Pulmonary retroviruses infection in sheep: a retrospective study in a slaughterhouse of Piemonte region, NW Italy

Small Ruminant Lentiviruses (SRLV), causing Visna-Maedi (MV) and Caprine Arthritis-Encephalitis (CAEV), and the Jaagsiekte sheep retrovirus, causing Ovine Pulmonary Adenocarcinoma (OPA) are important Retroviruses affecting lungs of small ruminants. An epidemiological and pathological study was carried out to evaluate the presence of Ovine Retroviruses from one of the largest small ruminants slaughterhouse in Piemonte, Northwestern Italy. The authors analyzed data collected by veterinary inspectors throughout 2000-2010, stored in the slaughterhouse registers. The computerized Livestock Regional system (ARVET) permitted to evaluate characteristics of affected farms, distribution of both diseases within the Region, as well as to analyze some risk factors (i.e. type of breeding and grazing). Histological (standard fixation, embedding and staining techniques) and molecular biology (PCR and nested-PCR) investigations were performed on lung samples with macroscopical lesions of OPA and MV, collected during the second semester 2012. Out of the 18,743 adult sheep examined, 5.4% (95%CI: 5.1-5.7) showed MV lesions, and 1.3% (95%CI: 1.2-1.5) OPA lesions. Both histological and molecular biology techniques confirmed MV macroscopical diagnosis in 76% of cases, and OPA in 100% of cases. Macroscopical examination at the slaughterhouse can thus represent a good method to identify retroviral pulmonary infection in small ruminants. Overall data obtained showed that in the study area (1,962.5 km2), 51% of farms bred animals with retroviral lung lesions, and 76% of sheep from the study area were affected. By evaluating the number of reports in the different types of farming (intensive vs. extensive, zero grazing vs. pasture), there is a highly significant difference in the extent of disease/infection amongst types of breeding. The decrease in disease reports from large farms (>200 sheep) could be related to extensive farming system: open grazing and mountain pasture greatly reduces the strict and continuous contacts between animals, thus the transmission by aerosol of both causative retroviruses.