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Debunking the Sea Lice Myth

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The latest information on sea bather's eruption

By G. Yancey Mebane, M.D.

Have you ever emerged from the salt waters of the southern regions with more than the itch to dive again? You know, the burning itch that threatens to spoil your mood, your day, even the remainder of your dive trip?

It happens from time to time, and, if medical reports are an indication, it's increased a great deal over the last few years in the popular waters off Florida and in the Caribbean.

The common symptoms include intensely itchy skin eruptions with small blisters and elevated areas of skin. Found primarily on parts of the body covered by swim wear, these lesions may also appear on the armpits and neck and occasionally on the arms and legs. Most divers and swimmers call it "sea lice." The term is a misnomer, however. Sea lice are actually fish parasites, do not affect humans, and have nothing to do with sea bather's eruption, which is caused by the larvae of jellyfish.

The primary offenders in Florida and Caribbean waters are the larvae of the thimble jellyfish, Linuche unguiculata. These larvae, generally half a millimeter in length, can find their way into bathing suits - even passing through the mesh of some suits - and become trapped against the skin and sting. The larvae are visible to the naked eye, but they become nearly invisible in the water. And just because there are no adult thimble jellies in the area is no guarantee that the youngsters aren't around. The best method of identifying when the larvae are about is simply by the appearance of the rash on swimmers or divers.

April through July are the months when the larvae are most prevalent, although they may appear at any time. The symptoms will appear very soon (24 hours or less) after exposure to the organism and will persist for several days. Some cases have been reported which have a three- or four-day delay in onset and a prolonged course lasting several weeks.

Symptoms may include fever, chills, headaches, nausea and vomiting. Severe symptoms occur in children particularly, although adults have also shown similar reactions.

Since many of these symptoms are consistent with many other illnesses, diagnosis is sometimes difficult unless the attending physician knows of the diver's exposure to contaminated water. Often the symptoms are very mild, and other causes may be considered or diagnosed incorrectly at first.

Many of these cases of sea bather's eruption will clear spontaneously, but others may require treatment. Antihistamines and antipruritic (anti-itching) agents may be used, but the results are not good in many cases.

Children and individuals with allergies or diseases affecting the immune system may be at risk for severe reactions. Fortunately, the severe reaction is rare, but it can be a danger for some individuals. In the severe case, some doctors prefer to use cortisone by tablet or injection.

Prevention for the diver means adequate protection by wetsuit or impermeable dive skin. Snorkelers wearing T-shirts, and women wearing one-piece bathing suits are vulnerable because of the trapping action of the fabric.

After diving or swimming in an area where the jellyfish larvae are present, remove your wetsuit, dive skin or bathing suit before showering since the fresh water may discharge the nematocysts trapped in the fabric. There have been reports of the condition recurring when the same bathing suit is worn again, suggesting that the larvae may remain in clothing.

If you want more information on sea bather's eruption, a more detailed reference is a paper by R.S. Tomchik, M.T. Russell, A.M. Szmant, and N.A. Black, which appeared in the Journal of the American Medical Association, 1993; 269: pages 1669-72.

(c) January/February 1994. Written by G. Yancey Mebane, M.D., associate medical director of Divers Alert Network at the time.