I reposted Mark Frauenfelder's query to my own weblog. These are the comments thus far:

From: James D. Macdonald,
August 20, 2003 05:08 PM:

He should see a health-care professional, sooner rather than later.

Consider he has cellulitis secondary to an insect or spider bite. He needs broad-spectrum IV antibiotics.

Meanwhile, if he has oral antibiotics, take them. Elevate it (higher than his heart) to minimize swelling, and apply warm, moist compresses.

Watch for swollen lymph nodes, fever, chills, sweats, drowsiness, lethargy, blistering at the site, or red streaks extending from it. Keep track of the size of the lesion. If it isn't getting smaller, he's getting in deeper and deeper trouble.

The entire episode will probably be over in seven to ten days, one way or the other.

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From: David Bilek,
August 20, 2003 05:26 PM:
 
If he were in a temperate zone rather than tropical, I'd say he better get on anti-Lyme antibiotics RIGHT NOW. You Do Not Want to develop late-stage Lyme disease. Trust me.

Exactly what "tropical location" is he at? Without that information it's impossible to even guess what that bite could be. Depending on where he is, it could be a Brown Recluse bite. If so, he'll know soon enough when the entire area goes black and necrotic.

Hell, it could be topical anthrax for all we know.

If he hasn't yet seen a doctor, what is he waiting for? The leg to fall off?

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From: James D. Macdonald,
August 20, 2003 05:56 PM:

David is right. It's been fifteen years since I lived in the tropics, and that was the Latin American sector. There's all kinds of great stuff in Africa, Asia, wherever it's too darn hot and humid. There's no way to diagnose this over the Internet. You can't rule out spider bites, fungi, viral or bacterial infections, or parasites.

Still, elevation and warm moist heat is the general solution while going to a medic.

Any open wound in the tropics is going to get a bacterial infection sooner or later.

If I had this, I would worry.

And here's a Just For Fun: http://rob.skelly.com/index.htm