CASE NOTES
Sudden Death caused by Bovine Herpes Virus Type 5 in Angus Calves in the Central West of NSW
Danielle Plummer, Central West Local Land Services, Nyngan NSW, Shaun Slattery, North West Local Land Services, Narrabri NSW, Emily Winkenwerder and Anthony Chamings, Elizabeth Macarthur Agricultural Institute, Menangle NSW
Posted Flock and Herd August 2025
Prepared as part of the author's participation in the 2024 NSW Animal Health Frontline Field Epidemiology Training Program
Introduction
This report describes a disease outbreak in the Central West of NSW, where 2-3-week-old Angus calves exhibited neurological signs and sudden death due to Bovine Herpesvirus type 5 (BoHV-5) infection.
BoHV-5 is an alpha-herpesvirus that causes meningoencephalitis in young cattle. Like other alpha-herpesviruses, BoHV-5 can establish latency in neural ganglia, with reactivation of the latent virus triggered by stress or glucocorticoid treatment.5
BoHV-5 is genetically and antigenically related to Bovine Herpesvirus type 1 (BoHV-1), which causes a range of clinical syndromes, including respiratory disease, conjunctivitis, abortion and genital infections.5
The first documented case of bovine meningoencephalitis in Australia, attributed to a herpesvirus infection, was reported in 1962. Since then, sporadic cases of BoHV-5 have occurred.4
Case Report
History
In late August 2023, a producer in the Central West of NSW reported the sudden onset of neurological signs and deaths in one mob of 2-3-week-old homebred Angus calves. According to the owner, affected calves appeared healthy and in good condition. Clinical signs developed rapidly and included hypersalivation, depression and seizures with affected calves dying within 24-48 hours.
The affected calves were the progeny of a mob of 53 two-year-old artificially inseminated first calvers. Heifers were routinely vaccinated with 7-in-1 vaccine (Leptospirosis L Hardjo and L Pomona and Clostridials) and Pestiguard® (Bovine Viral Diarrhoea Virus). The owner did not observe illness in the other two calving mobs on the property.
The heifers were calving in a marsh/naturalised pasture paddock. Monitoring during calving was typically limited and illness was first noted by the owner in late August. Five carcasses of varying decomposition were found by the owner in the paddock. The heifers were moved from this paddock to a holding paddock near the yards and house for ease of monitoring on 23 August 2023.
Two calves showing neurological signs were treated with Oxytetracycline 300mg/ml and Meloxicam 20mg/ml by the owner prior to notifying the Local Land Services District Veterinarian. Both calves failed to respond to treatment and died within 24 hours.
At the time of the property visit on the 25 August 2023 there were four calves showing clinical signs and two dead calves. The latter were those previously treated by the owner. Fifteen calves died during the outbreak and none of the animals observed by the owner with clinical signs survived.
Clinical Examination
The calves displayed signs of severe central nervous system (CNS) dysfunction, including rapid respiration rate, hypersalivation, circling and seizures, tremors, horizontal nystagmus and depression. They were normothermic and diarrhoea was not present.
Autopsy
Autopsy findings were generally unremarkable, with noted pallor of skeletal muscle.
Figures 1 and 2. Showing pallor of skeletal musculature
A range of tissue samples were collected for laboratory analysis, including brain, kidneys, liver, heart and aqueous humour.
Laboratory Results
Samples were submitted to the NSW Department of Primary Industries NSW Animal and Plant Health Laboratories at Menangle NSW.
An Infectious Bovine Rhinotracheitis (IBR) PCR test on fresh brain tissue returned positive results, which were subsequently typed as BoHV-5.
Histopathology examination of the rostral cerebrum revealed a severe, lymphohistiocytic, subacute meningoencephalitis with multifocal neuronal and glial cell necrosis and satellitosis, and neuronal and astrocytic intranuclear viral inclusions (Figs 3 - 5). Similar but milder changes were observed in the dorsal cerebrum, thalamus, and brainstem.
Figure 3. (10x) Encephalitis with severe lymphohistiocytic perivascular cuffing
Figure 4. (20x) Scattered shrunken, hypereosinophilic, necrotic neurons (green circles) occasionally surrounded by glial cells and karyorrhectic nuclear debris
Figure 5. (60x) Eosinophilic intranuclear viral inclusion body that peripheralises the chromatin within a degenerate neuron (blue arrow)
Cultures for Listeria and Chlamydia pecorum were negative.
Analysis of aqueous humour revealed high potassium levels, likely due to delayed post-mortem sampling or vitreous contamination.
Discussion
Bovine Herpesvirus 5 (BoHV-5) primarily affects young cattle, especially those under six months of age.2 In these animals, infection can cause rapid neurological deterioration and sudden death. Mortality rates are high, and clinical signs are mostly related to CNS involvement. Although BoHV-5 infection is generally sporadic, occasional outbreaks do occur.4
Neurological signs typically appear 8-10 days post-infection3 and include tremors, depression, opisthotonus, nystagmus, teeth grinding, circling and recumbency. These progressive symptoms are consistent with BoHV-5's classification as a classical neurotropic herpesvirus.5
There are no specific treatments available for BoHV-5 infection and, as in this case, supportive treatment is often unsuccessful. In countries where BoHV-5 is common, vaccination to prevent disease has mainly used BoHV-1 vaccines. However, this approach has been shown to provide incomplete protection against BoHV-5.1
Some studies have detected BoHV-5 in semen from subclinically infected bulls, suggesting AI could contribute to viral spread.3,6 However, it is unclear whether AI-related transmission leads to neurological disease in recipient cattle.
PCR testing of fresh brain and histopathology are effective methods for diagnosing BoHV-5 encephalitis as demonstrated in this case.
Acknowledgements
This investigation was conducted in collaboration with the NSW Animal and Plant Health Laboratories at Elizabeth Macarthur Agricultural Institute (EMAI) laboratory. The writing of this article was completed as part of the NSW Animal Health Frontline Field Epidemiology Training Program with the assistance of Shaun Slattery, District Veterinarian, North West Local Land Services.
References
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- Del Médico Zajac MP, Ladelfa MF, Kotsias F, Muylkens B, Thiry J, Thiry E & Romera SA (2010) Biology of bovine herpesvirus 5 The Veterinary Journal 184(2):138-45
- Gomes LI, Rocha MA, Souza JG, Costa EA & Barbosa-Stancioli EF (2003) Bovine herpesvirus 5 (BoHV-5) in bull semen: amplification and sequence analysis of the US4 gene Veterinary Research Communications 27:495-504
- Kessell A, Finnie J & Windsor P (2011) Neurological diseases of ruminant livestock in Australia. IV: viral infections, Australian Veterinary Journal 89(9):331-7
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- Rawat KD & Chaubey KK (2022) Bovine Herpesvirus Types 5 (BoHV5): A New and Emerging Threat in Indian Cattle Asian Journal of Dairy and Food Research 41(1):120-121