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The inner and outer membranes are similar to gram-negative bacteria but they differ in that they lack peptidoglycan between the membranes. The outer membrane contains cysteine-rich proteins (CRP) that are thought to be the functional equivalent to peptidoglycan. Most of their metabolic intermediates are synthesised themselves however as they are unable to make their own ATP, they rely on the host cell for ATP synthesis and are therefore unable to grow independently of the host cell. As a result of this they are known as obligate intracellular parasites.
Elementary bodies which are small, infectious but metabolically inert attach to a receptor on a host cell and enter the host cell via endocytosis. These then convert to a reticulate body which are metabolically active but non-infectious. These grow and replicate by binary fission until the host is fill. The reticulate bodies then convert back to elementary bodies and the nucleus is pushed to the side of the cell. The elementary bodies are released and drift until they come into contact with another host cell, triggering endocytosis by the new host cell. Once inside the host cell, the elementary bodies transform back into reticulate bodies and the cycle starts again.
The cells in which they are replicated are damaged by the action of toxic microbial products from Chlamydia. The damage is however confined only to the infected cell and do not damage other cells. Clinical indications of chlamydial infection develop from the inflammatory response to the destruction of the infected cells. The pathogen enters the body through abrasions and lacerations and infects a limited selection of human cells. Cells that can be infected have receptors for the elementary bodies. Examples of these are cells are the conjunctiva, cells lining the mucous membranes of trachea, bronchi, urethra, uterus, uterine tubes, anus and rectum.
There are three main species of Chlamydia which cause human infection: Chlamydia trachomatis, Chlamydia pneumoniae, Chlamydia psittaci. These are identified on the basis of growth, nucleic acid profile, the presence of plasmids, the antigens that they express and the inclusions in host cells which are morphologically different. C. Trachomatis produces a glycogen matrix which stains brown with iodine.
C.pneumoniae and C.psittaci both cause respiratory diseases: C.pneumoniae causes a mild form of pneumonia that is particularly prominent in young adults. It is transmitted from person to person through infectious aerosols. C.psittaci causes respiratory disease which is commonly found in birds and is transmitted to people in contact with an infected bird. C.trachomatis is the most common of the three species and as such this species will be discussed in some detail.
There are two main types of diseases caused by the different strains of C.trachomatis; ocular diseases trachoma and conjunctivitis and sexually transmitted diseases. C.trachomatis is expressed by 15 identified serotypes which are differentiated by the differing outer membrane proteins.
Trachoma is the world's leading cause of non traumatic blindness in humans which is particularly prevalent in developing countries where it affects tens of millions of people . It is caused by the serotypes A, B, Ba and C. The trachoma pathogen infects epithelial cells of the eye and reproduces in the conjunctiva, killing these cells and then an abundant puss filled discharge scars the conjunctiva and results in the eyelids turning inward. The eyelashes in turn irritate and scar the cornea causing an incursion of blood vessels into the normally clear area of the eye resulting in eventual blindness. Trachoma is generally found in children who have been infected during birth. It is however also found in adults where the LGV strain is transferred via fingers from infected genitalia.
Sexually transmitted diseases are caused by the servovars D to K which causes genital tract infections. It is important to note that these strains can also infect the respiratory epithelium. The serotypes L1, L2 and L3 infect the genital epithelium but disperse to the lymphatics and ultimately lead to lymphogranuloma venereum. The primary site for infection in women is the columnar epithelium of the endocervix where the bacteria will divide and infect neighbouring cells. Chlamydia can only be transmitted through infected secretions.
Signs and symptoms of sexually transmitted disease
Burning sensation when passing urine
Discharge from penis
No discharge - just pain
Lower abdominal pain or discomfort
Bleeding during sex
Change in vaginal discharges
As 90% of women are asymptomatic, in many cases, C.trachomatis will not be detected and as a result may spread to the fallopian tubes and finally lead to tubal factor infertility, ectopic pregnancy or pelvic inflammatory disease. Left undetected in men, C.trachomatis can affect sperm function and male fertility and in some cases joint inflammation, which is difficult to treat.
Testing for Chlamydiae trachomatis is done from collection of a urethral swab, cervical swab, first pass urine, anal swab and penile swab. As chlamydias are intracellular parasites, bird eggs and cultures of living cells are used to culture the organisms.
The Giemsa staining method reveals bacteria or inclusion bodies but the most definitive process involves growing the specimen in a culture of susceptible cells and then using a direct fluorescent antibody test (DFA). This test shows the major outer membrane characteristics of all 15 serotypes of C.trachomatis. Another test which is used is known as the nucleic acid amplification test (NAAT) .
Antibiotics, particularly doxycycline or azithromycin is used for treatment
In2009 there were 62,717 notification of Chlamydia in Australia.
In 2008 there were 58,510 notifications of which equates to 81% of all sexually transmitted infections (STI) in Australia.
2007 there were 52,040 notifications - 74% of total STI
2006 there were 47,472 notifications - 79.5% of total STI
2005 there were 29,493 notifications - 78% of total STI and . Sexually transmitted chlamydial infections are prevalent mostly in females between the ages of 15 and 29. In 2008 over 80% of infections were in 15-29 year olds
A Rapid urine test has been developed and currently being considered as a testing procedure for Chlamydia trachomatis. The benefit of the test is that it enables testing of the patient, providing results and treatment in the same clinical visit.
First 4-5ml of urine are collected, distilled with water and centrifuged. A fraction of the sample is mixed with lypophilised amplification and detection reagents and a test strip is added. This is then incubated at room temperature for 25 minutes. If Chlamydia is present, a line will appear on the test strip
How do the elementary bodies get released? Cell lysis
What's the best prevention for sexually transmitted chlamydial infections? Abstinence or faithful, mutual monogamy. Condoms may provide some protection, but it is believed by some researchers that condoms can cause irritation and therefore increase the risk of infection
What is the incubation period - from time infected to it showing up - 1 to 3 weeks
What are the risk factors? High frequency partner change, multiple partners, unprotected sex.