Laboratory evaluation of molecular xenomonitoring using mosquito excreta/feces to amplify Plasmodium, Brugia, and Trypanosoma DNA

Pilotte, Nils; Cook, Darren A.N.; Pryce, Joseph; Zulch, Michael F.; Minetti, Corrado; Reimer, Lisa J. and Williams, Steven A. (2020). Laboratory evaluation of molecular xenomonitoring using mosquito excreta/feces to amplify Plasmodium, Brugia, and Trypanosoma DNA. Gates Open Research, 3, article no. 1734.



Background: Results from an increasing number of studies suggest that mosquito excreta/feces (E/F) testing has considerable potential to serve as a supplement for traditional molecular xenomonitoring techniques. However, as the catalogue of possible use-cases for this methodology expands, and the list of amenable pathogens grows, a number of fundamental methods-based questions remain. Answering these questions is critical to maximizing the utility of this approach and to facilitating its successful implementation as an effective tool for molecular xenomonitoring.
Methods: Utilizing E/F produced by mosquitoes or tsetse flies experimentally exposed to Brugia malayi , Plasmodium falciparum, or Trypanosoma brucei brucei, factors such as limits of detection, throughput of testing, adaptability to use with competent- and incompetent-vector species, and effects of additional blood feedings post parasite-exposure were evaluated. Two platforms for the detection of pathogen signal (quantitative real-time PCR and digital PCR [dPCR]) were also compared, with strengths and weaknesses examined for each.
Results: Experimental results indicated that high throughput testing is possible when evaluating mosquito E/F for the presence of either B. malayi or P. falciparum from both competent- and incompetent-vector mosquito species. Furthermore, following exposure to pathogen, providing mosquitoes with a second, uninfected bloodmeal did not expand the temporal window for E/F collection during which pathogen detection was possible. However, this collection window did appear longer in E/F collected from tsetse flies following exposure to T. b. brucei. Testing also suggested that dPCR may facilitate detection through its increased sensitivity. Unfortunately, logistical obstacles will likely make the large-scale use of dPCR impractical for this purpose.
Conclusions: By examining many E/F testing variables, expansion of this technology to a field-ready platform has become increasingly feasible. However, translation of this methodology from the lab to the field will first require the completion of field-based pilot studies aimed at assessing the efficacy of E/F screening.

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