The technical
name for swimmer's itch is cercarial dermatitis. In developing
countries, swimmer's itch translates into "rice paddy
itch", "clam diggers itch", "sawah" to
the rice farmers in Malaysia, "kubure" or "kobanyo"
to the Japanese rice farmers or "hoi con" to Thai rice
farmers. . In these same places, all swimmers are usually exposed
to the risk of cercarial dermatitis as well. On costal New Jersey,
it is called "Duckworms".
WHAT IS SWIMMER'S ITCH?
Swimmer's itch is a patchy red pin point skin rash associated
with itching on the parts of the body that have been in the water.
Swimmer's itch is usually not severe. After the initial transient
itching it will disappear without treatment. The itching occurs
within 48 hours and may last up to 7 days. Rarely, it can be
severe if a large proportion of the body is affected. The major,
although not the only, cause of swimmer's itch are trematode
parasites of aquatic/migrating birds. The life cycles of these
parasites involve snails as the first host and aquatic birds or
some mammals as the final host.
The larval parasite called a "cercaria" is released
by aquatic or amphibious (moves both on land and water) snails and
causes dermatitis when it mistakenly penetrates a person's skin
rather than it rightful host - usually a duck! Swimmer's itch
occurs in BOTH freshwater and in the marine coastal environments.
WHAT ARE THE OTHER CAUSES OF ITCHING AMONG SWIMMERS?
Common lore in the media is that this is caused by "duck
fleas" in freshwater and "sea lice" in the marine
environment. Neither is correct. Trematode parasites cause the
freshwater swimmer's itch and both trematode parasites and
nematocysts cause marine swimmer's itch. Marine swimmers itch is
probably from contact with the larval form of the thimble
jellyfish (Linuche unguiculata), sea anenome (Edwardsiella lineata), Portuguese
Man-of-War (physalia utriculus), and probably numerous others. In unusual
circumstances, different algae, chemical pollutants and sewage may
cause dermatitis that is indistinguishable from cercarial
dermatitis. Don't forget that no matter what the cause, usually
many other people aside from yourself, have been affected. Thus,
it is important, when visiting the pharmacist or physician, to
mention that you think that the itching dermatitis was acquired by
swimming or bathing.
Jellyfish nematocysts (such as remain active for months, even
if dried out. They can persist in clothing or swimsuits with
recurrence of symptoms upon wearing the same clothes over again.
A delayed reaction can also be seen (a serum sickness-like
reaction). Treatment options said to help include washing
immediately in salt water, acetic acid (vinegar), methyl
alcohol or dilute (1:10)
household ammonia. Benadryl spray helps to reduce itch and pain,
and may kill the nematocysts. It is a self limited
eruption that rarely persists beyond 10-14 days.
WHERE DOES IT OCCUR?
The appropriate question might be, "Where doesn't it
occur". At one time or other in the past 70 years, since it's
major cause was first identified in Douglas Lake, Michigan, USA,
it has been reported in almost every country in the world. No
public health department requires that swimmer's itch be reported.
Therefore it may seem that it is not such widespread problem. In
fact, it is more often reported in newspaper media than in the
scientific literature! WHEN DOES IT OCCUR?
Swimmer's itch occurs when several factors converge at the
optimal time. In summer, 1) the water temperature reaches the
appropriate level for snails to reproduce and grow rapidly, 2)
migrating aquatic birds infected with the trematode parasite
return from their winter habitats or domesticated aquatic birds
return to full activity and 3) the frequency of swimmers and
bathers reaches its peak during this period. Over the past ten
years, the baseline temperatures of the freshwater bodies in
temperate zones have increased and migrating aquatic bird
populations have generally increased, creating a greater risk of
swimmer's itch.
HOW IS THE DIAGNOSIS CONFIRMED?
Specific diagnosis is difficult. Skin biopsies are not helpful.
There is no widely available blood test that gives specific
indication that cercariae have caused the itching. The best
confirmation of the cause is based on knowing from other people
that swimmer's itch occurs in the place where one swam or entered
the water. Other diseases have been confused with swimmers itch:
impetigo (bacterial infection of the skin), chickenpox, poison
ivy, herpes, or rare skin diseases.
WHAT IS THE TREATMENT?
Treatment may not be necessary when there are only a few
itching spots. An antihistaminic or mild corticosteroid cream
purchased over the counter in pharmacies can be beneficial. If the
initial itching is severe, then scratching can cause abrasions and
skin infections may develop. If the symptoms persist for longer
than 3 days, you should consult your dermatologist. Prescription
medications may help reduce the itching.
WHAT IS THE PREVENTION?
Swimmer's itch is caused by many different factors. Since the
disease is really a disease of aquatic birds, the target should be
to reduce the possibilities of the birds getting infected. In some
small ponds and lakes, the snail which harbor the parasite can be
killed by chemical molluscicides. The possible environmental
effects of chemical molluscicides mean that this approach cannot
be recommended in all situations. An newer approach has been to
place a drug for treatment of the parasite into food bait. Other
drugs are currently being tested. Indirectly, it is important that
the vegetation in the pond or the lake be kept to a minimum so
that the snails do not have the ideal environment to grow