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  • Shaken Baby Syndrome

    Tuesday, 21 July 2015 16:28
  • Amniotic fluid problems

    Thursday, 14 May 2015 12:54
  • Choosing a pre-school

    Friday, 10 April 2015 17:50
  • Newborn reflexes

    Tuesday, 03 March 2015 15:49
  • Mastitis

    Tuesday, 03 March 2015 15:41
  • Pelvic floor exercises

    Wednesday, 11 February 2015 17:20
  • Colic

    Wednesday, 11 February 2015 17:11
  • Antenatal Classes

    Monday, 03 June 2013 09:34
  • Strap-in-the-Future

    Thursday, 30 June 2011 13:52

Swimmer's Itch

Swimmers ItchSwimmer's itch, also called cercarial dermatitis is found worldwide and occurs most frequently during the summer months. Swimmer's itch is a rash that may occur after swimming in fresh or salt water that is contaminated by a certain microscopic parasite.

The skin rash develops as an allergic reaction to infestations of parasitic flatworms (called schistosomes), found in certain birds (including mergansers, mallards, Canadian geese, swans and red-winged blackbirds) and aquatic mammals (such as beavers, muskrats and mice).

Immature larva (also known as cercariae), of parasitic flatworms is released from snails into water. The parasite penetrates the human host through exposed skin or by oral ingestion.

Most species of flatworm (schistosomes) that cause swimmer's itch rely on only one species of bird and one species of snail to complete their life cycle. In other words, they are relatively host-specific. However, if someone is unfortunate to be in the wrong place at the wrong time, the cercariae can penetrate human skin.

Swimmer's Itch can also occur when a film of cercariae-infested water dries on exposed skin. The rash generally affects skin areas that are directly exposed to infested water. Skin covered by swimwear is often protected.

Cause:

The life history of the dermatitis-producing schistosomes (flatworms) is cyclic. There are two hosts during the parasites life cycle that cause swimmer's itch – the snail intermediate and the vertebrate final host, usually a bird.

Most worms that cause swimmer's itch use bird hosts for the adult parasite and aquatic snails as intermediate hosts for the larval (cercarial) stages. The parasite penetrates the skin of a bird or mammal, migrates through the various organs, and usually resides in the blood vessels of the small intestine. Once in the host's intestines, the parasite develops into an adult and the female lays eggs. The eggs pass out of the host during defecation, with the faeces. If the eggs are deposited in water, they will hatch within an hour under favourable conditions. The hatched eggs are called miracidium. The miracidium stage is aquatic, free-swimming, but non-feeding. The miracidium is able to move through the water for approximately one day.

If it comes into contact with the correct species of aquatic snail (e.g. Lynmnaeidae or Physidae), it penetrates the snail through the skin or mouth. Within the snail, the miracidium forms an elongated, reproductive sac, called the sporocyst. This will produce a second generation of sporocysts. Within approximately one month, the sporocysts produce the next stage, called the cercaria.

The cercaria burrows out of the snail and forms the second, non-feeding, swimming aquatic stage of the life cycle. Cercaria must find a suitable bird host and enter the bird through ingestion or skin penetration. The cercaria moves through the various organs and migrates to the host's intestines where it matures. The adult worms (the females are smaller than a single hair of a paintbrush) produce large numbers of eggs, which are voided with the faeces, and the cycle begins again.

There are a number of factors that influence whether swimmer's itch will be problematic at a given point in time, these include:

  • The distribution and number of bird species that can serve as hosts for the adult worm.
  • The distribution and number of certain snail species, which can serve as intermediate hosts.
  • Water temperature. Snails tend to reproduce and grow rapidly during the summer months.
  • Affected migrating birds returning from their winter habitats.
  • Domesticated aquatic birds becoming more active during the warm weather.
  • People swimming, as well as the number of hours spent in the water.
  • The time of day, water currents and wind direction.
  • Sensitivity of an individual to swimmer's itch, due to repeated exposure.

Symptoms:

Symptoms may occur within minutes or several days after swimming in contaminated water and include:

  • Burning, itching or tingling of the skin. Itching can last for up to a week or more, but will gradually subside.
  • After the initial exposure, the infected person may notice tiny red spots where the parasite has penetrated the skin.
  • Small reddish pimples often appear within 12 hours and may be accompanied by intense itching.
  • These pimples may develop into papules (larger bumps), hives or small blisters. This often occurs 24-48 hours after exposure.
  • Scratching the rash may result in a secondary bacterial infection.

Because swimmer's itch is an allergic reaction to infection, the longer or more frequent your exposure to contaminated water, the more severe and immediate your symptoms will be. People who have previously been exposed to swimmer's itch are more susceptible and after repeated exposure, sensitivity may develop. In severe cases, a person may develop a fever, become nauseous, and will have sleep difficulties due to intense itching.

Diagnosis:

Specific diagnosis may be difficult because swimmer's itch can resemble other skin conditions (such as chicken pox, poison ivy, impetigo or herpes). Skin biopsies are unhelpful and there is no blood test to specifically indicate that cercariae have caused the itching. Your doctor will probably make a differential diagnosis, by examining the rash, ruling out other conditions, asking if you have been swimming recently, and if others developed a similar rash after swimming in the same place.

Treatment:

Most cases of swimmer's itch do not require medical attention. Treatment generally involves symptomatic relief.

  • Apply cool compresses to the affected areas.
  • Bathe in Epsom salts or baking salt.
  • Soak in colloidal oatmeal baths.
  • Mix baking salt with water until it forms a paste-like consistency and apply directly to the rash.
  • Topical creams, such as corticosteroids help to reduce the inflammation.
  • Anti-itch lotions, such as calamine or antihistamines may help alleviate discomfort.
  • If itching and subsequent scratching is severe, your doctor may prescribe stronger prescription creams and lotions to prevent or treat secondary bacterial infection.
  • Oral antibiotics may be required if scratching has caused the skin to break and it has become infected.
  • Oral steroids (Prednisone) are appropriate if the reaction is severe.

Risk factors:

Anyone is at risk of developing swimmer's itch, if they swim or wade in infested water. Children tend to be affected more frequently because they swim, wade, and play in shallow water. Larvae are more likely to be present in shallow water near the shoreline. Children are also less likely to towel dry themselves after leaving the water.

Swimmers itch is not contagious. It cannot be spread from one person to another.

Prevention:

  • Avoid swimming in shallow water for prolonged periods.
  • Avoid swimming or wading in marshy areas where snails are commonly found.
  • Avoid swimming in areas where swimmer's itch is problematic and where there is an onshore wind.
  • Be aware of signs indicating water that is not safe for swimming purposes. Because several factors are involved in water becoming problematic, there is no way of knowing how long water may be unsafe. These factors also change over time (sometimes within a swim season). However, an infected snail will continue to produce cercariae throughout its life. For further snails to become infected, the parasite needs migratory birds or mammals in the area, to continue its life cycle.
  • Towel dry or shower immediately after leaving the water. This can prevent some species of schistosomes from penetrating the skin.
  • Avoid feeding ducks, geese and swans. Feeding birds in your area not only makes them dependent on humans for survival; but also may propagate swimmer's itch. Some birds serve as hosts to the schistosomes that cause swimmer's itch. Feeding birds may stimulate fecal deposits at the feeding site. The eggs of the parasite hatch from the host's faeces and are called miracidium during this next stage. Miracidium are able to swim in the water for up to a day.

Prognosis:

Swimmer's itch usually goes away in about one week. Call your doctor if you develop sigs of infection, such as increased pain, swelling, warmth, or redness. You notice red streaks leading from the area or the draining of pus. The rash persists for more than one week or you become feverish. You may be referred to a dermatologist if necessary.

References:

CDC. Parasites – Cercarial Dermatitis (also known as Swimmer's Itch). http://www.cdc.gov/parasites/swimmersitch/ . Updated January 10, 2012. Accessed August 23, 2013.

Medical MD. Swimmer's Itch – Topic Overview. Healthwise. http://www.webmd.com/skin-problems-and-treatments/tc/swimmers-itch-topic-overview . Updated May 17, 2011. Accessed August 27, 2013.

Hope College. Swimmer's Itch – Frequently Asked Questions. Hope College, Biology department, Michigan. http://www.swimmersitch.org/faq.html . Accessed August 23, 2013.

Mayo Clinic. Swimmer's Itch. Mayo Clinic. http://www.mayoclinic.com/health/swimmers-itch/DS00902/DSECTION=tests-and-diagnosis . Published February 3, 2011. Accessed August 27, 2013.

Williams, D. Swimmer's itch. OnlineDermClinic. http://www.onlinedermclinic.com/archive/swimmers-itch . Accessed August 26, 2013.