Bovine herpesvirus 4-associated ulcerative mammary dermatitis

Animal Health Laboratory, University of Guelph, Guelph, ON (DeLay); Tavistock Veterinary Services, Tavistock, ON (Bernardo); Ontario Ministry of Agriculture, Food and Rural Affairs, Guelph, ON (Miltenburg); Wisconsin Veterinary Diagnostic Laboratory, Madison, WI (Elsmo).

AHL Newsletter 2019;23(3):7-8.

Two lactating cows in a 200-cow free-stall Holstein dairy herd developed ulcerative, exudative teat skin lesions that spread over a period of several days to other teats (Fig. 1). Skin biopsies taken at the margin of affected and unaffected skin demonstrated segmentally ulcerated epidermis covered by thick plaques of necrotic cellular debris and clusters of bacterial cocci. Eosinophilic intranuclear inclusions were evident in a few epithelial cells of intact epidermis adjacent to the cutaneous ulcers (Fig. 2).

The intranuclear inclusions were suspicious for viral involvement (specifically herpesviruses), and other histologic lesions indicated secondary bacterial dermatitis. Bovine herpesvirus 2 (BoHV-2), the agent of bovine herpes mammilitis, was the main etiologic differential diagnosis, however the virus was not detected in skin biopsies by PCR. Subsequent PCR testing identified bovine herpesvirus 4 (BoHV-4) nucleic acid in the samples. This virus also produces intranuclear inclusions in infected epithelial and other cells.

BoHV-4 is gammaherpesvirus. The virus has been associated with many disease conditions in cattle including pneumonia, metritis, abortion, and dermatitis, although direct causation of these diseases by the virus has not been confirmed. BoHV-4 has also been associated with ulcerative dermatitis with vasculitis and pyrexia in haired, non-mammary skin of cattle. A potentially synergistic effect of bovine leukemia virus infection with BoHV-4-associated disease has been suggested. Further research is required to confirm BoHV-4 causation of mammary dermatitis and potentially of other diseases in cattle, and to determine the pathogenesis of skin lesions.

The original 2 affected cows were euthanized or culled given the severity and persistence of teat lesions. A third cow in the herd subsequently developed teat lesions that were successfully treated with topical antibiotic preparations targeting presumed secondary bacterial dermatitis. Other measures were also taken to reduce any potential effects of teat trauma, including proper milking machine function.   AHL

Figure 1. Ulcerative, exudative skin lesions involving multiple teats.

Figure 2. Intact epithelial cells with eosinophilic intranuclear inclusion bodies and peripheralized nuclear chromatin (arrows) in teat epidermis adjacent to ulcer.

References

Bellino C et al. Potential pathogenic role of bovine herpesivurs 4 in two dairy cows with dermatitis-pyrexia-hemorrhagic syndrome. J Clin Microbiol 2015;53:2763-2767.

Lyman D. BHV-4 contributes to udder lesions. Bovine Vet. January 2019

https://www.bovinevetonline.com/article/bhv-4-contributes-udder-lesions