Turkey rhinotracheitis virus and Escherichia coli experimental infection in chickens: histopathological, immunocytochemical and microbiological study

Abstract

The aim of this study was to evaluate the response of chickens to a combined infection with turkey rhinotracheitis virus (TRTV) and Escherichia coli O78:K80. Groups of specific-pathogen-free chickens were inoculated by eyedrop and intranasal routes with TRTV and/or E. coli O78:K80. Presence of E. coli O78:K80, histopathological changes and tissue distribution 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 groups given single infections. All 36 chickens inoculated with TRTV plus E. coli O78:K80 showed severe rhinitis. Moreover, periorbital edema and fibrinous airsacculitis and pericarditis were observed in one of the three chickens inoculated with both agents and sacrificed at day 5 p.i. In addition, purulent material in the air spaces of the cranial bones was seen in three of the six animals from the same group sacrificed at days 5 and 7 p.i. The distribution of viral antigen in tissues was similar in groups inoculated with TRTV and TRTV plus E. coli, but viral antigen was detected only in main bronchi of chickens from the latter group. The quantity of E. coli O78:K80 isolated from the nasal cavity was greater in the group given dual infection. The results obtained suggest that TRTV may act as primary agent, enhancing E. coli multiplication. The lesions observed in the group inoculated with both agents could correspond to an initial stage of swollen head syndrome (SHS) and contribute to the hypothesis that SHS could be due to a mixed infection with TRTV and E. coli.