Professor Mark Fox, Dr Damer Blake, Kim Stevens (RVC), Professor Arancha Meana (University of Madrid), Professor Paul Davis, Dr Corrine Austin (Austin Davis Biologics Ltd) and Professor John Pickett (Rothamsted Research) have been awarded a grant by the Petplan Charitable Trust for a project entitled: "Improved control of the equine tapeworm, Anoplocephala, through new insights into the biology of the oribatid mite intermediate host.”
Anoplocephala perfoliata, the commonest adult tapeworm of horses worldwide, is found at the junction between the small intestine and caecum and was originally thought to be non-pathogenic. However, more recent clinical reports suggest that large numbers of the parasite may be associated with colic caused by ‘telescoping’ of the caecum, caecal perforation, peritonitis and intestinal obstruction. A number of authors have also reported a high prevalence of infection in horses which appears to be increasing as a result of a greater reliance being placed on the use of drugs for worm control that have no effect on tapeworms. Although resistance to drug treatment has not yet been reported in tapeworms, increasingly frequent reports of resistance to drugs targeting other equine worms, such as small redworms, make it imperative for us to manage tapeworm in horses very carefully.
Infected horses pass tapeworm eggs in their faeces which are ingested by oribatid mite intermediate hosts found on pasture. The young tapeworm develops into a mature larva (or cysticercoid) inside the mite in 8-20 weeks. This infects horses when parasitised mites are ingested with grass at pasture. Despite researchers developing better methods for the detection of Anoplocephala infections in horses, we still know little about the biology of the cysticercoid stages in these mites or seasonal patterns of transmission to horses at pasture.
To address this gap in our knowledge, we will carefully select three horse premises known to be infected with tapeworms and collect pasture samples, together with horse saliva samples, on a monthly basis. Back in the laboratory, pasture mites will be recovered from the samples, identified and the levels of tapeworm infection established. These data will be linked to the salivary (mucosal) antibody responses present in grazing horses. We will compare the impact that dung removal has on tapeworm control on premises where this is practised, in addition to routine deworming treatments, and in comparison with premises where it is not. We will also look to see how quickly Anoplocephala-infected mites appear and move away from horse dung, whether a greater proportion of infected mites are found nearer the top of grass blades and also whether infected mites emerge onto pasture earlier during the day than parasite-free mites using experimental grass plots. Such changes in mite behaviour would increase the chances of grazing horses becoming infected with tapeworms.
In summary, this study will enable us to (1) monitor seasonal changes in exposure of grazing horses to stages of the tapeworm, Anoplocephala, in the mite intermediate hosts; (2) further understand the role of horse mucosal antibody responses in the complex balance between horse, parasite and the environment; and (3) develop more effective parasite control programmes by establishing (a) the optimum time(s) of treatment for tapeworm; (b) the value of removing dung from pastures in tapeworm control and the extent to which such measures result in a reduction in frequency of deworming treatments required; and (c) whether possible changes in infected pasture mite behaviour necessitate changes in turnout times and dates.