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Animal trials of chlamydia vaccine show promise

25 July 2016
Appeared in BioNews 861

A nasal spray vaccine given to mice shows effectiveness in protecting against chlamydia, a common sexually transmitted disease. 

It is estimated that chlamydia affects 113 million people; more women are affected than men, globally, every year. Dr David Bulir, co-author of the study, states: 'As most Chlamydia trachomatis [a common species affecting humans] infections are asymptomatic, chlamydia can often go untreated and lead to upper genital tract infections, pelvic inflammatory disease, and infertility. This is why the promise of a vaccine would be extremely beneficial'.

The vaccine was developed by researchers from Michael G. DeGroote Institute for Infectious Disease Research at McMaster University in Canada, and is made from a novel chlamydial antigen called BD584. The researchers immunised five mice and infected them with C. trachomatis. Compared against five controls, all immunised mice produced anti-chlamydia antibodies.

Researchers further vaccinated 10 subject and 10 control mice, and infected them with Chlamydia muridarum (a type of chlamydia that only affects mice). Vaccinated mice showed a 95 percent reduction in chlamydia shedding from the vagina on days five and seven. Moreover, 32 days post-infection, there were no signs of bacterial shedding in vaccinated mice compared with detectable levels in control mice. The immunised mice also experienced an 87.5 percent reduction in the blockage of the fallopian tubes – structures crucial for female fertility.

Co-author and McMaster PhD student, Steven Liang, further added, 'Not only is the vaccine effective, it also has the potential to be widely protective against all C. trachomatis strains, including those that cause trachoma.' Trachoma, an eye infection caused by chlamydia, is the leading cause of preventable blindness which affects millions of people in resource-poor regions of the world.

Due to the bacteria's high rate of evolution, it has been difficult to produce a vaccine for chlamydia, with efforts dating back to 1957. Although the study involved a small group of mice and has yet to be tested in humans for safety and efficacy, the researchers say the vaccine 'affords a significant degree of protection and could be an effective vaccine for human use'. As the vaccine is delivered nasally, it also does not require health professionals to administer it and so could be an inexpensive treatment for developing nations.

'Vaccine development efforts (for chlamydia) in the past three decades have been unproductive and there is no vaccine approved for use in humans,' said Dr Bulir. '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.'

The researchers intend to trial the vaccine on other animal models, before moving on to human trials.

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