Maedi, a progressive pneumonia, and visna, a neurotropic disease, found in sheep and goats are caused by the Maedi/visna virus, belonging to the family Retroviridae. It is a zoonotic disease. The disease has not been reported from India.Epidemiology: The transmission of disease takes place through inhalation, drinking contaminated water and colostrum by young ones. The intrauterine transmission of the virus has also been observed.
Clinical signs: Incubation period of over 2 years and has protracted clinical course lasting 6 months to several years.Maedi (progressive pneumonia): Progressive weight loss and dyspnoea, initially detected after exercise, and becomes more apparent over time. Affected sheep straggles, head jerking with inspiration and nostrils are flared. There may be nasal discharge and cough.
Visna: Weakness of the hindleg and stumbling. Progressive weight loss and trembling of facial muscels and limbs is seen leading to paraplegia.Diagnosis: The disease is diagnosed histopathology. Enzyme immunoassay, agar gel diffusion and syncytial plaque reduction assays are used for detection of antibodies. Western blotting is used for confirmation of the disease. Viral DNA is detected in cells by in situ hybridization or viral RNA amplification by RT-PCR.
Prevention and control: Slaughtering of sero-positive sheep is one of the approaches suggested for containing the infection. Dipping of sheep with acaricides and spraying in environment controls ticks.