Sunday, August 5, 2007

Campylobacter Jejuni, Guillain-Barré, and Cooking Chicken

Although I am a second year medical student, that is not the only position I currently hold. I also happen to be a second year chef. Yes, as a newcomer to the world of preparing my own meals thrice a day, I have been experiencing all of the thrills, and potential hazards, of cooking on my own. Perhaps more than most, I have also been acutely aware of the dangers of amateur cooking and my health.

Of these dangers, one that is rather unique to my station in life is a particular bacteria, Campylobacter jejuni. This is a seagull shaped gram negative bacteria with a flagella, or tail, that is one of the leading causes of diarrhea in the world, with 2 million cases a year in the United States. It is not spread person-to-person, but instead is carried in wild and domestic animals, especially birds. While most bacteria that infect the GI tract are only common to the very young and very old, C. jejuni has a large spike among people in their twenties, who you would think have excellent health; this might be because it is very common in undercooked chicken. My naive cooking skills, and the cleanliness of my prep area, are therefore constantly tested by this slender "S"-shaped bacteria.

C. jejuni is microaerophilic, which means that it likes a low oxygen environment, around 5-10%, such as that of your gut. It requires as few as 100 bacteria to be infectious, and the result is a watery or bloody diarrhea that is self-limited, ending in 4-5 days. While unpleasant, and unappetizing, this is nothing remarkable aside from its somewhat unusual target population. More unusual is that roughly 1 in every 1000 infected individuals go on to develop Guillain-Barré Syndrome, an autoimmune disease that affects the myelin coating of your peripheral, motor, and cranial nerves.

Many nerves are wrapped in a fatty cellular coating called myelin. In the periphery, this is composed of specialized cells called Schwann cells, which wrap around the nerve axon as it heads to or from its target tissue. This insulating layer helps the nerve transmission move more quickly, and also keeps it contained to that single axon. If you lose this layer, you can have slowed, abnormal, or even absent nerve signal conduction. Essentially, you may experience symptoms such as fatigue, loss of sensation or strange sensation, and possibly even paralysis, which can be dangerous if it affects your breathing.

In Guillain-Barré Syndrome, it is thought that following an infection, such as C. jejuni, you form an autoimmune response against the myelin coating your nerves. It may also occur after a viral infection, vaccination, or even medication. Any of these may cause your T cells to attack your myelin through molecular mimickry, where the myelin "looks like" the bodily insult. Recovery can take as long as 200 days, and while most people recover from even the most severe cases, there are often lingering effects, such as a degree of weakness. There is no current cure; replacing the serum of your blood or giving intravenous immune globulin (giving an outside antibody will decrease your own antibody production) have been shown to shorten recovery by up to 50%. Interestingly, steroids, which are known to lower your immune response, do not seem to be effective on their own in treating GBS.

What exactly induces Guillain-Barré Syndrome remains a mystery, confounded by the large number of suspected causes. If I were to avoid just one infectious cause, however, my money's on C. jejuni; it is found in the serology of up to 40% of people who present with GBS. Future research may help us solve this puzzle, but for now I might just stick to salad. Bon Appétit!

Thursday, August 2, 2007