Outbreak of post-parturient infectious pustular vulvovaginitis in a New Zealand dairy herd.

Abstract

Case history: In 2023, 160/245 (65%) 2-year-old KiwiCross dairy heifers from a seasonally calving Otago herd developed severe granular vulvovaginitis after calving.

Clinical findings: Affected heifers presented 3-12 days post-calving with tail elevation, vaginal discharge and, in most cases, vulval swelling. Heifers were afebrile although some were inappetent. Vaginal examination revealed severe mucosal inflammation, often featuring erosions and pustules. The heifers responded to treatment with systemic antibiotics and anti-inflammatories. The farm veterinarian became aware that milkers were blowing air through an alkathene pipe inserted into the vagina of some heifers, during milking, to improve milk let-down. The veterinarian advised the farm manager that the practice is prohibited in New Zealand, and it ceased immediately.

Laboratory findings: An initial 10 vaginal swabs from affected heifers gave positive results in PCR assays for bovine herpesvirus type 1 (BoHV-1) and Ureaplasma diversum. Subsequent samples requested by the Ministry for Primary Industries from four affected heifers included vaginal swabs and biopsies, and paired blood samples, 4 weeks apart. Of the swabs, 3/4 gave positive results in a BoHV-1 PCR assay, 4/4 gave positive results in a U. diversum PCR assay, 2/4 gave positive results in a Mycoplasma bovigenitalium PCR assay, and 1/4 gave a positive result in a bovine herpesvirus type 4 (BoHV-4) PCR assay. All gave negative results in a pan-poxvirus PCR assay. Histology revealed severe, chronic, ulcerative and neutrophilic vaginitis with granulation tissue in all biopsies and immunohistochemistry confirmed the presence of BoHV-1 in 2/4 (50%) biopsies. All four heifers had a rising BoHV-1 virus neutralisation test titre. Aerobic culture was unremarkable, while biochemistry found that the mean serum albumin, total protein, calcium, creatinine, sodium, and chloride concentrations were all just below the normal reference range, and haematology found that 3/4 (75%) affected heifers had mildly elevated fibrinogen concentrations.

Diagnosis: Infectious pustular vulvovaginitis, likely involving a mixed infection of BoHV-1, U. diversum and M. bovigenitalium.

Clinical relevance: Infectious pustular vulvovaginitis can occur post-calving, and mixed infections should be suspected in severe outbreaks. Vaginal insufflation likely contributed to this outbreak, and veterinarians need to be aware of and vigilant for this prohibited practice.