Infectious bovine rhinotracheitis is a highly contagious, upper respiratory tract infection caused by a herpes virus. Active or latent infections are widespread in the Australian cattle population. Most infections are mild or inapparent but may become severe in crowded, stressed cattle.
Spread is by coughing or by dropping virus laden secretions into shared feed and water troughs.
Some animals suffer life-long latent infections and may act as a source of virus if shedding is reactivated by stress or treatment with glucocorticosteroids.
Acute outbreaks occur mostly in groups of young susceptible cattle that are exposed to virus such as when groups of cattle from different origins are crowded together. IBR has been known to sweep through populations of cattle in assembly points and ships within days.
Its main significance in the live export process is in predisposing animals to secondary bacterial pneumonia. This may occur in severely affected cattle or those also suffering heat or other stress.
Disease due to IBR may raise suspicions of foot and mouth disease in overseas destinations during health inspections. Animals can look terrible at destination if the muzzle has become badly eroded and eye discharges have stained the face.
Clinical signs include mild to severe coughing, nasal and lachrymal discharges, and salivation. A clear bilateral eye discharge may be one of the earliest and only signs of IBR. More severe cases may develop mucopurulent ocular and nasal discharge, coughing, and ulcerative lesions on the muzzle and nasal mucosa.
Differential diagnoses include other respiratory tract infections. Pinkeye will cause lachrymal discharges only.
IBR is not fatal unless complicated by secondary pneumonia or heat stress. If necropsied, there will be changes to the mucosa of the respiratory tract from the muzzle to the trachea ranging from reddening and thickening to extensive patches of necrosis. Abortion is a feature of IBR strains present overseas but these strains are not present in Australia.
Specimens for laboratory confirmation are swabs from nasal cavities and conjunctivae for virus isolation, and acute and convalescent sera (3-6 weeks apart) to demonstrate a rising antibody titre.
In uncomplicated infections treatment is unnecessary. Lesions are confined to the upper respiratory tract and trachea, and recovery occurs within a week or two. At sea it is common practice to treat severe cases with antibiotics (procaine penicillin, oxytetracycline, tylosin, ceftiofur sodium, florfenicol, tilmicosin, or tulathromycin) to prevent development of secondary bacterial pneumonias.
Vaccines are available to assist prevention. Isolating early cases in an outbreak is unwarranted because infection is likely to have spread widely by the time first cases are identified.