Monday, October 22, 2007

Flesh Eating Bacteria

Growing up in Shawnigan Lake, just north of Victoria, I lived down the street from an elementary school called Elsie Miles. When I was about six, a little boy who attended Elsie Miles contracted the flesh eating disease Necrotizing Fasciitis and had to have his leg amputated to stop it from spreading to other parts of his body. I was horrified that bacteria could spread so quickly and efficiently that amputation was the only option to save the boy.

According to the BC Health Files, Necrotizing Fasciitis is a rare and serious disease that can destroy skin and underlying tissues. This disease is able to spread through human tissue at a rate of 3 centimetres per hour, and can cause death within 18 hours. Necrotizing Fasciitis is caused by several kinds of bacteria, but most notably Streptococcus pyogenes. 5-15% of normal healthy people harbour S. pyogenes in their respiratory system. S. pyogenes is responsible for strep throat, scarlet fever, skin infections, and rheumatic fever, but causes Necrotizing Fasciitis when it is able to enter the layers of tissue that surround muscle (Fascia).

Streptococcus pyogenes possesses several virulence factors that make it very successful as a pathogen. S. pyogenes is able to colonize and rapidly multiply by using lipoteichoic acids and fibronectin-binding proteins to adhere to host cells. Its lipid membrane and capsule help it to go undetected by host immune systems and avoid macrophages and neutrophils. The lipid membrane contains antigens similar to those found in cardiac, skeletal, smooth muscle, heart valve, and neuronal tissues. This allows the bacteria to blend in and mimic the host cells. The capsule is composed of hyaluronic acid, which is found in human connective tissue. This also helps camouflage the bacteria from the host immune system.

Because of the evasive tactics employed by S. Pyogenes, as well as the rapid colonization and replication, people who have contracted Necrotizing Fasciitis often see a doctor when the disease is already in an advanced state. Antibiotics (penicillin) are effective against S. pyogenes, however if the patient has Necrotizing Fasciitis, blood supply to the infected tissue is cut off and antibiotics are not able to reach the site of infection. Surgery is almost always a necessity and amputation may be necessary in serious cases.

In the case of the little boy, it was lucky that the infection was able to be halted through amputation of the leg. It scares me to think what would have happened had the infection occurred in an area that was not able to be removed.


Image is courtesy of the Centers for Disease Control and Prevention image library.

1 comment:

Dominic B. said...

Bacteria have this amazing way with our immune system. They can hide from anything. The real amazing thing is that our immune system is very effective and can detect virtually anything...the only problem is that it takes time! Bacteria can grow many generation in a few hours. Eventually they try every single possibility and adapt. When these bacteria adapt new ways to elude our own defenses...that's scary! Thanks for this blog!