Three Fatal Gestational Psittacosis Cases Caused by Chlamydia psittaci Strains Belonging to Closely Related Lineages, Japan

Gestational psittacosis is a rare infectious disease caused by Chlamydia psittaci that causes high maternal and fetal mortality rates. In Japan, gestational psittacosis has been reported in 7 patients, including 4 maternal deaths without antemortem diagnosis. We molecularly diagnosed C. psittaci infection postmortem in 3 patients treated during 2017-2024. We extracted DNA from formalin-fixed paraffin-embedded placenta, lung, and spleen tissues. Analysis of multilocus sequence typing indicated sequence type (ST) 269 in 1 patient and ST335 in 2; all 3 were closely related lineages that have not been previously reported in Japan or in animals. However, the ompA gene showed distinct clusters in the phylogenetic analysis. Quantitative PCR and immunostaining revealed higher amounts of C. psittaci detected in placenta than in lung or spleen, suggesting that proliferation of C. psittaci in the placenta might cause severe symptoms. ST335/ST269 lineage could be highly virulent strains for pregnant women.