Chlamydia psittaci: New insights into genomic diversity, clinical pathology, host–pathogen interaction and anti-bacterial immunity

Abstract

The distinctive and unique features of the avian and mammalian zoonotic pathogen Chlamydia (C.) psittaci include the fulminant course of clinical disease, the remarkably wide host range and the high proportion of latent infections that are not leading to overt disease. Current knowledge on associated diseases is rather poor, even in comparison to other chlamydial agents. In the present paper, we explain and summarize the major findings of a national research network that focused on the elucidation of host-pathogen interactions in vitro and in animal models of C. psittaci infection, with the objective of improving our understanding of genomics, pathology, pathophysiology, molecular pathogenesis and immunology, and conceiving new approaches to therapy. We discuss new findings on comparative genome analysis, the complexity of pathophysiological interactions and systemic consequences, local immune response, the role of the complement system and antigen presentation pathways in the general context of state-of-the-art knowledge on chlamydial infections in humans and animals and single out relevant research topics to fill remaining knowledge gaps on this important yet somewhat neglected pathogen.

First Identification ofChlamydia psittaciin the Acute Illness and Death of Endemic and Endangered Psittacine Birds in Mexico

“…The clinical history, signology, necropsy findings, and histologic lesions of all tested birds were compatible with those described previously for psittacine birds infected by C. psittaci (15,16,29,32). In this case, the presence of the bacteria was initially demonstrated through a 16S rRNA gene sequence analysis using specimens obtained from the liver of affected birds; together with the immunofluorescence results on the same hepatic tissue, these analyses confirmed the diagnosis.…”

“…It has been demonstrated that birds may remain carriers during latent infections, which can be reactivated if the birds are subjected to stressful conditions, such as those that occur during captivity (e.g., overcrowding, transportation, malnutrition, temperature changes, and manipulation). Therefore, when a latently infected bird restarts bacterial excretion, it becomes an infection source for other birds and humans (11,12,16).…”

“…Macroscopic and histopathologic lesions varied primarily according to strain virulence and inherent host factors, such as age, underlying diseases, or the infecting dose (15,16). The variation in the severity of the lesions in each diagnosed bird may be attributable to any of these factors.…”

Coxiella burnetii Infects Primary Bovine Macrophages and Limits Their Host Cell Response

“…In order to determine if the observed effect is specific for infection with C. burnetii, we exemplarily compared the temporal response pattern of IL-12 transcription in bovine MDM cultures to that in E. coli LPS and another intracellular pathogen, C. psittaci. C. psittaci has a broad host range, including cattle (61), and replicated efficiently in the bovine MDM cultures (K. Hillarius and A. Berndt, data not shown). Contrary to NMI infection, both treatments induced increasing IL-12 expression during the first 24 h, implying that C. burnetii specifically controls the host response in bovine macrophages to allow replication without significant inflammatory cytokine production.…”

Chlamydiae in corvids

“…Depending on the species and age of the bird and the virulence of the infectious bacterial strain, avian chlamydiosis can be subclinical or characterised by respiratory, digestive, or systemic disorders (Knittler and others 2014). …”