Pathogenicity of cyathostome infection

Cyathostomes are now the principle parasitic pathogen of the horse: a remar kable transformation during the last 25 years from virtual obscurity to foc us of attention in equine parasitology. This rise to prominence coincides w ith the marked decrease in prevalence of large strongyle infections as a re sult of widespread use of modern anthelmintic compounds. On the basis that strongyle-associated diseases continue to commonly occur in the absence of these large strongyle species, clinical attention has turned to the pathoge nicity of cyathostomes, Although many horses harbour burdens of tens of tho usands of cyathostomes without developing detectable illness, these parasit es can result in an inflammatory enteropathy affecting the caecum and colon . Although the principle clinical effect of cyathostomosis is weight loss, affected individuals may exhibit other signs including diarrhoea and/or sub cutaneous oedema and/or pyrexia. Clinical cyathostomosis occurs more common ly in young horses in late winter/early spring but there is lifelong suscep tibility to cyathostomes and they can cause clinical disease in any age of horse during any season. Animals with cyathostomosis often develop hypoalbu minaemia and/or neutrophilia but there are no clinicopathological features specific for the disease. Experimental infections with cyathostomes have re sulted in both clinical and pathological features similar to those of natur ally-occuring cyathostomosis cases. From the experimental infection studies , it is evident that cyathostomes are pathogenic at times of both penetrati on into and emergence from the large intestinal mucose. An unusual feature of cyathostome biology is the propensity for arrested larval development wi thin the large intestinal mucosa for more than 2 years. From limited studie s it appears that this arrested larval development is favoured by: feedback from luminal to mucosal worms; larger size of challenge dose of larvae and trickle (versus single bolus) infection. During arrested larval developmen t cyathostomes have minimal susceptibility to all anthelmintic compounds. t hus, limiting the effectiveness of therapeutic and/or control strategies, A lthough, the relative importance of individual cyathostomes is not known, t he development of species-specific DNA methods for identification of cyatho stomes provides a means by which the pathogenicity of different species mig ht be established. (C) 1999 Elsevier Science B.V. All rights reserved.