Swimmer’s itch

By Joshua D. Peugh

            Summer time is finally here, with the heat setting record breaking temperatures each day.  These phenomenal temperatures are leading more and more families to local recreational water areas like water parks and lakes.  What lies beyond the unseen eye in these mysterious waters? Parasites, of course!

            Many people at these recreational facilities are susceptive to any type of water-borne parasite infection unknowingly. A common water-borne parasite, known as schistosomatidae, causes an immune reaction occurring on the skin of humans.  The immune reaction is caused by an allergic reaction to certain parasites that infect some mammals and birds.  This water-borne infection is known as Swimmer’s itch, also called cercarial dermatitis, and the symptoms include itchy, raised papules, generally occurring within a few hours of the infection.  The infection does not generally last for more than a week.

            Once an egg of a schistosomatidae is submerged into a lake or pond, a free-living stage known as the miracidium is appears.  This stage is a short-lived non-feeding stage, where the miracidium uses cilia to follow physical and chemical cues.  These cues are thought to increase the opportunities of finding the first intermediate host in its life cycle, an aquatic snail.  When the miracidium has infected the aquatic snail, it develops into a mother sporocyst.  This will cause asexual reproduction in the organism, yielding very large number of daughter sporocysts, which asexually produce another short-lived, free-living stage, the cercaria.  This stage known as the cercariae is the stage that causes swimmer’s itch. In this stage the cercariae uses a tail-like appendage to swim to the top of the water, along with other chemical and physical cues, in order to target the final host in its life cycle, a bird.  After infecting a bird, the parasite develops into a schistosomulum.  Then the schistosomulum migrates through the host’s circulatory system to the final location within the host body where it matures and, if it encounters a mate, sheds eggs to start the life cycle over again.

            However, a bird is the preferred final host, but what happens when the host comes into contact with a human?  Once the parasite is in the infective stage, upon contact with a human the cercaria burrows through the skin.  Inside the skin, the parasite goes into its next stage the schistomulum, where it then migrates to the lungs and liver to form into an adult.  As an adult worm, depending on its species the parasite migrates to its preferred body part.  These body parts include the bladder, rectum, intestines, liver, portal venous system, spleen, and lungs.

            The symptoms that come from swimmer’s itch will depend on the type of parasite and how heavy the infestation is.  There may be fever, chills, and lymph node enlargement, along with liver and spleen enlargement.  The initial invasion by the parasite may cause itching and a rash.  If a rash occurs, this stage is known as swimmer’s itch and the parasite is being destroyed by the body.  Furthermore, if the parasite is not destroyed intestinal symptoms may occur with diarrhea and urinary symptoms with blood in the urine.

            Treatment before considerable damage or severe complications occur usually produces superior results.  Swimmer’s itch is usually treated with the drug praziquantel.  If the infection gets too severe or involves the central nerve system, corticosteroids may be given.  Prevention measures can be taken to avoid Swimmer’s itch all together.  First, do not swim in any water that may be contaminated and do not go in any water that may be unsafe.  Secondly, the aquatic snail is the intermediate host for schistosomiasis; therefore, controlling the snail population and getting rid of them in water used by humans would help prevent infections.

            The schistosomatidae that is frequently related with swimmer’s itch in humans are Trichobilharzia and Gigantobilharzia.  Schistosomiasis is not commonly found in the United States, it tends to reside in many tropical and subtropical areas worldwide.  There are currently no funds for swimmer’s itch; however research for schistomiasis is currently being held, but young scientist and investors are greatly needed to increase future funds.

For more information please visit:

http://en.wikipedia.org/wiki/Swimmer's_itch

http://www.ncbi.nlm.nih.gov/pubmed/15117691

http://www.cdc.gov/parasites/swimmersitch/

http://usf.academia.edu/DavidLewis/Papers/1216898/A_survey_of_swimmers_itch-causing_cercariae_and_their_intermediate_snail_host_species_in_Devils_Lake_Wisconsin

http://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0002298/