First Visna case in a lamb in Turkey

Visna is a neurological disease due to the Maedi Visna Virus (MVV) infection in sheep. The MVV infection is characterized by a long incubation period and sheep from 2 to 4 years of age are the most frequently affected. MVV usually causes a worldwide diffused respiratory disease called Maedi, consisting in lymphoproliferative pneumonia. The nervous form, called Visna, is unusual and no cases have been so far reported in Turkey. This work describes a severe Visna case in a lamb from a Turkish flock. A 10 months old male Merino lamb from a Turkish flock of 850 sheep suddenly showed nervous signs. A history of other four similar cases was recorded in the farm. The lamb died within 2 days after the first clinical signs and was submitted to the necropsy. Lung congestion and pneumonia were observed. In the CNS, the meninges appeared congested but some parts were discolored especially in the cerebellum region. In the left brain hemisphere, a Coenurus cerebralis cyst was found. Microscopically, severe non-purulent meningoencephalitis and lymphoproliferative pneumonia were observed. In order to detect MVV by PCR, the DNA was extracted from formalin fixed and paraffin embedded slides from the lung and the CNS. After the integrity of the extracted DNA was verified by PCR for the ovine mitochondrial DNA, a PCR for the LTR gene of MVV was carried out. MVV provirus was demonstrated in all the pulmonary and nervous samples collected. This is the first case of Visna reported in Turkey. Visna usually affects adult sheep and, in this case, it was surprising to find such severe neurological lesions in a young animal. These observations could depend on infection by a particularly virulent and neurotropic MVV strain or on the concurrent infection observed in the CNS.