Swimmer's itch
Encyclopedia
Swimmer’s itch, also known as lake itch, duck itch, cercarial dermatitis, and Schistosome cercarial dermatitis, is a short-term, immune reaction occurring in the skin
of humans that have been infected by water-borne schistosomatidae
. Symptoms, which include itchy, raised papules, commonly occur within hours of infection and do not generally last more than a week.
A number of different flatworm
parasites in the family Schistosomatidae
are what cause swimmer’s itch. These parasites use both freshwater snail
s and vertebrates as hosts in their parasitic life cycles
. Mostly waterfowl
are used as the vertebrate host.
During one of their life stages, the larvae of the parasite, cercaria, leave the water snails and swim freely in the freshwater, attempting to encounter water bird
s. 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 cercaria larvae cannot infect humans, but they cause an inflammatory immune reaction. This reaction causes initially mildly itch
y 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.
The schistosomatidae that give rise to swimmer’s itch should not to be confused with those of the genus Schistosoma
, which infect humans and cause the serious human disease
schistosomiasis
, or with larval stages of thimble jellyfish (Linuche unguiculata
), which give rise to seabather's eruption
.
Seabather's eruption mostly occurs in salt water, on skin covered by clothing or hair, whereas swimmer's itch mostly occurs in freshwater, on uncovered skin.
Since it was first described in Michigan
in 1928, swimmer's itch has been reported from around the world. Some suggest incidence
may be on the rise, although this may also be attributed to better monitoring.
most commonly associated with swimmer’s itch in humans are Trichobilharzia and Gigantobilharzia. Trematodes in these groups normally complete their life cycles in water birds. However, swimmer’s itch can also be caused by schistosome parasites of non-avian vertebrates, such as Schistosomatium douthitti, which infects snails and rodent
s. Other taxa
reported to cause the reaction include Bilharziella polonica and Schistosoma bovis. In marine
habitat
s, especially along the coast
s, swimmer’s itch can occur as well. In Australia
, the so called "pelican itch" is caused by cercariae of the genus Austrobilharzia employing marine gastropods
of the genus
Batillaria
(B. australis) as intermediate host
s.
schistosomes use two hosts in their life cycles. One is a snail, the other is a bird or mammal.
Note: 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.
into host skin
include unsaturated
fatty acids, such as linoleic
and linolenic acids. These substances occur naturally in human skin and are found in sun lotions and creams based on plant oils
.
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. 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 ecosystem
s are not well understood.
Another method targeting the snail host, mechanical disturbance of snail habitat, has been also tried in some areas of North America 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. Work on schistosomiasis showed that water-resistant topical applications of the common insect repellent DEET
prevented schistosomes from penetrating the skin of mice. Also 0.1-1% niclosamide
formulation in water resistant sun cream or Safe SeaTM cream protecting against jelly fish stings were shown to be highly reliable protectants, having lethal effect on schistosome cercariae.
Public education of risk factors, a good alternative to the above-mentioned interventionist strategies, can also reduce human exposure to cercariae. Experience at Higgins Lake, Michigan, where systematic research on Swimmer's Itch was conducted in the 1990s, shows that periodic brisk toweling of the lower extremities is effective in preventing Swimmer's Itch.
Orally administered hydroxyzine
, an antihistamine
, is sometimes prescribed to treat swimmer's itch and similar dermal allergic reactions.
nations, it is often named in reference to the rice paddies where it is contracted, producing names which translate to "rice paddy itch". For example, in Japan
it is called "kubure" or "kobanyo", in Malaysia, "sawah", and in Thailand
, "hoi con".
In the United States
it is known to some as "duckworms" (in coastal New Jersey
) or "clam digger's itch".
In certain parts of Canada
, mainly Ontario
, it is known as "Duck Lice" and "Beaver Lice".
In Australia it is known as "pelican itch".
In Western Minnesota, particularly on Lake Minnewaska, it is known as "lake itch."
Human skin
The human skin is the outer covering of the body. In humans, it is the largest organ of the integumentary system. The skin has multiple layers of ectodermal tissue and guards the underlying muscles, bones, ligaments and internal organs. Human skin is similar to that of most other mammals,...
of humans that have been infected by water-borne schistosomatidae
Schistosomatidae
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...
. Symptoms, which include itchy, raised papules, commonly occur within hours of infection and do not generally last more than a week.
A number of different flatworm
Flatworm
The flatworms, known in scientific literature as Platyhelminthes or Plathelminthes are a phylum of relatively simple bilaterian, unsegmented, soft-bodied invertebrate animals...
parasites in the family Schistosomatidae
Schistosomatidae
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...
are what cause swimmer’s itch. These parasites use both freshwater snail
Freshwater snail
A freshwater snail is one kind of freshwater mollusc, the other kind being freshwater clams and mussels, i.e. freshwater bivalves. Specifically a freshwater snail is a gastropod that lives in a watery non-marine habitat. The majority of freshwater gastropods have a shell, with very few exceptions....
s and vertebrates as hosts in their parasitic life cycles
Parasitic life cycles
Parasite life cycles can take a variety of forms, all involving the exploitation of one or more hosts. Those that must infect more than one host species to complete their life cycles are said to have complex or indirect life cycles, while those that infect a single species have direct life...
. Mostly waterfowl
Waterfowl
Waterfowl are certain wildfowl of the order Anseriformes, especially members of the family Anatidae, which includes ducks, geese, and swans....
are used as the vertebrate host.
During one of their life stages, the larvae of the parasite, cercaria, leave the water snails and swim freely in the freshwater, attempting to encounter water bird
Water bird
The term water bird or waterbird is used to refer to birds that live on or around water. Some definitions apply the term especially to birds in freshwater habitats, though others make no distinction from birds that inhabit marine environments. In addition, some water birds are more terrestrial or...
s. 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 cercaria larvae cannot infect humans, but they cause an inflammatory immune reaction. This reaction causes initially mildly itch
Itch
Itch is a sensation that causes the desire or reflex to scratch. Itch has resisted many attempts to classify it as any one type of sensory experience. Modern science has shown that itch has many similarities to pain, and while both are unpleasant sensory experiences, their behavioral response...
y 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.
The schistosomatidae that give rise to swimmer’s itch should not to be confused with those of the genus Schistosoma
Schistosoma
A genus of trematodes, Schistosoma, commonly known as blood-flukes and bilharzia, includes flatworms which are responsible for a highly significant parasitic infection of humans by causing the disease schistosomiasis, and are considered by the World Health Organization as the second most...
, which infect humans and cause the serious human disease
Disease
A disease is an abnormal condition affecting the body of an organism. It is often construed to be a medical condition associated with specific symptoms and signs. It may be caused by external factors, such as infectious disease, or it may be caused by internal dysfunctions, such as autoimmune...
schistosomiasis
Schistosomiasis
Schistosomiasis is a parasitic disease caused by several species of trematodes , a parasitic worm of the genus Schistosoma. Snails often act as an intermediary agent for the infectious diseases until a new human host is found...
, or with larval stages of thimble jellyfish (Linuche unguiculata
Linuchidae
Linuchidae is a family of jellyfish.-Linuche:Contains the following species:*Linuche aquila*Linuche unguiculata...
), which give rise to seabather's eruption
Seabather's eruption
Seabather's eruption is a pruritic dermatitis caused by a hypersensitivity reaction to the immature nematocysts of larval-stage thimble jellyfish , sea anemones and other larval cnidarians....
.
Seabather's eruption mostly occurs in salt water, on skin covered by clothing or hair, whereas swimmer's itch mostly occurs in freshwater, on uncovered skin.
Since it was first described in Michigan
Michigan
Michigan is a U.S. state located in the Great Lakes Region of the United States of America. The name Michigan is the French form of the Ojibwa word mishigamaa, meaning "large water" or "large lake"....
in 1928, swimmer's itch has been reported from around the world. Some suggest incidence
Incidence (epidemiology)
Incidence is a measure of the risk of developing some new condition within a specified period of time. Although sometimes loosely expressed simply as the number of new cases during some time period, it is better expressed as a proportion or a rate with a denominator.Incidence proportion is the...
may be on the rise, although this may also be attributed to better monitoring.
Cause
The schistosomatidae generaGenus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
most commonly associated with swimmer’s itch in humans are Trichobilharzia and Gigantobilharzia. Trematodes in these groups normally complete their life cycles in water birds. However, swimmer’s itch can also be caused by schistosome parasites of non-avian vertebrates, such as Schistosomatium douthitti, which infects snails and rodent
Rodent
Rodentia is an order of mammals also known as rodents, characterised by two continuously growing incisors in the upper and lower jaws which must be kept short by gnawing....
s. Other taxa
Taxon
|thumb|270px|[[African elephants]] form a widely-accepted taxon, the [[genus]] LoxodontaA taxon is a group of organisms, which a taxonomist adjudges to be a unit. Usually a taxon is given a name and a rank, although neither is a requirement...
reported to cause the reaction include Bilharziella polonica and Schistosoma bovis. In marine
Marine (ocean)
Marine is an umbrella term. As an adjective it is usually applicable to things relating to the sea or ocean, such as marine biology, marine ecology and marine geology...
habitat
Habitat
* Habitat , a place where a species lives and grows*Human habitat, a place where humans live, work or play** Space habitat, a space station intended as a permanent settlement...
s, especially along the coast
Coast
A coastline or seashore is the area where land meets the sea or ocean. A precise line that can be called a coastline cannot be determined due to the dynamic nature of tides. The term "coastal zone" can be used instead, which is a spatial zone where interaction of the sea and land processes occurs...
s, swimmer’s itch can occur as well. In Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
, the so called "pelican itch" is caused by cercariae of the genus Austrobilharzia employing marine gastropods
Gastropoda
The Gastropoda or gastropods, more commonly known as snails and slugs, are a large taxonomic class within the phylum Mollusca. The class Gastropoda includes snails and slugs of all kinds and all sizes from microscopic to quite large...
of the genus
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
Batillaria
Batillaria
Batillaria is a genus of small salt marsh or mudflat snails, marine gastropod mollusks in the family Batillariidae, the horn snails.-Species:Species within the genus Batillaria include:* Batillaria attramentaria Batillaria is a genus of small salt marsh or mudflat snails, marine gastropod mollusks...
(B. australis) as intermediate host
Intermediate host
A secondary host or intermediate host is a host that harbors the parasite only for a short transition period, during which some developmental stage is completed. For trypanosomes, the cause of sleeping sickness, humans are the primary host, while the tsetse fly is the secondary host...
s.
Life cycles of non-human schistosomes
The non-humanHuman
Humans are the only living species in the Homo genus...
schistosomes use two hosts in their life cycles. One is a snail, the other is a bird or mammal.
- Schistosomes are gonochoristic and sexual reproduction takes place in the vertebrate host. In genera that infect birds, adult worms occur in tissues and veins of the host’s gastrointestinal tractGastrointestinal tractThe human gastrointestinal tract refers to the stomach and intestine, and sometimes to all the structures from the mouth to the anus. ....
, where they produce eggs that are shed into water with host fecesFecesFeces, faeces, or fæces is a waste product from an animal's digestive tract expelled through the anus or cloaca during defecation.-Etymology:...
.
Note: One European species, Trichobilharzia regenti
Trichobilharzia regenti
Trichobilharzia regenti is a nasal parasite of birds that causes cercarial dermatitis in humans.-Life cycle:The life cycle for avian schistosomes is similar to that of human schistosomiasis. Adult flukes mate and produce eggs which are usually excreted with the bird's feces. Once in the water, the...
, instead infects the bird host’s nasal
Nose
Anatomically, a nose is a protuberance in vertebrates that houses the nostrils, or nares, which admit and expel air for respiration in conjunction with the mouth. Behind the nose are the olfactory mucosa and the sinuses. Behind the nasal cavity, air next passes through the pharynx, shared with the...
tissues
Biological tissue
Tissue is a cellular organizational level intermediate between cells and a complete organism. A tissue is an ensemble of cells, not necessarily identical, but from the same origin, that together carry out a specific function. These are called tissues because of their identical functioning...
and larvae hatch from the eggs directly in the tissue during drinking/feeding of the infected birds.
- Once a schistosome egg is immersed in waterWaterWater is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...
, a short-lived, non-feeding, free-living stage known as the miracidiumMiracidiumTrematodes are small parasitic flatworms that use vertebrates as their definitive host, and molluscs as their intermediate host. In order to accomplish this, they have several varied lifecyle stages....
emerges. The miracidium uses ciliaCiliumA cilium is an organelle found in eukaryotic cells. Cilia are slender protuberances that project from the much larger cell body....
to follow chemical and physical cues thought to increase its chances of finding the first intermediate host in its life cycle, a water snail.
- After infecting a snail, it develops into a mother sporocystSporocystSporocyst is a common name of a lifecycle stage in two unrelated groups of species:*Apicomplexa parasites: see Apicomplexa lifecycle stages*Trematode flatworms: see Trematode lifecycle stages...
, which in turn undergoes asexual reproductionAsexual reproductionAsexual reproduction is a mode of reproduction by which offspring arise from a single parent, and inherit the genes of that parent only, it is reproduction which does not involve meiosis, ploidy reduction, or fertilization. A more stringent definition is agamogenesis which is reproduction without...
, yielding large numbers of daughter sporocysts, which asexually produce another short-lived, free-living stage, the cercaria.
- The cercariae (often forked in generaGenusIn biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
), who cause swimmer’s itch, use a tail-like appendage to swim to the surface of the water, as well as other physical and chemical cues, in order to locate the next and final (definitive) host in the life cycle, a bird.
- After infecting a bird, the parasite develops into a schistosomulum and migrates through the host’s circulatory system (or nervous system in case of T. regenti) to the final location within the host body where it matures and, if it encounters a mate, sheds eggs to begin the cycle anew.
Risk factors
Humans usually become infected with avian schistosomes after swimming in lakes or other bodies of slow-moving fresh water. 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 positively correlated with increased risk of infection in Europe and North America, and shallow inshore waters—snail habitat—undoubtedly harbour higher densities of cercariae than open waters offshore. Onshore winds are thought to cause cercariae to accumulate along shorelines. 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 as well as instances where risk increases in endemic swimmer's itch "hotspots". 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. Stimuli for cercarial penetrationPenetration
Penetration may refer to:* Penetration depth of light or any electromagnetic radiation.* Penetrating trauma* Sexual penetration, a term which may mean**sexual intercourse in general or,...
into host skin
Skin
-Dermis:The dermis is the layer of skin beneath the epidermis that consists of connective tissue and cushions the body from stress and strain. The dermis is tightly connected to the epidermis by a basement membrane. It also harbors many Mechanoreceptors that provide the sense of touch and heat...
include unsaturated
Saturated fat
Saturated fat is fat that consists of triglycerides containing only saturated fatty acids. Saturated fatty acids have no double bonds between the individual carbon atoms of the fatty acid chain. That is, the chain of carbon atoms is fully "saturated" with hydrogen atoms...
fatty acids, such as linoleic
Linoleic acid
Linoleic acid is an unsaturated n-6 fatty acid. It is a colorless liquid at room temperature. In physiological literature, it has a lipid number of 18:2...
and linolenic acids. These substances occur naturally in human skin and are found in sun lotions and creams based on plant oils
Plant oils
Plant oils or vegetable oils are oils derived from plant sources, as opposed to animal fats or petroleum. There are three primary types of plant oil, differing both the means of extracting the relevant parts of the plant, and in the nature of the resulting oil:# Vegetable fats and oils were...
.
Control measures and treatment
Various strategies, targeting either the mollusc or avianBird
Birds are feathered, winged, bipedal, endothermic , egg-laying, vertebrate animals. Around 10,000 living species and 188 families makes them the most speciose class of tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Extant birds range in size from...
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
Michigan
Michigan is a U.S. state located in the Great Lakes Region of the United States of America. The name Michigan is the French form of the Ojibwa word mishigamaa, meaning "large water" or "large lake"....
, for decades authorities used copper sulfate as a molluscicide to reduce snail host populations and thereby the incidence of swimmer's itch. The results with this agent have been inconclusive, possibly because:
- snails become tolerant
- local water chemistry reduces the molluscicide's efficacy
- local currents diffuse it
- adjacent snail populations repopulate a treated area.
More importantly, perhaps, copper sulfate is toxic to more than just molluscs, and the effects of its use on aquatic ecosystem
Aquatic ecosystem
An aquatic ecosystem is an ecosystem in a body of water. Communities of organisms that are dependent on each other and on their environment live in aquatic ecosystems. The two main types of aquatic ecosystems are marine ecosystems and freshwater ecosystems....
s are not well understood.
Lake Annecy
Lake Annecy is a perialpine lake in Haute-Savoie in France .It is the second largest lake in France, after the Lac du Bourget, if the French part of Lake Geneva is excluded. It is known as "Europe's cleanest lake" because of strict environmental regulations introduced in the 1960s...
in France, with promising results.
Some work in Michigan suggests that administering praziquantel
Praziquantel
Praziquantel is an anthelmintic effective against flatworms. Praziquantel is not licensed for use in humans in the UK; it is, however, available as a veterinary anthelmintic, and is available for use in humans on a named-patient basis....
to hatchling waterfowl can reduce local swimmer's itch rates in humans. Work on schistosomiasis showed that water-resistant topical applications of the common insect repellent DEET
DEET
N,N-Diethyl-meta-toluamide, abbreviated DEET, is a slightly yellow oil. It is the most common active ingredient in insect repellents...
prevented schistosomes from penetrating the skin of mice. Also 0.1-1% niclosamide
Niclosamide
Niclosamide is a teniacide in the anthelmintic family especially effective against cestodes that infect humans...
formulation in water resistant sun cream or Safe SeaTM cream protecting against jelly fish stings were shown to be highly reliable protectants, having lethal effect on schistosome cercariae.
Public education of risk factors, a good alternative to the above-mentioned interventionist strategies, can also reduce human exposure to cercariae. Experience at Higgins Lake, Michigan, where systematic research on Swimmer's Itch was conducted in the 1990s, shows that periodic brisk toweling of the lower extremities is effective in preventing Swimmer's Itch.
Orally administered hydroxyzine
Hydroxyzine
Hydroxyzine is a first-generation antihistamine of the diphenylmethane and piperazine classes. It was first synthesized by Union Chimique Belge in 1956 and was marketed by Pfizer in the United States later the same year, and is still in widespread use today....
, an antihistamine
Antihistamine
An H1 antagonist is a histamine antagonist of the H1 receptor that serves to reduce or eliminate effects mediated by histamine, an endogenous chemical mediator released during allergic reactions...
, is sometimes prescribed to treat swimmer's itch and similar dermal allergic reactions.
Other names
Swimmer's itch has various other names. In easternEastern world
__FORCETOC__The term Eastern world refers very broadly to the various cultures or social structures and philosophical systems of Eastern Asia or geographically the Eastern Culture...
nations, it is often named in reference to the rice paddies where it is contracted, producing names which translate to "rice paddy itch". For example, in Japan
Japan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...
it is called "kubure" or "kobanyo", in Malaysia, "sawah", and in Thailand
Thailand
Thailand , officially the Kingdom of Thailand , formerly known as Siam , is a country located at the centre of the Indochina peninsula and Southeast Asia. It is bordered to the north by Burma and Laos, to the east by Laos and Cambodia, to the south by the Gulf of Thailand and Malaysia, and to the...
, "hoi con".
In the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
it is known to some as "duckworms" (in coastal New Jersey
New Jersey
New Jersey is a state in the Northeastern and Middle Atlantic regions of the United States. , its population was 8,791,894. It is bordered on the north and east by the state of New York, on the southeast and south by the Atlantic Ocean, on the west by Pennsylvania and on the southwest by Delaware...
) or "clam digger's itch".
In certain parts of Canada
Canada
Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...
, mainly Ontario
Ontario
Ontario is a province of Canada, located in east-central Canada. It is Canada's most populous province and second largest in total area. It is home to the nation's most populous city, Toronto, and the nation's capital, Ottawa....
, it is known as "Duck Lice" and "Beaver Lice".
In Australia it is known as "pelican itch".
In Western Minnesota, particularly on Lake Minnewaska, it is known as "lake itch."
External links
- Information portal for NSF funded research on avian schistosome diversity
- CDC
- Links to pictures of swimmer's itch (Hardin MD/Univ of Iowa)
- Schistosome Group Prague, a member of the European Cercarial Dermatitis Network (ECDEN)
- Swimmer's Itch
- Wisconsin Department of Natural Resources, With warm weather, Swimmers Itch makes annual appearance