Pathogenesis of osteopetrosis induced by rapid and slow onset plaque isolates of an avian osteopetrosis virus.

Examination of bone from chickens infected as 10-day-old embryos with isolates of an avian osteopetrosis virus revealed that MAV-2(O) plaque isolate 32/2/4 caused rapid bone growth, while MAV-2(O) plaque isolate 13 caused a mild form of bone growth. MAV-2(O) plaque isolate 32/2/4 caused anemia when injected into the 8-day-old hatched chick and bone growth in ovo when injected into the 4-day-old embryo. Passive administration of neutralizing antibody protected against MAV-2(O)-induced bone growth when antibody was given to the embryo 1 day after virus. Neutralizing antibody also protected against an acute anemia observed when normal and bursectomized chickens were given MAV-2(O) 32/2/4, but antibody did not prevent the appearance of a chronic anemia or osteopetrosis in bursectomized chickens. Repeated animal passage of a slow onset plaque isolate of MAV-2(O) caused the virus to progressively induce more severe bone growth and anemia.