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Strongyloides papillosus Update

Monday, November 26, 2018

(North America) Strongyloides papillosus has recently been implicated as the cause of an outbreak of sudden death in 3-month old dairy calves on a well-managed farm in New York State. During this outbreak, previously healthy calves were often found dead or presented suddenly weak and recumbent with increased respiratory rate followed by death or were observed to die abruptly after a brief period of convulsions. All heifer calves effected also had apparent precocious udder development.

These calves were group-housed in a barn that collected standing water in the scrape alley during heavy rain and were bedded on wood shavings. Extensive diagnostic evaluation was performed at the Cornell AHDC using New York State Contract subsidy pricing. Multiple necropsy submissions were largely unremarkable on gross examination and histopathology, however a consistent finding among deceased calves was heavy fecal loads of S. papillosus eggs and vascular congestion of the udder. Further investigation revealed the remaining living cohort of calves were also heavily parasitized with S. papillosus.

A series of publications out of Japan by Taira et al documented several nearly identical outbreaks of sudden death in calves housed in similar conditions with heavy burdens of S. papillosus, and ultimately demonstrated sudden death in calves following experimental infection with S. papillosus. The third larval stage of this parasite penetrates the skin, often in the coronary band region of the limb, and migrates to the gastrointestinal tract where it matures to the adult stage. The condition of standing water in the recorded outbreaks may have eased larval migration. Experimental studies by Naotoshi et al demonstrated that calves infected with adult female S. papillosus worms experienced cardiac arrhythmias 1-2 days prior to death along with ventricular arrhythmias immediately preceding respiratory arrest. It is hypothesized that S. papillosus may produce a cardiac toxin that leads to cardiac death of infected calves.

Deworming the calves in the New York State herd with doramectin pour-on resulted in immediate cessation of sudden death cases, resolution of mammary enlargement and the elimination of S. papillosus from fecal float evaluation. The Veterinary Support Services group at the AHDC encourages veterinarians to consider S. papillosus as a differential for sudden death in dairy calves, and submit feces for evaluation. Further investigation is underway at AHDC to elucidate the pathophysiology of this disease process.