Modelling the impact of a transmission blocking vaccine against leishmaniasis on sand fly vectorial capacity
Led by Dr Matthew Rogers (LSHTM, UK), with Dr Laith Yakob (LSHTM, UK), and Dr Godwin Kwayke-Nuako (University of Cape Coast, Ghana)
Transmission blocking vaccines could offer a new way of controlling Leishmania infection by preventing the parasite from establishing themselves in their sand fly vector. However, before such targets are sought the feasibility of such a strategy must first be explored using a combination of basic knowledge of the transmission dynamics between hosts and vectors, the biology of the interaction between the parasite and its vector host and mathematical modelling. By applying modelling to a limited data set from the literature we have found that a hypothetical transmision blocking vaccine (TBV), which prevents the parasites from attaching to the gut of the sand fly, could result in effective protection or, worryingly, more transmission. These drastically different scenarios were dependent on whether Leishmania influence the survival of the sand fly in the early or later stages of infection. In this study we aim to clarify this and develop an improved model of sand fly transmission to better assess the impact of TBVs in the future. To do this we propose to conduct a series of sand fly infections using variable infecting doses of parasites, under stressed and unstressed conditions to extract data to parameterize our model. In addition, we will take advantage of mutant Leishmania which fail to attach or survive beyond the infecting bloodmeal, to test which parasites stages are responsible for sand fly mortality. We will also apply our model to an emerging Leishmania-vector relationship involving a new group of pathogenic Leishmania in Ghana and midges, which can host these parasites to a mature, transmissible stage. Data from this study will enable us to develop better TBVs against leishmaniasis.