Phlebotomine sandfly responses to carbon dioxide and human odour in the field

Host preference and human blood index of Phlebotomus orientalis, an exophilic sand fly vector of visceral leishmaniasis in eastern Sudan

Visceral leishmaniasis (VL, kala azar), caused by Leishmania donovani, transmitted by Phlebotomus orientalis, is a serious systemic disease that causes high morbidity and mortality rates in Sudan and other parts of East Africa and the world. Despite progress in understanding the epidemiology of the disease in East Africa, little is known about the host preference of P. orientalis in kala azar endemic villages of Sudan, which have some of the highest VL incidence rates in the world. The present study used host choice experiments and blood-meal identification approaches to determine the host preference of P. orientalis in kala azar endemic villages in Gedarif state, eastern Sudan. In the host choice experiment, tent traps were used to compare the attractiveness of cows, donkeys, sheep and goats for host-seeking P. orientalis. In the blood-meal identification study, blood-fed P. orientalis females, captured inside houses and peri-domestic habitats, were subjected to molecular typing using cytochrome b gene (cyt b) amplification and sequence analysis. Cows and donkeys were the most attractive to blood-seeking P. orientalis, followed by goats. Similarly, the blood-meal analysis of P. orientalis showed that the vector preferentially feeds on cows, followed by donkeys, humans and goats. The human blood index of P. orientalis was 19.4% (42/216), indicating a high zoophilic habit of the vector, both inside and outside the houses. Although the order of host preference varied by location, it was clear that cows are the most preferred host of P. orientalis in the area. Results are discussed in relation to the role of domestic/livestock animals in VL zoopotentiation and zooprophylaxis. Inference is made on the potential impact of insecticide treatment of cows in control of the vector and the transmission of VL in Sudan and other parts of East Africa.

Evolutionary consequences of vector-borne transmission: how using vectors shapes host, vector and pathogen evolution

Transmission mode is a key factor that influences host–parasite coevolution. Vector-borne pathogens are among the most important disease agents for humans and wildlife due to their broad distribution, high diversity, prevalence and lethality. They comprise some of the most important and widespread human pathogens, such as yellow fever, leishmania and malaria. Vector-borne parasites (in this review, those transmitted by blood-feeding Diptera) follow unique transmission routes towards their vertebrate hosts. Consequently, each part of this tri-partite (i.e. parasite, vector and host) interaction can influence co- and counter-evolutionary pressures among antagonists. This mode of transmission may favour the evolution of greater virulence to the vertebrate host; however, pathogen–vector interactions can also have a broad spectrum of fitness costs to the insect vector. To complete their life cycle, vector-borne pathogens must overcome immune responses from 2 unrelated organisms, since they can activate responses in both vertebrate and invertebrate hosts, possibly creating a trade-off between investments against both types of immunity. Here, we assess how dipteran vector-borne transmission shapes the evolution of hosts, vectors and the pathogens themselves. Hosts, vectors and pathogens co-evolve together in a constant antagonistic arms race with each participant's primary goal being to maximize its performance and fitness.

Diagnosis and prevalence of canine leishmaniasis in the Atlas shepherd dog

The aim of this study was to determine the prevalence of canine leishmaniasis in the Atlas shepherd dogs from the Tiaret region of Algeria. A total of 161 dogs were included in this study and four diagnostic techniques were used, namely lymph node cytology, PCR, IFAT and ELISA. 110 out of 161 dogs were positive by at least one diagnostic technique, a percentage of 68.32% of the total number, which represent very high prevalence of canine leishmaniasis in this canine breed. 152 dogs underwent the two serological tests namely IFAT and ELISA among which 137 dogs underwent in addition the molecular examination by PCR. IFAT was positive in 9.86% of the dogs, ELISA was positive in 12.5% while 68% of the dogs proved positive by PCR. 47 dogs with lymph node enlargement underwent lymph node cytology, of which 26 dogs showed forms of amastigotes in their smears after microscopic examination, confirming the usefulness of this approach for the diagnosis of canine leishmaniasis. The clinical signs of the disease in this breed are similar to those of other canine breeds The dominant clinical signs in these dogs were onychogryphosis, poor general condition and lymph node hypertrophy. The autopsy was carried out on 7 dogs that died of canine leishmaniasis, all of which showed splenomegaly, while 5 dogs also showed hepatomegaly. Renal damage was found in 1 dog with frank jaundice. The splenic cytology was positive in all 7 dogs with the presence of amastigote forms in the smears after microscopic examination.

The Association Between the Syrian Crisis and Cutaneous Leishmaniasis in Lebanon

INTRODUCTION

Displacement of refugees from highly endemic areas of leishmaniasis to adjacent countries is associated with the spread of Leishmania. Syria is a country with a known high endemicity for cutaneous leishmaniasis and the presence of Syrian refugees in Lebanon has contributed to the re-emergence of the disease. The aim of this article is to evaluate the burden of cutaneous leishmaniasis in Lebanon in view of the presence of a large number of Syrian refugees.

METHODS

Data regarding all cases of leishmaniasis were collected from reports by the Lebanese Ministry of Public Health-Epidemiology Surveillance (LMPH-ESU), and the World Health Organization (WHO) between 2005 and 2018. All cases were reviewed in terms of area of residence, age and gender, clinical presentation, treatment, and outcome. An extensive literature review was conducted using "PubMed", "Medline", and "Google Scholar".

RESULTS

The annual number of leishmaniasis cases recorded in Lebanon between 2005 and 2011 ranged between 0 and 6 cases. In 2012, this number increased to 1275 cases and dropped to 263 in 2018, where all those infected were Syrian refugees from Aleppo, with zero cases of local transmission. Seventy-two percent of cases were seen in patients aged < 20 years. The predominant species of Leishmania was L. tropica followed by L. major.

CONCLUSION

Lebanon was affected by leishmaniasis following the Syrian crisis, and the influx of refugees to the country. Accurate disease monitoring and strategic training of healthcare personnel based within refugee camps are essential for proper containment. Preventative measures remain the best way to avoid both local and adjacent spread of leishmaniasis.

Field evaluation of four commercial light traps, trap placement, and effect of carbon dioxide on phlebotomine sand fly collection in northern Thailand

Several light trap devices have been invented and developed to assess the abundance of sand flies. Traps available in the market have different designs and attractant combinations to catch sand fly vectors. We evaluated the efficacy of four commercial light traps and determined the effect of trap placement and carbon dioxide (CO₂) on sand fly collection in northern Thailand. Trap evaluations were conducted at two natural caves located in Chiang Rai province, Thailand. In the first part of the study, the efficacies of four trap types including the Centers for Disease Control miniature light trap (CDC LT), Encephalitis Vector Survey trap (EVS), CDC Updraft Blacklight trap (CDC UB), and Laika trap (LK) were evaluated and compared using a Latin square experimental design. The second half of the study evaluated the influence of trap placement and CO₂ on sand fly collection. Additionally, CDC LT were placed inside, outside, and at the entrance of caves to compare the number of sand flies collected. For the trap efficacy experiment, a total of 11,876 phlebotomine sand flies were collected over 32 trap-nights. Results demonstrated that CDC LT, CDC UB, and LK collected significantly more sand flies than EVS (P > 0.05). However, there were no significant differences between the numbers of sand flies collected by CDC LT, CDC UB, and LK. A total of 6,698 sand flies were collected from the trap placement and CO₂ experiment over 72 trap-nights. Results showed that CO₂ did not influence the numbers of sand flies captured (P < 0.05), whereas trap placement at the entrance of the caves resulted in collection of significantly more sand flies than traps placed inside and outside of the caves. We found the CDC LT, CDC UB, and LK without CO₂ captured the greatest amount of sand flies. This was particularly observed when traps were placed at the entrance of a cave, perhaps because of the greater passage of stimuli caused by wind flow at the entrance of the cave. The light traps in this study can be used effectively to collect sand fly vectors in northern Thailand.

One Health Approach to Leishmaniases: Understanding the Disease Dynamics through Diagnostic Tools

Leishmaniases are zoonotic vector-borne diseases caused by protozoan parasites of the genus Leishmania that affect millions of people around the globe. There are various clinical manifestations, ranging from self-healing cutaneous lesions to potentially fatal visceral leishmaniasis, all of which are associated with different Leishmania species. Transmission of these parasites is complex due to the varying ecological relationships between human and/or animal reservoir hosts, parasites, and sand fly vectors. Moreover, vector-borne diseases like leishmaniases are intricately linked to environmental changes and socioeconomic risk factors, advocating the importance of the One Health approach to control these diseases. The development of an accurate, fast, and cost-effective diagnostic tool for leishmaniases is a priority, and the implementation of various control measures such as animal sentinel surveillance systems is needed to better detect, prevent, and respond to the (re-)emergence of leishmaniases.

Evaluation of Different Attractive Traps for Capturing Sand Flies (Diptera: Psychodidae) in an Endemic Area of Leishmaniasis, Southeast of Iran

Background:

The attraction of phlebotomine sand flies to plant and animal hosts is due to the produced chemical compounds, affecting the olfactory receptors of the insects. Therefore, novel and effective methods, such as Attractive Toxic Sugar Baits (ATSB) and Attractive Toxic Baits (ATB), are based on the effective materials that attract sand flies toward the host. The present study was designed to identify the attractive materials in plants and animals for using in ATSB and ATB.

Methods:

This cross-sectional study was carried out in July 2018 on endemic areas of leishmaniasis in Iran. Different baits, including mango, nectarine, grape, banana, melon and watermelon, defibrinated blood of cattle, sheep, goat and chicken, urine of cattle, sheep, goat and ultimately, simple and complex chemicals, such as CO₂, 1-octanol, lactic acid and human sweat were placed inside the traps, and the rate of the sand flies attraction to these materials was studied. Furthermore, data were analyzed using the Kruskal-Wallis test and Mann Whitney U test.

Results:

There was a significant difference in the sand flies attraction between the traps containing watermelon, urine of cattle, and sheep, and chemicals such as CO₂ and human sweat and the control trap (p< 0.05).

Conclusion:

This study showed that watermelon and CO₂ are the potential candidates for using in ATSB and ATB, respectively.

Two new phlebotomine sandflies (Diptera: Psychodidae) from the forest edge in Madagascar: the anthropophilic Phlebotomus artemievi sp. nov. and Sergentomyia maroantsetra ensis sp. nov

A few data are related to the anthropophily of Malagasy Phlebotomine sandflies. Prior studies focussed mainly to inventories and description of new species. Our goal was to emphasize the anthropophily of Malagasy Phlebotomine sandflies. We worked in the Makira region, using two simultaneous methods: human landing catches (HLC) and CDC light traps. We collected sandflies in three rural communities adjacent to the Makira Natural Park. In each community, three different biotopes were sampled: within community settlements; at the edge of forest, typically in agricultural land; and within the forest. We collected 61 sandflies belonging to two new species presently described: Phlebotomus artemievi sp. nov. and Sergentomyia maroantsetraensis sp. nov. These sandflies were caught exclusively in the forest edge biotope. None were captured within communities or within forests. HLC provided 97% of the collected sandflies, corresponding to a human-biting rate of 15 females per human per night. CDC provided only two females. Ph. artemievi sp. nov. was predominantly captured by HLC and appears to be highly anthropophilic. Here, we update the behavioural ecology of sandflies and describe two new species. Further research is required to understand their vector competence and their ability to transmit arboviruses and other pathogens such as Leishmania.

Comparison of BG-Lure and BG-Sweetscents attractants for field sampling of phlebotomine sand flies

Phlebotomines are important vectors of bacteria, viruses and protozoan parasites. Protozoans of the genus Leishmania which cause visceral and cutaneous leishmaniases, are among the most important etiologic agents transmitted by sand flies. Different blends of human and animal volatiles have been evaluated for use in surveillance and/or control of hematophagous insects. With regard to phlebotomine sand flies there are few records of attraction under laboratory and field conditions. This study was carried out at two collecting sites located in a Brazilian town with a high prevalence of cutaneous leishmaniasis. The aim of the present study was to evaluate the effect of adding two kinds of commercial bait which mimic human odors to light traps to attract sand flies and compare the results with those of light traps without any additional bait. The commercial baits, BG-Lure® and BG-Sweetscent®, were developed to catch anthropophilic mosquitoes. Three treatments were evaluated: 1 - HP light trap with BG-Lure® added; 2 - HP light trap with BG-Sweetscent® added and 3- HP light trap without any attractant. A total of 3,682 sand flies were collected during the study. Constrained correspondence analysis was applied to perform ordination of the captured community of sand fly species that could be explained by attractant, sampling site and sex. The most abundant species: Pintomyia nevesi, Nyssomyia whitmani and Nyssomyia antunesi were further investigated by fitting generalized linear mixed models. Only Ny. whitmani showed a slight indication of an increase in catches with BG-Lure®.

Influence of Leishmania (Viannia) braziliensis infection on the attractiveness of BALB/c mice to Nyssomyia neivai (Diptera: Psychodidae)

BACKGROUND

Phlebotomine sand flies are vectors for several pathogens, with Leishmania being the most important. In Brazil, the main aetiological agent of American cutaneous leishmaniasis (ACL) is Leishmania (Viannia) braziliensis, and Nyssomyia neivai is one of its main vectors in São Paulo state and other areas of South America. Similar to other haematophagous insects, sand flies use volatile compounds called kairomones to locate their hosts for blood meals. A possible increase in the attractiveness of hosts infected with Leishmania infantum to their vectors has been demonstrated. In the present study, we aimed to investigate whether L. braziliensis-infected hosts present higher attractiveness to Ny. neivai and to identify differences in the volatile compounds released by infected and uninfected mice.

RESULTS

Behavioural experiments in which sand fly females directly fed on infected or uninfected mice showed no significant differences in the attractiveness of the mice or the blood volume ingested. Y-tube olfactometer bioassays also revealed no significant differences in the attractiveness of these hosts to Ny. neivai. No differences were observed in the profiles of the volatile compounds released by the two groups of mice. However, PCA and cluster analysis were able to classify the 31 identified compounds into three clusters according to their abundances. This classification showed a possible role for individual variation in the absence of differences in volatile profiles and attractiveness between infected and uninfected mice.

CONCLUSION

In this first cross-sectional study with an aetiological agent of ACL, there were no statistically significant differences in the attractiveness of infected hosts to their vector.

Attraction of phlebotomine sandflies to volatiles from skin odors of individuals residing in an endemic area of tegumentary leishmaniasis

Background

Many studies have investigated what could attract insects of medical importance and a crucial role has lately been attributed to human skin odors. Most of these researches have been concerned with mosquitoes, e.g., vectors of dengue and malaria. Little is known about volatile organic compounds (VOCs) from human skin odors and their effects on leishmania vectors.

Objective

The present study aimed to identify the VOCs from human skin that can be attractive to female anthropophilic phlebotomine sandflies.

Results

Forty-two VOCs were identified from skin odors of 33 male volunteers, seven of which were tested in wind tunnel assays employing field-captured phlebotomine sandflies (75.4% identified as Lutzomyia intermedia). Hexane and (E)-oct-3-en-1-ol (octenol) were used as negative and positive controls, respectively. 2-Phenylacetaldehyde (hereafter called phenylacetaldehyde), 6-methylhept-5-en-2-one (also known as sulcatone), nonadecane and icosane were found to activate female phlebotomine sandflies, but only phenylacetaldehyde, 6-methylhepten-5-en-2-one and icosane elicited attraction responses.

Conclusions

These results suggest that phenylacetaldehyde, 6-methylhepten-5-en-2-one and icosane may be suitable candidates for attractiveness experimentation in the field which can be an important tool to develop strategies concerning human beings protection against phlebotomine sandflies bites and consequently against leishmaniasis.

Experimental infection and transmission of Leishmania by Lutzomyia cruzi (Diptera: Psychodidae): Aspects of the ecology of parasite-vector interactions

Several parameters should be addressed before incriminating a vector for Leishmania transmission. Those may include its ability to become infected by the same Leishmania species found in humans, the degree of attractiveness for reservoirs and humans and capacity to sustain parasite infection under laboratory conditions. This study evaluated the vectorial capacity of Lutzomyia cruzi for Leishmania infantum and gathered information on its ability to harbor L. amazonensis. Laboratory-reared Lu. cruzi were infected experimentally by feeding them on dogs infected naturally with L. infantum and hamsters infected with L. amazonensis. Sand fly attractiveness to dogs and humans was determined using wild caught insects. The expected daily survival of infected Lu. cruzi, the duration of the gonotrophic cycle, and the extrinsic incubation period were also investigated for both parasites. Vector competence was investigated for both Leishmania species. The mean proportion of female sand flies that fed on hosts was 0.40. For L. infantum and L. amazonensis, Lu. cruzi had experimental infection rates of 10.55% and 41.56%, respectively. The extrinsic incubation period was 3 days for both Leishmania species, regardless of the host. Survival expectancy of females infected with L. infantum and L. amazonensis after completing the gonotrophic cycle was 1.32 and 0.43, respectively. There was no association between L. infantum infection and sand fly longevity, but L. amazonensis–infected flies had significantly greater survival probabilities. Furthermore, egg-laying was significantly detrimental to survival. Lu. cruzi was found to be highly attracted to both dogs and humans. After a bloodmeal on experimentally infected hosts, both parasites were able to survive and develop late-stage infections in Lu. cruzi. However, transmission was demonstrated only for L. amazonensis–infected sand flies. In conclusion, Lu. cruzi fulfilled several of the requirements of vectorial capacity for L. infantum transmission. Moreover, it was also permissive to L. amazonensis.

Leishmaniasis is a vector-borne disease caused by the Leishmania parasite. It is transmitted by phlebotomine sand flies when infected females take a bloodmeal from a mammalian host. The transmission of Leishmania species involves complex ecological interactions between parasite–vector and vector–host. Until recently, the sand fly Lutzomyia longipalpis, which belongs to a species complex, had been solely incriminated in Latin American transmission of Leishmania infantum. However, there are still uncertainties concerning the L. infantum transmission, especially in an urban area endemic for visceral leishmaniasis in Brazil. Along the years, Lutzomyia cruzi has been suspected of transmitting L. infantum in Corumbá and vicinity, and this study aimed to provide more accurate evidence of this phenomenon. Laboratory-reared Lu. cruzi were infected experimentally by allowing them to feed on dogs naturally infected with L. infantum and on hamsters infected with L. amazonensis. Our results identified important life cycle parameters of Lu. cruzi infected by Leishmania in laboratory conditions. We identified the components related to vectorial capacity, and also the vector incrimination criteria of Lu. cruzi for L. infantum. Additionally, we demonstrated the experimental transmission of L. amazonensis by Lu. cruzi to a naïve host, and revealed strong evidence that supports Lu. cruzi as a vector of L. infantum and as a permissive vector for L. amazonensis.

Entering and exiting behaviour of the phlebotomine sand fly Lutzomyia longiflocosa (Diptera: Psychodidae) in rural houses of the sub-Andean region of Colombia

The present study identified the entering and exiting sites for Lutzomyia longiflocosa in rural houses of the sub-Andean region in Colombia. Entering sites were identified with sticky traps set up outside the bedrooms, around the eave openings, and with cage traps enclosing the slits in the doors and windows inside the bedrooms. Exiting sites were identified by releasing groups of females indoors. These females were blood fed and marked with fluorescent powders. Females were recaptured with the trap placement described above but set up on the opposite sides of the openings. In the entering experiment, a significantly higher number of females were captured in the sticky traps at the zone nearest the eave openings (n = 142) than those captured in the other zones of the trap (n = 52); similarly, a higher number of females were captured on the front side of the house (n = 105) than at the rear side (n = 37). Only two females were collected in the cage trap. In the exiting experiment, at the ceiling, the highest percentage (86.2%) of females was recaptured with sticky traps nearest the eave openings and on the front side of the house (70.0%). Seven females were collected in the cage trap. Lu. longiflocosa entered and exited houses primarily through the eave openings in a non-random pattern in relation to the sides of the house.

Comparison of In Vivo and In Vitro Methods for Blood Feeding of Phlebotomus papatasi (Diptera: Psychodidae) in the Laboratory

Phlebotomus papatasi Scopoli is a medically important insect that has been successfully colonized in the laboratory, and blood feeding is critical for colony propagation. There has been much interest in developing established protocols for in vitro blood-feeding systems. The objective of this study was to determine if a Parafilm membrane and a hog's gut membrane could be successfully used with in vitro feeding systems. We evaluated percentages of P. papatasi females that blood fed on different blood-feeding systems (a mouse, a Hemotek feeder, or a glass feeder) used with either a Parafilm or a hog's gut membrane, with cohorts of 250 and 500 P. papatasi females, and with or without external exhalations. For all feeding system combinations, female P. papatasi blood fed in higher percentages when in cohorts of 500 individuals and in the presence of exhalations. Higher percentages of P. papatasi fed on a mouse, but this study also demonstrates that P. papatasi will readily feed with in vitro feeding systems using a Parafilm membrane or a hog's gut membrane. This study suggests that female P. papatasi may use an invitation effect to blood feed and are attracted to blood sources via chemical olfaction cues, both of which have been characterized in other blood-feeding arthropods. Our study demonstrates that a Parafilm membrane or a hog's gut membrane, in conjunction with the Hemotek or glass feeder system, is potentially a viable alternative to live rodents to blood feed a colony of P. papatasi.

Blood-Feeding Behaviors of Anopheles stephensi but not Phlebotomus papatasi are Influenced by Actively Warming Guinea Pigs (Cavia porcellus) Under General Anesthesia

Animal models are often used to study hematophagous insect feeding behavior and evaluate products such as topical repellents. However, when these models are used the study animals often experience significant drops in core body temperature because of the effects of anesthesia. This study used a guinea pig model to investigate whether maintaining a normothermic core body temperature during anesthesia influenced the rate of Anopheles stephensi and Phlebotomus papatasi blood feeding. Experiments were conducted with anesthetized animals that had their body temperatures either maintained with a warming device or were allowed to drop naturally. Results showed that when guinea pigs were actively warmed by a heating device, An. stephensi feeding behavior was similar at the beginning and end of anesthesia. However, when a warming device was not used, fewer An. stephensi took a blood meal after the animals' temperatures had dropped. Phlebotomus papatasi were not as sensitive to changes in temperature and feeding rates were similar whether a warming device was used or not. These results are discussed and it is recommended that warming devices are used when conducting feeding experiments with insects sensitive to changes in host body temperature, such as An. stephensi.

Response of the sand fly Phlebotomuspapatasi to visual, physical and chemical attraction features in the field

In this study, 27 CDC traps were modified with various attractive features and compared with a CDC trap with no light source or baits to evaluate the effects on attraction to Phlebotomus papatasi (Scopoli) north of the Dead Sea near Jericho. Attractive features included CO2, lights, colored trap bodies, heat, moisture, chemical lures and different combinations of the same. Traps were placed 20m apart and rotated from one trap location to the next after 24h trapping periods. The most significant attractive feature was CO2, which attracted more sand flies than any other feature evaluated. Ultraviolet light was the next most attractive feature, followed by incandescent light. When evaluated alone, black or white trap bodies, heat and moisture, all influenced trap catch but effects were greater when these attractive features were used together. The results of this study suggest that traps with CO2 and UV light could be used in batteries as control interventions if suitable CO2 sources become available.

[Cutaneous leishmaniasis by Leishmania major and Leishmania tropica in Morocco: comparative epidemioclinical aspects of 268 cases]

Introduction

Depuis 1995, le Maroc a connu une réactivation des foyers de leishmanioses cutanées (LC) à L. major et une nouvelle répartition géographique des foyers à L. tropica. Le but de cette étude est de comparer les aspects épidémio-cliniques associés aux LC potentiellement dûes à L. major et à L. tropica.

Méthodes

Une étude rétrospective a colligé 268 cas de LC au service de dermatologie du CHU Ibn Rochd de Casablanca entre Janvier 1995 et Septembre 2010. Les données étaient analysées par Epi info version 3.5.1. Le test X2 était appliqué (Différence significative = p< 0,05).

Résultats

Deux cent soixante-huit cas de LC ont été colligés, dont 160 femmes et 108 hommes. Ils ont été répartis en 123 patients originaires des foyers à L.major et 145 patients originaires des foyers à L. tropica. L'aspect ulcéronodulaire, ulcérovégétant ou végétant était retrouvé dans 58 cas (47,2%) des cas de LC à L. major versus 24 cas (16,7%) dans la L.C à L. tropica. L'aspect papulonodulaire était retrouvé dans 84 cas (58%) de LC à L. tropica contre 41 cas (33,3%) de LC à L. major.

Conclusion

Dans la LC à L. major, l'atteinte des membres et les aspects cliniques végétant ou ulcéro-végétant restent toujours prédominants. Dans la L.C à L. tropica, l'atteinte papulonodulaire unique du visage reste prédominante mais des formes ulcéronodulaires, végétantes ou ulcérovégétantes existent également dans les foyers récents à L. tropica, prêtant à confusion cliniquement avec des LC à L. major.

Morphology and physiology of the olfactory system of blood-feeding insects

Several blood-feeding (hematophagous) insects are vectors of a number of diseases including dengue, Chagas disease and leishmaniasis which persistently affect public health throughout Latin America. The vectors of those diseases include mosquitoes, triatomine bugs and sandflies. As vector control is an efficient way to prevent these illnesses it is important to understand the sensory biology of those harmful insects. We study the physiology of the olfactory system of those insects and apply that knowledge on the development of methods to manipulate their behavior. Here we review some of the latest information on insect olfaction with emphasis on hematophagous insects. The insect olfactory sensory neurons are housed inside hair-like organs called sensilla which are mainly distributed on the antenna and mouthparts. The identity of many of the odor compounds that those neurons detect are already known in hematophagous insects. They include several constituents of host (vertebrate) odor, sex, aggregation and alarm pheromones, and compounds related to egg-deposition behavior. Recent work has contributed significant knowledge on how odor information is processed in the insect first odor-processing center in the brain, the antennal lobe. The quality, quantity, and temporal features of the odor stimuli are encoded by the neural networks of the antennal lobe. Information regarding odor mixtures is also encoded. While natural mixtures evoke strong responses, synthetic mixtures that deviate from their natural counterparts in terms of key constituents or proportions of those constituents evoke weaker responses. The processing of olfactory information is largely unexplored in hematophagous insects. However, many aspects of their olfactory behavior are known. As in other insects, responses to relevant single odor compounds are weak while natural mixtures evoke strong responses. Future challenges include studying how information about odor mixtures is processed in their brain. This could help develop highly attractive synthetic odor blends to lure them into traps.

Dispersal and memory of sand flies in an endemic area of cutaneous leishmaniasis, southern Brazil

The dispersal of and the existence of memory in sand flies were measured in a transmission area of cutaneous leishmaniasis, in the municipality of Bandeirantes, Paraná, Brazil. Sand flies were caught in a rural area, with Shannon trap installed in the forest and three Falcão traps installed in a human-inhabited environment (HIE) and three others in an impacted environment presently uninhabited by humans (EUH), from 1800 to 0600 hours. The captured sand flies were marked with yellow, blue, or red fluorescent powder, according to the environments where they were captured. All marked sand flies were released at 0700 hours at a point between the three environments. The recaptures were made with 28 Falcão traps, distributed in the environments from for 10 consecutive days. The sand flies recaptured were examined under a stereomicroscope and later identified. It was concluded that sand flies are able to disperse over an average distance of 73 m, reaching 130 m in 24 h, showing that: 1) the sand flies were attracted with different intensities to each environment, and the ability to move among different environments allows the existence of enzootic cycle of Leishmania; 2) the sand flies possess a spatial memory, olfactory memory, or both, that enable them to return to the environment where they were captured initially, although the distances were different.

Clinical and epidemiologic profile of cutaneous leishmaniasis in Colombian children: considerations for local treatment

Treatment alternatives have seldom been evaluated in children with cutaneous leishmaniasis (CL). We examine the clinical/epidemiological profile of children with CL considering international guidelines for local treatment. Descriptive analyses were conducted using International Center for Medical Research and Training (CIDEIM) case reports of parasitologically diagnosed patients ≤ 14 years of age from 2004 to 2010. Eligibility for local treatment based on World Health Organization/Pan American Health Organization (WHO/PAHO) criteria was determined. Among 380 children, 90% presented lesions of < 3 months duration, 54% presented single lesions < 30 mm in diameter, and 45% were ≤ 5 years old. Lesions on the head and neck were more frequent among children 0-5 years, and lesions below the head/neck were more frequent among 11- to 14-year-old children (P = 0.004). Using PAHO and WHO criteria, 26% and 53% of children, respectively, were eligible for local treatment. Recommended local treatments for New World CL have potential but limited applicability in children. Individual risk-benefit assessment and effectiveness data in children may increase eligibility.

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.

Olfactory carbon dioxide detection by insects and other animals

Carbon dioxide is a small, relatively inert, but highly volatile gas that not only gives beer its bubbles, but that also acts as one of the primary driving forces of anthropogenic climate change. While beer brewers experiment with the effects of CO2 on flavor and climate scientists are concerned with global changes to ambient CO2 levels that take place over the course of decades, many animal species are keenly aware of changes in CO2 concentration that occur much more rapidly and on a much more local scale. Although imperceptible to us, these small changes in CO2 concentration can indicate imminent danger, signal overcrowding, and point the way to food. Here I review several of these CO2-evoked behaviors and compare the systems insects, nematodes, and vertebrates use to detect environmental CO2.

Attraction of the cutaneous leishmaniasis vector Nyssomyia neivai (Diptera: Psychodidae) to host odour components in a wind tunnel

BACKGROUND

Laboratory studies of host-seeking olfactory behaviour in sandflies have largely been restricted to the American visceral leishmaniasis vector Lutzomyia longipalpis. In comparison, almost nothing is known about the chemical ecology of related species, which transmit American cutaneous leishmaniasis (ACL), due in part to difficulties in raising these insects in the laboratory. Understanding how ACL vectors locate their hosts will be essential to developing new vector control strategies to combat this debilitating disease.

METHODS

This study examined host-odour seeking behaviour of the ACL vector Nyssomyia neivai (Pinto) (=Lutzomyia neivai) using a wind tunnel olfactometer. The primary aim was to determine whether field-collected female N. neivai would respond to host odours in the laboratory, thereby eliminating the need to maintain colonies of these insects for behavioural experiments. Responses to two key host odour components, 1-octen-3-ol and lactic acid, and a commercially-available mosquito lure (BG-Lure™) were assessed and compared relative to an air control. We also tested whether trials could be conducted outside of the normal evening activity period of N. neivai without impacting on fly behaviour, and whether the same flies could be used to assess baseline responses to air without affecting responses to octenol, thereby reducing the number of flies required for experiments.

RESULTS

Octenol was found to both activate host-seeking behaviour and attract female N. neivai in the wind tunnel, while lactic acid elicited weaker responses of activation and attractiveness under identical conditions. The BG-Lure did not activate or attract N. neivai under test conditions. Further experiments showed that sandfly behaviour in the wind tunnel was not affected by time of day, such that experiments need not be restricted to nocturnal hours. Moreover, using the same flies to measure both baseline responses to air and attraction to test compounds did not affect odour-seeking behaviour.

CONCLUSIONS

The results of this study demonstrate that N. neivai taken from the field are suitable for use in laboratory olfactometer experiments. It is hoped this work will facilitate further research into chemical ecology of this species, and other ACL vectors.

American visceral leishmaniasis in Chiapas, Mexico

We report the results of a study conducted during 1990-2006 with 89 cases of American visceral leishmaniasis in Chiapas State in southeastern Mexico and a seroprevalence study performed with 726 persons and 224 dogs that lived near cases of American visceral leishmaniasis. Clinical aspects, epidemiologic profiles, and risk factors are described. Most cases were in children ≤ 5 years of age, the prevalence of seropositive persons was 77%. The main risk factors associated with this disease were having 1-3 rooms in a house compared with ≥ 4 rooms, having a roof that was not made of cement, and having domestic animals. In contrast, only 19% of dogs were seropositive, suggesting that this species is not important in the transmission cycle of Leishmania. These data indicate that active transmission is taking place in the central valley of Chiapas State, Mexico, in communities located < 1,000 meters above sea level near the Grijalva River.

Attraction of Phlebotomus papatasi to common fruit in the field

Sand flies have been reported feeding on various plant organs including stems, leaves, and flowers but the attraction of sand flies to sugar-rich fruits has received little attention. In this study, we tested 24 commercially available fruits for their attractiveness to sand flies, and found that the top three attractive fruits were nectarine (Prunus persica var. nectarina), cactus fruit, (Opuntia ficus-indica), and guava (Psidium guajava). These fruits were fed upon equally by both males and females. There were slight differences in the order of preference to the less-attractive fruits by males and females, but these were not statistically significant. The knowledge of fruit preference may help to improve existing methods that use plant phytochemicals to attract and kill biting flies.

Comparison of various configurations of CDC-type traps for the collection of Phlebotomus papatasi Scopoli in southern Israel

We conducted two experiments to determine the best CDC-trap configuration for catching male and female Phlebotomus papatasi. First, visual features were evaluated. Standard CDC traps were modified to have black or white catch bags, black or white lids, or no lids and these were tried in different combinations. Significantly more male sand flies were caught by darker traps; significantly more females were captured by traps with either all black or a combination of black and white features. Attraction may be due to dark color or contrast in colors. CDC traps with suction and the following features were also evaluated: no light; incandescent light; ultraviolet (UV) light; combination of black color, heat and moisture; CO(2) alone, or a combination of black color, heat, moisture, and CO(2) simultaneously, all in upright and inverted positions, with the opening for insect entry always 50 cm above the ground. Significantly more females than males were caught by all traps (standard and inverted) except the control traps with suction only. Traps with CO(2) caught more sand flies than traps without CO(2.) Traps with black color, heat and moisture captured significantly more sand flies than the control traps, but with the addition of CO(2) , these traps catch significantly more sand flies than the other traps evaluated. Inverting traps increased the catch for like traps by about two times.

Octenol as attractant to Nyssomyia neivai (Diptera:Psychodidae:Phlebotominae) in the field

The kairomone octenol is known as attractive to hematophagous Diptera such as mosquitoes, tsetse flies, and midges. There is little evidence that traps baited with octenol are also effective in attracting phlebotomine sand flies. The present report evaluated octenol in modified Centers for Disease Control and Prevention (CDC) traps in two experiments: 1) modified CDC trap without light and 2) modified CDC trap with light. The traps were baited with octenol at concentrations of 0.5, 27, and 43 mg/h in Rincão locality, São Paulo, Brazil. Traps without octenol were used as controls. The sand fly Nyssomyia neivai (Pinto) (= Lutzomyia neivai) (Diptera: Psychodidae: Phlebotominae) was the prevalent species (99.9%) in both experiments. The results of the experiments showed that traps baited with octenol at 27 and 43 mg/h caught significantly more N. neivai than control and octenol at 0.5 mg/h with and without light. This is the first report that shows that octenol itself is attractive to N. neivai and associated with light traps significantly increases the catches.

[Spatial and/or olfactory memory in sandflies in an endemic area for American cutaneous leishmaniasis, southern Brazil]

The results from an investigation on the possibility that sandflies in an endemic area for American cutaneous leishmaniasis, in the state of Paraná, may have memory are reported. Sandflies were caught in Recanto Marista, Doutor Camargo, State of Paraná, Brazil, using Falcão traps in two chicken sheds (G1 and G2), between November 15 and 26, 2007. A total of 2,080 sandflies were caught (1,000 in G1 and 1,080 in G2) and these were marked and released. Nyssomyia neivai was the most (90.5%) frequent species. Out of the total released, 168 sandflies (8%) were recaptured and the recapture rate in G2 was significant. The results show that it is possible that spatial or olfactory memory and/or host loyalty exists, and that this will guide the sandflies in recognizing the places where sources of blood are available.

Are light traps baited with kairomones effective in the capture of Lutzomyia longipalpis and Lutzomyia intermedia? An evaluation of synthetic human odor as an attractant for phlebotomine sand flies (Diptera: Psychodidae: Phlebotominae)

Phlebotomine sand flies are often captured with human bait and/or light traps, either with or without an animal bait. More recently, synthetic attractants have been used as bait in traps to improve the capture of phlebotomine sand flies as well as other insects of medical and veterinary importance. The aim of the present study was to evaluate the effects of the kairomone 1-octen-3-ol (octenol) and the synthetic human odor BG-Mesh Lure (BGML--lactic acid, caproic acid and ammonia) baited in modified CDC light traps on the capture of phlebotomine sand flies. The experiments followed the 5x5 Latin square design. Among the species caught, Lutzomyia intermedia apparently presented a dose-dependent response to octenol. The response obtained with the BGML, alone or in combination with octenol (5 mg/h), indicated some degree of attractiveness of these baits to different phlebotomine sand fly species. Octenol seems to be more attractive to L. intermedia than to Lutzomyia longipalpis, while the BGML presented a higher success in capturing L. longipalpis. When the components of the BGML were used separately, there was no increase in catching the female of L. intermedia. Apparently, there was no synergistic effect between the octenol and the BGML. In conclusion, the octenol and the BGML were demonstrated to be possible baits to attract some phlebotomine sand fly species.

Roles and effects of environmental carbon dioxide in insect life

Carbon dioxide (CO(2)) is a ubiquitous sensory cue that plays multiple roles in insect behavior. In recent years understanding of the well-known role of CO(2) in foraging by hematophagous insects (e.g., mosquitoes) has grown, and research on the roles of CO(2) cues in the foraging and oviposition behavior of phytophagous insects and in behavior of social insects has stimulated interest in this area of insect sensory biology. This review considers those advances, as well as some of the mechanistic bases of the modulation of behavior by CO(2) and important progress in our understanding of the detection and CNS processing of CO(2) information in insects. Finally, this review briefly addresses how the ongoing increase in atmospheric CO(2) levels may affect insect life.

Behavioral responses of Drosophila to biogenic levels of carbon dioxide depend on life-stage, sex and olfactory context

Drosophila melanogaster (Meigen) detects and uses many volatiles for its survival. Carbon dioxide (CO2) is detected in adults by a special class of olfactory receptor neurons, expressing the gustatory receptor Gr21a. The behavioral responses to CO2 were investigated in a four-field olfactometer bioassay that is new for Drosophila. We determined (1) whether the sensitivity of this response changes with odor context, and (2) if it depends on sex and life stage. When CO2 was added to ambient air in one field and tested against ambient air in the three other fields, individually observed adults avoided CO2 (0.1-1%above ambient), but did not respond to a low rise of 0.02%. We relate this behavior to measurements of CO2 production in bananas and flies. When 0.02% CO2 was combined with the odor of apple cider vinegar in one field of the olfactometer and tested against ambient air in the three other fields, the addition of CO2 did not affect the attractiveness of apple cider vinegar alone. However, this combination of CO2 and vinegar became repellent when it was tested against vinegar at ambient CO2 concentrations in the three other fields. This `odor background effect' was female-specific, revealing a sexually dimorphic behavior. The new assay allowed us to test larvae under similar conditions and compare their behavior to that of adults. Like adults, they avoided CO2, but with lower sensitivity. Larvae lacking neurons expressing Gr21a lost their avoidance behavior to CO2, but kept their positive response to vinegar odor. Hence, Gr21a-expressing neurons mediate similar behaviors in larvae and adults.

Household structure and urban services: neglected targets in the control of visceral leishmaniasis

Visceral leishmaniasis (VL) caused by Leishmania chagasi is a growing public-health problem in many parts of the New World. Although several studies have focused on the consequences of environmental damage, human migration and land occupation on the incidence of VL, the effects on the disease of the substandard living conditions that often result from the process of urbanization have not been investigated in detail. The present study was based in the Brazilian city of Teresina, where, since 1980, there have been two large outbreaks of VL (one in 1981-1985 and the other in 1993-1996), each involving at least 1000 newly reported cases. The role of household structure and the provision of urban services in the city, as predictors of the occurrence of VL, was studied in a case-control investigation. After controlling for age, crowding, and the background incidence of VL in the area where the subjects lived, the risk of acquiring the disease was found to be significantly higher for those who lived in houses with an inadequate sewage system and those who had no regular rubbish collection. Improving household structure and providing basic urban services might be effective strategies for controlling the spread of VL in urban areas.

Structure and distribution of sensilla on maxillary palps and labella ofLutzomyia longipalpis (Diptera: Psychodidae) sand flies

The typology, number, size, and distribution pattern of labellar and palpal sensilla of male and female Lutzomyia longipalpis (Lutz and Neiva, 1912) sand flies were analyzed by scanning electron and light microscopy, contributing to the construction of a gustatory and olfactory map in this important vector species. About 35 trichoid sensilla, sorted into three different classes according to their lengths, are present on the two labellar lobes. Five distinct structures are observed in the maxillary palps, which could be classified as noninnervated (microtrichia and scales) or the following innervated structures: 1) campaniform sensilla, found near the distal end of palpal segments II and III; 2) multiporous capitate peg sensilla, found in reduced number (1-6) on segment II, but located in a group of 15-25 on the distal third part of segment III; and 3) trichoid sensilla, distributed linearly on segment IV and spirally on segment V. Light microscopy analysis of silver-stained specimens indicated the presence of pores in the trichoid sensilla and their chemosensory function is discussed, as well as the possible function of the other sensilla.

West Nile virus outbreak in North American owls, Ontario, 2002

From July to September 2002, an outbreak of West Nile virus (WNV) caused a high number of deaths in captive owls at the Owl Foundation, Vineland, Ontario, Canada. Peak death rates occurred in mid-August, and the epidemiologic curve resembled that of corvids in the surrounding Niagara region. The outbreak occurred in the midst of a louse fly (Icosta americana, family Hippoboscidae) infestation. Of the flies tested, 16 (88.9 %) of 18 contained WNV RNA. Species with northern native breeding range and birds >1 year of age were at significantly higher risk for WNV-related deaths. Species with northern native breeding range and of medium-to-large body size were at significantly higher risk for exposure to WNV. Taxonomic relations (at the subfamily level) did not significantly affect exposure to WNV or WNV-related deaths. Northern native breeding range and medium-to-large body size were associated with earlier death within the outbreak period. Of the survivors, 69 (75.8 %) of 91 were seropositive for WNV.

The prolonged epidemic of anthroponotic cutaneous leishmaniasis in Kabul, Afghanistan: ‘bringing down the neighbourhood’

In order to investigate the distribution and causes of the spread of anthroponotic cutaneous leishmaniasis (ACL) in Kabul, Afghanistan, a cross-sectional study was conducted during 1997-98 amongst 75,787 residents in the 13 central districts of the city. Using data on active lesions and scars with their times of onset, migration patterns and age of subjects, 2 independent methods were used to estimate, retrospectively, the annual incidence of ACL in recent years. Results indicated a rapid increase in incidence from 1987, peaking in 1996 when an estimated 12% of the population had active disease. Active prevalence was lowest in infants (aged < 2 years), and while risk was gender-independent in children and adolescents, active prevalence in those aged > 20 years was significantly higher amongst females than males (odds ratio [OR] = 1.51, 95% CI 1.34-1.70). About 44% of lesions were located on the head, 38% on upper limbs, 16% on lower limbs and 2% elsewhere. The relative frequency of head lesions dropped with age (P < 0.001), and amongst adults was lowest amongst males (P < 0.001), possibly due to the protective effect of a beard. Within the study population, 32% reported that they had immigrated from outside Kabul, 34% that they had been born in Kabul but had since migrated to another district of the city, and 34% that they had been born in the district of their present residence. Active prevalence amongst those born in their current district of residence was positively associated with the percentage of immigrants in their district (P = 0.027), indicating that a 1% increase in the percentage of immigrants increased the odds of an active lesion by 12% (OR = 1.12, 95% CI 1.01-1.24), but there was no association with the percentage of migrants from other districts in Kabul (P = 0.65) or with war damage (P = 0.33). As active prevalence was not significantly greater in immigrants than local Kabulis, these results support the hypothesis that the epidemic in Kabul has been maintained by a steady influx of susceptible immigrants. It is important that the new opportunities for social development that now exist in Kabul are not hampered by this unpleasant and stigmatizing disease. As population movement is clearly a contributing factor to its transmission, this threat is very real.

Feeding behavior of Lutzomyia pseudolongipalpis (Diptera: Psychodidae), a putative vector of visceral leishmaniasis in Venezuela

Lutzomyia pseudolongipalpis Arrivillaga & Feliciangeli is the first new sand fly species in the L. longipalpis species complex that has been formally described since it was separated by genetic as well as by morphological characters. It is the putative vector of the American visceral leishmaniasis in La Rinconada, Curarigua, a restricted focus in central western Venezuela. We investigated the feeding behavior of this species. The blood meals from 210 of 429 (48.9%) engorged females caught by CDC light traps were identified by a dot enzyme-linked immuno-absorbent assay using antisera against humans and common domestic animals. We propose a new index, the host selectivity index, which is the number of sand flies fed on a given host relative to the available biomass of that host, as an indicator of the feeding behavior of this phlebotomine sand fly. The host selectivity index is compared with the forage ratio, which is the percentage of sand flies fed on a given host by the percentage which that host represented in the total census of available animals and humans. The most attractive animal for L. pseudolongipalpis in Curarigua was the dog, whereas humans were shown to be relatively unattractive. However, not only selectivity or biomass, but also the accessibility to this host may have influenced these results. The low population density of dogs and the low accessibility of L. pseudolongipalpis to humans in relation to domestic animals might help to explain the sporadic transmission of visceral leishmaniasis in this focus.