Interaction between major pathogens in a finishing turkey flock: results of a longitudinal study.

This study investigated the spectrum of mortality-associated pathogens in a Italian finishing male turkey commercial flock. The survey mainly focuses on the interaction between Avian Pathogenic Escherichia Coli (APEC), Avian Metapneumovirus (AMPV) and Turkey Hemorrhagic Enteritis Virus (THEV). Cloacal swabs, rhino-pharyngeal swabs and blood samples were collected from 10 birds weekly until turkeys were 14 weeks old for virus isolation and/or PCR detection or microbiological examinations. Mortality was recorded and a sample of birds showing clinical signs or deceased birds were examined post mortem. When colisepticemic lesions were observed, microbiological examination were performed from selected organs. All E. coli detected were assessed for the presence of virulence-associated genes and were serotyped. Random amplified polymorphic DNA (RAPD) was used to analyse the relationships between E.coli clones. Serum samples were examined for antibodies against AMPV, THEV, Avian Influenza, Paramyxovirus -1 Mycoplasma gallisepticum and Mycoplasma synoviae. During a severe episode outbreak of mortality (0,5%) occurred in the 4th week of age, 4 strains of APEC were isolated and AMPV subtype B was detected. Later on, during the whole trial, 8 more APEC strains were isolated from lesions of colisepticaemia. THEV was detected from 8th to 9th weeks of age. The final results show that the higher mortality rate, at week 4, was due to more than APEC strains and it occurred in young birds in association with AMPV infection. No role was played by THEV in increasing mortality. An APEC serotype O111 was detected; to our knowledge this is the first report of its detection in turkeys.