March 13, 2012

STD Tracing Shows Chlamydia Evolved More Actively Than Thought

A recent study posted in Nature Genetics explains that researchers have found that Chlamydia has been evolving differently than previously thought. The researchers used whole genome sequencing to find these results. Their findings show the exchange of DNA between different strains of the STD to form new strains is more common than expected.

The researchers came about their findings while working with hospitals to improve their testing and detection of Chlamydia, particularly different strains of the STD. In their study, the team points out that current clinical testing does not detect the variation between Chlamydia strains.

While little is currently known about the different strains of Chlamydia trachomatis, it remains the most common STD in the United States and all over the world. Around 100 million cases of Chlamydia are diagnosed every year. In the developing world, Chlamydia is also the most common cause of trachoma, or infectious blindness.

Lead author Dr. Simon Harris from the Wellcome Trust Sanger Institute explains to Nature Genetics “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.”

The research team found that, when the circumstances allowed, there was no barrier to swapping the DNA. They were even able to swap the DNA between bacterial strains that affected different parts of the body. This means not only that the disease is able to evolve and change, but furthermore that scientists understand less about this global disease than previously thought.

In a press release about these findings, a senior author from the University of Southampton, Faculty of Medicine commented “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.”

This type of study is not only important in learning how Chlamydia evolves and grows, but also helps to advance the methods used to test for the disease. As it stands, clinical diagnoses of Chlamydia only return a positive or negative result, with no information as to the type or strand of Chlamydia contracted. Therefore, it is impossible to determine if a person who has tested positive and received treatment picked up a second strain or if the initial treatment was ineffective.

This study will also help scientists and doctors learn more about the non-sexually transmitted strains of Chlamydia, such as the strains found in Africa responsible for trachoma, or infectious blindness. Just like the sexually-transmitted strains studied in the UK, the African strains of Chlamydia also uses recombination to trick the human immune system.

“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” says Dr. Martin Holland from the London School of Hygiene & Tropical Medicine. “This provides real clues as to how this bacterium is able to avoid the human immune system and cause disease.”

Scientists from the Sanger institute are working to bring the technology used in these studies to hospitals in order to improve the quality of STD testing.


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