Zoonotic infections due to avian Chlamydia abortus: what are we missing?

Chlamydia abortus is an obligate intracellular bacterium primarily affecting ruminants and causing reproductive failures in sheep and goats. As a recognised zoonotic pathogen, C abortus can cause obstetric and respiratory infections in humans, with severe consequences in pregnant women and immunocompromised individuals. Previous studies have identified novel C abortus strains in avian species, closely related to the zoonotic Chlamydia psittaci, with some strains associated with cases of human pneumonia. In this Personal View, we review the evolving taxonomy of C abortus in light of these novel avian strains, propose subspecies distinctions, and describe the different zoonotic risks associated with both avian and ruminant strains. Challenges in diagnostics, host preference, and case detection are discussed, emphasising the need for a One Health approach to fully understand and mitigate these risks. With increasing reports of human C abortus infections, precise strain classification and differentiation between avian and ruminant subspecies, along with targeted surveillance, are essential to limit their zoonotic transmission.