Parachlamydia acanthamoebae: disease-causing pathogen or opportunistic bystander?

Introduction. Parachlamydia acanthamoebae is an obligate intracellular bacterium related to disease-causing bacteria like Chlamydia trachomatis and Chlamydia pneumoniae and is thus classified within the Chlamydiales order. Parachlamydia was initially discovered within an Acanthamoeba strain isolated from water in a humidifier during an investigation of an outbreak of respiratory infections in humans.Gap Statement. The disease-causing potential of this bacterium is not fully understood, but Parachlamydia has been associated with bronchiolitis, bronchitis, aspiration pneumonia and community-acquired pneumonia in humans. Additionally, diagnostic testing for Parachlamydia infection is not routinely performed, indicating that prevalence is underreported.Aim. This JMM profile aims to gauge what is currently known about the pathogenic potential of P. acanthamoebae and bring awareness to gaps in knowledge.Results. Amoebae appear to be the main reservoir of P. acanthamoebae and likely enter the nasal passages through contaminated water sources or contact with contaminated animals. The infected amoebae may then descend to the lower respiratory tract where the lytic cycle is triggered, causing human infection.Conclusion. By implementing serology and molecular testing, as well as conducting additional epidemiological studies, a better understanding of the association of human colonization with disease outcomes can be achieved.