Written by Professor Russell Stothard, Dr Peter Makaula and Dr Sam Jones
Following our activity timetable, or project Gantt chart, in February 2025, the HUGS team completed the final proposed fieldwork component, the E12 survey. This E12 survey was the final excursion to visit, sample and collect various freshwater snails at our 12 surveillance sites, seven in the Mangochi District and five in the Chikwawa and Nsanje Districts combined. In total, it is the fruition of three years of regular surveillance to assess local environmental change. It has been a tremendous logistical and physical effort.
A key task when collecting snails is to record the water chemistry at each site, and screen collected snails for patent schistosome infections. This is done by exposing field-caught snails to intense natural light in a clean glass jar containing bottled water. If schistosome cercariae are present, these can be viewed under a dissecting microscope and then individually harvested by spotting with a pipette onto FTA cards for safe short-term storage at room temperature.
Once back in the laboratory, these FTA spots can be punched out, and then genomic DNA can be extracted for subsequent DNA identification of the schistosome cercariae present. A significant finding within this E12 survey was identifying a ‘new’ transmission site within Samama village, Mangochi District. The intelligence to do so was gleaned from spatial epidemiological maps presented by Lucas Cunningham at the recent Royal Society meeting in London in early February.
Spatial epidemiological information from Samama village points towards a new transmission site
The white arrow labelled A is the designated snail collection site within Samama village that has been regularly sampled since 2022. However, in light of the disease map, we also inspected the small drainage ditch, as denoted by the white arrow labelled B. At the time of the E12 survey, this drainage ditch was flooded and contained a large number of Bulinus snails, but more importantly, 10% of these collected snails were shedding schistosome cercariae. Until now, infected snails have not been encountered at Samama village, where the transmission in the town is taking place, which remains an unsolved puzzle.
Another interesting observation on site was that goats were present within this water body and grazing nearby. After an ad hoc parasitological examination of their faecal droppings, these animals were confirmed to be infected with schistosomes. This is also the first time infected goats have been observed locally within Samama village. These animals were likely infected with S. mattheei and perhaps hybrid forms, which have been contributing to the spatial patterning of schistosome infections in people.
Across this E12 survey, we also found that Bulinus snails were shed in the Nsanje and Chikwawa Districts. These collected schistosome cercariae will soon be genotyped to assemble a more detailed picture of the transmission dynamics of schistosomiasis through time. Also of note, although we found shells of Biomphalaria, no living snails were found. This points towards seasonal transmission of intestinal schistosomiasis, whereas urogenital schistosomiasis is more engrained through time. We expect our environmental results to be written up shortly in a forthcoming paper for the special edition of Philosophical Transactions of the Royal Society - B, so watch this space.