Most people tend to associate Streptococcus with sore throats and tonsillitis. But one strain of the bacteria has a far darker secret: if it gets into muscles or connective tissue it can become a gruesome and deadly flesh-eating infection.
A new study has looked into how Streptococcus pyogenes manages to do this and stay undetected in the body despite being so clearly damaging, discovering that it basically commandeers the neurons in the tissue and controls what information is therefore sent to the immune system. Their results are published in the journal Cell.
The flesh-eating disease caused by the bacteria is officially known as necrotizing fasciitis, although technically the bacteria does not eat the flesh but rather releases a toxin that breaks it down. The condition is rare – infecting about 1,200 people in the US each year and 200,000 globally – but the results can be devastating.
The mortality rate for necrotizing fasciitis is high at up to 30 percent, due in part to the way in which the disease takes hold, but also the extreme amount of damage it can wreak. After infection, the area tissue develops flu-like symptoms and what is described as an intense and localized pain. This is then followed rapidly by the death of muscle and connective tissue, often occurring so quickly treatment is limited.
Because of the speed of progression from pain to tissue death, the mortality rate remains high. Those who are fortunate enough to survive frequently end up disfigured, as extensive surgery is often required to excise the infected muscle. In some cases, the only option is for limbs to be amputated. The need to diagnose infections at an early stage is therefore vital.
In an attempt to help develop this, researchers wanted to understand exactly how the bacteria invades and stays undetected for such a long period of time. It turns out that as the bacteria makes its way through the tissue, it begins to hijack the neurons running throughout it. It then intercepts and exploits the neurons blocking their communication with the immune system, allowing the bacteria to remain hidden.
“Necrotizing fasciitis is a devastating condition that remains extremely challenging to treat and has a mortality rate that's unacceptably high,” explained Isaac Chiu, who led the research. “Our findings reveal a surprising new role of neurons in the development of this disease and point to promising countermeasures that warrant further exploration.”
One way they have identified is by blocking this immune-suppressing activity. Experiments on mice showed that this did indeed prevent the spreading of the bacteria. This provides a potential treatment for the disease, and may offer some hope for those infected.