Susceptibility of 7 freshwater gastropod species in Zimbabwe to infection with Gastrodiscus aegyptiacus (Cobbold, 1876) Looss, 1896.

The research article presents a study investigating the susceptibility of seven different freshwater snail species to the Gastrodiscus aegyptiacus parasite, in response to the recorded outbreak among horses in Zimbabwe, even in the absence of known intermediate hosts. The results reveal that five of the snail species studied can indeed act as intermediate hosts to the parasite, which could explain the unforeseen transmission of the disease.

Research Background

• Against the backdrop of gastrodiscosis outbreaks due to the parasite Gastrodiscus aegyptiacus among horses in Harare, Zimbabwe, this research study was instigated.
• Despite the absence of previously established intermediate host snails, Bulinus forskalii, B. senegalensis, and Cleopatra sp., infections were still occurring, suggesting the possibility of other snail species taking up this role.

Research Method

• The experiment tested the susceptibility of seven different freshwater snail species to G. aegyptiacus infection.
• The five species (Bulinus tropicus, Bulinus globosus, Biomphalaria pfeifferi, Helisoma dyuri and Physa acuta) were first-generation, laboratory-bred, while the other two (Melanoides tuberculata and Cleopatra sp.) were directly collected from the field.
• Data on mortalities and the shedding of cercariae (larval form of parasitic flukes) were constantly recorded.

Research Findings

• Results showed that M. tuberculata and Cleopatra sp. were susceptible to G. aegyptiacus with respective prepatent periods (time from infection to when the disease can be detected) of 45 days and 54 days.
• B. tropicus, P. acuta, and H. duryi also revealed susceptibility as shown by the presence of different generations of rediae (another developmental stage in the flukes’ life cycle) and mature cercariae, even though attempts to shed were unsuccessful until 59 days post-infection.
• However, B. globosus and B. pfeifferi poles showed resistance to the infection.

Significance of the Study

• The study unearthed the potential of G. aegyptiacus to infect M. tuberculata, Cleopatra sp., B. tropicus, P. acuta, and H. duryi, shedding light on the source of gastrodiscosis outbreaks among equine populations in the absence of known intermediate hosts.
• B. tropicus, in particular, due to its wide distribution in Zimbabwe and being well-adapted to diverse environments, stands out as a significant new intermediate host of G. aegyptiacus.