Clinical Case Review : Infectious Bovine

Rhinotracheitis and Other Disease Manifestations of Bovine Herpesvirus-1

By: Jose Valles and Lisa Taylor, Production Animal Consultation

Infectious bovine rhinotracheitis (IBR) is a viral infection that affects the upper respiratory tract of infected animals. It was first recognized in the western United Stated during the 1950s. IBR was one of the first viral infections linked with bovine respiratory disease (BRD), and it is one of many factors that can contribute to shipping fever. This acute viral infection affects beef and dairy cattle and other wild ruminants worldwide. While IBR is common in U.S. cattle herds, some European countries have successfully eradicated the disease. Outbreaks of this particular disease can result in significant economic losses for cattle operations.

IBR is caused by bovine herpesvirus-1 (BHV-1), a member of the Herpesviridae family. In addition to IBR, this highly contagious virus causes conjunctivitis; infectious pustular vulvovaginitis (IPV) and infectious pustular balanoposthitis (IPB); abortion; and encephalitis. BHV-1 infection in young calves can result in systemic infection, leading to death. The disease associated with BHV-1 infection depends on the virus route of infection, strain, and dose, as well as environmental factors and the animal’s age and immune function. IBR is common in feedlot settings, while IPV, IPB, and abortion are more common in breeding herds. IBR infection can cause immunosuppression, making animals more susceptible to BRD.

Transmission of IBR occurs through saliva, nasal secretions, or contaminated aerosols. When affecting other organ systems, BHV-1 can be transmitted in utero, at birth, or venereally. Incubation for the virus is 2-6 days. Without complicating bacterial infections, the animal will usually recover 4-5 days after the onset of clinical signs. The virus becomes latent in the animal’s nervous tissue and can be reactivated by various factors including calving, stress, transportation, corticosteroid treatment, and weather changes. After reactivation, the animal usually does not display clinical signs, but it still sheds the virus, spreading disease to susceptible herd mates.

BHV-1 can affect cattle of all ages and breeds. Calves 6 months of age and older tend to be more susceptible because their passive immunity is fading. Disease outbreaks generally remain active for 14 to 28 days and are more likely to occur when cattle are commingled and confined. Consequently, IBR outbreaks are common in feedlots in the fall and winter. Mortality due to IBR is not common unless complicated by secondary infection.

Clinical signs of animals infected with IBR may include coughing, depression, fever, inflamed nose and muzzle, labored or rapid breathing, loss of appetite, nasal discharge, open mouth breathing, reduced milk yield, salivation, and weight loss. These symptoms may vary when a secondary infection is present. Cattle may also present symptoms of conjunctivitis including red eyes, ocular discharge, and, in some cases, corneal opacity. In cases of IPV, clinical signs may include elevated tail head, elevated temperature, frequent urination, lesions on the vulvar and vaginal lining, tail switching, vulvar discharge, and vulvar inflammation. Similarly, symptoms of IPB may include decreased libido, an inflamed prepuce or penis, and pustular lesions. Abortion associated with BHV-1 infection is most likely during the second half of gestation.

Recommended medical examination for cattle suspect of IBR includes lung score, rectal temperature, visual clinical signs, feed intake, water consumption, and movement. Suspect animals should be closely monitored and provided supportive care.

At necropsy, cattle infected with IBR commonly present hemorrhages or mucofibrinous exudate in the sinuses. The trachea is typically inflamed, with petechial hemorrhages and hyperemia (Figures 1 and 2). Necrotic lesions can be found in the nose, trachea, larynx, pharynx, and, in some cases, the bronchi. These lesions may form yellowish plaques.

Definitive diagnosis of IBR and other diseases caused by BHV-1 can be made by laboratory analysis either anteor post-mortem. For ante-mortem diagnosis, nasal, ocular, or genital swabs should be collected 3 to 4 weeks apart (the first during the early stages of acute infection). Tissue samples collected from bronchial lymph nodes and trachea at necropsy can be used for post-mortem diagnosis. In cases of abortion, fixed or frozen samples from the fetal liver and kidney, frozen placental samples, or fetal thoracic cavity fluid can be submitted for laboratory analysis. Laboratory testing may include virus isolation, polymerase chain reaction (PCR), virus neutralization (VN), and enzyme-linked immunosorbent assays (ELISA).

Currently there are no products available to specifically treat IBR infection. Supportive care is essential in all cases. IBR-infected animals must be isolated to help control the spread of disease. Antibiotic therapy can be used to treat or minimize the possibility of secondary bacterial infections.

Prevention practices are the primary line of defense against IBR. Practices to reduce IBR outbreaks such as stress reduction through low-stress handling practices are important. Adequate bunk, water and pen space allocation are a priority throughout the feeding period, and increased biosecurity measures, including sanitation and reduction of commingling, are essential for disease prevention. Timely vaccination is also important. Calves should be vaccinated

2 to 3 weeks before weaning, at feedlot arrival, and again at the time of re-implantation if necessary. Vaccines for IBR prevention are commercially available in parenteral modified-live virus (MLV), intranasal (IN) MLV, and killed-virus (KV) forms. Parenteral MLV vaccines should not be used in pregnant cows that have no IBR vaccination history because they can cause abortion. In contrast, intranasal MLV vaccines, which replicate locally only, can be used safely in pregnant cows. Marker vaccines are also being developed, with advantages for BHV-1 eradication.

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World Organization for Animal Health. 2010. “Infectious Bovine Rhinotracheitis/Infectious Pustular Vulvovaginitis”, Chapter 2.4.13 in Manual of Diagnostic Tests and Vaccines for Terrestrial Animals. Accessed November 23, 2015, from http://www. oie.int/international-standard-setting/terrestrial-manual/access-online/.

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