Cooperative Blood-feeding and the Function and Implications of Feeding Aggregations in the Sand Fly,Lutzomyia longipalpis (Diptera: Psychodidae)

Given the importance that the evolution of cooperation bears in evolutionary biology and the social sciences, extensive theoretical work has focused on identifying conditions that promote cooperation among individuals. In insects, cooperative or altruistic interactions typically occur amongst social insects and are thus explained by kin selection. Here we provide evidence that in Lutzomia longipalpis, a small biting fly and an important vector of leishmaniasis in the New World, cooperative blood-feeding in groups of non-kin individuals results in a strong decrease in saliva expenditure. Feeding in groups also strongly affected the time taken to initiate a bloodmeal and its duration and ultimately resulted in greater fecundity. The benefits of feeding aggregations were particularly strong when flies fed on older hosts pre-exposed to sand fly bites, suggesting that flies feeding in groups may be better able to overcome their stronger immune response. These results demonstrate that, in L. longipalpis, feeding cooperatively maximizes the effects of salivary components injected into hosts to facilitate blood intake and to counteract the host immune defences. As a result, cooperating sand flies enjoy enormous fitness gains. This constitutes, to our knowledge, the first functional explanation for feeding aggregations in this species and potentially in other hematophagous insects and a rare example of cooperation amongst individuals of a non-social insects species. The evolution of cooperative group feeding in sand flies may have important implications for the epidemiology of leishmaniasis.     

Phlebotomine sand flies (Diptera: Psychodidae) associated with the appearance of urban Leishmaniasis in the city of Sincelejo,Colombia

Although once associated only with rural areas, the American leishmaniasis vectors now appear to be associated also with urban and suburban areas of the Neotropics. Following the appearance of the first autochthonous visceral and cutaneous leishmaniasis cases in the urban area of the city of Sincelejo, Colombia, a preliminary entomological survey of the sand fly species composition was performed using Shannon and CDC light traps. A total of 486 sand flies representing six Lutzomyia species were collected. L. evansi, L. panamensis and L. gomezi, known vectors of Leishmania spp. were the predominant sand fly species around dwellings. The finding of these species in relation to the appearance of the first cases of leishmaniasis in the city mentioned is discussed.     

A summary of the evidence for the change in European distribution of phlebotomine sand flies (Diptera: Psychodidae) of public health importance

The phlebotomine sand flies (Diptera: Psychodidae, Phlebotominae) are vectors of several infectious pathogens. The presence of a sand fly vector is considered to be a risk factor for the emergence of leishmaniasis in temperate Europe. Hence, the occurrence of phlebotomine sand flies and any changes in their distribution is important in determining the potential change in distribution of leishmaniasis in Europe. Therefore, published evidence for a changing distribution of the important phlebotomine sand fly vectors of leishmaniasis and phlebovirus infection in Europe is reviewed. This paper presents evidence of an increasing risk of establishment by sand fly species, especially for the Atlantic Coast and inland parts of Germany, Switzerland, and Austria. In addition to detection in potentially appropriate areas, the findings show areas of potential future establishment of the species. The most important and urgent necessity within the community of entomologists working on phlebotomines is the need to record the extremes of distribution of each species and obtain data on their regional presence/absence along with increased sharing of the data throughout European projects.     

Epidemiology of visceral leishmaniasis through spatial analysis, in Belo Horizonte municipality, state of Minas Gerais, Brazil

The geographic information system approach has permitted integration between demographic, socio-economic and environmental data, providing correlation between information from several data banks. In the current work, occurrence of human and canine visceral leishmaniases and insect vectors (Lutzomyia longipalpis) as well as biogeographic information related to 9 areas that comprise the city of Belo Horizonte, Brazil, between April 2001 and March 2002 were correlated and georeferenced. By using this technique it was possible to define concentration loci of canine leishmaniasis in the following regions: East; Northeast; Northwest; West; and Venda Nova. However, as for human leishmaniasis, it was not possible to perform the same analysis. Data analysis has also shown that 84.2% of the human leishmaniasis cases were related with canine leishmaniasis cases. Concerning biogeographic (altitude, area of vegetation influence, hydrographic, and areas of poverty) analysis, only altitude showed to influence emergence of leishmaniasis cases. A number of 4673 canine leishmaniasis cases and 64 human leishmaniasis cases were georeferenced, of which 67.5 and 71.9%, respectively, were living between 780 and 880 m above the sea level. At these same altitudes, a large number of phlebotomine sand flies were collected. Therefore, we suggest control measures for leishmaniasis in the city of Belo Horizonte, giving priority to canine leishmaniasis foci and regions at altitudes between 780 and 880 m.     

Sand flies of Nicaragua: a checklist and reports of new collections

Sand flies within the genus Lutzomyia serve as the vectors for all species of the protozoan parasite Leishmania in the New World. In this paper, we present a summary of the 29 species of Lutzomyia and one of Brumptomyia previously reported for Nicaragua and report results of our recent collections of 565 sand flies at eight localities in the country from 2001-2006. Lutzomyia longipalpis was the predominant species collected within the Pacific plains region of western Nicaragua, while Lutzomyia cruciata or Lutzomyia barrettoi majuscula were the species most frequently collected in the central highlands and Atlantic plains regions. The collection of Lutzomyia durani (Vargas & Nájera) at San Jacinto in July 2001 is a new record for Nicaragua. Leishmaniasis is endemic to Nicaragua and occurs in three forms: cutaneous, mucocutaneous and visceral leishmaniasis. Cutaneous infections are the most prevalent type of leishmaniasis in Nicaragua and they occur in two different clinical manifestations, typical cutaneous leishmaniasis and atypical cutaneous leishmaniasis, depending on the species of the infecting Leishmania parasite. The distribution of sand flies collected during this study in relation to the geographic distribution of clinical forms of leishmaniasis in the country is also discussed.     

Lutzomyia longipalpis in Clorinda, Formosa province, an area of potential visceral leishmaniasis transmission in Argentina

Phlebotomine captures were performed during 2004 in Clorinda, Argentina. Clorinda is located across the branches of the Paraguay river in front of Asunción city, Paraguay. Reports of canine and human visceral leishmaniasis in Asunción have been increasing since 1997, however neither leishmaniasis cases nor sand flies were ever recorded from Clorinda. Light traps were located in migration paths (bridges, port), and peridomestic environments of Clorinda and surrounding localities. Lutzomyia longipalpis was found in Clorinda and Puerto Pilcomayo, first report in a potential visceral leishmaniasis transmission area for Argentina. Active surveillance is required immediately in the localities involved and the surrounding area.     

The protective effect against Leishmania infection conferred by sand fly bites is limited to short-term exposure

Under laboratory conditions, hosts exposed twice to sand fly saliva are protected against severe leishmaniasis. However, people in endemic areas are exposed to the vector over a long term and may experience sand fly-free periods. Therefore, we exposed mice long- or short-term to Phlebotomus duboscqi bites, followed by Leishmania major infection either immediately or after a sand fly-free period. We showed that protection against leishmaniasis is limited to short-term exposure to sand flies immediately before infection. Our results may explain the persistence of leishmaniasis in endemic areas and should be taken into account when designing anti-Leishmania vaccines based on sand fly saliva.     

The Lutzomyia longipalpis species complex: does population sub-structure matter to Leishmania transmission?

Leishmania chagasi causes visceral leishmaniasis and, to a lesser extent, atypical cutaneous leishmaniasis in Central and South America. Its main sand fly vector, Lutzomyia longipalpis s.l. (Diptera: Psychodidae) displays a complex population structure that might contribute to the observed clinical pleomorphism and to recent major urban epidemics. This article summarises our understanding on reproductive barriers and hybridisation among this vector's sibling incipient species. Identifying genes important for sand fly ecological adaptability and sand fly-Leishmania genetic co-variation could be helpful for interrupting Leishmania transmission.     

Lutzomyia vectors for cutaneous leishmaniasis in Southern Brazil: ecological niche models,predicted geographic distributions,and climate change effects

Geographic and ecological distributions of three Lutzomyia sand flies that are cutaneous leishmaniasis vectors in South America were analysed using ecological niche modelling. This new tool provides a large-scale perspective on species' geographic distributions, ecological and historical factors determining them, and their potential for change with expected environmental changes. As a first step, the ability of this technique to predict geographic distributions of the three species was tested statistically using two subsampling techniques: a random-selection technique that simulates 50% data density, and a quadrant-based technique that challenges the method to predict into broad unsampled regions. Predictivity under both test schemes was highly statistically significant. Visualisation of ecological niches provided insights into the ecological basis for distributional differences among species. Projections of potential geographic distributions across scenarios of global climate change suggested that only Lutzomyia whitmani is likely to be experiencing dramatic improvements in conditions in south-eastern Brazil, where cutaneous leishmaniasis appears to be re-emerging; Lutzomyia intermedia and Lutzomyia migonei may be seeing more subtle improvements in climatic conditions, but the implications are not straightforward. More generally, this technique offers the possibility of new views into the distributional ecology of disease, vector, and reservoir species.     

New molecular markers for phlebotomine sand flies

Using degenerate-primers PCR we isolated and sequenced fragments from the sand fly Lutzomyia longipalpis homologous to two behavioural genes in Drosophila, cacophony and period. In addition we identified a number of other gene fragments that show homology to genes previously cloned in Drosophila. A codon usage table for L. longipalpis based on these and other genes was calculated. These new molecular markers will be useful in population genetics and evolutionary studies in phlebotomine sand flies and in establishing a preliminary genetic map in these important leishmaniasis vectors.     

Horizontal stratification of the sand fly fauna (Diptera: Psychodidae) in a transitional vegetation between caatinga and tropical rain forest, state of Bahia, Brazil

A study about the horizontal stratification of the sand fly fauna in two distinct ecosystems, caatinga area, endemic for visceral leishmaniasis, and the tropical rain forest area, endemic for cutaneous leishmaniasis, was performed in the state of Bahia, Brazil. Lutzomyia longipalpis was predominant in the caatinga, and following it came the species L. capixaba and L. oswaldoi. In the tropical rain forest other species were found, such as L. intermedia, L. migonei, L. whitmani, L. yuilli, L.fischeri, L. damascenoi, L. evandroi, L. monticola, and L. lenti. It was found that the geographical limits of the vector species of visceral and cutaneous leishmaniasis are clearly defined by the biological and phytogeographic characteristics.     

Experimental assessment of the ability of different species of sandfly to transmit the causative agent of visceral leishmaniasis

The authors succeeded in transmission of the visceral leishmaniasis agent (kazakh strain of Leishmania infantum) through the sand flies Phlebotomus longiductus, P. smirnovi and P. papatasi under experimental conditions. Infected P. longiductus and P. smirnovi are capable of preserving the agent and infecting the susceptible mammals after the cessation of the 1st and 2nd gonotrophic cycles. P. papatasi transmitted the agent of visceral leishmaniasis only after the cessation of the 2nd gonotrophic cycle. Under the same conditions the transmission of visceral leishmaniasis agent through P. caucasicus failed. Informative value of characteristics of virtual vectors for differentiation of sand flies as carriers is analysed. A question of the necessity of obtaining additional data, which prove the role of P. caucasicus and P. papatasi as vectors of visceral leishmaniasis agent, is raised.     

Ecological and Control Techniques for Sand Flies (Diptera: Psychodidae) Associated with Rodent Reservoirs of Leishmaniasis

Background

Leishmaniasis remains a global health problem because of the substantial holes that remain in our understanding of sand fly ecology and the failure of traditional vector control methods. The specific larval food source is unknown for all but a few sand fly species, and this is particularly true for the vectors of Leishmania parasites. We provide methods and materials that could be used to understand, and ultimately break, the transmission cycle of zoonotic cutaneous leishmaniasis.

Methods and Findings

We demonstrated in laboratory studies that analysis of the stable carbon and nitrogen isotopes found naturally in plant and animal tissues was highly effective for linking adult sand flies with their larval diet, without having to locate or capture the sand fly larvae themselves. In a field trial, we also demonstrated using this technique that half of captured adult sand flies had fed as larvae on rodent feces. Through the identification of rodent feces as a sand fly larval habitat, we now know that rodent baits containing insecticides that have been shown in previous studies to pass into the rodents'' feces and kill sand fly larvae also could play a future role in sand fly control. In a second study we showed that rubidium incorporated into rodent baits could be used to demonstrate the level of bloodfeeding by sand flies on baited rodents, and that the elimination of sand flies that feed on rodents can be achieved using baits containing an insecticide that circulates in the blood of baited rodents.

Conclusions

Combined, the techniques described could help to identify larval food sources of other important vectors of the protozoa that cause visceral or dermal leishmaniasis. Unveiling aspects of the life cycles of sand flies that could be targeted with insecticides would guide future sand fly control programs for prevention of leishmaniasis.     

Chemical control and insecticide resistance status of sand fly vectors worldwide

BackgroundPhlebotomine sand flies are prominent vectors of Leishmania parasites that cause leishmaniasis, which comes second to malaria in terms of parasitic causative fatalities globally. In the absence of human vaccines, sand fly chemical-based vector control is a key component of leishmaniasis control efforts.Methods and findingsWe performed a literature review on the current interventions, primarily, insecticide-based used for sand fly control, as well as the global insecticide resistance (IR) status of the main sand fly vector species. Indoor insecticidal interventions, such as residual spraying and treated bed nets are the most widely deployed, while several alternative control strategies are also used in certain settings and/or are under evaluation. IR has been sporadically detected in sand flies in India and other regions, using non-standardized diagnostic bioassays. Molecular studies are limited to monitoring of known pyrethroid resistance mutations (kdr), which are present at high frequencies in certain regions.ConclusionsAs the leishmaniasis burden remains a major problem at a global scale, evidence-based rational use of insecticidal interventions is required to meet public health demands. Standardized bioassays and molecular markers are a prerequisite for this task, albeit are lagging behind. Experiences from other disease vectors underscore the need for the implementation of appropriate IR management (IRM) programs, in the framework of integrated vector management (IVM). The implementation of alternative strategies seems context- and case-specific, with key eco-epidemiological parameters yet to be investigated. New biotechnology-based control approaches might also come into play in the near future to further reinforce sand fly/leishmaniasis control efforts.     

A soil emergence trap for collections of phlebotomine sand flies

The identification of breeding sites of sand flies is of great epidemiological interest. A soil emergence trap for investigating potential sand fly breeding sites is described. The trap was tested in two rural areas in the Mogi Gua?u River Valley where the American cutaneous leishmaniasis is an endemic disease. Seventy-three sand fly individuals of three species, Lutzomyia intermedia s. l., L. whitmani and L. pessoai, were collected on the forest floor and peridomicile.     

First Assessment for the Presence of Phlebotomine Vectors in Bavaria,Southern Germany,by Combined Distribution Modeling and Field Surveys

Leishmaniasis is caused by protozoa of the genus Leishmania and transmitted by sand flies from mammalian reservoirs to humans. In recent years, a northward spread of L. infantum from highly endemic Mediterranean countries into previously non-endemic Central European areas has been suspected based on presumed sporadic cases of autochthonous leishmaniasis. Here, we investigated whether sand flies are prevalent in Bavaria in Southern Germany, a federal state in which autochthonous cases have previously been reported. Considering the present and future climatic conditions, we determined whether Bavaria is suitable for five sand fly species with assumed spreading tendencies towards Central Europe: Phlebotomus ariasi, P. neglectus, P. perfiliewi and P. perniciosus that are known vectors for Leishmania in Europe, and P. mascittii, a suspected but not proven vector. Within Bavaria we defined sampling regions based on their climatic suitability and their spatial distance to the sites of the autochthonous cases and/or to areas of reported sand fly detection in states adjacent to Bavaria. At 155 locations in 7 sampling regions, CDC light traps were placed during 38 nights in the summers of 2009 and 2010, resulting in 202 trap-nights. All traps were negative for sand flies. The results suggest that Bavaria is not yet endemic for sand flies, but do not exclude the possibility of sporadic cases of autochthonous human or zoonotic Leishmania infections. This study, which combined methodological approaches from different disciplines, serves as reference for future surveys and risk analyses of sand flies and leishmaniasis in so far non-endemic areas of Europe.     

Vector soup: high‐throughput identification of Neotropical phlebotomine sand flies using metabarcoding

Phlebotomine sand flies are haematophagous dipterans of primary medical importance. They represent the only proven vectors of leishmaniasis worldwide and are involved in the transmission of various other pathogens. Studying the ecology of sand flies is crucial to understand the epidemiology of leishmaniasis and further control this disease. A major limitation in this regard is that traditional morphological‐based methods for sand fly species identifications are time‐consuming and require taxonomic expertise. DNA metabarcoding holds great promise in overcoming this issue by allowing the identification of multiple species from a single bulk sample. Here, we assessed the reliability of a short insect metabarcode located in the mitochondrial 16S rRNA for the identification of Neotropical sand flies, and constructed a reference database for 40 species found in French Guiana. Then, we conducted a metabarcoding experiment on sand flies mixtures of known content and showed that the method allows an accurate identification of specimens in pools. Finally, we applied metabarcoding to field samples caught in a 1‐ha forest plot in French Guiana. Besides providing reliable molecular data for species‐level assignations of phlebotomine sand flies, our study proves the efficiency of metabarcoding based on the mitochondrial 16S rRNA for studying sand fly diversity from bulk samples. The application of this high‐throughput identification procedure to field samples can provide great opportunities for vector monitoring and eco‐epidemiological studies.     

Domestic and peridomestic transmission of American cutaneous leishmaniasis: changing epidemiological patterns present new control opportunities

Predictions that deforestation would reduce American cutaneous leishmaniasis incidence have proved incorrect. Presentations at a recent international workshop, instead, demonstrated frequent domestication of transmission throughout Latin America. While posing new threats, this process also increases the effectiveness of vector control in and around houses. New approaches for sand fly control and effective targeting of resources are reviewed.     

Maxadilan, a PAC1 receptor agonist from sand flies

In 1991, a potent 61 amino acid vasodilator peptide, named maxadilan, was isolated from the salivary glands of the sand fly. Subsequently, it was shown that this peptide specifically and potently activated the mammalian PAC1 receptor, one of the three receptors for PACAP. These studies and the link between maxadilan and leishmaniasis are discussed.