Chlamydia is a 'cunning' STI that easily evolves into new strains, discover scientists
More than 150,000 people aged under 25 in England tested positive for chlamydia in 2010
Study provides insight into how chlamydia avoids the human immune system



10:12 GMT, 12 March 2012

Warning: More than 150,000 adults aged under 25 were diagnosed with chlamydia in 2010 alone

Warning: More than 150,000 adults aged under 25 were diagnosed with chlamydia in 2010 alone

Chlamydia – the world's most common sexual infection – is a more cunning and highly evolved bacterium than thought, scientists say.

Researchers analysed the entire genome of Chlamydia trachomatis and discovered that exchanges of DNA between different strains of the disease to form new versions are more common than believed.

But current screening methods do not differentiate between the different strains, reports Nature Genetics, meaning the bacteria have the potential to become anti-biotic resistant without anyone realising.

Across the world there are around 100 million new cases of chlamydia each year, making it the most commons STI in both the UK and globally.

Researchers from the Wellcome Trust Sanger Institute found that if two strains of the disease infect the same host they are able to exchange DNA and create an entirely new strain.

This can happen even when the strains are in different parts of the body, they say.

Dr Simon Harris explained: 'Scientists recently discovered that if two Chlamydia strains co-infect the same person at the same time, they can swap DNA by a process called recombination.

'This was originally thought only to affect a few 'hotspots' within the genome. We were very surprised to find recombination is far more widespread than previously thought.'

Prof Ian Clarke of the University of Southampton added: 'Despite this being the most important sexually transmitted infection in the world, until now it's clear that there are major gaps in our knowledge of the strains that are currently circulating, their evolution and natural history.'

Because current tests do not distinguish different strains, if a patient tests positive again after anti-biotic treatment it is not known whether the drugs have failed or they have picked up a second infection.

This photo micrograph reveals what chlamydia looks like up close

This photo micrograph reveals what chlamydia looks like up close

This means that if anti-biotic resistance did occur in the general population, it would not be detected by current diagnostic procedures.
No strains of resistant bacteria have been seen in patients, although they have been created in the laboratory, said Dr Nicholas Thomson, of Wellcome.

He said: 'Until now a person treated with antibiotics with a reoccurring infection of C. trachomatis was assumed to have been re-infected.

'The current gaps in our understanding of the population makeup of Chlamydia limit our ability to implement health policies, because we do not fully understand how Chlamydia spreads within our population.'

The findings are also important for the treatment of African Chlamydia, a form of the bacteria that can cause eye infection trachoma or blindness.

These strains also use recombination to avoid the immune system, said Dr Martin Holland, from the London School of Hygiene and Tropical Medicine.

He said: 'For many years various groups have observed co-circulating strains of Chlamydia causing trachoma. In our study we have shown that some strains appear to have swapped only their surface coat.

'This provides real clues as to how this bacterium is able to avoid the human immune system and cause disease.'

More than 150,000 adults aged under 25 tested positive for chlamydia in England in 2010. However, most people don't noticed any symptoms and so don't know they have it.

The STD is treated with anti-biotics. However, the NHS warns it can cause problems such as pelvic inflammatory disease and infertility if left untreated.

Anyone under 25 in the UK can get a free and confidential chlamydia test. Visit for more information.