May 2014

Euthanized horse

A 2-yr-old 240 kg female horse pastured with a herd in Okmulgee, Oklahoma was euthanitized after being found down and unable to rise in mid-April. Necropsy revealed marked reduction of skeletal msucle, prominent gelatinous edema along the ventral midline, and pale musculature and mucous membranes. Cyathostome larvae were observed embedded in the mucosa of the large colon and cecum. Three types of nematodes were found in the small and large intestines. The stalk of the cranial mesenteric artery was obstructed by a thrombus containing an approximately 0.5 cm nematode larva. Several cyathostome adults and the following 3 nematodes were submitted to a diagnostic lab for identification.

​Nematodes from euthanitized horse submitted for identification:

A closer view of the anterior end of one of the 3 nematodes:

What is your diagnosis?

Answer

This horse likely died of severe parasitism by both large and small strongyles. The thrombus in the mesenteric artery is a a hallmark finding of Strongylus vulgaris infection. However, the nematodes submitted to the diagnostic lab for identification lacked the characteristic "teeth" ofS. vulgaris within the buccal cavities. Based on morphological characteristics, the submitted strongyles are likely Strongylus edentatus.