Chlamydia psittaci: update on an underestimated zoonotic agent

Abstract

Chlamydia (C.) psittaci is an economically relevant pathogen in poultry and pet birds, where it causes psittacosis/ornithosis, and also a human pathogen causing atypical pneumonia after zoonotic transmission. Despite its well-documented prevalence, the agent has received less attention by researchers than other Chlamydia spp. in the last decades. In the present paper, we review recently published data on C. psittaci infection and attempt to single out characteristic features distinguishing it from related chlamydial agents. It is remarkable that C. psittaci is particularly efficient in disseminating in the host organism causing systemic disease, which occasionally can take a fulminant course. At the cellular level, the pathogen's broad host cell spectrum (from epithelial cells to macrophages), its rapid entry and fast replication, proficient use of intracellular transport routes to mitochondria and the Golgi apparatus, the pronounced physical association of chlamydial inclusions with energy-providing cell compartments, as well as the subversive regulation of host cell survival during productive and persistent states facilitate the characteristic efficient growth and successful host-to-host spread of C. psittaci. At the molecular level, the pathogen was shown to upregulate essential chlamydial genes when facing the host immune response. We hypothesize that this capacity, in concert with expression of specific effectors of the type III secretion system and efficient suppression of selected host defense signals, contributes to successful establishment of the infection in the host. Concerning the immunology of host-pathogen interactions, C. psittaci has been shown to distinguish itself by coping more efficiently than other chlamydiae with pro-inflammatory mediators during early host response, which can, to some extent, explain the effective evasion and adaptation strategies of this bacterium. We conclude that thorough analysis of the large number of whole-genome sequences already available will be essential to identify genetic markers of the species-specific features and trigger more in-depth studies in cellular and animal models to address such vital topics as treatment and vaccination.

Community-acquired pneumonia related to intracellular pathogens

“…However, if the first upper respiratory signs associated with C. pneumoniae infection are not treated, severe disease or even death may result [43]. Diagnosis of psittacosis can be difficult, and many more cases may occur that are not correctly diagnosed or reported.…”

“…Radiographic findings may include lobar or interstitial infiltrates. In some cases there are complications such as pericarditis, endocarditis or myocarditis, hepatomegaly, and splenomegaly [43]. Persons exposed to infected birds are at risk of infection with C. psittaci, and this disease is found worldwide, with approximately 70 % of the cases having a known source of infection as a result of exposure to pet birds [75].…”

Simkania negevensis, an insight into the biology and clinical importance of a novel member of the Chlamydiales order

“…Additional hypotheses of transmission include direct human to human transmission through aerosols or droplets due to the association with respiratory diseases (see pathogenic potential, hereafter), as well as sexual contacts or contacts with animals, which were described for other Chlamydiales (Baud & Greub, 2011;Baud et al, 2007;Gottlieb et al, 2013;Knittler & Sachse, 2015;Schachter, 1986). Sexual contact seems unlikely due to the high seroprevalence in children and the absence of cross-prevalence with C. trachomatis .…”

“…This infection can cause pelvic inflammatory disease (PID) (Bartlett et al, 2013) and lead to infertility as well as obstetrical complications such as miscarriage and preterm birth (Baud et al, 2011a(Baud et al, , 2008Gimenes et al, 2014;Pellati et al, 2008). Similarly, Chlamydia pneumoniae commonly causes bronchitis and pneumonia in children and young adults (Asner et al, 2014;Blasi et al, 2009;Principi & Esposito, 2001) and Chlamydia psittaci is an important zoonotic agent associated with atypical pneumonia as well as systemic infections (Knittler & Sachse, 2015;Schachter, 1986). In the past decades, various Chlamydia-related bacteria have been discovered, notably Simkania negevensis (S. negevensis).…”

Subversion of Cell-Autonomous Host Defense by Chlamydia Infection

“…On the contrary, Cpn cause infections of the upper respiratory tract leading to community-acquired pneumonia, bronchitis (Grayston et al 1993;Hahn 1998), or asthma (Hahn 1998) and are discussed to be associated with atherosclerotic cardiovascular disease (Boman and Hammerschlag 2002), Alzheimer's disease, and multiple sclerosis (Stratton and Sriram 2003). Besides the two major human pathogenic Chlamydia species, Chlamydia psittaci (Cps) can be transmitted from birds to humans, thereby causing severe pneumonia called psittacosis (Knittler and Sachse 2015). Simkania negevensis (Sn) was thought to be an environmental bacterium; however, recent work shows that Sn can infect several human cell lines and is discussed to be associated with lung infections in humans Greenberg et al 2003).…”