Abstract
Chlamydia psittaci is an avian pathogen and zoonotic agent of atypical pneumonia. The most pathogenic C. psittaci strains cluster into the 6BC clade, predicted to have recently emerged globally. Exposure to infected parrots is a risk factor with limited evidence also of an indirect exposure risk. Genome sequencing was performed on six Australian human and a single avian C. psittaci strain isolated over a 9 year period. Only one of the five human patients had explicit psittacine contact. Genomics analyses revealed that the Australian C. psittaci strains are remarkably similar, clustering tightly within the C. psittaci 6BC clade suggested to have been disseminated by South America parrot importation. Molecular clock analysis using the newly sequenced C. psittaci genomes predicted the emergence of the 6BC clade occurring approximately 2,000 years ago. These findings reveal the potential for an Australian natural reservoir of C. psittaci 6BC strains. These strains can also be isolated from seriously ill patients without explicit psittacine contact. The apparent recent and global spread of C. psittaci 6BC strains raises important questions over how this happened. Further studies may reveal whether the dissemination of this important zoonotic pathogen is linked to Australian parrot importation rather than parrots from elsewhere.
Highlights
Chlamydiae are obligate intracellular bacteria that infect a wide variety of anatomical sites in a diverse number of hosts
Humans are considered an opportunistic host for C. psittaci; infections occurring by zoonotic transmission as a result of direct contact with birds[14]
An investigation of an outbreak of psittacosis in the Blue Mountain region of New South Wales (NSW), Australia in 2002, found that only 50% of cases were linked to direct contact with birds[3]
Summary
Chlamydiae are obligate intracellular bacteria that infect a wide variety of anatomical sites in a diverse number of hosts. Perhaps one of the most interesting observations to have come from these comparative genomics studies has been the revelation that the most virulent strains of C. psittaci, associated with infections of parrots and zoonotic risk to humans, appear to be clonal[8,9] Strains within this clade (the C. psittaci 6BC clade) have been reported in association with epidemics worldwide, highlighting the potential public health impacts of these virulent strains globally. Molecular dating of these strains, performed by Read et al.[9], further suggests that these C. psittaci clones emerged recently with a current hypothesis that the importation of South American parrots may be the ultimate source As another “new world” source of psittacines, little or nothing is known about the genetic identity of endemic C. psittaci strains in Australian humans and parrots and the public health risks for this recognised zoonotic pathogen. We show that that these isolates cluster within the most pathogenic clade of this zoonotic pathogen described to date, reinforcing the public health risk of direct and indirect exposure to native parrots and raising questions over the ultimate origin of these globally disseminated strains
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