- MULTIFOCAL TO COALESCING COLONIC GRANULOMAS
- Armed Forces Institute of Pathology
- The Cyathostominae, or small strongyles, are a subfamily of the class Nematoda that include four main genera. It is the larvae, typically, that are clinically significant, mainly in equid hosts. Larval stages (L3) migrate into the deep mucosa or submucosa of the large bowel (mainly cecum and ventral colon) from the gut lumen and enter the glands to molt and develop, before emerging into the lumen to molt again and mature. If larvae undergo a period of arrested development, most anthelmentics are ineffective. If arrested larvae synchronously emerge from these cysts (hypobiosis), edema, rupture of the muscularis mucosa and ulceration of the overlying mucosa may occur. Alternatively, larvae can complete development in the cecumand colon lumen, and shed eggs into the feces. It is postulated that cyathostomes have become resistant to certain anthelmintic drugs.A combination of lack of penetration of anthelmintics during the encysted stage along with current inconsistent deworming practicespracticed by horse owners and managers haslikely led to these new resistant populations, which in turn has led to an increase in incidence of infection over the last 10 years. As a result, cyathostomes are considered the primary parasitic pathogen of horses.