Discipline: liver fluke; Keywords: Bacillus, molluscicidal activity, snail host, pathogenicity, Lymnaea columella.
This report is about progress on the research done by UKZN, cited below. The aim of the project is to identify a biological control agent antagonistic to the aquatic snails which serve as intermediate host of liver fluke. It is believed that Bacillus spp. are potential bacterial antagonists of these aquatic snail hosts, and therefore the intention is to screen a large number of Bacillus isolates for molluscicidal activity.
In 2020, 320 isolates were screened from 11 sources which brings the total isolates tested to 1193. While indications of molluscicidal activity have been demonstrated by some isolates, none have shown an adequate level of pathogenicity towards the snail species under assay conditions. Considering the difficulties imposed by the COVID-19 pandemic for 2020, isolate evaluation progress nevertheless compares favourably with the 296 isolates screened in 2018 and 577 in 2019.
Maintenance of the P. acuta culture during lockdown was sub-optimal, however the population has bounced back over the last few months and is in good shape for 2021. The population of Lymnaea columella sourced suffered a crash early in 2020, where all the adult snails died. The population has since recovered and has been distributed to two new tanks. Screening on tank debris and water did not yield any apparent molluscicidal activity when tested against P. acuta. Currently the population has recovered and has been established in two further tanks housed at the UKZN Animal House Unit.
For 2021 the 128 isolates in the subset that may have demonstrated molluscicidal activity will be reassessed under higher standards. Testing parameters will be expanded from the crude initial screening, briefly: age of inoculum, increasing assay duration, and assessing reproductive efficiency. If molluscicidal activity is indeed present amongst these isolates determining the parameters to best test for that activity would be helpful in any future screening. If a true molluscicidal strain is not identified from these isolates, it is hoped that information from this experiment will inform improvements to the current screening procedure.
M.D. Laing & M.G.D van Wyngaard, 2020. Biological Control of Liver fluke in Cattle. Annual project report: 2020; Milk SA.