Many Canadian lakes prone to ‘swimmer’s itch’ parasites: what you need to know

Shine On
A busy beach in the summer in Alberta (Courtesy University of Alberta)

Have you ever had a bumpy red rash after taking a dip in a lake? Did you know that it’s caused by parasitic flatworm larvae that penetrate your skin while you swim?

Take a moment to let your stomach settle back down.

Swimmer’s Itch is a a rash caused by an allergic reaction to certain microscopic parasites that infect some birds and mammals. Symptoms can include itchy or burning skin, small blisters or reddish pimples, and can last for up to a week or more.

What causes swimmer’s itch?

Trichobilharzia, one of the parasites that causes Swimmer's Itch in Alberta (University of Alberta)

Primarily found in lakes, it occurs when adult parasites infect the blood of aquatic animals such as ducks, geese, and swans, as well as mammals such as muskrats and raccoons. The parasites produce eggs that are passed in the feces of the infected animals. Once released into the water, the eggs hatch, releasing free-swimming microscopic larvae, which search for a certain type of snail to infect.

Infected snails pollute the water in their area with microscopic larvae, which then search for a suitable host, to continue the cycle. Luckily humans are not suitable hosts, but the larvae can still burrow into skin, which can cause a rash.

Dr. Patrick Hanington and his team of researchers at the University of Alberta’s School of Public Health are trying to better understand the transmission of parasites to humans from snails, which will ideally lead to prevention strategies for swimmer’s itch. They have created a website to track where outbreaks occur,

Where does swimmer’s itch occur?

The website shows the bulk of the activity happens in Alberta, where the research team is based, but also in southern British Columbia and southern Ontario. “We find that most lakes in Alberta have all the conditions in place to have swimmer’s itch,” he says.

Does this always occur in lakes?

Primarily yes, but Hanington says that he has seen a couple of examples of swimmer’s itch happening on beaches in marine environments, and a couple of examples along the Pacific coast as well. “It’s the exact same system, just a different species of parasite, so the real question in marine environments is: what species of parasite is causing it, and what are the hosts that are important to that transmission cycle?”

Does the weather affect the chance of getting Swimmer’s Itch?

Yes. “We know that temperature has an impact on the timing of the both parasite lifecycle within the snail, and the snail’s lifecycle itself,” explains Dr. Hanington. “We know that in higher temperatures up to a point, the parasite will develop faster within the snail, and we know that the snail will develop to maturity faster. And so we tend to find that if it’s really warm earlier in the summer, we tend to find the parasites coming out of the snail earlier and causing swimmer’s itch earlier in the season.”

Helen Reed from Bar Harbour Camp on Buffalo Lake in Alberta said that they have had swimmer’s itch in previous years, but not this year. She said it tends to happen earlier in the summer at the beginning of July, and because camps started later this year, it hasn’t been an issue.

Typical habitat where you'd find parasite-carrying snails (Courtesy University of Alberta)

How long does the risk last once reported in a lake?

Even the day after, there may or may not be a risk of getting swimmer’s itch.

“Depending on how many snails are infected and how long those snails live for and the direction of water movement towards or away from the beach, a certain location may have a persistent problem throughout the entire summer or it may never have a problem or only certain situations when the wind happens to be blowing towards the beach,” says Hanington.

What can I do to avoid swimmer’s itch?

Rubbing yourself down quickly with a towel when you come out of the water might help. “There are five species of parasites that are known to cause swimmer’s itch, and one of them can get into the skin and cause swimmer’s itch within 10 minutes in the water. So if you’re in the water and you get exposed to that species, toweling off won’t help. Likewise if you’re in the water for two hours, that’s more than enough time for these parasites to get into the skin, and once they’ve penetrated the skin, there’s nothing you can do.”

Hanington’s team has also found that waterproof sunscreens, especially the sport sprays that leave a film on your skin, can help create a barrier on your skin.

Christina Ample of Rochon Sands Provincial Park in Alberta agrees. She said that there is some swimmer’s itch in the area, but she’s a firm believer that waterproof sunscreen can prevent a rash. She says her six children and two grandchildren have never had swimmer’s itch, thanks to the sunscreen.

Waterproof sunscreen can help create a barrier against the parasites. (Yahoo Shine)

How can beach operators control outbreaks?

The biggest factor is the design of the beach itself and the location of the beach on the lake, not necessarily whether or not there are snails or birds or whatever else present, explains Hanington.

His team has found that when the swimming area is isolated from the vegetation which houses the snails, and if the location of the lake itself permits the flow of water away from the swimming area rather than towards it, then swimmer’s itch outbreaks are significantly reduced.

A representative from Ol’ MacDonalds Resort on the south shore of Buffalo Lake in Alberta said that the resort hasn’t had any closures all summer, but other areas of the lake had.

“We have a couple of lakes in Alberta where we tend to see quite a few reports very consistently through the whole year. And then we have other lakes that are very close in proximity but have very different beach designs and we haven’t seen reports from them in three years,” Hanington says.

What other problems can I face while swimming in lakes?

Alberta has also had a problem with blue-green algae, or cyanobacteria, so a lot of our lakes tend to have algal-blooms. That’s more of a health concern than swimmer’s itch is.

Some bloom-forming cyanobacteria can produce toxins that, if contacted, may cause skin and eye irritation, or, can result in intestinal discomfort or severe illness in humans if ingested. For more information, visit My Wild Alberta’s page on blue-green algae.

“They do a lot to monitor that, and put up signs informing people about when and where there are cyanobacteria problems, and so we’re trying to integrate that beach monitoring program into a swimmer’s itch monitoring program as well,” says Hanington. “And so when they would monitor for sanabacteria they could also collect a couple of snails and then detect whether or not the correct parasites are in the snails at that beach."

A representative from Wabamun Lake Provincial Park said that the health unit checks the lake weekly, and while they’ve had some mild cases of swimmer’s itch, there’s nothing serious to report. At Camp Wohelo on Pigeon Lake, Alta. a volunteer said that they haven’t had to restrict swimming yet this year, but swimming bans tend to happen in late August when it’s hotter.

This blue-green algae can be a bigger concern than the parasites in lakes.

Can health authorities test for swimmer’s itch?

Not yet. “From this project, what we’re striving for is a water-based test, so somebody could go and test the water with a molecular DNA-based test,” says Hanington.

“We can do the test in the lab right now, the next step is to integrate that test into a field environment ... we want it to be able to be used by any of the health inspectors, the people who go out into the field. It would have to be very simple to use, and also give a very clear readout: a yes or a no, whether or not there’s a problem.”

What should I do if I get swimmer’s itch?

“We don’t want to you to not go swimming, but if you do go swimming and get swimmer’s itch, you can use any of the anti-itch creams at the drug store. That should help you get through the first couple of days, which is usually the worst time,” says Hanington.

To relieve symptoms, apply corticosteroid cream or calamine lotion, add baking soda to lukewarm baths or make a paste with it using water, or use an anti-itch cream.

Should I go to the doctor?

No. “We usually suggest that people don’t go see a physician, we don’t really think of it so much as a health concern,” explains Hanington.

Go to your family doctor only if you can’t hold back scratching the itch, because you can get a secondary bacterial infection. If the itchy red bumps start filling up with white puss, get to the clinic.

Hanington goes on to say that the only other situation where you should seek medical help is if you suspect you’re developing an allergic response.

“Kind of like a bee sting, after your first time getting it you can develop a sensitization to the swimmer’s itch parasite,” Hanington says, which can result in hives around the original spots. See a doctor to make sure you’re not coming down with something more serious.

But if all you have are some swimmer’s itch spots, grab some anti-itch cream, buckle down and hope it goes away soon.

If you find yourself with a swimmer’s itch this summer, visit and report it.