Maedi-Visna (MV) virus and caprine arthritis encephalitis (CAE) virus known as small ruminant lentiviruses (SRLVs) cause chronic diseases in susceptible animals. The main reservoirs of these viral agents are sheep and goat. In sheep, MV virus causes a disease as the same name of the virus. This is the first seroprevalence survey of SRLVs in sheep population of Khorasan-e-Razavi province in Iran. Two hundred and twenty sheep from 30 flocks in 12 regions of the province were selected by random cluster sampling method. Serum samples were analyzed for the presence of antibodies against MV/CAE viruses. The seroprevalence in sheep was 34.5% (95.0% CI: 28.3 to 40.7%). Totally, the seroprevalence was in the range of 6.7 to 72.2 %. In 26 flocks of sheep (89.6%; 95.0%CI: 74.4 to 98.8%), at least one seropositive case was detected. The relationship between seropositivity and age, sex, flock size and breeds of sheep were statistically analyzed. In logistic regression model, only age was correlated with SRLV seroprevalence (p < 0.05). This study showed relatively high seroprevalence against SRLVs in sheep population in this area of the country. Due to difficulty in clinical diagnosis, chronic course of the disease, the absence of effective vaccine and treatment and huge economic loss, more epidemiological studies with regards to prevention and control of the disease are necessary.

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