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Water itch

Water Itch- annoying, but harmless

Teija Kirkkala

What is it?

Water Itch or Swimmer’s Itch is due to trematode parasites from aquatic and migrating birds. The life cycle of such parasites use aquatic snails as the initial host and acquatic birds or some other type of mammal as the final host. The adult trematode worm lives in the blood veins of birds. Eggs of the parasite exit the bird via faeces. The eggs hatch into free-swimming larval parasites known as “ cercaria”, which then find a suitable gastropod aquatic snail for their intermediate host. The cercaria larva penetrates the snail, grows and reproduces rapidly. Half a millimeter long cercaria larvae then exit the snail and enter the water again. Particularly on a warm summer’s day thousands of larvae exit their intermediate hosts and appear in dense shoals. As the larvae swim in the water and search for a new host they might penetrate a human or dog that is wading or swimming in the water. Humans and dogs are not natural hosts of the larvae. If the larvae penetrate human skin they will die in a few days and be removed by natural secretions.

Why does water itch exist in Lake Pyhäjärvi?

Lake Pyhäjärvi offers favourable living conditions for development and spreading of the parasite. Shallow shores and vegetation zones offer good habitats for the aquatic snails. Cercaria-infested gastropod populations are mainly located in the shallow vegetation zones of the water bodies. Aquatic birds also seek shelter and feeding areas amongst vegetation. Aquatic snails are particularly abundant in Lake Pyhäjärvi, but as the area of the shallow vegetation zone is extensive, so the total number of gastropods becomes relatively high. It still remains unknown why water itch does not appear in other lakes in the area. Apart from Lake Pyhäjärvi, water itch has been found only in two other lakes in the whole of Southwestern Finland.  

What are the symptoms of Water Itch?

The symptoms of water itch include itching or stinging sensations of the skin. Red spots appear a few hours after being in contact with the infected water. Some people might have no other symptoms or there are no symptoms at all. People with sensitive skin are those that suffer from the actual water itch. The itch will disappear only after the spots disappear in a couple of days. In more severe cases, fever, headache or other symptoms might appear. Although the symptoms are annoying, water itch is luckily harmless and usually goes without any treatment.
Can water itch be prevented or avoided?

Globally, water itch is a common problem. It is known in many European countries and USA and Canada in particular. There are at least 20 parasite species that cause water itch. Despite this, there is no commonly accepted prevention method. Water itch can be removed from some areas mainly by controlling the amount of gastropod snails or by preventing birds from thriving by making their habitat less appealing. Removal of shore vegetation has been proven a good method in some places. However, cutting vegetation does not always help because cercaria might be transported from another area by water currents. On the other hand, gastropod snails can hardly be totally eradicated from even a small area and as one single gastropod may produce over 20000 cercaria larvae, the existence of even a few gastropods is enough to spread water itch. Water itch can be avoided, for example, by staying out of shallow vegetated waterfronts with an abundance of gastropod snails where cercaria larvae usually swarm. It is advisable to start swimming only in deeper water from the end of a jetty. Feeding ducks near a beach might increase water itch. It is advisable to wash yourself with water other than lake water after swimming and to dry yourself thoroughly with a rough towel so that the cercaria is not able to penetrate the skin. Many have reported they are able to avoid water itch by oiling themselves with certain essential or other such oils prior to swimming. Some have even used tar soap successfully. However, if you are infected with water itch, the itch can be treated with over-the-counter cortisone creams available at the pharmacist. If the symptoms become unbearable it is advisable to see a doctor.

Pyhäjärven suojeluohjelma, Sepäntie 7, 27500 Kauttua (Eura), puh. (02) 838 0600