3 October 2019

Hot Summer Caused Parasite Infections at Lakes


If you swim in fresh water lakes in Denmark, when it is hot, there is a risk of contracting the harmless, but unpleasant parasitic infection ‘swimmer's itch’ in the skin. Researchers from the University of Copenhagen, amongst others, have examined several cases from the hot summer of 2018 and have confirmed the risk of swimming in several Danish lakes.

A small parasitic flatworm that drills its way into the skin is probably something most people would like to be without. Nevertheless, if they choose to take a swim in a freshwater lake, that seems to be a risk that Danes must learn to live with during hot summers.

There is a risk of contracting the skin condition ‘swimmer's itch’ when swimming in Danish lakes while it is hot. Researchers from the University of Copenhagen, Aarhus University Hospital and Odense University Hospital have investigated several reported cases from the hot summer of 2018 and confirmed the risk of contracting this skin condition in a new study in the scientific journal Acta Dermato-Venereologica.

‘We have previously seen individual cases of “swimmer's itch” here and there, but in 2018 we saw it on a whole new scale with several cases being reported to the Danish Nature Agency and stories in the media. Because of all the attention, we examined people with symptoms, and they did indeed display the clinical signs of “swimmer’s itch”. Subsequently, we took samples from the lakes in which they had been swimming and found that the parasite was present in five Danish lakes. Thus, we were able to confirm the risk of contracting the skin condition when it is hot in Denmark, and we could do it based on a much larger data base than before’, says Kurt Buchmann, Professor at the Department of Veterinary and Animal Sciences.

Five Lakes Tested Positive

The project was a collaboration between veterinarians at the University of Copenhagen, who have extensive knowledge about the parasites, and dermatologists from hospitals in Aarhus and Odense, who are specialists in skin conditions. While it was still summer, the researchers were publicly on the lookout for people who experienced the symptoms, such as itching, bumps and rashes.

In doing so, they were able to follow up and inquire about the persons’ symptoms of the condition and at the same time examine the lakes people had been swimming in and other lakes in geographical proximity. PhD Student and Veterinarian Azmi Al-Jubury was the one who collected samples in the Danish lakes.

In this way, the researchers confirmed that the parasites leading to the skin condition as a minimum were present in: Arresø, Darup lake, Farum lake, Furesø and Ringen lake. Most people who had volunteered and reported the symptoms had been swimming in Esrum lake, but here the researchers did not find the parasites behind the condition.

From Snails to Birds
The parasites have the Latin name ’Trichobilharzia, belong to the flatworms species and usually live in birds and snails. They are excreted in the lake water by snails that serve as an ‘intermediate host’ to them while they are larvae. From there, they swim on in order to drill into the skin of birds.

’Unfortunately for us, the parasites can go wrong because they are attracted to fatty acids that occur in the skin of both birds and humans. Therefore, they try to drill into the skin of humans, even though it is not possible for them. Instead, they die in the skin, leaving itching, bumps and rashes for 1-3 weeks afterwards’, says Kurt Buchmann.

The condition is harmless, but can be very unpleasant. That is why scientists are urging us to think before jumping into lakes on a hot summer day. You can also prevent the condition by taking a shower right after you have been in the lake, or by drying yourself off with a towel immediately after the swim.

Read the scientific article: ’Outbreak of Swimmer’s Itch in Denmark’ 

Professor Kurt Buchmann
+45 30 52 15 88

Press Officer Mathias Traczyk
93 56 58 35