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We have studied the expression of the inducible form of nitric oxide synthase (iNOS) in joints of goats infected with the caprine arthritis encephalitis virus (CAEV). Nitric oxide generated by iNOS is thought to play an important role in the pathogenesis of various types of arthritis, especially rheumatoid arthritis (RA) in humans. Surprisingly, iNOS immunoreactivity was found only in joints of long-term infected goats with severe clinical arthritis, whereas-despite the presence of high numbers of inflammatory cells in the synovial tissue-no iNOS immunoreactivity was detected in mildly arthritic and in short-term experimentally infected goats. Most iNOS-positive cells expressed neither MHC class II nor CD68, which suggests that they were fibroblast-like synoviocytes. In situ hybridization studies showed that there was no correlation between iNOS immunoreactivity and detectable virus expression in the joint. In addition, infection of macrophages in vitro-the major host cells of CAEV in vivo-did not lead to increased iNOS mRNA expression. In response to stimulation, similar levels of iNOS expression were observed in infected and in uninfected macrophages. These findings suggest that the expression of iNOS is a feature of late-stage chronic arthritis and is not involved in the development of the inflammatory lesions. Both the lack of co-localization of iNOS protein and viral transcripts in the joint and the finding that CAEV does not stimulate the expression of iNOS in vitro further suggest that iNOS is not directly induced by the virus or the anti-viral immune response in the joint, that it may well, however, be involved in tissue remodelling or scar formation.

Bacteriology, somatic cell counts (SCC) and N-acetyl-beta-glucosaminidase (NAGase) activity determinations were conducted on milk samples collected from does in three dairy herds with caprine arthritis-encephalitis virus (CAEV) infection. In two herds, CAEV-infected does were more likely to have a subclinical bacterial infection of the udder than CAEV-free does (P < 0.05). Does with CAEV but no bacterial udder infection had significantly greater mean SCC and NAGase activity than CAEV-free does without udder infection (P < 0.01). In two herds, changes in milk SCC and NAGase associated with CAEV infection were similar to those produced by coagulase-negative staphylococcal infections. The findings confirm that indirect indicators of bacterial mastitis infection may have reduced specificity in dairy goat herds with CAEV.