Diversity of cercariae in Lake Victoria: A confounding factor for environmental monitoring of schistosomiasis?
Schistosome cercariae shed by freshwater snails are the immediate source of infection for communities at risk of schistosomiasis. Transmission potential can therefore be monitored by collecting snails and identifying infection. Such methods are a component of control monitoring in China but rarely used in Africa, one disadvantage being the considerable work involved in such surveys. Many host snails must be collected and identified since infection prevalence among the snails is usually low.
The advent of environmental DNA (eDNA) methods in molecular ecology has renewed attention on monitoring free-swimming cercariae in water bodies. Field sampling for these methods is simple relative to snail collection, but more investigation is needed before it is possible to say whether they will be useful for identifying location and force of transmission.
One potential drawback of eDNA detection is the potential for false positives caused by cross-reactivity with non-target species. Lake Victoria has a diverse array of digenean cercariae, many of which are very abundant compared to schistosomes. Care must therefore be taken in choice of DNA target as even a small degree of cross-reactivity could lead to ambiguous results. Here we present a preliminary survey of cercarial diversity in lake Victoria being tested against eDNA methods currently in use.