Infectious Bovine Rhinotracheitis
Synonyms: Viral bovine rhinotracheitis, Red nose, Necrotic rhinitis
Introduction
• It is an acute highly contagious viral disease of cattle characterized by high temperature, rhinitis, dyspnoea, abortion, meningoencephalitis, keratoconjunctivitis, and pustular vulvovaginitis.
• Dairy and beef cattle are equally susceptible. Besides cattle, the disease is also reported in goat, swine, and water buffaloes. The disease is widely prevalent in all parts of the world.
Etiology
• The disease is caused by a DNA virus called bovine herpes virus-1 belonging to the family herpes viridae, subfamily Alpha herpes virinae, and genus Varicella virus.
Host susceptible
• Cattle of all ages are affected.
• Dairy and beef cattle are equally susceptible.
• Besides cattle the disease is also reported in goats, swine, and water buffaloes, and wild ruminants.
Transmission
• The virus is transmitted through infected feed and water.
• The virus can spread through the ocular, nasal, and reproductive secretion and excretion of infected cattle.
• Droplet infection is an important way of transmission.
Clinical signs
• The clinical signs have been grouped as
- Respiratory form
- Vulvo-vaginal form
- Ocular form
- Encephalomyelitic form
- Abortive form
Respiratory form
• This form is characterized by mild to the severe rise of temperature, depression of appetite, acceleration of respiration, and dyspnoea.
• The nasal discharges are initially serous which later turn to mucopurulent. The whole of the upper respiratory tract show hyperemia, edema along with mucopurulent exudation causing dyspnoea.
• Affected cattle may exhibit open-mouth breathing in severe cases. The animal may show signs of bronchitis and pneumonitis.
• The nasal mucosa is severely congested hence the disease is named “Red Nose”.
• The recovered cattle may remain as carriers and thus shed the virus for a considerable period.
Vulvo-vaginal form
• This form is characterized by a sharp fall in milk yield and the appearance of erythematous and pustular lesions on the vulvar and vaginal mucosa.
• There is swelling of the vulva and frequent urination. There may be mucopurulent discharge from the vulva and vagina.
• Animal is unable to put its tail in a normal position after urination due to pain. The virus produces pustular balanoposthitis in the bull.
• The semen of the affected bull become contaminated and thus pose a problem in natural or artificial breeding
Ocular form
• This form may appear along with the respiratory form. There is inflammation of the conjunctiva in addition to respiratory changes.
• But in some occasions severe conjunctivitis and ocular discharges may be noted without respiratory involvement.
• The ocular discharges vary from serous to purulent.
• Petechial hemorrhages may be noted on the conjunctiva and sometimes corneal opacity may appear as the main attribute of the disease.
Encephalomyelitic form
• The virus may produce severe encephalomyelitis syndrome in the calf terminating to death.
• The signs of encephalomyelitis comprise the high rise of temperature, incoordination, tremor, circling, falling, coma and death.
• Death ensures within 4 days following the appearance of neurological signs.
Abortive form
• The pregnant cattle may abort following infection. The abortion may supervene as an “abortion storm”.
• Foetus died at 4 months of gestation and was expelled. The fetus is autolyzed in most cases.
Diagnosis
Samples to be collected
• Live animals- nasal swabs or genital swabs or conjunctival swabs during the acute phase of infection, aborted materials, tissue samples from the fetal liver, brain, and spleen, semen, placenta, uterine mucus, and serum
• Dead animals- Lymph nodes, liver, lungs, brain, aborted fetal liver, brain, and spleen
Based on clinical signs
Identification of the agent
• The virus can be isolated from nasal swabs or genital swabs, from animals with vulvovaginitis or balanoposthitis, taken during the acute phase of the infection, and from various organs collected at post-mortem.
• For virus isolation, various cell cultures of bovine origin are used, for example, secondary lung or kidney cells or the Madin–Darby bovine kidney cell line.
• The virus produces a cytopathic effect in 2– 4 days. It is identified by neutralization or antigen detection methods using monospecific antisera or monoclonal antibodies.
• Viral DNA detection methods have been developed, and the polymerase chain reaction technique is increasingly used in routine diagnosis.
Serological tests
• The virus neutralization test and various enzyme-linked immunosorbent assays (ELISA) are most widely used for antibody detection.
• ELISA antibodies can be detected in serum and with lower sensitivity in milk.
• Fluorescent antibody technique (FAT) and electron microscopy can be made for the diagnosis of disease.
Differential diagnosis
• This disease should be differentiated from,
Pasteurellosis: Respiratory signs alone present and responds to broad-spectrum antibiotic therapy
Parainfluenza: Toxaemia, dyspnea, – Antibiotic treatment for secondary bacterial complications and recovery in 3-5 days
Verminous pneumonia: Respiratory signs, eosinophilia, responds to broad-spectrum antibiotic therapy
CBPP: Fibrinous pneumonia, pleurisy, deep cough, the extension of the head, abduction of the elbow, pleural rub, differentiated with IBR with serological tests
Prevention and control
• No successful treatment. Antibiotics are given to avoid or prevent secondary bacterial complications
• Best way to control this disease is to prevent contact between infected animals and seronegative animals.
• Since the virus is latent in seropositive animals, they should be identified and eliminate from the herd
• Good hygiene, management, and isolation do not seem to control the disease adequately
• Most control efforts are based on vaccination. The best practice is to vaccinate females kept for breeding once or twice before their first breeding with modified live virus vaccines or inactivated vaccines. Age of vaccination – calves after 5 months of age. Immunity develops within 10-14 days.
• Live vaccines induce a relatively rapid immune response comprising both humoral and cell-mediated responses, including mucosal immunity that resembles a natural infection.
• Live attenuated vaccine administered through intramuscular or intranasal route, but modified live virus (MLV) vaccines contraindicated in pregnant cows because MLV has the property of antigenicity. In outbreaks- the intranasal route is selected. The vaccine may be instilled into one or two nostrils.
• Killed vaccines are administered by intramuscular route. Primary and secondary inoculation should be given four weeks apart followed by booster inoculations annually.