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Researchers Seek Genetic Clues to Deadly Bacterial Epidemics

An international team of researchers looking for the cause of severe bacterial epidemics has deciphered the genome of group A streptococcus, a normally harmless sore throat pathogen that occasionally turns deadly. Experts say the breakthrough could speed the development of a vaccine to prevent the leading cause of heart disease in children.

The scientists mapped the genetic material of nearly 100 samples of strep-A bacteria involved in three severe epidemics in Ontario, Canada, during the past 17 years.

The focus of their interest was strep A's ability to transform itself from a relatively benign microbe into a potent pathogen responsible for the lethal disease known as necrotizing fasciitis, which causes widespread skin destruction. It can also lead to a deadly blood infection, according to Jim Musser, co-director of the Methodist Research Institute in Houston, Texas.

Musser says patients may be extremely sick before seeking medical help because severe strep-A infections may at first mimic other milder diseases like the flu. Musser says lethal forms of strep A often go undetected by physicians, because such infections occur infrequently and many doctors fail to recognize them.

"Many of these patients show up at their doctor or the hospital too late in the course of their disease to be adequately treated," he explained. "There is too much tissue destruction; the disease has progressed too far to be able to really save the patient."

Musser led the team of researchers that deciphered the genetic make-up of bacteria responsible three successive epidemics in Canada, hoping to learn the molecular underpinnings of the bacteria.

"This has permitted us for the first time to have a precise molecular portrait of how the organisms change over this time, which organisms have the propensity to cause a more severe type of illness and the exact molecular changes in the pathogen that are responsible," he added.

Musser says having the bacterial genome helps researchers understand how the flesh-eating pathogen takes advantage of people who become infected with it so better diagnostics and treatments can be developed.

Musser is hopeful the work also leads to the development of a vaccine against group-A streptococcus to prevent rheumatic fever, the leading cause of childhood heart disease in developing countries, where poverty is widespread. Strep A causes inflammation of the heart muscle and damages the internal valves.

According to the World Health Organization, the infection is responsible for more than three million cardiovascular deaths each year.

"Rheumatic fever, followed by rheumatic heart disease remains the most common cause of preventable childhood heart disease globally," he added. "So we really need to develop vaccines not against for rheumatic fever and rheumatic heart disease caused by streptococcus but also sore throat and the invasive disease."

An article on the genetics of aggressive streptococcus, by Methodist University's Jim Musser and colleagues, is published this week in Proceedings of the National Academy of Sciences.