Progressive sheep pheumonia and maedi are terms that denote chronic virus sheep disease. Maedi-visna virus causes a disease named visna, which is a disease of nervous system with the symptoms of paresis and paralyses. Besides pneumonia, maedi-visna is characterized by arthritis, heavy mastitis and slow growth of lambs. This diseases is closely related to encephalitis and goat arthritis. Virus maedi-visna and the virus of sheep progressive pneumonia are neoncogen sheep retroviruses that belong to a subfamily Lentvirinae. They cause persistent infection with lymphoproliferatic changes, mammary gland tissues, brain and joints. The earliest reports on the disease come from South Africa and SAD, but nowadays the disease is present in all the countries where sheep are raised. The ways of transmission and their importance are still not detected. Incubation period is very long, and most of sheep with clinical symptoms are older than 3 years. The most common symptoms are apathy, weight loss and exhaustion. It may be followed by coughing and nasal discharge, pneumonia as a consequence of secondary bacterial infection. The changes on mammary gland appear slowly, the udders are enlarged and hard, but papillae are flaccid. Due to changes on mammary glands lambs of the infected sheep are often weak and less developed. Clinically, the disease lasts 3-10 months always with fatal outcome. The virus may be isolated on tissue culture or identified with the method of complement fixation and virus neutralisation test. Different serology methods are used for diagnostics: agar gel immunodiffusion test, indirect immunofluorescence test and ELISA test. This survey included 2000 sera samples from sheep in 4 epizootiology areas of the Scientific Veterinary Institute of Serbia (NIVS) Belgrade, Veterinary Specialist Institute (VSI) Sombor, Veterinary Specialist Institute (VSI) Subotica and Veterinary Specialist Institute (VSI) Zrenjanin, each with 500 representative samples. The detection of specific antibodies against maedi-visna virus (MVV) was done by ELISA technique, using commercial set kit CHEKIT-CAEV/MVV, produced by IDEXX. Based on the obtained results from 2000 seep sera tested forMVVantibodies, in 325 cases (16.24%) sheep were seropositive, while only 45 (2.25%) sheep were suspicious (ambiguous). The disease is important because of economic losses, what restricts trade. The fact that MVVis proved in sheep population points out the fact that more attention should be given to this infection.
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