ClinQuiz: Equine parasites, answer 4C

4) C - Correct.

The trematode vector of Neorickettsia risticii uses aquatic flies as an intermediate host. Horses are thought to become infected when they inadvertently ingest aquatic flies that harbor infected stages of the trematode vector while grazing.15   Outbreaks of Potomac horse fever are often associated with exposure of horses to streams and other aquatic environments, presumably because it increases the likelihood that the horses will ingest the fly intermediate hosts that harbor infected vector flukes.17

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