Vector-borne pathogen transmission

National Institute Of Allergy And Infectious Diseases

Investigators

Linked publications & trials

Abstract

The accomplishments of this project for this year are: We investigated the antibody Responses to Phlebotomus papatasi Saliva in American Soldiers With Cutaneous Leishmaniasis Versus Controls. Using a case-control study design, we compared sand fly saliva-specific human IgG levels and recognized antigens between the two groups. Serologic responses to Ph. papatasi salivary gland homogenate were studied with ELISA and Western blot, using serial samples obtained from before travel, during cutaneous leishmaniasis (CL) treatment or at time of return to US (controls), as well as (for CL cases) six to 24 months after return to non-endemic US. The mean change in optical density (MCOD), reflecting the change in sand fly saliva-specific IgG before and after exposure in Iraq. The most frequently recognized Ph. papatasi salivary antigens were MW30 (PpSP32) and MW64, although other salivary proteins recognized were MW12/14, 15, 18, 28, 32, 36, 42, 44, 46, 52. Logistic regression suggested that MW15, 28 and 42 were associated with the largest effect on the MCOD. MW30 was the most frequently recognized antigen suggesting a role as biomarker for sand fly exposure and CL risk. Anti-Ph. papatasi saliva IgG waned within months of return to the US. This study suggests that immunity to specific vector antigenic saliva proteins may correlate with features of CL pathology such as less lesion area, ulcer versus papule/plaque. With collaborators, we tested a composite vaccine against Leishmania that incorporates immunogenic molecules from sand fly saliva to promote better efficacy. The novel vaccine consists of the Leishmania membrane protein KMP11, LEISH-F3+ (a recombinant fusion protein, composed of epitopes of the parasite proteins nucleoside hydrolase, sterol-24-c-methyltransferase, and cysteine protease B), and the sand fly salivary protein LJL143. The vaccine was tested in two dose ratios delivered in virosomes (VS) in a hamster model of visceral leishmaniasis. Hamsters immunized with the complete combination (i.e., all antigens in VS + GLA-SE) showed significantly lower parasite burdens in the spleen compared to those in control animals. This protection was underpinned by a more intense, specific humoral response against the KMP11, LEISH-F3+, and LJL143 antigens in vaccinated animals, but a significantly less intense antibody response to the pool of soluble Leishmania antigens (SLA). Overall, these results indicate that this innovative vaccine formulation confers protection against experimental L. infantum infection, and shows promise as a novel approach to vaccine development against leishmaniasis. We developed a marker of vector exposure specific to Phlebotomus argentipes responsible for transmission of Leishmania donovani, the etiological agent of visceral leishmaniasis (VL), throughout the Indian subcontinent (ISC). To develop this tool, we identified PagSP02 and PagSP06 from saliva of Phlebotomus argentipes, as immunodominant proteins in humans. We also established the absence of cross-reactivity with Phlebotomus papatasi saliva, the only other human-biting sand fly in the ISC. Importantly, by combining recombinant rPagSP02 and rPagSP06 we achieved greater antibody recognition and specificity than observed for single salivary proteins.sand-fly-based tool to assess the intensity of vector-human contact in VL endemic areas. This composite biomarker can be used to accurately measure the success of current vector control strategies and to improve vector management approaches. Such tools can also evaluate infection risk and rapidly address outbreaks, both critical to overcoming last mile challenges to VL elimination in the ISC. We have established a novel mechanism of genetic exchange of Leishmania promastigoTes in the sand fly vector via formation of mating clumps induced by IgM antibodies present in the blood meal. Using this approach we were able for the first time to obtain hybrid of the parasite species Leishmania major, that has been elusive thus far, as well as reproducibly generating back crosses that open prospects for investigating the genetics of this parasite. We have developed a novel model of sand fly-transmitted visceral leishmaniasis to malnourished animals for both early and chronic stages of the infection. Our data revealed a distinct innate immune response in the early stages of disease as well as a distinct pathogenicity in the chronic phase that provides insight on the contribution of vector-transmission and malnutrition to disease. In this fiscal year, we have visited our study sites in Bihar India in April and another visit is planned for September as part of our ongoing collaboration with Care India and UCSF. We have trapped sand flies on a monthly basis throughout the year and collected serum samples from a subset of study subjects that were tested with our salivary marker of vector exposure as well as with rK39 to assess Leishmania infection. In this fiscal year, we undertook quarterly blood collections of our two endemic villages with recurrent VL cases chosen for long-term follow up and a recent outbreak village have been completed. By August 2022, both rPagSP02/rPagSP06 salivary marker and rk39 ELISA assays have been successfully standardized and ran for the study villages Chotka Baniya (2171 samples), Rahardiyara (900 samples), and Murbhanga (350 samples). The results will be associated to reported clinical cases of visceral leishmaniasis using data analysis approaches developed by the Care India team towards the overall objective of understanding the dynamics of visceral leishmaniasis transmission in our foci. We continue to collaborate with the Medical School and Dentistry at the USTTB in Mali, to investigate new emerging CL foci in the Northern Districts of Mali.