 
Swimmer's
Itch
Cercarial
dermatitis
(SIR-care-ee-uhl DER-muh-TIGHT-iss)
What is swimmer's
itch?
Swimmer's
itch, also called cercarial dermatitis, is a skin rash caused by an allergic
reaction to infection with certain parasites of birds and mammals. These
microscopic parasites are released from infected snails to swim in fresh
and salt water, such as lakes, ponds, and oceans used for swimming and
wading. Infection is found throughout the world. Swimmer's itch generally
occurs during summer months.
What are the signs
and symptoms of swimmer's itch?
Within minutes
to days after swimming in contaminated water, you may experience tingling,
burning, or itching of the skin. Small reddish pimples appear within 12
hours. Pimples may develop into small blisters. Itching may last up to
a week or more, but will gradually go away.
Because swimmer's
itch is caused by an allergic reaction to infection, the more often you
swim or wade in contaminated water, the more likely you are to develop
more serious symptoms. The greater the number of exposures to contaminated
water, the more intense and immediate symptoms of swimmer's itch will
be.
Be aware
that there are other causes of rash that may occur after swimming in fresh
and salt water.
Do I need to see
my health care provider for treatment?
No. Most
cases do not require medical attention.
If you have
a rash, you may try the following for relief:
- corticosteroid
cream
- cool compresses
- bath with
baking soda
- baking
soda paste to the rash
- anti-itch
lotion
- Calamine*
lotion
- colloidal
oatmeal baths, such as Aveeno*
Try not to
scratch. Scratching may cause the rash to become infected. If itching
is severe, your health care provider may prescribe lotion or creams to
lessen your symptoms.
How does water
become infested with the parasite?
The adult
parasite lives in the blood of infected animals such as ducks, geese,
gulls, swans, as well as certain aquatic mammals such as muskrats and
beavers. The parasites produce eggs that are passed in the feces of infected
birds or mammals.
If the eggs
land in the water, the water becomes contaminated. Eggs hatch, releasing
small, free-swimming larvae. These larvae swim in the water in search
of a certain species of aquatic snail.
If the larvae
find one of these snails, they infect the snail and undergo further development.
Infected snails release a different type of larvae (cercariae, hence the
name cercarial dermatitis) into the water. This larval form then searches
for a suitable host (bird, muskrat) so they can start the lifecycle over
again. Although humans are not a suitable host, the larvae burrow into
the skin of swimmers, which may cause an allergic reaction/rash. The larvae
cannot develop inside a human and they soon die.
Can swimmer's
itch be spread from person-to-person?
No.
Who is at risk
for swimmer's itch?
Anyone who swims
or wades in infested water may be at risk. Larvae are more likely to be
swimming along shallow water by the shoreline. Children are most often affected
because they swim, wade, and play in the shallow water more than adults.
Also, they do not towel dry themselves when leaving the water.
Once an outbreak
of swimmer's itch has occurred in water, will the water always be unsafe?
No. Many
factors must be present for swimmer's itch to become a problem in water.
Since these factors change (sometimes within a swim season), swimmer's
itch will not always be a problem. However, there is no way to know how
long water may be unsafe. Larvae are generally infective for 24 hours
once they are released from the snail. However, an infected snail will
continue to produce cercariae throughout the remainder of its life. For
future snails to become infected, migratory birds or mammals in the area
must also be infected so the lifecycle can continue.
What can be done
to reduce the risk of swimmer's itch?
- Avoid
swimming in areas where swimmer's itch is a known problem or where signs
have been posted warning of unsafe water.
- Avoid
swimming near or wading in marshy areas where snails are commonly found.
- Towel
dry or shower immediately after leaving the water.
- Encourage
health officials to post signs on shorelines where swimmer's itch is
a current problem.
- Do not
attract birds by feeding them to areas where people are swimming.
For further
information on protecting yourself from recreational water illnesses, please
visit www.healthyswimming.org
Is my swimming
pool safe to swim in?
Yes. As long
as your swimming pool is well-maintained and chlorinated, there is no
risk of swimmer's itch.
This fact
sheet is for information only and is not meant to be used for self-diagnosis
or as a substitute for consultation with a health care provider. If you
have any questions about the disease described above or think that you
may have a parasitic infection, consult a health care provider.
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