Chronic myocarditis and circulatory syndrome in a White Leghorn strain induced by an avian leukosis virus: light and electron microscopic study.

Specific-pathogen-free white leghorn chickens were inoculated at 1 day of age with avian leukosis virus (ALV, RAV-1). All chickens in Expt. 1, killed 33 or 64 days postinoculation, had focal chronic lymphocytic or lymphoplasmacytic myocarditis. Among those held beyond 33 days, eight of 22 developed lesions in the myocardium that resulted in a chronic circulatory syndrome (CCS) typical of right-sided heart failure. Chickens in Expt. 2 were held for 210 days, and 21% of 125 developed CCS. In Expt. 2, ALV particles were found by electron microscopy in myocardium of 100%, 72%, and 89% of inoculated chickens that developed CCS, lymphoid leukosis, or that had no gross lesions, respectively. These findings were in accord with the immunoperoxidase staining of tissue sections for group-specific antigen of ALV. In areas of extensive virus replication, there were often abnormal virus particles and also round bodies, which may have been remnants of host-cell membranes formed in the budding process. In contrast to findings in hearts, the spleens were usually negative for virus and viral antigen.