Researchers at Neiker-Tecnalia (the Basque Institute for Agricultural Research and Development) have undertaken a study on the epidemiology and diagnosis of infection by visna/maedi virus. This is a virus that affects sheep herds causing chronic interstitial pneumonia, mastitis and neurological disorders. The study confirmed that horizontal transmission (direct contact between infected animals) of the virus is the most likely path of infection, rather than vertical transmission (from infected suckling milk or colostrum). Since there is no current effective treatment against this virus, the study demonstrated the importance of control methods aimed at reducing direct contact between infected animals.
Visna/maedi virus (VMV) causes a slow and fatal disease in sheep. It is mainly associated with clinical symptoms of chronic interstitial pneumonia, but it is also linked to other clinical conditions such as arthritis, encephalitis and mastitis. The disease is widespread throughout the world and the infection has considerable historical importance. It gave rise to the discovery of slow viral infections and pointed to the difficulty in controlling them in international trade. Moreover, while it does not affect humans, it was first described within the group in which AIDS was subsequently included.
The studies carried out by Dr. Iratxe Leginagoikoa, PhD, have shown that VMV horizontal transmission is more important than vertical transmission. Thereby the need to detect infected animals rapidly, rearing the flocks in good conditions of space and ventilation and, reduce contact with infected animals in order to avoid its propagation within the flock.
Intensive stabling increases infection
During the first part of the study transmission of VMV through direct contact was monitored amongst 190 one-year-old lambs of the Latxa breed. Animals were divided into two groups: one subjected to horizontal infection at high pressure and the
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