Waterborne parasite latches onto Lake Mead swimmers

Anyone up for a nice, refreshing, early-autumn swim on the Nevada side of Lake Mead? Well, steer clear of Boulder Beach, which has been infected with – ick – swimmer’s itch.

Rangers say that an above-normal waterfowl population may be to blame for the poison ivy-like rash that was reported by at least a dozen swimmers over the weekend.

Also known as schistosome cercarial dermatitis, swimmer’s itch is caused when flatworm parasites that are found in some birds burrow into human skin and cause an allergic reaction. In some areas of the country, it’s also known as lake itch or duck itch.

“The symptoms include tingling, burning, itching, small reddish pimples and small blisters that can appear within 12 hours,” a park official told the Los Angeles Times.

The Centers for Disease Control and Prevention say most cases of the rash don’t require medical attention and can be relieved with anti-itch cream. Officials say they are monitoring the shoreline along Boulder Beach just outside Las Vegas and warn anyone to stay away from areas with a large amount of waterfowl droppings.

The park official gave a brief tutorial about how the parasites have come to be in the water: “It’s kind of a funny little thing,” she said.

Parasites in infected birds produce eggs that are carried in bird droppings and are then released in the water and onshore. These eggs produce “free-swimming aquatic larvea” that fan out in search of snails as hosts.

Once a snail is found, the new host releases a different kind of larvea into the water that goes in search of birds. (Call it nature’s payback.)

But the snail larvae often attach to humans in the water, burrowing into their skin. Since swimmers are not a natural host, the larvea die after a few days — but not without causing those itchy-scratchy symptoms.

Jeepers, just when you thought it was safe to go back into the water.

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john.glionna@latimes.com