Polyomavirus-Associated Nephritis in 2 Horses

Abstract

Polyomaviruses produce latent and asymptomatic infections in many species, but productive and lytic infections are rare. In immunocompromised humans, polyomaviruses can cause tubulointerstitial nephritis, demyelination or meningoencephalitis in the central nervous system and interstitial pneumonia. This report describes 2 Standardbred horses with tubular necrosis and tubulointerstitial nephritis associated with productive equine polyomavirus infection that resembles BK polyomavirus nephropathy in immunocompromised humans.Keywords kidney, horse, myocarditis, nephritis, polyomavirusPolyomaviruses have been identified in humans, primates, laboratory rodents, cattle, wild mammals, and birds. In many species, latent infections are common, and disease from productive, lytic infections is not seen in immunocompetent individuals. In immunocompromised hosts, however, polyomavirus infections can be lytic or oncogenic.6 Immunosuppressed humans latently infected with BK polyomavirus can develop BK polyomavirus nephropathy (BKN) with tubular epithelial cell necrosis, intranuclear viral inclusion bodies, and variable inflammation. 8 Recently, an equine polyomavirus has been identified, but no lesions associated with this virus have been described. 10 This report describes 2 Standardbred horses with a polyomavirus-associated nephritis resembling BKN with 1 horse exhibiting widespread viral distribution and myocarditis. Case 1A 2-year-old, female Standardbred horse from a racing training facility presented after several months of recurrent upper respiratory tract infections, anemia, mandibular lymph node abscesses, and relapsing fevers. The Coggins test, culture, polymerase chain reaction (PCR) for Streptococcus equi subspecies equi, and PCR tests for tick-borne agents were negative. During 6 weeks of hospitalization, the horse developed an immune-mediated hemolytic anemia (IMHA) and suspected vasculitis. In addition to antibiotics for the respiratory tract infection, the horse was treated with immunosuppressive doses of intravenous (IV) dexamethasone (40 mg/d with dose tapering as packed cell volume stabilized). Ultimately, the horse developed severe pneumonia, collapsed, and was euthanized.A chemistry panel from the day prior to euthanasia showed potassium, serum urea nitrogen, and creatinine values within reference ranges. Immunoglobulin (Ig) levels were evaluated during hospitalization and at the time of euthanasia by radial immunodiffusion. IgG levels were within the reference range at both points. IgM and IgA levels were low during the peak of dexamethasone therapy, but both levels were within the reference range at euthanasia. Lymphocyte counts were low during dexamethasone

Beyond H&E

“…30 In a recent report, this VP1 gene-targeted PCR was used to detect a polyomavirus in FFPE kidney samples from Standardbred horses with nephritis reminiscent of BK polyomavirus nephropathy in humans. 49 The VP1 protein sequence of this virus was identical to that of the equine polyomavirus that was isolated from the eyes of horses by another group of investigators. 109…”

Diseases of the Equine Urinary System

“…Renal tubular necrosis and tubulointerstitial nephritis similar to that seen in human kidney transplant recipients with BK polyomavirus has been reported in horses with confirmed equine polyomavirus infection. 38,39 In domestic animals, leptospirosis is frequently associated with reproductive loss and acute disease, such as septicemia, hepatitis, and nephritis. 1 Leptospirosis in horses, however, is more often subclinical or manifests as chronic disease, such as uveitis and reproductive failure.…”

Pathology in Context

“…Both strategies have generously contributed to the growing family of animal polyomaviruses. Focused virus hunting by consensus polymerase chain reaction led to the discovery of raccoon polyomavirus, which is associated with brain tumors in raccoons, 1 and in this issue, Jennings et al 4 describe a nephritis associated with a novel equine polyomavirus. Both polyomaviruses have a genomic structure and gene organization similar to that of the canonical polyomavirus simian virus 40 (SV40), but significant differences in sequence might have an impact on viral life cycle and species or cell tropism.…”