Epidemiological investigation of Chlamydiaceae in poultry of Mexico and comparison of growth characteristics of Chlamydia gallinacea in different experimental trials

Résumé fourni par la source

Chlamydiaceae infections in poultry are mainly due to Chlamydia psittaci and Chlamydia gallinacea. While C. psittaci has long been known to affect birds and to have zoonotic potential, C. gallinacea is a newly described species that has been found to be widespread in chickens and whose pathogenicity and zoonotic potential have not yet been shown. Good husbandry and biosecurity practices, coupled with antimicrobial treatment in punctual cases, are the most effective means to control chlamydial infections among poultry. Few studies had been conducted on Mexican poultry farms assessing on-farm biosecurity practices implementation and no data were available regarding the presence of Chlamydiaceae in poultry of Mexico. The aims of this thesis were to detect the presence of Chlamydiaceae on commercial and backyard farms, to identify risk factors associated with its potential presence on poultry and to characterize the on-farm management and biosecurity practices. Results showed that apparent prevalence of Chlamydiaceae increased inversely to the level of poultry confinement. C. gallinacea was the only chlamydial species found. On backyard poultry, the lack of antimicrobial usage and an impaired health status were found to be associated with the presence of Chlamydiaceae, while on commercial farms laying hens had higher odds of being Chlamydiaceae-infected than chicken broilers. Five biosecurity practices were identified as the most significantly associated with farm clustering. Three of these practices concerned directly the staff or visitors while two were related to farm facilities. Farms within the cluster in which laying hen farms predominated were more prone to not implement some of these five biosecurity practices. Recommendations were provided to improve the on-farm biosecurity. Finally, in vitro studies carried out to optimize the growth protocol for C. gallinacea were not conclusive; however, an enhanced growth of one C. gallinacea positive field specimen was identified. The cause of this enhanced growth needs to be determined; differences at genetic or transcriptional level should be considered, as well as the influence of external parameters. If in vitro observations can be extrapolated to an in vivo phenomenon, it could shed light on the pathogenic potential of this newly described species.

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