HUGS finds Biomphalaria and a lot of water hyacinth during the E7 malacological survey

Blog 17 Oct 2023
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Snail collecting images with a focus upon Chikwawa 1 location where a single shell of Biomphalaria was found within the oxbow lake.This oxbowis now heavily colonised by water hyacinth, choking the shoreline designated "-X-" whereas previously, it was much clearer of this invasive water plant.

According to our HUGS workplan, the seventh malacological inspection, “E7” took place in Mangochi, Chikwawa and Nsanje Districts this October. Regular environmental monitoring is important not only to detect schistosome infections within snails but also keep abreast of any important changes in the local flora and fauna. For example, whilst Biomphalaria pfeifferi has been regularly encountered within Mangochi District, it was not until this summer that this species was started to be found in Chikwawa. Furthermore, there has been a notable increase of water hyacinth across all sampled locations. This invasive aquatic plant is known locally as “namasupuni” and was first reported to occur in Malawi during the 1960s.

The first detection of Bi. pfeifferi was within the irrigation canals of the Illovo Estate at Nchalo. This was part of an expanded snail surveillance programme undertaken with Mr Clinton Nkolokosa’s Wellcome Trust MSc Training Fellowship. Clinton’s activities are supported by HUGS as well as Shire_vec projects, and he is actively working on a soon-to-be-submitted manuscript on the landscape ecology of Biomphalaria in the Lower Shire River Valley. Our snail surveys build upon his most recent paper as was published in Environmental Monitoring and Assessment, entitled “Monitoring and simulating landscape changes: how do long-term changes in land use and long-term average climate affect regional biophysical conditions in southern Malawi?”.

Since the start of HUGS, we have been continuously searching for evidence of Biomphalaria across our two sampling sites in Chikwawa and three sampling sites in Nsanje. In a previous blog, we were alerted to the possible presence of this snail. However, upon molecular characterisation of collected specimens in the DNA laboratory, these snails proved to be Gyraulus, a genus of snail that’s shell can be often confused with that of smaller specimens of Biomphalaria. During E7, snails of the genus Bulinus were collected at Nsanje Port and were noted to shed schistosome cercariae, an important observation on urogenital schistosomiasis transmission.

Coupled with the prior observations at Nchalo and again here at Chikwawa 1, Bi. pfeifferi has now been shown to be present in the Lower Shire River Valley for just under 6-months. The colonisation of Bi. pfeifferi here is a public health concern as its presence is a strong environmental facilitator for local transmission of intestinal schistosomiasis. During October the Shire_vec malaria and schistosomiasis school surveys also took place. Importantly, these surveys detected several children with the unusual excretion of Schistosoma mansoni eggs in their urine, with up to 10% of other children positive by urine-CCA dipsticks. This dipstick is a convenient point-of-care diagnostic test for intestinal schistosomiasis and is flagging that underlying infections with intestinal schistosomiasis seem to be strongly connected with the presence of hybrid Schistosoma mattheei infections in people.