Infectious bovine rhinotracheitis (IBR)
The disease is caused by a Bovine Herpesvirus -I belonging to the family Herpesviridae and subfamily Alphaherpesvirinae. It is a DNA virus spherical in shape, enveloped and cubical in symmetry, with linear double stranded DNA of 125-235 kbp in size. The virus replicates in the nucleus and hence intra-nuclear inclusion bodies are formed. BHV-1 (infectious bovine rhinotracheitis-IBR; infectious pustular vulvovaginitis-IPVV) causes a variety of diseases in cattle, including rhinotracheitis, vulvovaginitis, abortion or balanoposthitis and conjunctivitis in cattle and buffaloes. Serology and virus isolation showed presence of this disease in India.
Clinical features: The disease has a high morbidity and low mortality
Genital disease: Affected cow develop fever, depression and stand apart, with tail held away from vulva, urination is frequent and painful. The vulval labia are swollen with small pustules and vulval discharge. Adjacent pustules coalesce to form fibrinous pseudomembranes. In bulls, there is balanoposthitis. The affected bul is reluctant to serve. Semen may be contaminated with the virus and may transmit the virus to cow during service causing vulvo-vaginitis.
Respiratory disease: Morbidity may be 100% and mortality less than 10%. Initial signs include fever, profuse nasal discharge which is serous initially and mucopurulent later on. The breath may be fetid, dyspnoea, mouth breathing, salivation and a deep bronchial cough ar common.
Unilateral or bilateral conjunctivitis, often with profused lacrimation is common with IBR. Gastroenteritis may occur. Abortion may occur at 4-7 months of gestation. The virus has also been reported to cause mastitis.
Lifelong latent infection with periodic virus shedding occurs in Bovine Herpes virus-I infection. The sciatic and trigerminal ganglia are the sites of latency following genital and respiratory disease, respectively. The administration of corticosteroids results in reactivation of the virus and has been used as a means for detecting and eliminating carrier bulls in artificial insemination centers.
Diagnosis: The disease is difficult to diagnose on the basis of clinical observations alone. The methods used for laboratory confirmation include virus isolation, fluorescent antibody test, ELISA, virus neutralization test, histopathology and detection of viral nucleic acids by PCR. Virus isolation and characterization provides definite diagnosis. BHV-1 grows readily in cell cultures derived from natural host and is highly cytopathic, with syncytia and characteristic eosinophilic intra-nuclear inclusion bodies
Prevention and control: A number of modified live virus vaccines both as single or combined forms are available in the United States of America and Europe. A killed vaccine for IBR, developed in India is commercially available.