A first report of Pseudosuccinea columella (Say, 1817), an alien intermediate host for fascioliasis, in Malawi

Abstract

Starting in October 2021, quarterly malacological surveys have been undertaken in Malawi, sampling 12 specified freshwater habitats throughout a calendar year. Each survey monitors the presence of aquatic intermediate snail hosts of medical and veterinary importance; in March 2023, the alien lymnaeid species Pseudosuccinea columella was first encountered in Nsanje District. This species identity was later confirmed upon DNA analysis of mitochondrial ribosomal 16S sequences. In July 2023, P. columella was also noted at single sites within Mangochi and Chikwawa Districts, and again in Nsanje District, with an additional location observed. Of particular importance, our sampled location in Mangochi District was directly connected to Lake Malawi which expands the species list of invasive molluscs in this lake. Whilst P. columella is a well-known intermediate snail host for human and animal fascioliasis, screening collected snails for trematode cercariae, alongside molecular xenomonitoring, did not yield equivocal evidence of active fluke infection. However, the newly recognized presence of this alien intermediate snail host within Lake Malawi, and along the Shire River Valley, flags a new concern in altered local transmission potential for human and animal fascioliasis.