A 6-year-old boy comes to the clinic for evaluation of a rash. It began about three days earlier. The main complaint is itching. He is otherwise healthy with no other complaints. The family history is positive; his sister has a similar rash, only not as bad. The family had been on their annual vacation to a south Texas Gulf Coast beach area, returning on the day this rash began. There was initially a prickly, stinging sensation with what appeared to be hives after swimming on the last day, followed by the development of the current rash. They did report seeing numerous large jellyfish in the water the last day of their vacation.
Examination was positive only for the rash, which was an erythematous, macular, patchy rash with some papular and urticarial components in places (figure 1). There was an area of excoriation from the intense itching (figure 2).
1. Swimmer's itch
2. Jellyfish rash
This is a case of swimmer's itch, which in this example is also known as schistosome cercarial dermatitis due to one of numerous nonhuman schistosomes, usually avian. The miracidium, which finds its way to the water by bird droppings, is taken up by snails. After maturing into the larval stage in the proper snail, the larvae or cercariae emerge and inappropriately penetrate the skin of the human swimmer, producing the rash described. The cercariae are unable to penetrate through the dermis, and are destroyed by the normal immune response, which provokes an inflammatory response.
Typically, the first exposure results in an insignificant rash. On re-exposure, the sensitized individual may have a much more intense, symptomatic rash. A history of exposure by swimming in natural bodies of water is very important to obtain, as well as the progression of the rash described above, as there is nothing specific about the appearance of this rash that will differentiate it from a wide variety of other causes of aquatic dermatoses. In fact, the term "swimmer's itch," and other colloquial terms for these marine-associated rashes, should probably be abandoned in favor of more specific, etiology-related diagnoses. The treatment is with antihistamines and/or steroids. However, vigorous towel drying immediately after swimming is thought to be preventive by physically removing the larvae from the skin before they penetrate. This condition can be seen in North and South America, Europe, Asia and Africa.
One can certainly get stung by jellyfish, which produces immediate pain and can leave linear marks where their tentacles touch the skin. However, this resolves fairly rapidly, usually within hours. Certainly, within a few days there would be no residual, pruritic marks on the skin. Contact with the larvae of certain small or "thimble" jellyfish can produce an allergic reaction if swimming nearby. This jellyfish dermatitis usually begins within about 12 hours of contact, and can look the same as this case.
To read more about these marine rashes, and take some of the confusion out of the terminology, I recommend reading chapter 37, "Aquatic Dermatoses," in Fisher's Contact Dermatitistextbook, edited by Robert L. Rietschel and Joseph F. Fowler Jr. Read it AFTER your trip to the beach because it's enough to make you not ever want to go swimming in natural water again.
Scabies can certainly result in a pruritic rash that may look similar to this. The location of the rash is typically about the hands and wrists (figure 3), but they can appear anywhere, especially in young children and infants. In these young patients, scabies will appear as papulovesicular lesions (figures 4 and 5). In infants, the face and scalp is frequently involved (figure 6), and should be treated as well as the rest of the skin (figure 7), but avoiding the eyes. Also, the palms and soles are frequently involved in infants (8 and 9). In fact, when the palms and/or the soles of a young child or infant has papulovesicular lesions, scabies is by far the most likely diagnosis.
Additionally, I have found that the primary caregiver, usually the mother, will also have pruritic lesions consistent with scabies when asked. Figures 10 and 11 are the hands of the mother of the baby in figures 6-9, showing typical lesions between her fingers. Figure 12 is another baby whose mother is shown in figures 13-15. Classically, one may see burrowing tracts, but these are frequently absent. To prove the diagnosis, you can scrape a lesion, preferably at the end of one of the burrows, with the edge of a blade and place the material on a slide with oil under a cover slip. If you're lucky, you may see recognizable mite parts and/or feces. However, as shown in the figures above, a little family history is often all that is needed. Also, don't forget to treat the other infested family members as well as the usual laundering of bedding and clothing.
The recommended treatment for infants and children is 5% permethrin cream, applied to the entire body from scalp to feet, then washed off after about 10 to 12 hours. For severe cases, such as Norwegian scabies, one may consider using ivermectin (Stromectol, Merck) at 200 mg/kg in a single oral dose.
There may be an urticarial component to the rash of swimmer's itch, but it is mostly maculopapular in nature, not like what one thinks of with hives as shown in figure 16.
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For more information:
- James H. Brien, DO, Pediatric Infectious Disease, Scott and White's Children's Health Center and Texas A&M University, College of Medicine, Temple, Texas
- Rietschel RL, Fowler JF, eds. Fisher's Contact Dermatitis. 4th ed. Philadelphia, Pa: Lippincott, Williams & Wilkins;1995.
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