Chlamydia Pneumoniae

From MicrobeWiki, the student-edited microbiology resource
This student page has not been curated.

Etiology/Bacteriology

Taxonomy

| Order = Chlamydiales | Family = Chlamydiaceae | Genus = Chlamydia | Species = Chlamydia pneumoniae
|NCBI: Taxonomy Genome: Genome|}

Description

Chlamydophila pneumonia (TWAR) is a recently recognized third species of the genus Chlamydia that causes acute respiratory disease. The strain name TWAR was derived from the first conjunctival isolates of the species (TW-183 and AR-39), although the pathogen initially colonizes the reparatory tract. [1]

Pathogenesis

Incubation and Colonization

The incubation period of C pneumoniae is approximately 3-4 weeks, with a usually gradual onset.[6] If upper respiratory tract symptoms (eg. rhinitis, laryngitis, pharyngitis, sinusitis) increase in severity to bronchitis or pneumonia, symptoms can present in an additional 1-4 weeks.[6] The symptoms are not always biphasic, however, and many hosts do not show symptoms beyond a mild initial respiratory infection. As C. pneumoniae is a respiratory pathogen, its initial sites of colonization are the oral and nasal mucosa. Once it colonizes the lungs, it is distributed by monocytes through blood circulation to other areas of the body.

Epidemiology

The estimated number of cases of pneumonia caused by C pneumoniae in the United States is 300,000 cases per year, and the pathogen is estimated to cause 10-20% of community-acquired pneumonia (CAP) cases among adults.[6] While all ages are at risk, C. Pneumoniae infection is most common in children between 5 and 14 years old. In the United States, about 50% of adults have evidence of past infection by age 20, and reinfection throughout life is common.[7] C. pneumoniae appears to have a worldwide distribution, although the prevalence of infection varies by region.[7] Studies of adults from 10 areas of the world have shown a higher population prevalence in tropical, less developed countries.[7]

Most of the fatalities associated with C. pneumoniae infection have been in persons with underlying illness and complications [7]. C. pneumonia has been known to contribute to serious morbidity and mortality among populations with weakened immune responses such as residents of nursing homes who suffer respiratory disease outbreaks.[17]

Transmission

C. pneumoniae exists in one of two states. Its infectious, non-replicating state, known as the elementary body (EB) is stationary and extracellular. In this stage, C. pneumoniae has the ability to withstand environmental stresses until it is transferred to a new host’s lungs through small droplets. Once in the lungs, the EB is taken up into an endosome by phagocytosis. However, the EB is not destroyed by fusion of the endosome with a lysosome, as is typical for phagocytosed pathogens. Instead, it transforms into a larger intracellular form, or reticulate body (RB), that begins to replicate within the endosome. [7] After multiple rounds of division, the RBs are re-differentiated into an infectious EBs that are released into the cytoplasm to initiate new cycles in new host cells. [16] C. pneumoniae also tends to infect endothelial cells, the cells that line blood vessels[4] . The ensuing inflammation results in the creation of new blood cells that draw in the pathogen, providing additional hosts for the bacterial parasite that allow it to further spread through the body. If Chlamydia is residing in peripheral blood cells and inflammation occurs in the host’s body, the inflammatory process can become secondarily infected by Chlamydia, no matter what the source of the inflammation. [4] Vascular infection further infects bone marrow cells, which then produce infected and dysfunctional immune cells (macrophages, neutrophils, etc.). [18]

Clinical Presentation

Symptoms

Because the initial site of colonization is the lungs and ciliated cells of the airways, pneumonia and bronchitis are the most common clinical manifestations of infection by C. pneumonia. Additional symptoms include gradual onset of cough with low-grade fever. Less common presentations are pharyngitis, laryngitis, and sinusitis. [3] Respiratory manifestations can be biphasic, with resolution of pharyngitis prior to development of a more typical bronchitis or pneumonia syndrome [7]. A cough can persist for weeks to months despite appropriate use of antibiotics. [6]

Associated Diseases

Alzheimer's Disease

Atherosclerosis

Diagnosis

Diagnosis of acute infections is reasonably well established in most laboratories, but chronic infections pose a different problem as the manifestation of infection is often caused by a multitude of factors. Diagnosis is typically based on direct microscopy and serology[19] . The majority of C. pneumoniae infections are asymptomatic or mild upper respiratory tract infections, most of which are mild and self-restricted and therefore often go undiagnosed.[16] Atypical pneumonia, bronchitis and sinusitis are the most frequent respiratory diseases caused by C. pneumonia, and persistent respiratory infections such as these can serve as an indicator for possible Chlamydia infection.[1]

Treatment

Host Immune Response

Damage Response Framework

References

1. Grayston, J. T., C.-C. Kuo, L. A. Campbell, and S.-P. Wang. 1989. Chlamydia pneumoniae sp. nov. for Chlamydia sp. strain TWAR. Int. J. Syst. Bacteriol. 39:88–90.
2. Kuo, C., & Grayston, J. (n.d.). Chlaymydia spp. strain TWAR A newly recognized organism associated with atypical pneumonia and other respiratory infections. Clinical Microbiology Newsletter, 137-140.
3. "Chlamydophila Pneumoniae Infection." Centers for Disease Control and Prevention. Centers for Disease Control and Prevention, 7 Feb. 2014. Available at: http://www.cdc.gov/pneumonia/atypical/chlamydophila.html
4. Humphrey, Nancy. "Chlamydia Pneumoniae Not Caught like You Thought (04/23/99)." Reporter: Vanderbilt University Medical Center. Available at: http://www.mc.vanderbilt.edu:8080/reporter/index.html?ID=779.
5. Oba, Yuji. "Chlamydial Pneumonias." : Overview, Pathophysiology, Epidemiology. 2 Nov. 2013. Available at: http://emedicine.medscape.com/article/297351-overview#a1.
6. Kuo CC, Jackson LA, Campbell LA, Grayston JT. Chlamydia pneumoniae (TWAR). Clinical Microbiology Reviews. 1995;8(4):451-461.
7. Casadevall A, Pirofski L. 2003. The Damage Response Framework of Microbial Pathogenesis. Nat Rev 1:17-24.
8. Hudson, MAP. What is the evidence for a relationship between Chlamydia pneumoniae and late-onset Alzheimer's disease? Laboratory Medicine. 2001:680–685.
9. Gérard, H. C., Dreses-Werringloer, U., Wildt, K. S., Deka, S., Oszust, C., Balin, B. J., Frey, W. H., Bordayo, E. Z., Whittum-Hudson, J. A. and Hudson, A. P. (2006), Chlamydophila (Chlamydia) pneumoniae in the Alzheimer's brain. FEMS Immunology & Medical Microbiology, 48: 355–366. doi: 10.1111/j.1574-695X.2006.00154.x
10. Mahony JB, Coombes BK. Chlamydia pneumoniae and atherosclerosis: does the evidence support a causal or contributory role? FEMS Microbiol Lett. 2001;197:1-9.
11. Farb A, Tang AL, Burke AP, Sessums L, Liang Y, et al. Sudden coronary death. Frequency of active coronary lesions, inactive coronary lesions, and myocardial infarction. Circulation. 1995;92:1701–1709.
12. Kalayoglu, M. V., & Byrne, G. I. (1998). A Chlamydia pneumoniae Component That Induces Macrophage Foam Cell Formation Is Chlamydial Lipopolysaccharide. Infection and Immunity, 66(11), 5067–5072.
13. Layh-Schmitt G, Bendl C, Hildt U, Dong-Si T, Juttler E, Schnitzler P, Grond-Ginsbach C, Grau AJ: Evidence for infectionwithChlamydiapneumoniaeina subgroupofpatientswithmultiplesclerosis.AnnNeurol47,652-655 (2000).
14. Hahn DL, Schure A, Patel K et al. (2012). "Chlamydia pneumoniae-specific IgE is prevalent in asthma and is associated with disease severity". PLoS ONE 7 (4): e35945. doi:10.1371/journal.pone.0035945. PMC 3335830. PMID 22545149.
15. Bailey, Leslie. "Infection Biology of Chlamydia Pneumoniae." Department of Molecular Biology: Laboratory for Molecular Infection Medicine Sweden (MIMS), 2008. <http://www.diva-portal.org/smash/record.jsf?pid=2:141442>.
16. Troy CJ, Peeling RW, Ellis AG, et al. Chlamydia pneumoniae as a New Source of Infectious Outbreaks in Nursing Homes. JAMA. 1997;277(15):1214-1218. doi:10.1001/jama.1997.03540390044033.


Created by Erika Cummings, a student of Tyrrell Conway at the University of Oklahoma.