ABSTRACT
CASE DESCRIPTION: Outbreaks of sudden death in apparently healthy weaned dairy calves due to Strongyloides papillosus parasitism were diagnosed on 2 separate and independent New York (NY) dairies. CLINICAL FINDINGS: Most calves were found dead; however, 1 calf observed while dying showed signs of tachycardia, tachypnea, vocalization, and convulsions shortly before death. In 6 affected heifers that underwent post-mortem examination, precocious bilaterally symmetric mammary gland enlargement was seen. A portion of their parasitized living cohorts also demonstrated similar mammary gland enlargement. A diagnosis of S papillosus hyperinfection was made based upon the presence of high numbers of S papillosus ova in feces, and confirmation by S papillosus-specific PCR assays. Consistent histopathological findings in affected calves included generalized mammary gland vascular congestion, interstitial edema and hemorrhage with ductal hyperplasia. Mild multifocal cardiomyocyte degeneration was found in 5 of 14 calves examined. Factors believed to contribute to the parasite's environmental amplification and host hyperinfection included group housing on wood shavings and high environmental temperatures and humidity. TREATMENT AND OUTCOME: Treatment of calves with doramectin pour-on stopped mortality and resolved the udder enlargement. CLINICAL RELEVANCE: Similar outbreaks have previously been described in Japan and South Bohemia (Czech Republic), where researchers hypothesized that sudden death may be due to fatal arrhythmia caused by a parasite-associated cardiotoxin. This report highlights the importance of including S papillosus among the differential diagnoses for sudden death alone or together with precocious udder enlargement in calves kept in confinement housing.
