Faculty of Veterinary Medicine University of Zagreb
Abstract
A total of 142 black-headed gulls (BHGs), Chroicocephalus ridibundus, were captured during February and March 2009 at the Zagreb city rubbish dump (45.45 N 16.01 E) in order to collect cloacal swabs and serum samples. Cloacal swabs were tested by virus isolation in embryonated chicken eggs, which resulted in isolation of one avian influenza virus (AIV) that was of the H16 subtype. The collected sera were tested by blocking ELISA for avian influenza antibodies, resulting in 28.2% positive samples, which were retested by haemagglutination inhibition (HI) using H5 and H7 subtype antigens. Only one serum sample was positive for H5 and none for H7 antibodies. Statistically, no significant difference was found between the ages of AIV seropositive birds (2 = 2.08, df = 1, P = 0.15). In contrast, regarding seroprevalence in different months of capture, a higher proportion of positive gulls was found during March than during February (2 = 4.53, df = 1, P = 0.03), especially in younger birds (2 = 7.67, df = 1, P = 0.006). This finding suggests that BHGs might contract AIV infection during their aggregations in large numbers on rubbish dumps or similar feeding sites during the winter. Although only one of the 142 tested birds was positive for H5 subtype antibodies, this finding cannot be neglected seeing that apparently healthy BHGs can carry highly pathogenic AIV of the H5N1 subtype. Nevertheless, the results of our study have shown that BHGs are more often infected with other AIV subtypes and therefore are most likely not the primary carriers of H5 AIV. To our knowledge this is the first detection of H16 AIV in Croatia.Tijekom veljače i ožujka 2009. na gradskom odlagalištu otpada u Zagrebu (45.45 N 16.01 E) uhvaćena su 142 riječna galeba (Chroicocephalus ridibundus) u cilju prikupljanja brisova nečisnica i uzoraka krvi. Brisovi nečisnica su pretraženi izdvajanjem virusa u embrioniranim kokošjim jajima što je rezultiralo izdvajanjem virusa influence ptica koji je bio podtipa H16. Prikupljeni uzorci seruma su pretraženi imunoenzimnim testom za protutijela virusa influence ptica od kojih je 28,2% bilo pozitivno. Pozitivni uzorci su dodatno pretraženi inhibicijom hemaglutinacije s antigenima podtipa H5 i H7 među kojima je samo jedan bio pozitivan na H5 i nijedan na H7 protutijela. Statistički nije ustanovljena značajna razlika među skupinama različite dobi seropozitivnih ptica (2 = 2,08, df = 1, P = 0,15). Nasuprot tome, seroprevalencija u različitim mjesecima lova je imala veći udio tijekom ožujka nego tijekom veljače (2 = 4,53, df = 1, P = 0,03), naročito u mlađih ptica (2 = 7,67, df = 1, P = 0,006). Ovakav nalaz ukazuje na moguću infekciju riječnih galebova tijekom njihovoga brojnog okupljanja na odlagalištima otpada ili sličnim mjestima za hranjenje tijekom zime. Iako je samo jedna od 142 ptice bila pozitivna na protutijela za H5 podtip, nalaz se ne smije zanemariti znajući da naizgled zdravi riječni galebovi mogu nositi virus jako patogene influence podtipa H5N1. Unatoč tome, rezultati našeg istraživanja pokazuju da riječni galebovi češće bivaju inficirani drugim podtipovima virusa influence ptica te stoga najvjerojatnije nisu primarni nosioci virusa influence podtipa H5. Sukladno našim spoznajama, ovo je prvi dokaz virusa influence podtipa H16 u Hrvatskoj
