Swimmer's itch

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Swimmer's itch
Other namesSchistosome dermatitis
Cercarial dermatitis lower legs.jpg
Cercarial dermatitis on lower legs, four days after spending a day in the shallows of a lake
Specialty Infectious diseases   OOjs UI icon edit-ltr-progressive.svg

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]

Contents

The main symptom is itchy papules (raised skin) that commonly occur within 2 days of infection. Initially, 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. [5] Orally administered hydroxyzine, an antihistamine, is sometimes prescribed to treat swimmer's itch and similar dermal allergic reactions. In addition, bathing in oatmeal, baking soda, or 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 dermatitis was caused by the larval stage of a group of flatworm parasites in the family Schistosomatidae. [7] The genera most commonly associated with swimmer's itch in humans are Trichobilharzia [4] and Gigantobilharzia . It can also be caused by schistosome parasites of non-avian vertebrates, such as Schistosomatium douthitti, which infects snails and rodents. Other taxa reported to cause the reaction include Bilharziella polonica and Schistosoma bovis. In marine environments, especially along the coasts, swimmer's itch can occur as well. [8]

These parasites use both freshwater snails and vertebrates as hosts in their 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 Cercarial LifeCycle.png
    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 (schistosomula) develop into mature male and female worms, mate and migrate through the host's circulatory system (or nervous system in case of T. regenti ) to the final location (veins feeding the gastrointestinal tract) within the host body. There they lay eggs in the small veins in the intestinal mucosa from which the eggs make their way into the lumen of the gut, and are dumped into the water when the bird defecates. One European species, Trichobilharzia regenti , instead infects the bird host's nasal 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 Schistosomal cercaria.jpg
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 [10] and North America, [11] and shallow inshore waters may harbour higher densities of cercariae than open waters offshore. Onshore winds are thought to cause cercariae to accumulate along shorelines. [12] Studies of infested lakes and outbreaks in Europe and North America have found cases where infection risk appears to be evenly distributed around the margins of water bodies [10] as well as instances where risk increases in endemic swimmer's itch "hotspots". [12] Children may become infected more frequently and more intensely than adults but this probably reflects their tendency to swim for longer periods inshore, where cercariae also concentrate. [13]

Control

Mechanical removal of snails in Lake Annecy, France Lake Annecy.jpg
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

Related Research Articles

<span class="mw-page-title-main">Schistosomiasis</span> Human disease caused by parasitic worms called schistosomes

Schistosomiasis, also known as snail fever, bilharzia, and Katayama fever, is a disease caused by parasitic flatworms called schistosomes. The urinary tract or the intestines may be infected. Symptoms include abdominal pain, diarrhea, bloody stool, or blood in the urine. Those who have been infected for a long time may experience liver damage, kidney failure, infertility, or bladder cancer. In children, schistosomiasis may cause poor growth and learning difficulties.

<span class="mw-page-title-main">Trematoda</span> Class of parasitic flatworms

Trematoda is a class of flatworms known as flukes or trematodes. They are obligate internal parasites with a complex life cycle requiring at least two hosts. The intermediate host, in which asexual reproduction occurs, is usually a snail. The definitive host, where the flukes sexually reproduce, is a vertebrate. Infection by trematodes can cause disease in all five traditional vertebrate classes: mammals, birds, amphibians, reptiles, and fish.

<span class="mw-page-title-main">Schistosomatidae</span> Family of flukes

Schistosomatidae is a family of digenetic trematodes with complex parasitic life cycles. Immature developmental stages of schistosomes are found in molluscs and adults occur in vertebrates. The best studied group, the blood flukes of the genus Schistosoma, infect and cause disease in humans. Other genera which are infective to non-human vertebrates can cause mild rashes in humans.

<span class="mw-page-title-main">Trematode life cycle stages</span>

Trematodes are parasitic flatworms of the class Trematoda, specifically parasitic flukes with two suckers: one ventral and the other oral. Trematodes are covered by a tegument, that protects the organism from the environment by providing secretory and absorptive functions.

A cercaria is the larval form of the trematode class of parasites. It develops within the germinal cells of the sporocyst or redia. A cercaria has a tapering head with large penetration glands. It may or may not have a long swimming "tail", depending on the species. The motile cercaria finds and settles in a host where it will become either an adult, or a mesocercaria, or a metacercaria, according to species.

Schistosoma japonicum is an important parasite and one of the major infectious agents of schistosomiasis. This parasite has a very wide host range, infecting at least 31 species of wild mammals, including nine carnivores, 16 rodents, one primate (human), two insectivores and three artiodactyls and therefore it can be considered a true zoonosis. Travelers should be well-aware of where this parasite might be a problem and how to prevent the infection. S. japonicum occurs in the Far East, such as China, the Philippines, Indonesia and Southeast Asia.

<i>Trichobilharzia regenti</i> Species of fluke

Trichobilharzia regenti is a neuropathogenic parasitic flatworm of birds which also causes cercarial dermatitis in humans. The species was originally described in 1998 in the Czech Republic and afterwards it was detected also in other European countries, e.g. Denmark, Germany, France, Iceland, Poland, Switzerland, or Russia, and even in Iran. For its unique neurotropic behaviour in vertebrate hosts, the host-parasite interactions are extensively studied in terms of molecular biology, biochemistry and immunology.

<i>Schistosoma mansoni</i> Species of fluke

Schistosoma mansoni is a water-borne parasite of humans, and belongs to the group of blood flukes (Schistosoma). The adult lives in the blood vessels near the human intestine. It causes intestinal schistosomiasis. Clinical symptoms are caused by the eggs. As the leading cause of schistosomiasis in the world, it is the most prevalent parasite in humans. It is classified as a neglected tropical disease. As of 2021, the World Health Organization reports that 251.4 million people have schistosomiasis and most of it is due to S. mansoni. It is found in Africa, the Middle East, the Caribbean, Brazil, Venezuela and Suriname.

<i>Schistosoma intercalatum</i> Species of fluke

Schistosoma intercalatum is a parasitic worm found in parts of western and central Africa. There are two strains: the Lower Guinea strain and the Zaire strain. S. intercalatum is one of the major agents of the rectal form of schistosomiasis, also called bilharzia. It is a trematode, and being part of the genus Schistosoma, it is commonly referred to as a blood-fluke since the adult resides in blood vessels.

<i>Schistosoma haematobium</i> Species of fluke

Schistosoma haematobium is a species of digenetic trematode, belonging to a group (genus) of blood flukes (Schistosoma). It is found in Africa and the Middle East. It is the major agent of schistosomiasis, the most prevalent parasitic infection in humans. It is the only blood fluke that infects the urinary tract, causing urinary schistosomiasis, and is a leading cause of bladder cancer. The diseases are caused by the eggs.

<i>Radix auricularia</i> Species of gastropod

Radix auricularia, the big-ear radix, is a species of medium-sized freshwater snail, an aquatic pulmonate gastropod mollusk in the family Lymnaeidae.

<i>Nanophyetus</i> Genus of flukes

Nanophyetus salmincola is a food-borne intestinal trematode parasite prevalent on the Pacific Northwest coast. The species may be the most common trematode endemic to the United States.

Schistosoma mekongi is a species of trematodes, also known as flukes. It is one of the five major schistosomes that account for all human infections, the other four being S. haematobium, S. mansoni, S. japonicum, and S. intercalatum. This trematode causes schistosomiasis in humans.

<i>Indoplanorbis</i> Genus of gastropods

Indoplanorbis is a genus of air-breathing freshwater snail. Its only member species is Indoplanorbis exustus, an aquatic pulmonate gastropod mollusk in the family Planorbidae, the ram's horn snails. The species is widely distributed across the tropics. It serves as an important intermediate host for several trematode parasites. The invasive nature and ecological tolerance of Indoplanorbis exustus add to its importance in veterinary and medical science.

<i>Schistosoma spindale</i> Species of fluke

Schistosoma spindale is a species of digenetic trematode in the family Schistosomatidae. It causes intestinal schistosomiasis in the ruminants.

<span class="mw-page-title-main">Bivitellobilharzia nairi</span> Species of fluke

Bivitellobilharzia nairi is a species of trematodes, part of the family Schistosomatidae. This is a fairly new identified endoparasite that was found in 1945 by Mudaliar and Ramanujachari, who first recorded the parasite in India. Researchers collected fecal samples of the Indian rhinoceros and were startled to find B. nairi eggs.

<i>Metagonimus yokogawai</i> Species of fluke

Metagonimus yokogawai, or the Yokogawa fluke, is a species of a trematode, or fluke worm, in the family Heterophyidae.

Schistosoma bovis is a two-host blood fluke, that causes intestinal schistosomiasis in ruminants in North Africa, Mediterranean Europe and the Middle East. S. bovis is mostly transmitted by Bulinus freshwater snail species. It is one of nine haematobium group species and exists in the same geographical areas as Schistosoma haematobium, with which it can hybridise. S. bovis-haematobium hybrids can infect humans, and have been reported in Senegal since 2009, and a 2013 outbreak in Corsica.

<i>Trichobilharzia</i> Genus of flukes

Trichobilharzia is a genus of trematodes in the family Schistosomatidae. They are worldwide distributed parasites of anatid birds and causative agents of human cercarial dermatitis.

Heterobilharzia is a genus of trematodes in the family Schistosomatidae. The species Heterobilharzia Americana is a parasite of the Southeastern United States and typically found in raccoons. Species of this genus are responsible for Schistosoma in canines. Cercariae found in freshwater may also cause Swimmer's itch in humans.

References

  1. ↑ "Avian Schistosome Biodiversity". www.schistosomes.net. Retrieved 2016-03-07.
  2. ↑ Horák P, Mikeš L, Lichtenbergová L, Skála V, Soldánová M, Brant SV (January 2015). "Avian schistosomes and outbreaks of cercarial dermatitis". Clinical Microbiology Reviews. 28 (1): 165–190. doi:10.1128/CMR.00043-14. ISSN   1098-6618. PMC   4284296 . PMID   25567226.
  3. ↑ Bonamonte D, Romita P, Vestita M, Angelini G (2016). "Dermatitis Caused by Aquatic Worms". In Bonamonte D, Angelini G (eds.). Aquatic Dermatology. Springer. p. 142. doi:10.1007/978-3-319-40615-2_9. ISBN   978-3-319-40615-2.
  4. 1 2 Macháček T, Turjanicová L, Bulantová J, Hrdý J, Horák P, Mikeš L (2018-10-09). "Cercarial dermatitis: a systematic follow-up study of human cases with implications for diagnostics". Parasitology Research. 117 (12): 3881–3895. doi:10.1007/s00436-018-6095-0. ISSN   0932-0113. PMID   30302587. 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. ↑ Brant S, Cohen A, James D, Hui L, Hom A, Loker E (2010). "Cercarial Dermatitis Transmitted by Exotic Marine Snail". Emerging Infectious Diseases. 16 (9): 1357–65. doi:10.3201/eid1609.091664. PMC   3294964 . PMID   20735918.
  9. ↑ Horák P., Kolářová L., Dvořák J. (1998). "Trichobilharzia regenti n. sp. (Schistosomatidae, Bilharziellinae), a new nasal schistosome from Europe" (PDF). Parasite. 5 (4): 349–357. doi: 10.1051/parasite/1998054349 . PMID   9879557.
  10. 1 2 Chamot E, Toscani L, Rougemont A (1998). "Public health importance and risk factors for cercarial dermatitis associated with swimming in Lake Leman at Geneva, Switzerland". Epidemiol. Infect. 120 (3): 305–14. doi:10.1017/S0950268898008826. PMC   2809408 . PMID   9692609.
  11. ↑ Lindblade KA (1998). "The epidemiology of cercarial dermatitis and its association with limnological characteristics of a northern Michigan lake". J. Parasitol. 84 (1): 19–23. doi:10.2307/3284521. JSTOR   3284521. PMID   9488332.
  12. 1 2 3 Leighton BJ, Zervos S, Webster JM (2000). "Ecological factors in schistosome transmission, and an environmentally benign method for controlling snails in a recreational lake with a record of schistosome dermatitis". Parasitol. Int. 49 (1): 9–17. doi:10.1016/S1383-5769(99)00034-3. PMID   10729712.
  13. ↑ Verbrugge LM, Rainey JJ, Reimink RL, Blankespoor HD (2004). "Prospective study of swimmer's itch incidence and severity". J. Parasitol. 90 (4): 697–704. doi:10.1645/GE-237R. PMID   15357056. 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. ↑ Blankespoor CL, Reimink RL, Blankespoor, HD (2001). "Efficacy of praziquantel in treating natural schistosome infections in common mergansers". Journal of Parasitology. 87 (2): 424–6. doi:10.1645/0022-3395(2001)087[0424:EOPITN]2.0.CO;2. PMID   11318576. S2CID   45216385.
  16. ↑ Salafsky B, Ramaswamy K, He YX, Li J, Shibuya T (November 1999). "Development and evaluation of LIPODEET, a new long-acting formulation of N, N-diethyl-m-toluamide (DEET) for the prevention of schistosomiasis". Am. J. Trop. Med. Hyg. 61 (5): 743–50. doi:10.4269/ajtmh.1999.61.743. PMID   10586906. S2CID   25327748.
  17. ↑ "Swimmer's Itch Reported at Lakes". Bureau of Land Management.[ failed verification ]
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