Investigation of viral infections of ring-billed gulls (Larus delawarensis) in southern Ontario, Canada

Between mid-May and mid-July 2000, 360 ring-billed gulls (Larus delawarensis) were sampled (120 adults; 120 three weeks old; 120 five weeks old). The prevalence of antibodies specific to avian influenza virus (AIV) H13 differed significantly among age groups (92%, 53%, and 15% for adult, five-, and three-week-old gulls, respectively). Hemagglutinating agents, all of which were avian influenza A virus H13N6, were isolated from the cloacal swabs/tissue samples of 53 gull chicks. Three-week old chicks were 3.24 times more likely to be shedding AIV than five-week-old chicks. Infection with Newcastle disease virus (NDV), previously rare in gulls on the lower Great Lakes, was common (90%) based on the serologic findings; its clinical significance is unknown. The prevalence in adults was significantly lower (79%) than in three-week-old gulls (98%) or five-week-old gulls (93%). Newcastle disease virus was not isolated from any of the gulls.; The H13N6 avian influenza A subtype has low virulence in gulls. However, lesions such as lymphocytic infiltration in heart, kidney, pancreas, liver, and respiratory tract were significantly associated with the presence of antibodies against AIV and not with the presence of antibodies against NDV or isolation of AIV from cloacal, kidney, or lung tissues. Chickens are susceptible to infection with an AIV H13N6 after intravenous inoculation. No clinical signs were seen but the virus replicated in renal tubular epithelial cells and was associated with lymphocytic interstitial nephritis. These results are similar to other low pathogenic AIV isolated from waterfowl.; Circovirus infection was only detected in 6% of the juvenile birds. Inclusions were restricted to the lymphoreticular tissue. No significant differences between infected and non-infected birds were seen in eight different biological paramenters. The first evidence of circovirus infection, in a retrospective study, was in a juvenile ring-billed gull in 1973. Cirvovirus-like inclusions also were seen in juvenile herring gulls (Larus argentatus) and a great black-backed gull (Larus marinus). Birds with circovirus-like inclusions were 2.89 times (odds ratio) more likely to have septicemia/aspergillosis than birds with no circovirus-like inclusions.