Indurative lymphocytic mastitis in sheep after experimental infection with maedivisna virus

In order to provide further evidence for the association of an indurative lymphocytic mastitis in sheep with MVV (maedi-visna virus) infection, an experimental study was performed. Fourteen MVV-free pregnant ewes, 2 years of age, were divided into two groups. Eight were intravenously inoculated with MVV (strain ZZV-1050); six ewes served as sham-inoculated controls. Post-mortem examinations were carried out at 8, 16 and 28 months. After 8 months, the 3 infected ewes had indurated udders with extensive lymphoid proliferation around lactiferous ducts and in the acinar tissue. The ducts were often partially obliterated. After 16 months, one of the two infected ewes suffered from indurative lymphocytic mastitis. The other was free of specific udder lesions. After 28 months only one of three infected ewes had mild lymphocytic infiltration in the udder. None of the controls, two in each post-mortem session, had lesions typical of this form of mastitis. The lesions were most severe 8 months after infection. At 16 and 28 months lesions were of a lesser degree or were absent. The lung lesions in the infected ewes 8 months after inoculation were similar to the changes in the udder regarding the lymphoid accumulation, although the proliferation around bronchial tree and blood vessels was less pronounced. After 16 and 28 months all infected ewes had peribronchial and perivascular lymphocytic infiltration though of a lesser degree than after 8 months. From these results it is concluded that in addition to the lung and brain lesions MVV infections may cause a specific indurative lymphocytic mastitis.