PREreview of Widespread transmission in diverse ecotypes challenges visceral leishmaniasis control in East Africa

Summary:

This preprint investigates the influence of different ecotypes on visceral leishmaniasis transmission to inform current approaches for control in East Africa. The authors first conducted a field test to collect sand flies with light traps from different ecotypes (peridomestic and sylvatic) throughout the three counties that they were surveying. They morphologically identified which sand fly species were dominant, which ecotypes they populated, and where breeding sites were located. They then extracted DNA from the collected sand flies and isolated non sand fly DNA through qPCR to identify blood meal sources and preferences of the sand flies. They also quantified the amount of leishmaniasis in the collected sand flies to investigate transmission dynamics. Lastly, they collected blood samples from humans in the area to determine the importance of human transmission dynamics through seroprevalence testing to expand upon findings regarding the localization of infected sand flies near positive cases of VL. 

The sand fly collection methods and association found between sand fly preferences and prevalence in certain ecotypes provided necessary insight into VL transmission dynamics. As VL is locally unique, these insights allow for more targeted interventions for VL elimination proposed by WHO. Most findings regarding ecotypes align with previous studies and analyses done in other regions with VL transmission. The seasonality of sand fly collection also provides additional insight into year round transmission dynamics. The high prevalence of indoor sand flies in Sudan observed in this study challenges current control methods that focus on outdoor control during the dry seasons, opening up discussion and a need to evaluate year round transmission dynamics of sand flies. 

This preprint’s findings has potential to improve VL control in East Africa, however the implications of this paper’s findings are unclear. The title of this preprint claims the findings challenge current control frameworks, but in the discussion there is no explicit analysis on which specific parts of the framework are being challenged by the findings of this study. This study points out holes in control and provides insight into the seasonal dynamics of transmission and the influence of human reservoirs in transmission, however is unclear as to what part of current control methods the authors thought were being challenged. As the preprint is unclear with its interpretation of its implications, I believe that the preprint should be revised. 

Major Concerns:

• Throughout this study it was unclear which findings were directly challenging current VL control in East Africa. The claim made in the title of the preprint is inconsistent with the discussion throughout the preprint. The findings from this study’s impact on WHO goals for targeting VL control was not readdressed in the discussion resulting in uncertainty of the strength of the claim in the title of this preprint. 

  • To address this the authors should revisit the WHO goals and address the impact of specific findings from this study on current control methods and explain how they contradict or challenge the framework or assumptions made by WHO. 

• The limitations of the serological testing were addressed in the introduction but there was no follow up in the design of the study or later analysis to determine how many participants were HIV positive. 

  • If the data is available, the authors should include whether those further from positive cases were more/less likely to be HIV positive. An explanation regarding implications of HIV status for the serological testing results and overall influence of humans on transmission dynamics would provide the clarity necessary to overcome the limitations of the rK39 rapid test’s decreased sensitivity and specificity. 

  • If information regarding patients’ HIV status is not available, the authors should address the overall potential impact of HIV carriers on the results of the serological testing and how that impacts their evaluation of human risk of infection for individuals based on distance from cases. 

Minor Concerns:

• It was clear that Kenya, Sudan, and Ethiopia were chosen as study sites because of stable VL transmission, but there was no explanation provided as to why human blood spot collection was only done in Kenya and Sudan.

  • To address this, the authors should include a short sentence or two within the methods or discussion section explaining why Ethiopia was left out of the sampling and what the generalizability is for Ethiopia and other East African countries.

Competing interests

The authors declare that they have no competing interests.

Use of Artificial Intelligence (AI)

The authors declare that they did not use generative AI to come up with new ideas for their review.