There are several different species of parasitic worms that become a problem when ingested, but worms that burrow into your skin are a rarer breed. These include a few types of the tiny, thread-like filarial worm, which can infect the body cavities, lymph system, eyes, or the fat layer just under your skin's surface. The latter two types cause an infectious disease called subcutaneous filariasis [source: DPDx]. These worms include the Loa loa (African eye worm), Onchocera volvulus and the guinea worm. They are found mostly along bodies of water in tropical areas of Africa, South America and Southeast Asia.
You can catch subcutaneous filariasis if you are bitten by a mosquito or fly infected with larvae. The filarial worm completes its entire life cycle in its human host. Once the larvae are injected by an infected bug, they grow into adult worms and reproduce, creating microfilariae. These juvenile worms' location just under the skin makes them ripe for being ingested by feeding mosquitoes and the cycle begins anew. People infected with filarial worms may have them for years, and adult worms can live for more than a decade. If the infection is to the eye, it is called onchocerciasis, or river blindness [source: DPDx]. This is the second-leading infectious cause of blindness in the world.
A diagnosis is difficult because the symptoms look like those associated with many other types of infections, and sometimes symptoms don't appear for years. Victims have an itchy rash and open sores, along with inflammation and pain. These symptoms can progress to a fever, body aches and headaches. Dying worms and bacteria can also cause secondary skin infections. There may be changes in skin color, or the worms can be seen crawling under the skin or the eye. The only way to diagnose for certain is to look for the microfilariae in the blood, which has to be drawn at night when the worms are most active.
According to the World Health Organization, filariasis is a potentially eradicable disease. To treat it, patients must take a drug called ivermectin to kill the microfilaria. However, as with other mosquito-borne skin parasites, avoiding getting bitten is the best way to keep from being infected. Use mosquito nets, avoid being in jungle areas at night, wear long sleeves and pants, and use insect repellent.
In the next section, we'll look at a worm that isn't a worm at all as well as a potentially new skin parasite.