A small herd of Woodland caribou resides in a wildlife sanctuary in eastern Washington. Over the summer, one of the animals, nicknamed “Rudolph”, is noted to have a head tilt, is wandering away from the rest of the herd, and appears to be circling to the right. Rudolph’s condition rapidly worsens, and he is humanely euthanatized. Necropsy reveals the presence of many trichostrongyles in the stomach and small intestine and the following organism in the cranial meninges. Fecal analysis shows a large number of trichostrongyle eggs.
Many thanks to Yoko Nagamori, DVM, MS, clinical parasitologist at Oklahoma State University, who provided the photo of P. tenuisin the the crianial meninges.
This is likely Parelaphostrongylus tenuis, or brainworm. Terrestrial snails serve as the intermediate host of this parasitic nematode, and upon accidental ingestion of snails through grazing, a variety of ruminant hosts can become infected. The natural definitive host of P. tenuis is the white-tailed deer, which shed larvae in feces infective to snails. Other ruminants are considered aberrant hosts, as infections are rarely patent (no larvae observable in feces) and neurologic illness develops in response to migrating and developing worms.
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