Pathogenicity of avian nephritis virus in chicks previously infected with infectious bursal disease virus

Pathogenicity of avian nephritis virus (ANV) was studied in 7-day-old chicks previously infected with infectious bursal disease virus (IBDV) at 1 day of age. Three IBDV+ANV infected chicks were found dead with no apparent clinical signs within 10 days of inoculation with ANV and they had marked urate deposits throughout the body. All of the surviving IBDV+ANV infected chicks had reduced body weight gain, unlike the ANV-only infected, IBDV-only infected and non-infected control chicks. In a chronological study, all of the ANV-infected chicks revealed interstitial nephritis accompanied by tubular cell degeneration and lymphoid cell infiltration. Avian nephritis virus antigen was detected with equal sensitivity by fluorescent antibody and immunoperoxidase techniques and was widely distributed in the degenerated epithelial cells. The concentration of serum uric acid in IBDV+ANV infected chicks was higher than that in ANV-only infected chicks. The antibody against ANV in ANV-only infected chicks was first detected 8 dpi and its titre increased gradually. In contrast, the antibody in the IBDV+ANV infected chicks was very low and was detected in only three out of seven chicks 16 dpi; the titre was 1:4 in one chick and 1:8 in the other 2 chicks. Coincident with serological results, the number of lgG- and IgM-containing cells in the kidneys and spleen were less in IBDV + ANV-infected chicks than in ANV-only infected chicks. These finding suggested that IBDV infection in chicks might influence the immunological response and susceptibility to subsequent ANV infection.