A vector excreta surveillance system (VESS) to support the rapid detection of vector-borne diseases

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More than half of the global population is at risk for deadly and debilitating vector-borne diseases (VBD). VBDs, which include malaria, dengue, filariasis and many others, cause 1 million deaths each year and leave communities in economic hardship. While many efforts to control VBDs have been successful, we are working against the challenges of globalisation, insecticide resistance and climate change. The spread of Zika virus is a very relevant example of how these factors have fostered the rapid expansion of VBDs. The World Health Organization has called for more research to improve infectious disease surveillance so that we can prevent and control emerging and re-emerging diseases. Fortunately, there has been renewed political and financial momentum to provide interventions such as vector control and mass drug administration to combat these diseases. An early detection system would allow for a rapid response to help contain the spread, however these approaches can be costly and are out of reach of many developing nations.We have developed a low cost, VBD surveillance tool which allows us to detect the presence of VBDs in a community. Mosquitoes pick up pathogens when they feed on a person. If the mosquito is a competent vector, the pathogen will go on to develop within the mosquito body and the mosquito becomes infective a week or two later. We have shown that when non-vector mosquitoes ingest infected blood, they excrete the pathogen DNA in their faeces over the next few days. When vectors ingest infected blood, they also excreta small amounts of pathogen DNA. The vector excreta surveillance system (VESS) collects mosquito excreta for the purposes of screening for pathogen DNA. Mosquitoes are actively or passively collected using one of many commercial or home-made trap types for the purposes of disease-specific surveillance or research. We have made a modification to mosquito holding cups, where mosquitoes may be held prior to sorting and preservation. We have included a super hydrophobic lining below where mosquitoes rest which concentrates the excreta into a small reservoir or a funnel which deposits onto special preservative. This is a significant improvement over current monitoring methods because we are able to screen very large pools of mosquitoes at once. The mosquito samples are not used in the process so there are opportunities to integrate this method with other surveillance activities. The role of non-vectors is particularly useful since it would enable screening of other fly-borne illnesses without species-specific collections (including the parasites that cause leishmaniasis, river blindness, sleeping sickness.) There is scope for further development of excreta collection from a passive trap which would eliminate the need to actively collect the mosquitoes.In our lab based studies we have successfully detected DNA from malaria, the filarial worm that causes lymphatic filariasis, and a trypanosome species that causes animal trypanosomiasis. This proposal aims to field-test this approach in a village in Ghana where we have already characterised disease prevalence, mosquito species and local ecology. We will use three different trap types so allow us to determine which species and life-stage (bloodfed resting mosquitoes, or gravid mosquitoes ready to lay eggs) is the most sensitive for detecting parasite DNA in the excreta. We will compare the detection from our pools of excreta with the detection from individual mosquito carcasses. We also aim to extend this methodology to the detection of viral particles from the mosquito-borne viruses West Nile, dengue, chikungunya and Zika.This is an approach that disease control programmes in developing countries could implement in order to monitor the presence of a diverse range of blood-borne pathogens without having to collect blood from participants or process mosquitoes individually.