Researchers have made progress toward the first ever vaccine for chlamydia, after revealing how a novel antigen reduced symptoms triggered by the bacterium Chlamydia trachomatis - the most common cause of the disease.

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Researchers have identified an antigen that reduces symptoms caused by the chlamydia bacterium C. trachomatis.

Study co-author David Bulir, of the Michael G. DeGroote Institute for Infectious Disease Research at McMaster University in Canada, and colleagues report their findings in the journal Vaccine.

Chlamydia is one of the most common sexually transmitted infections in the United States, with around 2.86 million infections occurring every year.

Chlamydia is usually transmitted through having vaginal, anal, or oral sex with an infected person. There are four species of bacteria that can cause infection - the most common of which is C. trachomatis.

However, the infection often presents no symptoms, and many people do not seek testing. As a result, most individuals with chlamydia are unaware they have it, so the infection often goes untreated.

Untreated chlamydia can have serious health consequences, particularly for women. It may lead to pelvic inflammatory disease, and it can cause irreversible damage to the reproductive system, resulting in long-term pelvic pain, infertility, or ectopic pregnancy.

At present, the only ways to reduce the risk of chlamydia are to use a condom during sexual intercourse or to avoid sexual contact completely. Now, Bulir and colleagues believe they are well on the way to developing the world's first widely protective vaccine for the disease.

BD584 antigen reduced chlamydia symptoms by up to 95 percent

For their study, the researchers immunized female mice with a novel antigen called BD584, which is made up of three T3SS proteins from C. trachomatis: CopB, CopD, and CT584.

On infecting the mice with Chlamydia muridarum - a species of C. trachomatis - they found the antigen reduced chlamydial shedding by 95 percent. Chlamydial shedding is a symptom of C. trachomatis infection.

Another symptom of the infection - hydrosalpinx, where the fallopian tubes become filled with fluid - was reduced by 87.5 percent in immunized mice.

Based on their results, Bulir and colleagues suggest BD584 is a promising candidate for a chlamydia vaccine.

"Vaccination would be the best way to way to prevent a chlamydia infection, and this study has identified important new antigens which could be used as part of a vaccine to prevent or eliminate the damaging reproductive consequences of untreated infections."

David Bulir

What is more, they suggest BD584 has the potential to protect against all strains of C. trachomatis, including those that cause trachoma - a type of eye infection.

If the BD584 antigen proves successful as a chlamydia vaccine, the researchers say it would be administered through the nose.

"This is easy and painless and does not require highly trained health professionals to administer, and that makes it an inexpensive solution for developing nations," notes study co-author Steven Liang, also of the Michael G. DeGroote Institute for Infectious Disease Research at McMaster.

Next, the team plans to conduct further testing of different BD584 formulations to see how they fare against different strains of chlamydia.

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