Viral testing of 10 cases of Theiler's disease and 37 in-contact horses in the absence of equine biologic product administration: A prospective study (2014-2018)

Abstract

Background: A novel equine parvovirus (EqPV-H) was recently discovered in the equine liver with Theiler's disease.

Objectives: To determine the prevalence of EqPV-H infection in naturally occurring Theiler's disease cases and in-contact horses in the absence of historical equine biologic product administration.

Animals: Ten cases of Theiler's disease from 6 separate properties were included in the study, based on the criteria of acute onset of clinical signs of liver failure with laboratory or histopathologic findings characteristic of Theiler's disease and no history of receiving an equine biologic product within the preceding 4 months. In addition, 37 in-contact horses from 4 of the 6 properties were screened for EqPV-H infection and hepatitis.

Methods: In prospective case series, cases were diagnosed with Theiler's disease by the attending veterinarian and were tested for EqPV-H by PCR of liver or serum. In-contact horses were assessed via serum chemistry and PCR at the attending veterinarian's discretion. Hepatitis was defined as serum gamma-glutamyltransferase activity above reference interval. The association of EqPV-H with hepatitis was determined by Fisher's exact test.

Results: Nine of 10 (90%) Theiler's disease cases and 54% of tested in-contact horses were EqPV-H positive. Hepatitis was significantly associated with EqPV-H infection (P = .036).

Conclusions and clinical importance: Although further study is required to identify EqPV-H as the causative agent of Theiler's disease, EqPV-H appears strongly associated with cases of fatal Theiler's disease and subclinical hepatitis in horses in contact with those cases. The prevalence of EqPV-H infection on affected properties can be high.

Keywords: acute hepatitis; hepatic failure; hepatic insufficiency; horses; liver; serum hepatitis.

Figure 1

Case analysis outline. The numbers of Theiler's disease and in‐contact horses and the groupings are shown in the boxes. The analyses applied are indicated in red and italics

Figure 2

Timing of non‐biologic product–associated cases of Theiler's disease and predicted exposure periods. Ten non‐biologic‐associated cases of Theiler's disease were diagnosed on 6 properties (properties A‐F) between January 2014 and February 2018. Each property is indicated by a different color. On 4 properties, there was follow‐up monitoring of in‐contact horses by examination, serum chemistry, and equine parvovirus‐hepatitis quantitative‐PCR. The time span during which new cases of hepatitis were identified on each farm is shown above the timeline (diamonds indicate that only 1 case occurred on that farm). In equine biologic product–associated cases, hepatitis typically occurs 4‐10 weeks after administration of an equine biologic product. Assuming a similar time frame between exposure and disease for non‐biologic‐associated cases, a predicted timeline of exposure for each farm was constructed, calculated as 10 weeks before the 1st case to 4 weeks before the last case