A reader wrote to us on behalf of a friend who is believed to have a “worm in his foot.” The foot worm, to give the creature a concise and descriptive name, is only visible some of the time, and by “visible” we mean that a bulge can be seen on the reader’s friend’s foot, not that the worm itself can be seen. The victim of the foot worm went to a doctor, but the worm “disappeared” during the visit, which left the doctor unable to extract the worm from the foot of our reader’s friend. What exactly is this foot worm, and what kind of damage can it do?

Whenever we are confronted with any sort of medical question, we proceed with extreme caution. We are not medical doctors, and thus cannot provide any sort of medical advice or guidance. If our reader’s friend is suffering any sort of ailment, he must seek medical help, even if he has already done this. In the best case scenario, we correctly identify the foot worm (which we can’t guarantee given the limited information we are working with), and this still doesn’t solve the problem. Our answer is no replacement for medical care.

In general, the worms that afflict humans affect our digestive systems. This is the case with hookworms, and it is also the case with the most common worms found in humans, pinworms. Although hookworm and pinworm infections are common, we are confident our reader’s friend is not contending with either type of worm – his symptoms, centering as they do on his foot, are totally different.

We can only think of two responses to our reader’s identification question: screwworms, white worms that can be found in wounds, cuts, and sores, and guinea worms, an African worm found in humans. While Guinea worms are nematodes and hence fit our definition of the word “worm,” the same cannot be said of screwworms, which are fly larvae.

Screwworm infections are rare in humans because we tend to dress our wounds. The adult flies must lay their eggs inside an open wound, and generally it is only animals that “allow” this to happen. Furthermore, screwworm infections have been eradicated from lots of countries, so it might not even be possible for our reader’s friend to be suffering from this type of ailment. Still, we suppose it is a possibility to consider, especially if our reader’s friend had or has an open wound on his foot.

Like screwworm infection, the infections that are caused by guinea worms (called guinea worm disease) have been eradicated from much of the globe. Indeed, the disease is only endemic in a few countries in Africa (at least among humans). So, again, this suggestion may be a non-starter depending on where our reader lives. However, guinea worm disease generally does involve an infected person’s feet. In particular, once guinea worms are ingested, generally by drinking water contaminated by guinea worm larvae, they can work their way out of a host’s stomach and eventually into the lowermost level of human skin, the subcutaneous tissue. After about a year of infection, the guinea worm will start to cause a blister on the host’s skin, and this blister is generally found on one’s foot. This isn’t exactly the ailment our reader describes, but it shares some similarities. However, we must stress that guinea worm disease, in contrast to 20 years ago, is rare these days.

As we conclude, though, we must reemphasize that we are not at all diagnosing the ailment of our reader’s friend. It is for this reason we also won’t speculate on the damage that any of the aforementioned creatures might do to the reader’s friend (although we will say that screwworm infections and guinea worm disease need to be treated). We have used our knowledge of worms to list some types of worms that afflict humans, not to supply medical advice. All we can say is that our reader’s friend should seek medical attention if he is experiencing any pain or discomfort, or if he is experiencing any other concerning symptoms. We wish him the best of the luck.