Efficient fecal-oral and possible vertical, but not respiratory, transmission of emerging Chlamydia gallinacea in broilers.

Chlamydia gallinacea is an endemic Chlamydia agent in poultry with a worldwide distribution. The aim of this study was to investigate whether C. gallinacea can be transmitted via fecal-oral, respiratory and vertical routes. After co-housing with C. gallinacea-inoculated broilers (n = 10) for 15 days, over 90.0% of SPF broilers (n = 10) became C. gallinacea-positive in their oropharyngeal and cloacal swabs. Connection of isolators with ventilation tubing resulted in transmission of infectious bronchitis virus, but not of C. gallinacea, from infected broilers in one isolator to uninfected ones in the other isolator. Chlamydia-qPCR determined that 97.6% of shells of embryonated eggs (287/294) from a breeding farm were positive for C. gallinacea. C. gallinacea positivity in egg albumen increased significantly from 7.6% (10/128) before incubating to 44.4% (8/18) of 7-day incubation, and from 5.5% (7/128) to 38.9% (7/18) in egg yolk. After incubating for 19 days, C. gallinacea DNA was detected in heart (5/55, 9.1%), liver (3/55, 5.5%), spleen (7/55, 12.7%), lung (6/55, 10.1%), kidney (8/55; 14.5%) and intestine (4/55, 7.3%) of chicken embryos. Taken together, our data indicate that C. gallinacea can be efficiently transmitted by the fecal-oral route, but not via aerosol. Additionally, vertical transmission can occur via penetration of C. gallinacea from eggshell to albumen, yolk, and the growing embryo. Our findings provide essential information for the control of C. gallinacea in poultry farms.