Vector-borne pathogen transmission

National Institute Of Allergy And Infectious Diseases

Investigators

Linked publications, trials & patents

Abstract

The accomplishments of this project for this year are: 1-Development o 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. 2-We 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 a hybrid of the parasite species Leishmania major, as well as reproducibly generating back crosses that open prospects for investigating the genetics of this parasite. 3-A long-term collaboration with Dr. Hira Nakhasi on a live attenuated vaccine based on centrin gene-deletion in Leishmania parasites. A centrin gene-deleted new world L. mexicana (LmexCen/) parasites protect against visceral leishmaniasis caused by L. donovani in a hamster model. Immunization with LmexCen/ parasites is safe and does not cause lesions. Furthermore, such immunization conferred protection against visceral leishmaniasis caused by a needle-initiated L. donovani challenge, as indicated by a significant reduction in the parasite burden as well as reduced mortality. Similar control of parasite burden was also observed against a sand fly mediated L. donovani challenge. Importantly, immunization with LmexCen/ down-regulated the disease promoting cytokines IL-10 and IL-4 and increased pro-inflammatory cytokine IFN-g compared to non-immunized animals. LmexCen/ immunization resulted in long-lasting protection against L. donovani infection. Taken together, this study demonstrates that immunization with LmexCen/ parasites is safe and efficacious against the Old World visceral leishmaniasis. 4- Another collaborative study evaluated the safety and immunogenicity of AGS-v PLUS, a mosquito salivary peptide vaccine, in healthy adults. We conducted a randomized, double-blind, placebo-controlled Phase 1 study of AGS-v PLUS administered subcutaneously on Days 1 and 22 at the Center for Vaccine Development and Global Health, Baltimore, MD, USA. Participants were block randomized 1:1:1:1:1 to two doses saline placebo, two doses AGS-v PLUS, AGS-v PLUS/ISA-51 and saline placebo, two doses AGS-v PLUS/ISA-51, or two doses AGS-v PLUS/Alhydrogel. Primary endpoints were safety (all participants receiving 1 injection) and antibody and cytokine responses (all participants with day 43 samples). 51 participants were enrolled and randomized, 11 into the single dose AGS-v PLUS/ISA-51 group and ten in other groups. Due to COVID-19, 15 participants did not return for day 43 samplings. Participants experienced no serious adverse events. All solicited symptoms in 2/10 placebo recipients and 22/41 AGS-v PLUS recipients after dose one and 1/10 placebo recipients and 22/41 AGS-v PLUS recipients after dose two were mild/moderate except for one severe fever the day after vaccination (placebo group). Only injection site pain was more common in vaccine groups (15/51 after dose 1 and 11/51 after dose 2) versus placebo. Compared to placebo, all vaccine groups had significantly greater fold change in anti-AGS-v PLUS IgG and IFN- from baseline. Further research is needed to determine if the above findings translate into clinical efficacy against mosquito-borne diseases. 5-In this collaborative work we demonstrated that the salivary molecule PpSP32 from Phlebotomus papatasi, the immunodominant antigen in humans, induces a potent immunomodulatory effect on monocytes and THP-1-derived macrophages. This inhibition could be mediated, among others, by the modulation of the NF-kB signaling pathway. Peripheral mononuclear cells from healthy volunteers were stimulated with anti-CD3/anti-CD28 antibodies, phytohemagglutinin, phorbol 12-myristate 13-acetate/ionomycin, or lipopolysaccharide in the presence of increasing doses of PpSP32. Our data showed that PpSP32 down-modulated the expression of activation markers in LPS-stimulated monocytes and THP1-derived macrophages. PpSP32 negatively modulated the secretion of Th1 and Th2 cytokines by human lymphocytes as well as pro-inflammatory cytokines by monocytes, and THP1-derived macrophages. PpSP32 treatment led to a dose-dependent reduction of IB phosphorylation. 6-In a community effort, we participated in a genomic analysis of two phlebotomine sand fly vectors of Leishmania from the New and Old Worlds. Phlebotomize sand flies are of global significance as important vectors of human disease, transmitting bacterial, viral, and protozoan pathogens, including the kinetoplastid parasites of the genus Leishmania. Having a reference genome can facilitate our understanding of the biology of sand flies, including the mechanisms involved in their vectorial capacity, insecticide resistance, and population structures, among others. We sequenced the genomes of two important sand fly vector species: Phlebotomus papatasi, a vector of Leishmania parasites that cause cutaneous leishmaniasis, (distributed in Europe, the Middle East and North Africa) and Lutzomyia longipalpis, a vector of Leishmania parasites that cause visceral leishmaniasis (distributed across Central and South America). We categorized and curated genes involved in processes important to their roles as disease vectors, including chemosensation, blood feeding, circadian rhythm, immunity, and detoxification, as well as mobile genetic elements. We also defined gene orthology and observed micro-synteny among the genomes. These genomes will be a foundation on which to base future efforts to prevent vector-borne transmission of Leishmania parasites. 8-The response by mast cells (MC) to the parasite and vector-derived factors, delivered by sand fly bites, has not been characterized. We analyzed MC numbers and their mediators in BALB/c mice naturally infected in the ear with Leishmania major by bite of the sand fly vector Phlebotomus duboscqi. MC were found at the bite sites of infective and non-infected sand flies throughout 48h, showing the release of granules with intense TNF-, histamine, and tryptase staining. At 30 min and 48h, the MC numbers were significantly higher (p < 0.001) in infected as compared to non-infected bites or controls. Neutrophil recruitment was intense during the first 6 h in the skin of infected and non-infected sand fly bites and decreased thereafter. An influx of neutrophils also occurred in lymph nodes, where a strong TNF- stain was observed in mononuclear cells. Our data show that MC orchestrate an early inflammatory response after sand fly bites, leading to neutrophilic recruitment, which potentially provides a safe passage for the parasite within the mammalian host. 7- We continue our work on a novel model of chronic malnutrition to assess its influence on sand fly-transmitted visceral leishmaniasis. Our data revealed a distinct innate immune response in early disease stages and a distinct pathogenicity in the chronic phase.