Rapid induction of hypothyroidism by an avian leukosis virus

Infection of 10-day chicken embryos with an avian leukosis virus, RAV-7, resulted in hypothyroidism within 3 weeks posthatching. Histological examination of the thyroids from infected chickens showed an extensive infiltration of lymphoblastoid cells by 7 days posthatching. Areas resembling germinal centers were present in the thyroids of infected chickens by 3 weeks posthatching. Examination of circulating thyroid and pancreas hormones showed a significant reduction in T3 and T4 levels and a trend toward higher insulin levels after 16 days posthatching. T4 supplementation of RAV-7-infected chickens alleviated some aspects of the disease syndrome but did not abrogate all symptoms. Marked involution of both bursa and thymus glands was noted. RAV-7 had an RNA genome of 8.2 kilobases and a polypeptide composition characteristic of an avian leukosis virus. The hypothyroidism followed a dose response to RAV-7 infection.