CASE NOTES

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Infectious bovine rhinotracheitis diagnosed in an outbreak of upper respiratory disease in a Central Tablelands Angus herd

Bruce Watt, Central Tablelands Local Land Services, Bathurst and Phil Hayton, Mark Hazelton and Pedro Pinczowski, Elizabeth Macarthur Agricultural Institute, Menangle

Posted Flock and Herd September 2025

INTRODUCTION

In 1964, the Infectious Bovine Rhinotracheitis (IBR) virus was isolated from seven cases of infectious pustular vulvovaginitis (IPV) and two cases of rhinitis in Victorian dairy herds (Snowdon, 1964). Snowdon commented that both IPV and rhinitis had been seen in Australian cattle for many years but suggested most cases of viral rhinitis went unnoticed as they were relatively mild. The virus, now known as bovine herpesvirus 1 (BoHV-1), causes an acute, highly contagious disease in cattle, typically presenting with either respiratory signs such as rhinitis, tracheitis and conjunctivitis, or with genital lesions. The clinical presentation of BoHV-1 varies with management. Under intensive conditions (e.g. feedlots), it commonly causes respiratory disease and is a key pathogen in the Bovine Respiratory Disease (BRD) complex (Jones & Chowdhury, 2010). In extensively managed, grazing cattle, genital lesions are more frequently observed (Gu & Kirkland, 2008). Although abortigenic strains of BoHV-1 have been reported overseas, they are not currently present in Australia (Gu & Kirkland, 2008; Young et al., 1994).

The closely related herpesvirus, BHV-5 causes sporadic outbreaks of encephalitis in calves in Australia, most recently reported by Plummer et al., (2025).

HISTORY

On 22 February 2024, respiratory signs were reported in a herd of Angus cattle in the Central Tablelands of NSW, affecting 15% (8/53) of 18-month-old heifers but none of the 100 mature cows in the same mob. For the previous five weeks, this herd had been in a paddock consisting of 50% timber with scattered fresh green bracken fern (Pteridium esculentum).

CLINICAL FINDINGS

At the initial property visit, the eight affected heifers (cases 1-8) were yarded for examination. They were approximately 500 kg each and in good body condition (3/5). Respiratory 'snoring' and a soft cough were observed in all eight heifers. While they were bright, alert and responsive, the heifers seemed agitated. They were also mildly febrile (temperatures ranging from 39.5 to 39.8ºC). Despite the respiratory 'snoring', suggestive of partial nasal obstruction, there was no evidence of significant dyspnoea. Most of the affected heifers had a scant muco-purulent nasal discharge, and three animals had blood in their nasal discharge. None of the 100 pregnant mature cows running in the same paddock appeared to be affected. The initial differential diagnoses considered were IBR, Bovine Respiratory Syncytial virus (BRSV), Bovine Parainfluenza-3 virus (PI3), bracken fern poisoning and allergic rhinitis. Blood samples (clotted and EDTA) were taken from four (cases 1-4) of the affected heifers for haematology and IBR/BRSV/PI3 and pestivirus serology.

Two weeks later, the eight heifers were re-examined. All eight index cases were no longer showing signs of disease, however, there were three new cases among the 18-month-old heifers (cases 9-11). These new cases had rectal temperatures ranging from 39.3 to 40.8ºC, snoring respiration and moderate to abundant bilateral mucoid nasal discharge with no abnormal lung sounds or oral lesions. Convalescent blood samples were taken from the four previously examined heifers (cases 1-4) and nasal swabs (in PBGS) were collected from the three new cases (cases 9-11).

Figure 1. Case 10, one of the clinically affected heifers, examined on 7 March 2024

Six weeks after the initial property visit, a well grown two-year-old Angus bull in a neighbouring paddock from the affected heifer mob was examined (case 12). This bull had been across the fence from the affected heifers one week prior. The other bulls, in the same neighbouring paddock as the affected bull, were healthy. The bull had similar snoring nasal respiration, with a profuse bilateral mucopurulent nasal discharge. No oral lesions were seen and there was no evidence of penile/preputial lesions, swelling or discharge, although the penis was not exteriorised. The bull had a rectal temperature of 38.9ºC, normal heart and respiratory rates and no abnormal lung sounds.Blood (EDTA and clotted) and a nasal swab were collected from this bull.

On April 3, one of the heifers that had been running with the clinically affected animals was observed to abort. The observed abortion in early April was a moderately autolysed hairless male foetus with a crown-rump length of 44 cm, weighing approximately 8 kg (approx. 5-6 months gestation). The foetus was collected for testing.

LABORATORY FINDINGS

Bracken fern poisoning was excluded based on haematological analysis of two of the affected heifers from the initial site visit, which showed a mildly elevated PCV/haemoglobin and a normal leucocyte and platelet count.

All four of the clinically affected heifers that were sampled at the initial visit were seropositive for BoHV-1 and PI3 and a single heifer had an agar gel immunodiffusion (AGID) result of '1' for pestivirus (others were negative). None of the four convalescent collected blood samples showed a >4-fold increase in BoHV-1 virus neutralisation titre.

The nasal swabs from the three affected heifers, and the later sampled neighbour bull, tested positive by real-time polymerase chain reaction (qPCR) for BoHV-1 and negative for PI3 and BRSV. Serum from the bull also gave positive ELISA results for BoHV-1 Ab. A summary of the BoHV-1 diagnostic test results for each clinical case is presented in Table 1.

Table 1. Bovine Herpes virus-1 diagnostic test results from clinically affected cattle.

	Animal Identification	BoHV-1 virus neutralisation test	BoHV-1 ELISA	BoHV-1 qPCR
	Acute Blood	Convalescent Blood		Nasal Swab
T17 (Case 1)	Titre 128	Titre 64	n/a	n/a
T122 (Case 2)	Titre 16	Titre 32	n/a	n/a
T268 (Case 3)	Titre 32	Titre 128	n/a	n/a
T044 (Case 4)	Titre >=128	Titre 64	n/a	n/a
T38 (Case 9)	n/a	n/a	n/a	Positive
T46 (Case 10)	n/a	n/a	n/a	Positive
T005 (Case 11)	n/a	n/a	n/a	Positive
Bull 507	n/a	n/a	Positive	Positive

The abortion case in early April tested negative for BoHV-1 and Leptospira sp. by PCR and for pestivirus by PACE. Furthermore, blood from the foetus had an IgG AGID result of <121 μg/ml, which indicated that an infectious aetiology for the abortion was unlikely, but an acute infection (preceding foetal seroconversion) could not be excluded.

DISCUSSION

This case report highlights the capacity for BoHV-1 to cause respiratory disease in extensively managed cattle under seemingly low-stress conditions. The affected heifers were in a well-managed herd and were in good body condition, had not undergone recent yarding or handling and were on pasture typical of grazing cattle herds in the Central Tablelands of NSW. Affected heifers showed mild but consistent clinical signs, including nasal discharge, fever and 'snoring' respiration. Notably, a bull located in an adjacent paddock, with across-the-fence contact, subsequently developed similar clinical signs. This bull could have been infected via direct contact or aerosol spread of BoHV-1, which has been documented previously (Mars et al., 2000). The infection of the bull is particularly significant, as BoHV-1 is also capable of venereal transmission (Davies & Duncan, 1974; Kupferschmied et al., 1986; van Oirschot, 1995). Infected bulls may shed virus in their semen, even in the absence of overt clinical signs, posing a risk of transmission during natural service or by contaminated collections for artificial insemination.

BoHV-1 is most often associated with feedlot disease and post-weaning environments where stress increases viral shedding (Davies & Duncan, 1974; Griebel et al., 2014). However, this outbreak highlights that respiratory disease due to BoHV-1 infection can still occur under grazing conditions. The calf abortion that occurred during this outbreak raised suspicion of abortigenic BoHV-1. However, laboratory testing did not support BoHV-1 as the causative agent, a finding consistent with previous research into the strains of BoHV-1 currently circulating in Australia (Gu & Kirkland, 2008; Smith et al., 1993; Young et al., 1994).

In this case the diagnosis of BoHV-1 infection was made by positive PCR results from nasal swabs taken from clinically affected animals. Serology confirmed prior exposure of this herd to BoHV-1, however, the convalescent titres showed less than a fourfold rise compared to the acute samples. As a greater than fourfold increase in titre is typically required to confirm recent infection by serology, this finding suggests that the clinical signs observed were more likely due to recrudescence of latent BoHV-1 infection rather than new cases of acute transmission. (Davies & Duncan, 1974; Griebel et al., 2014; Ostler & Jones, 2023). This case highlights the diagnostic utility of nasal swabs in detecting disease due to respiratory pathogens such as BoHV-1 in field settings.

Vaccination against BoHV-1 is available in Australia but rarely used outside feedlots. Although herd-level serological surveillance is recommended in international control programs, it is not routinely practised in Australia. Testing and management strategies should therefore be tailored to the individual herd's risk profile - particularly in breeding operations, when introducing new stock or when presenting livestock at agricultural shows.

REFERENCES

1. Davies D & Duncan J (1974) The pathogenesis of recurrent infections with infectious bovine rhinotracheitis virus induced in calves by treatment with corticosteroids Cornell Veterinarian 64(No.3), 340–366
2. Griebel P, Hill K & Stookey J (2014) How stress alters immune responses during respiratory infection Animal Health Research Reviews 15(2), 161-165 doi.org
3. Gu X & Kirkland PD (2008) Infectious Bovine Rhinotracheitis Aquatic and Terrestrial Australian and New Zealand Standard Diagnostic Procedures (ANZSDPs)
4. Jones C & Chowdhury S (2010) Bovine herpesvirus type 1 (BHV-1) is an important cofactor in the bovine respiratory disease complex Veterinary Clinics of North America: Food Animal Practice 26(2), 303-321 doi.org
5. Kupferschmied HU, Kihm U, Bachmann P, Müller KH & Ackermann M (1986) Transmission of IBR/IPV virus in bovine semen: A case report Theriogenology 25(3), 439-443 doi.org
6. Mars MH, de Jong MC, van Maanen C, Hage JJ & van Oirschot JT (2000) Airborne transmission of bovine herpesvirus 1 infections in calves under field conditions Veterinary Microbiology 76(1), 1-13 doi.org
7. Ostler JB & Jones C (2023) The Bovine Herpesvirus 1 Latency-Reactivation Cycle, a Chronic Problem in the Cattle Industry Viruses 15(2) doi.org
8. Plummer D, Slattery S, Winkenwerder E and Chamings A (2025) Sudden Death caused by Bovine Herpes Virus Type 5 in Angus Calves in the Central West, August 2023 Proceedings of the NSW District Veterinarians' Conference, Tamworth, May 2025 www.flockandherd.net.au
9. Smith GA, Young PL & Mattick JS (1993) Bovine herpesvirus 1.1—an exotic disease agent? Australian Veterinary Journal 70(7), 272-273 doi.org
10. Snowdon WA (1964) Infectious Bovine Rhinotracheitis and Infectious Pustular Vulvovaginitis in Australian Cattle Australian Veterinary Journal 40(8), 277-288 doi.org
11. van Oirschot JT (1995) Bovine herpesvirus 1 in semen of bulls and the risk of transmission: A brief review Veterinary Quarterly 17(1), 29-33 doi.org
12. Young PL, Sweeney JL, Smith GA & Rodwell BJ (1994) Failure to detect infection of the bovine foetus after inoculation of a prototype Australian strain of bovine herpesvirus 1 Australian Veterinary Journal 71(3), 92-93 doi.org