A morphological, immunohistochemical and polymerase chain reaction (PCR) study was performed on eight ewes experimentally infected with an Italian strain of Maedi-Visna Virus (MVV) in order to evaluate the lesions and the viral distribution after three years of
infection. At the moment of
euthanasia, seven sheep were seropositive for MVV, while one sheep in poor body conditions was seronegative since one year. Lungs, pulmonary lymph nodes, udder, supramammary lymph nodes, carpal joints, the CNS, spleen and bone marrow of the eight infected sheep were collected for histology, for immunohistochemical detection of the MVV core
protein p28 and for PCR amplification of
a 218 bp
viral DNA sequence of the pol region. The most common histological findings consisted of interstitial lymphoproliferative
pneumonia and lymphoproliferative
mastitis of different severity, while no lesions were observed in the CNS. MVV p28
antigen was immunohistochemically labelled in lungs, udder, pulmonary lymph nodes, spleen and bone marrow but not in the CNS of all the eight infected sheep.
A 218 bp sequence of MVV pol region was detected in lung of a seropositive and of the seroconverted negative sheep. The results suggest that (i) MVV causes heterogeneous lesions in homogeneously reared ewes, (ii) MVV p28
antigen is detectable not only in inflammed target organs, but also in pulmonary lymph nodes, spleen and bone marrow, and (iii) immunohistochemistry and PCR are useful methods for
Maedi-
Visna diagnosis in suspected cases, also when serological tests are negative.