HISTOLOGIC AND IMMUNOCYTOCHEMICAL CHARACTERIZATION OF CANINE DISTEMPER-ASSOCIATED METAPHYSEAL BONE-LESIONS IN YOUNG-DOGS FOLLOWING EXPERIMENTAL-INFECTION

The proximal metaphyses of the humerus of weanling gnotobiotic dogs ex perimentally infected with canine distemper virus (CDV) were investiga ted histologically and immunocytochemically between 4 and 41 days afte r infection. Viral antigen was demonstrated in hematopoietic marrow an d bone cells at postinfection day (PID) 5 and PID 7, respectively. Bet ween PID 8 and 27, CDV antigen was abundantly present in marrow cells, osteoclasts, and osteoblasts and less frequently in osteocytes. Immun opositive cells in both osseous tissues and bone marrow declined betwe en PID 29 and PID 36 and were absent by PID 41. Chondrocytes of the gr owth plate were negative for viral antigen throughout the observation period. In bone, viral antigen was more frequently observed in bone ce lls of the primary spongiosa than in the secondary spongiosa. There wa s a strong correlation between occurrence of CDV antigen and osseous c hanges. Associated metaphyseal bone lesions were mild and most promine nt between PID 8 and PID 32. Lesions consisted of necrosis of osteocla sts, which was associated with subsequent persistence of the primary s pongiosa (growth retardation lattice). Atrophy and necrosis of osteobl asts and marrow cells were also noted. Infection of metaphyseal bone c ells appears to be common in young dogs with experimental systemic dis temper. Bone cell infection is preceded by infection of marrow cells, and infected bone cells may experience degeneration and necrosis. This subtle viral effect may result in defects in bone modeling in CDV-inf ected dogs.