How do you recognize these creatures in a swimming lake and what can you do about them?

Every year here in Ascona, a rumor circulates among mothers that "there are duck fleas again, so no more swimming in Lake Maggiore." When we moved here six years ago, I thought the people of Ticino were just exaggerating, but then I heard from several German-speaking Swiss women that they had been infected once and now never go swimming again. This year, I wanted to investigate the matter and find out what's true and what can be done about it.

First of all, spoiler warning, I'll tell you right away: the bites itch a lot, the rash can be severe, but it's harmless and the larvae can't be transmitted from person to person!

But what are these darn duck fleas?

If you swim in a shallow lake at water temperatures of around 23 degrees and are subsequently plagued by an itchy rash , you probably have duck fleas.

Duck fleas are n't actually fleas at all, but rather free-swimming larvae of duck parasites (known in technical terms as cercariae ). When water temperatures warm up, they swarm out and seek out waterfowl as their final host. While searching, they sometimes encounter bathing humans ( the intermediate host) and attempt to penetrate their skin. However, the larvae die in the skin during this process, triggering severe itching shortly after bathing .

How can I prevent it?

Well, unfortunately there is no one tip, but the following advice will help you protect yourself . It has certainly worked for us over the last 6 years:

Symptoms of bathing dermatitis - this is what it looks like

The itching caused by the cercariae is annoying but actually harmless. Depending on your skin type, the rash heals after one to two weeks. However, if you come into contact with the larvae again, the cercariae can cause severe symptoms such as itching (noticeably more severe than after mosquito bites) , red spots, hives, pustules, and even small blisters. The sensation of itching varies from person to person, is often very unpleasant at night, and can disrupt sleep.

Treatment for duck flea infestation

For itchy mosquito bites, the Stay Cool refreshing spray helps because it contains cooling aloe vera and lavender water. You know, I'm not a fan of chemically produced products, but if the itching gets too severe, definitely see a doctor and get a prescription for a gel or lotion with a local anesthetic like polidocanol or lidocaine. In an emergency, an antihistamine, antihistamine tablets , or drops can also help .

Can you spot duck fleas in the lake?

No, unfortunately not. The nasty larvae are invisible to the naked eye. Infestations in lakes only become known when the first cases of bathing dermatitis are documented. Shallow water depths ( at the edge of the lake), stagnant freshwater, the presence of water snails and birds, reed beds or other aquatic plants, prolonged heat waves, and high bathing water temperatures all favor the occurrence of these unpleasant larvae.

Should you avoid swimming if it’s too hot?

Those on vacation in Ticino can head to the valleys. When the Ascona Lido gets too touristy, we also swim only in the wonderfully cool Maggia River, because cercariae aren't found in flowing water. Here's a photo of one of our favorite spots: a beautiful waterfall in Bignasco, Valle Maggia.

Is the lake dirty then?

Cercariae have nothing to do with the microbiological quality of the water. So, if you're out on a pedal boat or a boat with older children, for example, you can still swim in the lake.

So, my dears, I wish you a wonderful summer and hope I was able to take away some of your fear of these mysterious duck fleas.

Heartfelt

Ursula