TURKEY RHINOTRACHEITIS VIRUS AND ESCHERICHIA-COLI EXPERIMENTAL-INFECTION IN CHICKENS - HISTOPATHOLOGICAL, IMMUNOCYTOCHEMICAL AND MICROBIOLOGICAL STUDY

The aim of this study was to evaluate the response of chickens to a co mbined infection with turkey rhinotracheitis virus (TRTV) and Escheric hia coli O78:K80. Groups of specific-pathogen-free chickens were inocu lated by eyedrop and intranasal routes with TRTV and/or E. coli O78:K8 0. Presence of E. coli O78:K80, histopathological changes and tissue d istribution of viral antigen in the respiratory tract of chickens were evaluated. Dual infection resulted in increased severity of clinical signs, and macroscopic and microscopic lesions compared with those gro ups given single infections. All 36 chickens inoculated with TRTV plus E. coli O78,K80 showed severe rhinitis. Moreover, periorbital edema a nd fibrinous airsacculitis and pericarditis were observed in one of th e three chickens inoculated with both agents and sacrificed at day 5 p .i. In addition, purulent material in the air spaces of the cranial bo nes was seen in three of the six animals from the same group sacrifice d at days 5 and 7 p.i. The distribution of viral antigen in tissues wa s similar in groups inoculated with TRTV and TRTV plus E. coli, but vi ral antigen was detected only in main bronchi of chickens from the lat ter group. The quantity of E. coli O78:K80 isolated from the nasal cav ity was greater in the group given dual infection. The results obtaine d suggest that TRTV may act as primary agent, enhancing E. coli multip lication. The lesions observed in the group inoculated with both agent s could correspond to an initial stage of swollen head syndrome (SHS) and contribute to the hypothesis that SHS could be due to a mixed infe ction with TRTV and E. coli. (C) 1997 Elsevier Science B.V.