Enjoyed a swim in Lac Léman only to discover an intensely itchy rash a few hours later? You may have encountered what locals call ‘duck fleas’ (puces de canard). Despite the name, they’re not fleas at all but they can turn a perfect summer day at the lake into several days of discomfort.
What are ‘duck fleas’?
‘Duck fleas’ (or ‘les puces de canard’ in French) are a relatively common problem that can result from swimming in Lac Léman. They can lead to an itchy skin rash known as ‘swimmer’s itch’ or ‘swimmer’s dermatitis’. Swimmer’s itch is not caused by fleas exactly but by a worm-like parasite whose usual host is the ducks that live in the lake. Whilst you are swimming in the lake, immature forms of the parasite larvae can penetrate ‘mistakenly’ through your skin rather than finding their usual host, a duck. So, humans are infected ‘accidentally’. The parasite dies when it enters your skin. However, your body can develop an allergic reaction to the parasite, and it is this that causes the rash.
What are the symptoms?
On your first exposure, you may not have any reaction or develop any symptoms. However, you can still become ‘sensitized’ to the parasite and the next time you are exposed to it, symptoms can develop.
If symptoms do develop, you may notice tiny red spots at the points at which the larvae have penetrated your skin. The spots can be tingly or itchy. After a few hours, the spots tend to become bigger and more ‘pimple-like’ or bumpy. Intense itching is usual at this stage. Occasionally, blistering can occur over the next few days. The rash will develop on areas of the skin exposed to the water. So, skin under a swimsuit can therefore be spared from the rash.
If you’ve developed swimmer’s itch before, you may develop a more severe rash the next time you are exposed to the parasite.
What treatment do I need if I get ‘duck fleas’?
The rash will eventually go away of its own accord, but it may take between 10-20 days to disappear completely.
If you have just a few itchy patches, you may not need any treatment. However, most of the time, itching is quite intense. It’s important to control itching because scratching can damage your skin further and sometimes lead to a secondary bacterial infection which may need treatment with antibiotics.
Calamine lotion or an antihistamine may help to treat itching. Antihistamine liquid is available for children. However, do take care when using antihistamines as some can make you drowsy, so you should not drive or operate machinery whilst taking them. Always read the packet leaflet carefully and get advice from your local pharmacist to make sure they are safe for you. For example, antihistamines may not be safe in certain medical conditions, or if you are pregnant or breastfeeding.
A mild corticosteroid cream may also be helpful. Again, get advice from a pharmacist before using this. Rarely, in very severe cases, steroids taken by mouth may be needed.
How can I avoid ‘duck fleas’?
Some useful advice as suggested by CIPEL (International Commission for the protection of Leman Waters):
- Avoid swimming close to the plants and vegetation at the water’s edge as these can be a particular habitat for the parasite.
- Take a shower as soon as you get out of the water. Most of the beaches around the lake have showers available on the lakeside.
- Dry yourself off with a towel after your shower. The brisk rubbing motion with a towel can help to stop the larvae from penetrating your skin.
The good news is that swimmer’s itch is usually harmless and will settle on its own. Knowing how to recognise the symptoms, manage the itching and reduce your risk of exposure can help you continue to enjoy everything Lac Léman has to offer during the summer months.
Whether you’re swimming, hiking, cycling or spending time outdoors with your family, being prepared for minor medical problems and emergencies can make all the difference. To learn practical first aid skills for life around the lake and in the mountains, explore HealthFirst’s range of first aid courses.
