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Background: Three flaviviruses (equine pegivirus [EPgV]; Theiler's disease-associated virus [TDAV]; non-primate hepacivirus [NPHV]) and equine parvovirus (EqPV-H) are present in equine blood products; the TDAV, NPHV, and EqPV-H have been suggested as potential causes of serum hepatitis., Objective: To determine the prevalence of these viruses in horses with equine serum hepatitis., Animals: Eighteen horses diagnosed with serum hepatitis, enrolled from US referral hospitals., Methods: In the prospective case study, liver, serum, or both samples were tested for EPgV, TDAV, NPHV, and EqPV-H by PCR., Results: Both liver tissue and serum were tested for 6 cases, serum only for 8 cases, and liver only for 4 cases. Twelve horses received tetanus antitoxin (TAT) 4-12.7 weeks (median = 8 weeks), 3 horses received commercial equine plasma 6-8.6 weeks, and 3 horses received allogenic stem cells 6.4-7.6 weeks before the onset of hepatic failure. All samples were TDAV negative. Two of 14 serum samples were NPHV-positive. Six of 14 serum samples were EPgV-positive. All liver samples were NPHV-negative and EPgV-negative. EqPV-H was detected in the serum (N = 8), liver (N = 4), or both samples (N = 6) of all 18 cases. The TAT of the same lot number was available for virologic testing in 10 of 12 TAT-associated cases, and all 10 samples were EqPV-H positive., Conclusions and Clinical Importance: We demonstrated EqPV-H in 18 consecutive cases of serum hepatitis. EPgV, TDAV, and NPHV were not consistently present. This information should encourage blood product manufacturers to test for EqPV-H and eliminate EqPV-H-infected horses from their donor herds., (© 2018 The Authors. Journal of Veterinary Internal Medicine published by Wiley Periodicals, Inc. on behalf of the American College of Veterinary Internal Medicine.)

A 3-year-old Standardbred gelding with a history of pyrexia, persistent hemorrhage from the oral cavity, and a large, soft swelling at the junction of the caudal aspect of the mandibular rami and proximal neck was evaluated. The horse had neutropenia and anemia, with atypical granulated cells in a blood smear. Additional tests confirmed acute myeloid leukemia with basophilic differentiation, which has been reported in humans, cats, dogs, and cattle but not horses.