In my previous Dairy R & D in SA contribution I have indicated that I will from time to time report on progress made with research funded by Milk SA. One of the projects is on liver fluke (Fasciola) with participation by farmers in the Tsitsikamma area where the parasite is of concern. An objective of the investigation by Onderstepoort is to study the prevalence, seasonal occurrence and favourable/unfavourable environmental conditions of the intermediate snail host (Lymnaea truncatula) of the liver fluke parasite. The principle is that if one understands these factors, one can possibly control or manage the intermediate host more effectively, and as a result limits the development and infestation of the parasite which needs the snail to complete its life cycle.
The results thus far have confirmed the farmers’ observation of dramatic differences in the importance of Fasciola prevalence between farms situated near, even bordering, each other. Mean totals of respectively zero and 42 of the intermediate hosts have been counted over 16 months per sampling site on two adjacent farms and even greater differences between adjacent sampling spots per farm. In fact, the number of L. truncatula present on one occasion in one of the most highly snail-infested sites was estimated to be greater than three million in total. This, compared to mean totals of fewer than four L. truncatula recovered per sampling site in a survey of a large number of Belgian farms where F. hepatica is highly prevalent. The consequence is that there is no doubt that this parasite would seriously threaten milk production on three of the four farms presently involved in the project, should the liver fluke develop resistance to all of the available anthelmintics, as already of importance elsewhere, notably involving triclabendazole.
The prevalence and distribution of L. truncatula over seasons are clearly water and temperature dependent, but rain vs irrigation often have different outcomes as it affects the texture of muddy patches and therefore suitability of habitat of L. truncatula to thrive.
The strong pattern of seasonal cycling in numbers of L. truncatula, as well as the striking differences between sampling sites have now led to: (i) plans for a novel approach to use of existing electrified fencing systems on dairy farms for essentially non-chemical, biological control of the parasite; and (ii) a method for rating farms for potential to harbour the parasite. This will be followed up in Phase II of the project.