Leishmania Manipulation of Sand Fly Feeding Behavior Results in Enhanced Transmission

In nature the prevalence of Leishmania infection in whole sand fly populations can be very low (<0.1%), even in areas of endemicity and high transmission. It has long since been assumed that the protozoan parasite Leishmania can manipulate the feeding behavior of its sand fly vector, thus enhancing transmission efficiency, but neither the way in which it does so nor the mechanisms behind such manipulation have been described. A key feature of parasite development in the sand fly gut is the secretion of a gel-like plug composed of filamentous proteophosphoglycan. Using both experimental and natural parasite–sand fly combinations we show that secretion of this gel is accompanied by differentiation of mammal-infective transmission stages. Further, Leishmania infection specifically causes an increase in vector biting persistence on mice (re-feeding after interruption) and also promotes feeding on multiple hosts. Both of these aspects of vector behavior were found to be finely tuned to the differentiation of parasite transmission stages in the sand fly gut. By experimentally accelerating the development rate of the parasites, we showed that Leishmania can optimize its transmission by inducing increased biting persistence only when infective stages are present. This crucial adaptive manipulation resulted in enhanced infection of experimental hosts. Thus, we demonstrate that behavioral manipulation of the infected vector provides a selective advantage to the parasite by significantly increasing transmission

Immunity to Distinct Sand Fly Salivary Proteins Primes the Anti-Leishmania Immune Response towards Protection or Exacerbation of Disease

In vector-borne diseases, the role of vectors has been overlooked in the search for vaccines. Nonetheless, there is a body of evidence showing the importance of salivary proteins of vectors in pathogen transmission. Leishmaniasis is a neglected vector-borne disease transmitted by sand flies. Pre-exposure to sand fly saliva or immunization with a salivary protein protected mice against cutaneous leishmaniasis. Using DNA immunization we investigated the immune response induced by abundant proteins within the saliva of the sand fly Phlebotomus papatasi. We found that one salivary protein protected while another exacerbated L. major infection, suggesting that the type of immune response induced by specific salivary proteins can prime and direct anti-Leishmania immunity. This stresses the importance of the proper selection of vector-based vaccine candidates. This work validates the powerful protection that can be acquired through vaccination with the appropriate salivary molecule and more importantly, shows that this protective immune response is efficiently recalled by sand fly bites, the natural route of transmission

Incrimination of Phlebotomus kandelakii and Phlebotomus balcanicus as Vectors of Leishmania infantum in Tbilisi, Georgia

A survey of potential vector sand flies was conducted in the neighboring suburban communities of Vake and Mtatsminda districts in an active focus of visceral Leishmaniasis (VL) in Tbilisi, Georgia. Using light and sticky-paper traps, 1,266 male and 1,179 female sand flies were collected during 2006–2008. Five Phlebotomus species of three subgenera were collected: Phlebotomus balcanicus Theodor and Phlebotomus halepensis Theodor of the subgenus Adlerius; Phlebotomus kandelakii Shchurenkova and Phlebotomus wenyoni Adler and Theodor of the subgenus Larroussius; Phlebotomus sergenti Perfil'ev of the subgenus Paraphlebotomus. Phlebotomus sergenti (35.1%) predominated in Vake, followed by P. kandelakii (33.5%), P. balcanicus (18.9%), P. halepensis (12.2%), and P. wenyoni (0.3%). In Mtatsminda, P. kandelakii (76.8%) comprised over three fourths of collected sand flies, followed by P. sergenti (12.6%), P. balcanicus (5.8%), P. halepensis (3.7%), and P. wenyoni (1.1%). The sand fly season in Georgia is exceptionally short beginning in early June, peaking in July and August, then declining to zero in early September. Of 659 female sand flies examined for Leishmania, 12 (1.8%) specimens without traces of blood were infected including 10 of 535 P. kandelakii (1.9%) and two of 40 P. balcanicus (5.0%). Six isolates were successfully cultured and characterized as Leishmania by PCR. Three isolates from P. kandelakii (2) and P. balcanicus (1) were further identified as L. infantum using sequence alignment of the 70 kDa heat-shock protein gene. Importantly, the sand fly isolates showed a high percent identity (99.8%–99.9%) to human and dog isolates from the same focus, incriminating the two sand fly species as vectors. Blood meal analysis showed that P. kandelakii preferentially feeds on dogs (76%) but also feeds on humans. The abundance, infection rate and feeding behavior of P. kandelakii and the infection rate in P. balcanicus establish these species as vectors in the Tbilisi VL focus

Exploring the midgut transcriptome of Phlebotomus papatasi: comparative analysis of expression profiles of sugar-fed, blood-fed and Leishmania major-infected sandflies

<p>Abstract</p> <p>Background</p> <p>In sandflies, the blood meal is responsible for the induction of several physiologic processes that culminate in egg development and maturation. During blood feeding, infected sandflies are also able to transmit the parasite Leishmania to a suitable host. Many blood-induced molecules play significant roles during Leishmania development in the sandfly midgut, including parasite killing within the endoperitrophic space. In this work, we randomly sequenced transcripts from three distinct high quality full-length female <it>Phlebotomus papatasi </it>midgut-specific cDNA libraries from sugar-fed, blood-fed and <it>Leishmania major</it>-infected sandflies. Furthermore, we compared the transcript expression profiles from the three different cDNA libraries by customized bioinformatics analysis and validated these findings by semi-quantitative PCR and real-time PCR.</p> <p>Results</p> <p>Transcriptome analysis of 4010 cDNA clones resulted in the identification of the most abundant <it>P. papatasi </it>midgut-specific transcripts. The identified molecules included those with putative roles in digestion and peritrophic matrix formation, among others. Moreover, we identified sandfly midgut transcripts that are expressed only after a blood meal, such as microvilli associated-like protein (<it>PpMVP1</it>, <it>PpMVP2 </it>and <it>PpMVP3</it>), a peritrophin (<it>PpPer1</it>), trypsin 4 (<it>PpTryp4</it>), chymotrypsin <it>PpChym2</it>, and two unknown proteins. Of interest, many of these overabundant transcripts such as <it>PpChym2</it>, <it>PpMVP1</it>, <it>PpMVP2, PpPer1 </it>and <it>PpPer2 </it>were of lower abundance when the sandfly was given a blood meal in the presence of <it>L. major</it>.</p> <p>Conclusion</p> <p>This tissue-specific transcriptome analysis provides a comprehensive look at the repertoire of transcripts present in the midgut of the sandfly <it>P. papatasi</it>. Furthermore, the customized bioinformatic analysis allowed us to compare and identify the overall transcript abundance from sugar-fed, blood-fed and Leishmania-infected sandflies. The suggested upregulation of specific transcripts in a blood-fed cDNA library were validated by real-time PCR, suggesting that this customized bioinformatic analysis is a powerful and accurate tool useful in analysing expression profiles from different cDNA libraries. Additionally, the findings presented in this work suggest that the Leishmania parasite is modulating key enzymes or proteins in the gut of the sandfly that may be beneficial for its establishment and survival.</p

Comparative salivary gland transcriptomics of sandfly vectors of visceral leishmaniasis

BACKGROUND: Immune responses to sandfly saliva have been shown to protect animals against Leishmania infection. Yet very little is known about the molecular characteristics of salivary proteins from different sandflies, particularly from vectors transmitting visceral leishmaniasis, the fatal form of the disease. Further knowledge of the repertoire of these salivary proteins will give us insights into the molecular evolution of these proteins and will help us select relevant antigens for the development of a vector based anti-Leishmania vaccine. RESULTS: Two salivary gland cDNA libraries from female sandflies Phlebotomus argentipes and P. perniciosus were constructed, sequenced and proteomic analysis of the salivary proteins was performed. The majority of the sequenced transcripts from the two cDNA libraries coded for secreted proteins. In this analysis we identified transcripts coding for protein families not previously described in sandflies. A comparative sandfly salivary transcriptome analysis was performed by using these two cDNA libraries and two other sandfly salivary gland cDNA libraries from P. ariasi and Lutzomyia longipalpis, also vectors of visceral leishmaniasis. Full-length secreted proteins from each sandfly library were compared using a stand-alone version of BLAST, creating formatted protein databases of each sandfly library. Related groups of proteins from each sandfly species were combined into defined families of proteins. With this comparison, we identified families of salivary proteins common among all of the sandflies studied, proteins to be genus specific and proteins that appear to be species specific. The common proteins included apyrase, yellow-related protein, antigen-5, PpSP15 and PpSP32-related protein, a 33-kDa protein, D7-related protein, a 39- and a 16.1- kDa protein and an endonuclease-like protein. Some of these families contained multiple members, including PPSP15-like, yellow proteins and D7-related proteins suggesting gene expansion in these proteins. CONCLUSION: This comprehensive analysis allows us the identification of genus- specific proteins, species-specific proteins and, more importantly, proteins common among these different sandflies. These results give us insights into the repertoire of salivary proteins that are potential candidates for a vector-based vaccine

Coinfection with Trypanosoma brucei confers protection against cutaneous leishmaniasis

Infection with certain bacteria, parasites, and viruses alters the host immune system to Leishmania major influencing disease outcome. Here, we determined the outcome of a chronic infection with Trypanosoma brucei brucei on cutaneous leishmaniasis (CL) caused by L. major. C57BL/6 mice infected with T. b. brucei were given a sub-curative treatment with diminazene aceturate then coinfected with L. major by vector bites. Our results revealed that infection with T. b. brucei controls CL pathology. Compared to controls, coinfected mice showed a significant decrease in lesion size (P < 0.05) up to 6 weeks post-infection and a significant decrease in parasite burden (P < 0.0001) at 3 weeks post-infection. Protection against L. major resulted from a non-specific activation of T cells by trypanosomes. This induced a strong immune response characterized by IFN-gamma production at the site of bites and systemically, creating a hostile inflammatory environment for L. major parasites and conferring protection from CL

Expression plasticity of Phlebotomus papatasi salivary gland genes in distinct ecotopes through the sand fly season

<p>Abstract</p> <p>Background</p> <p>Sand fly saliva can drive the outcome of <it>Leishmania </it>infection in animal models, and salivary components have been postulated as vaccine candidates against leishmaniasis. In the sand fly <it>Phlebotomus papatasi</it>, natural sugar-sources modulate the activity of proteins involved in meal digestion, and possibly influence vectorial capacity. However, only a handful of studies have assessed the variability of salivary components in sand flies, focusing on the effects of environmental factors in natural habitats. In order to better understand such interactions, we compared the expression profiles of nine <it>P. papatasi </it>salivary gland genes of specimens inhabiting different ecological habitats in Egypt and Jordan and throughout the sand fly season in each habitat.</p> <p>Results</p> <p>The majority of investigated genes were up-regulated in specimens from Swaymeh late in the season, when the availability of sugar sources is reduced due to water deprivation. On the other hand, these genes were not up-regulated in specimens collected from Aswan, an irrigated area less susceptible to drought effects.</p> <p>Conclusion</p> <p>Expression plasticity of genes involved with vectorial capacity in disease vectors may play an important epidemiological role in the establishment of diseases in natural habitats.</p