Swimmer's itch

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Swimmer's itch
Other namesSchistosome dermatitis
Cercarial dermatitis on lower legs, four days after spending a day in the shallows of a lake
SpecialtyInfectious diseases Edit this on Wikidata

Swimmer's itch, cercarial dermatitis or schistosome dermatitis is a short-term allergic contact dermatitis occurring in the skin of humans that have been infected by water-borne schistosomes, a type of flatworm. It is common in freshwater, brackish and marine habitats worldwide.[1] The incidence of this condition may be increasing, although this may be attributed to better monitoring and reporting. Nevertheless, the condition is considered to be an emerging infectious disease.[2]

The main symptom is itchy

wheals develop quickly, then turn into maculae in about half an hour. Within 10–12 hours these turn into very itchy papules that reach their worst by the second or third day. The papules disappear in 1–2 weeks but secondary effects from scratching can continue longer. The intense itching, which peaks after 48–72 hours, is associated with pain and swelling of the affected areas.[3] People repeatedly exposed to cercariae develop heavier symptoms with faster onset.[4]

There are no permanent effects to people from this condition.

Epsom salts can also provide relief of symptoms.[6]

Cause

Swimmer's itch was known to exist as early as the 19th century, but it was not until 1928 that a biologist found that the

marine environments, especially along the coasts, swimmer's itch can occur as well.[8]

These parasites use both

parasitic life cycles
as follows:

  1. Once a schistosome egg is immersed in water, a short-lived, non-feeding, free-living stage known as the miracidium emerges. The miracidium uses cilia to follow chemical and physical cues thought to increase its chances of finding the first intermediate host in its life cycle, a freshwater snail.
  2. After infecting a snail, it develops into a mother
    sporocyst, which in turn undergoes asexual reproduction, yielding large numbers of daughter sporocysts, which asexually produce another short-lived, free-living stage, the cercaria
    .
  3. Cercariae use a tail-like appendage (often forked in genera causing swimmer's itch) to swim to the surface of the water; and use various physical and chemical cues in order to locate the next and final (definitive) host in the life cycle, a bird. These larvae can accidentally come into contact with the skin of a swimmer. The cercaria penetrates the skin and dies in the skin immediately. The cercariae cannot infect humans, but they cause an inflammatory immune reaction. This reaction causes initially mildly itchy spots on the skin. Within hours, these spots become raised papules which are intensely itchy. Each papule corresponds to the penetration site of a single parasite.
    Life-cycle of swimmers itch
  4. After locating a bird, the parasite penetrates through the skin (usually the feet), dropping the forked tail in the process. Inside the circulatory system, the immature worms (
    tissues and larvae hatch from the eggs directly in the tissue during drinking/feeding of the infected birds.[9]

Risk factors

Image of infectious cercariae

Humans usually become infected after swimming in slow-moving rivers, lakes or ponds. Some laboratory evidence indicates snails shed cercariae most intensely in the morning and on sunny days, and exposure to water in these conditions may therefore increase risk. Duration of swimming is correlated with increased risk of infection in Europe

fatty acids, such as linoleic and linolenic acids. These essential fatty acids are found in many edible crops, derived plant oils, sun lotions and creams based on plant oils.[citation needed
]

Control

Mechanical removal of snails in Lake Annecy, France

Various strategies targeting the

mollusc and avian hosts of schistosomes have been used by lakeside residents in recreational areas of North America to deal with outbreaks of swimmer's itch. In Michigan, for decades, authorities used copper sulfate as a molluscicide to reduce snail host populations and thereby the incidence of swimmer's itch.[citation needed
] The results with this agent have been inconclusive, possibly because:

More importantly, perhaps, copper sulfate is toxic to more than just molluscs, and the effects of its use on aquatic ecosystems are not well understood.[citation needed]

Another method targeting the snail host, mechanical disturbance of snail habitat, has been also tried in some areas of North America[12] and Lake Annecy in France, with promising results. Some work in Michigan suggests that administering praziquantel to hatchling waterfowl can reduce local swimmer's itch rates in humans.[15] Work on schistosomiasis showed that water-resistant topical applications of the common insect repellent DEET prevented schistosomes from penetrating the skin of mice.[16] Public education of risk factors, a good alternative to the aforementioned interventionist strategies, can also reduce human exposure to cercariae.[17]

See also

References

  1. ^ "Avian Schistosome Biodiversity". www.schistosomes.net. Retrieved 2016-03-07.
  2. PMID 25567226
    .
  3. ISBN 978-3-319-40615-2
    .
  4. ^
    S2CID 52945883
    .
  5. ^ "With warm weather, Swimmers Itch makes annual appearance". dnr.wi.gov. Retrieved 2016-03-07.
  6. ^ "Swimmers Itch FAQS". CDC. Retrieved 12 May 2014.
  7. ^ "Swimmer's Itch in Michigan" (PDF). State of Michigan. 2014. Retrieved 5 March 2015.
  8. PMID 20735918
    .
  9. PMID 9879557
    .
  10. ^
    PMID 9692609
    .
  11. PMID 9488332
    .
  12. ^
    PMID 10729712
    .
  13. S2CID 43205388
    .
  14. ^ Blankespoor HD, Reimink RL (1991). "The control of swimmer's itch in Michigan: Past, present, and future". Michigan Academician. 24 (1): 7–23.
  15. S2CID 45216385
    .
  16. S2CID 25327748
    .
  17. ^ "Swimmer's Itch Reported at Lakes". Bureau of Land Management.[failed verification]

External links

Wikimedia Commons has media related to Schistosome cercarial dermatitis.
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