Chlamydophila pneumoniae is a species of Chlamydophila, an obligate intracellular bacterium that infects
humans and is a major cause of pneumonia.
It was known as the Taiwan acute respiratory agent from the names of the two original isolates –
Taiwan and an acute respiratory isolate designated AR-39.
Until recently, it was known as Chlamydia pneumoniae, and that name is used as an alternate
in some sources.
In some cases, to avoid confusion, both names are given.
C. pneumoniae has a complex life cycle and must infect another cell to reproduce; thus,
it is classified as an obligate intracellular pathogen.
The full genome sequence for C. pneumoniae was published in 1999.
It also infects and causes disease in koalas, emerald tree boas, iguanas, chameleons, frogs,
and turtles.
The first known case of infection with C. pneumoniae was a case of sinusitis in Taiwan.
This atypical bacterium commonly causes pharyngitis, bronchitis and atypical pneumonia, mainly
in elderly and debilitated patients, but in healthy adults, also.
Life cycle and method of infection
Chlamydophila pneumoniae is a small gram negative bacterium that undergoes several transformations
during its life cycle.
It exists as an elementary body between hosts.
The EB is not biologically active, but is resistant to environmental stresses and can
survive outside a host for a limited time.
The EB travels from an infected person to the lungs of an uninfected person in small
droplets and is responsible for infection.
Once in the lungs, the EB is taken up by cells in a pouch called an endosome by a process
called phagocytosis.
However, the EB is not destroyed by fusion with lysosomes, as is typical for phagocytosed
material.
Instead, it transforms into a reticulate body and begins to replicate within the endosome.
The reticulate bodies must use some of the host's cellular metabolism to complete its
replication.
The reticulate bodies then convert back to elementary bodies and are released back into
the lung, often after causing the death of the host cell.
The EBs are thereafter able to infect new cells, either in the same organism or in a
new host.
Thus, the lifecycle of C. pneumoniae is divided between the elementary body, which is able
to infect new hosts but cannot replicate, and the reticulate body, which replicates
but is not able to cause new infection.
Diseases C. pneumoniae is a common cause of pneumonia
around the world; it is typically acquired by otherwise-healthy people and is a form
of community-acquired pneumonia.
Its treatment and diagnosis are different from historically recognized causes, such
as Streptococcus pneumoniae.
Because it does not gram stain as well as gram-negative and gram-positive organisms
and because C. pneumoniae bacteria is very different from the many other bacteria causing
pneumonia, pneumonia caused by C. pneumoniae is categorized as an "atypical pneumonia".
In addition to pneumonia, C. pneumoniae less commonly causes several other illnesses.
Among these are meningoencephalitis, arthritis, myocarditis, and Guillain-Barré syndrome.
Multiple studies have evaluated prior C. pneumoniae infection and a possible connection to lung
cancer.
One meta-analysis of serological data comparing prior C. pneumoniae infection in patients
with and without lung cancer found results suggesting prior infection was associated
with a slightly increased risk of developing lung cancer.
In research into the association between C. pneumoniae infection and atherosclerosis and
coronary artery disease, serological testing, direct pathologic analysis of plaques, and
in vitro testing suggest chronic infection with C. pneumoniae may be a risk factor for
development of atherosclerotic plaques. C. pneumoniae infection increases adherence of
macrophages to endothelial cells in vitro and aortas ex vivo.
However, the current data do not define how often C. pneumoniae is found in atherosclerotic
or normal vascular tissue, nor does it allow for determining whether C. pneumoniae infection
has a causative effect on atheroma formation or is merely an "innocent passenger" in these
plaques.
The largest trials that studied the use of antibiotics as a prevention for diseases associated
with atherosclerosis, such as heart attacks and strokes, did not show any significant
difference between antibiotics and placebo. C. pneumoniae has been found in the cerebrospinal
fluid of some patients diagnosed with multiple sclerosis.
Serological evidence for possible chronic C. pneumoniae infection was first associated
with wheezing, asthmatic bronchitis, and adult-onset asthma in 1991.
Subsequent studies of bronchoalveolar lavage fluid from pediatric patients with severe
chronic respiratory illnesses including asthma have demonstrated that over half had evidence
of C. pneumoniae by direct organism identification.
The only prospective study of new-onset adult asthma carried out in a primary-care clinic
diagnosed acute C. pneumoniae infection serologically in 5/5 patients with acute wheezing that became
chronic and that was later diagnosed as asthma, and in another patient who developed new-onset
chronic bronchitis who had the organism cultured from his sputum 6 months after illness onset.
These observations suggest that acute C. pneumoniae infection is capable of causing protean manifestations
of chronic respiratory illness, some of which diagnosed as asthma.
That these associations are clinically relevant in the primary-care setting is suggested by
the results of two observational trials and two randomized controlled trials of azithromycin
treatment for asthma.
One of these RCTs and another macrolide trial suggest that the treatment effect may be greatest
in patients with severe, refractory asthma.
These clinical results correlate with epidemiological evidence that C. pneumoniae is positively
associated with asthma severity and laboratory evidence that C. pneumoniae infection creates
steroid-resistance.
Currently available asthma guidelines do not address this evidence.
Vaccine research There is no vaccine to protect against Chlamydophila
pneumoniae.
Research is on-going.
Identification of highly immunogenic antigens is critical for the construction of an efficacious
subunit vaccine against C. pneumoniae infections.
References
External links Chlamydia Pneumoniae cpnhelp.org