodiversity that offer genuine opportunities to explore the relationship between the risk of transmission of Chagas disease and the diversity of its triatomine vectors. Over 730 triatomines were light-trapped in four geomorphological landscapes shaping French-Guiana, and we determined their taxonomic status and infection by Trypanosoma cruzi. We used a model selection approach to unravel the spatial and temporal variations in species abundance, diversity and infection. The vector community in French-Guiana is typically made of one key species (Panstrongylus geniculatus) that is more abundant than three secondary species combined (Rhodnius pictipes, Panstrongylus lignarius and Eratyrus mucronatus), and four other species that complete the assemblage. Although the overall abundance of adult triatomines does not vary across French-Guiana, their diversity increases along a coastal-inland gradient. These variations unravelled a non-monotonic relationship between vector biodiversity and the risk of transmission of Chagas disease, so that intermediate biodiversity levels are associated with the lowest risks. We also observed biannual variations in triatomine abundance, representing the first report of a biannual pattern in the risk of Chagas disease transmission. Those variations were highly and negatively correlated with the average monthly rainfall. We discuss the implications of these patterns for the transmission of T. cruzi by assemblages of triatomine species, and for the dual challenge of controlling Amazonian vector communities that are made of both highly diverse and mostly intrusive species.

Physiological Age Structure and Leishmania spp. Detection in Phlebotomus (Larroussius) orientalis (Parrot, 1936) (Diptera: Psychodidae) at an Endemic Focus of Visceral Leishmaniasis in Northern Ethiopia

Visceral leishmaniasis (VL) caused by Leishmania donovani is endemic in northern Ethiopia, where P. orientalis is the most important presumed vector. This study was designed to determine the physiological age structure and the occurrence of Leishmania infection in the vector of VL in Tahtay Adiyabo district, northern Ethiopia. Sand flies were collected using CDC light traps from peridomestic and agricultural fields between May 2011 and April 2012 and P. orientalis females were dissected for age determination and detection of Leishmania promastigotes. Sand flies were also analyzed for L. donovani detection using molecular methods. Of 1,282 P. orientalis examined for abdominal stages and age characterization, 66.2%, 28.2%, 4.1%, and 1.6% were unfed, freshly fed, half-gravid, and gravid. Parous rate in unfed females was 34.1% and 35.4% in peridomestic and agricultural fields, respectively. Out of 921 P. orientalis females dissected, one specimen (0.1%) was found naturally infected with promastigotes. Five pools (25 females) of unfed P. orientalis were also found with DNA of Leishmania spp. In particular, a single P. orientalis was positive for L. donovani (0.5%). Based on this and other evidences (abundance, human blood feeding, and xenodiagnostic studies), P. orientalis is the principal vector of VL in this endemic focus.