Angiostrongylus cantonensis

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Geographic Range

Angiostrongylus cantonensis was discovered in China. Since then it has been found in Australia, the southwestern Pacific including Hawaii, South and southeast Asia, Madagascar, Japan, Taiwan, Egypt, Ivory Coast of Africa, India, Samoa, Fiji, Cuba, the Caribbean, Puerto Rico, and Southeastern USA. Angiostrongylus cantonensis probably originated in eastern Asia, but because of its large dispersal as a result of human activity, there is no way to be sure. (Prociv, et al., 2000)

Habitat

Angiostrongylus cantonensis is not specific for either definitive or intermediate hosts. The requirement is that the intermediate host must be an invertebrate while the definitive is a terrestrial mammal. Paratenic hosts, where the parasites don't develop to the next stage, can be either invertebrate or vertebrate. The definitive hosts for Angiostrongylus cantonensis are usually rodents from the genus Rattus, with some main ones being Rattus norvegicus and Rattus rattus. Angiostrongylus cantonensis can survive in humans and monkeys as well. Two cases of monkeys dying from complications of eosinophilic meningoencephalitis in zoos were attributed to their contact with snails serving as intermediate hosts.

The main intermediate hosts include slugs and snails. Achatina fulica, or the African giant land snail, can contain thousands of third-stage larvae. Although it's not the major intermediate host, this particular snail is important because it may be a primary reason why Angiostrongylus cantonensis has spread. This snail is considered a delicacy in several regions and typically eaten raw. With the amount of larvae in one Achatina fulica, A. cantonensis can easily be dispersed to new areas.

Paratenic hosts include anything that eats the mollusks. Some main ones include terrestrial planarians and crabs, fresh-water shrimp and frogs, toads, marine fish, and sea snakes. However, recent evidence indicates it may be intolerant of salinity, so marine species may be questionable as hosts. (Anderson, et al., 1990; Janovy and Roberts, 2000; Prociv, et al., 2000)

  • Aquatic Biomes
  • lakes and ponds
  • rivers and streams
  • temporary pools
  • coastal

Physical Description

As a nematode, A. cantonensis is cylindrical, and has a cuticle with three main outer layers made of collagen and other compounds. The outer layers are non-cellular and are secreted by the epidermis. The cuticle layer protects nematodes so they can invade digestive tracts of animals. The worms molt four times, the first two before hatching, and then before their adult stage.

As a member of the Secernentea, A. cantonensis has a specialized tubular excretory system system with three canals. The canals are arranged to from an "H".

Angiostrongylus cantonensis is a flimsy and slender worm with a simple mouth and no lips or buccal cavity. The bursa, a structure used to clasp females when copulating, is small and dorsal lobe is not present. The males have long and slender spicules which are almost equal in length and form. The gubernaculum, used to guide spicules when mating, is present but is not immediately noticeable.

There are obvious differences between male and female A. cantonensis. The males are 15.9 to 19 mm in length, while the females can grow 21 to 25 mm in length. Females are easily distinguished from males by the noticeable barber-pole appearance in their bodies. This is actually the interweaving of the intestine and uterine tubules. Females have a vulva, which is located 0.2 mm in front of the anus. (Barnes, 1987; Brusca and Brusca, 2003; Janovy and Roberts, 2000)

  • Sexual Dimorphism
  • female larger
  • sexes shaped differently
  • Range length
    15.9 to 25 mm
    0.63 to 0.98 in

Development

The worms molt before becoming adults, two molts occuring before they hatch from the eggs. Most all adult structures except certain reproductive parts are found in the young just after hatching. As adults, the worms will not molt, but can grow in size.

Angiostrongylus cantonensis has a complex life cycle that involves intermediate, paratenic, and definitive hosts as well as several larval stages before becoming an adult. Adults are found in the right ventricles of hearts and the pulmonary arteries. The females release their eggs in these arteries. They are carried to the lungs, and within the capillaries here they embryonate. The thin-shelled egg breaks open and the first larval stage hatches. The larvae break through the alveoli and move up the trachea, where they wait to be swallowed and then expelled in the feces.

The intermediate host starts eating the fecal matter, also ingesting the parasitic larvae. There is some development in the intermediate host, but not to sexual maturity. The larvae develop into the 3rd stage in the molluscan muscle tissue. A parantenic host such as a frog or fish may eat the intermediate host, where the larvae survive in their muscle but no development occurs. The larvae enters the definitive host either by ingestion of the intermediate host, ingestion of paratenic host, or ingestion of material that contains the slimy path that a slug or snail leaves behind. Larvae may escape the intermediate host and be present on that trail.

Once inside the intestine of the definitive host, the larvae go through obligatory migration through the central nervous system via bloodstream to the brain and spinal cord. They leave the capillaries and start wandering randomly through the tissues. At the same time, they reach the fifth stage larvae. When the larvae reach the surface of the brain or spinal cord, they penetrate the veins to reenter the circulatory system. The larvae end up at the pulmonary arteries where they mature into adults in about six weeks. However, some larvae wander to other places in the body and mature there. Common places are in the central nervous system, the meninges, and the eyes. (Barnes, 1987; Brusca and Brusca, 2003; Prociv, et al., 2000)

Reproduction

Females may produce a pheromone to attract males. The male coils around a female with his curved area over the female genital pore. The gubernaculum, made of cuticle tissue, guides spicules which extend through the cloaca and anus. Males use spicules to hold the females during copulation. Nematode sperm are amoeboid-like and lack flagella. (Barnes, 1987; Brusca and Brusca, 2003)

  • Average age at sexual or reproductive maturity (female)
    6 weeks
  • Average age at sexual or reproductive maturity (male)
    6 weeks
  • Parental Investment
  • pre-fertilization

Lifespan/Longevity

Lifespan and growth to the next parasitic larval stage depends on what host is infected. In paratenic hosts, the larval may not develop to the next stage. (Janovy and Roberts, 2000)

Behavior

Nematodes such as Angiostrongylus cationensis are able to swim intermittently. The worms are usually only able to move effectively when the pseudocoel is filled with fluid and hypertonic to the surrounding media. (Barnes, 1987; Brusca and Brusca, 2003)

Communication and Perception

Nematodes within the Secernentea have phasmids, which are unicellular glands. Phasmids likely function as chemoreceptors. Females may produce pheromones to attract males.

Nematodes in general have papillae, setae and amphids, which are the main sense organs. Setae detect motion (mechanoreceptors), while amphids detect chemicals (chemoreceptors). (Barnes, 1987; Brusca and Brusca, 2003)

Food Habits

Angiostrongylus cantonensis has a simple mouth and no buccal cavity. Pharyngeal glands and intestinal epithelium produce digestive enzymes, and feed on the body fluids of its hosts. Extracellular digestion begins within the intestine, and the digestive cycle is completed intracellularly.

As an endoparasite, Angiostrongylus cantonensis is usually found in the pulmonary arteries and in the right ventricle of the heart. The larvae are found circulating in the blood, spinal fluid, cerebrospinal fluid, or in the blood vessels of the brain and the meninges. Angiostrongylus cantonensis is mainly found in rodents, especially rats, which are the definitive hosts. The worm has also been able to survive and sexually mature in other mammals including humans and monkeys. (Anderson, et al., 1990; Barnes, 1987; Brusca and Brusca, 2003; Prociv, et al., 2000)

  • Animal Foods
  • body fluids

Predation

These parasites are usually not preyed on directly, but are ingested from host to host. Larval mortality is high as most of the parasites do not reach appropriate hosts. (Barnes, 1987; Brusca and Brusca, 2003)

Ecosystem Roles

Angiostrongylus cantonensis is not specific for either definitive or intermediate hosts. The requirement is that the intermediate host must be an invertebrate while the definitive is a terrestrial mammal. Paratenic hosts, where the parasites don't develop to the next stage, can be either invertebrate or vertebrate. The definitive hosts for Angiostrongylus cantonensis are usually rodents from the genus g. Rattus, with some main ones being Rattus norvegicus and Rattus rattus. Angiostrongylus cantonensis can survive in humans and monkeys as well.

The main intermediate hosts include slugs and snails. Paratenic hosts include anything that eats the mollusks. Some main ones include terrestrial planarians and crabs, fresh-water shrimp and frogs, toads, marine fish, and sea snakes. However, recent evidence indicates it may be intolerant of salinity, so marine species may be questionable as hosts. (Barnes, 1987; Brusca and Brusca, 2003; Janovy and Roberts, 2000)

Species Used as Host

Economic Importance for Humans: Negative

Angiostrongylus cantonensis is the primary cause of human eosinophilic meningoencephalitis in many parts of the Indo-Pacific region. The hosts become infected when the third stage larva is ingested. Humans get severe headaches, stiff necks, clouded consciousness, meningeal irritations, and extensive tissue damage from wandering worms in the brain. Eosinophil counts are increased in peripheral blood and spinal fluid, and lymphocyte counts are increased in the cerebrospinal fluid. The final results of these symptoms lead to neural disorders, paralysis of 5th cranial nerve, comas, and even death.

Dead worms that are present in the blood stream can cause inflammatory responses. Immune responses are evoked by dead worms and cause the destruction of brain and spinal cord cells. However, symptoms are so vague that they can be mistaken for a variety of other parasitic diseases. With this delay in correct diagnosis, dead worms can be worse than live worms. (Ishih, et al., 1998; Janovy and Roberts, 2000; Jitpimolmard, et al., 2000)

Other Comments

Angiostrongylus cantonensis was initially found in the lungs of rodents in China. It was given little notice since it was not yet found in humans. In 1944, the first case of A. cantonensis in a human was found. A young adult worm was in the cerebrospinal fluid of a young boy in Taiwan who had come in for treatment for meningitis. Since then, many cases have been linked to eosinophilic meningoencephalitis. Even though its symptoms are similar to other diseases, if it shows up in an area that didn't have it before, research will be prompted to start to see if the worm has reached that area. If symptoms show up in an area that is known to have the worm, then the worm will be the first suspect. (Aguiar, et al., 1981; Prociv, et al., 2000)

Contributors

Renee Sherman Mulcrone (editor).

Sofia Syed (author), University of Michigan-Ann Arbor, Barry OConnor (editor), University of Michigan-Ann Arbor.

Glossary

Australian

Living in Australia, New Zealand, Tasmania, New Guinea and associated islands.

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Ethiopian

living in sub-Saharan Africa (south of 30 degrees north) and Madagascar.

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Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

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Neotropical

living in the southern part of the New World. In other words, Central and South America.

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Palearctic

living in the northern part of the Old World. In otherwords, Europe and Asia and northern Africa.

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agricultural

living in landscapes dominated by human agriculture.

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

carnivore

an animal that mainly eats meat

causes disease in humans

an animal which directly causes disease in humans. For example, diseases caused by infection of filarial nematodes (elephantiasis and river blindness).

chemical

uses smells or other chemicals to communicate

coastal

the nearshore aquatic habitats near a coast, or shoreline.

cosmopolitan

having a worldwide distribution. Found on all continents (except maybe Antarctica) and in all biogeographic provinces; or in all the major oceans (Atlantic, Indian, and Pacific.

ectothermic

animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature

estuarine

an area where a freshwater river meets the ocean and tidal influences result in fluctuations in salinity.

fertilization

union of egg and spermatozoan

forest

forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.

freshwater

mainly lives in water that is not salty.

internal fertilization

fertilization takes place within the female's body

intertidal or littoral

the area of shoreline influenced mainly by the tides, between the highest and lowest reaches of the tide. An aquatic habitat.

marsh

marshes are wetland areas often dominated by grasses and reeds.

motile

having the capacity to move from one place to another.

natatorial

specialized for swimming

native range

the area in which the animal is naturally found, the region in which it is endemic.

oceanic islands

islands that are not part of continental shelf areas, they are not, and have never been, connected to a continental land mass, most typically these are volcanic islands.

oriental

found in the oriental region of the world. In other words, India and southeast Asia.

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oviparous

reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.

parasite

an organism that obtains nutrients from other organisms in a harmful way that doesn't cause immediate death

pheromones

chemicals released into air or water that are detected by and responded to by other animals of the same species

rainforest

rainforests, both temperate and tropical, are dominated by trees often forming a closed canopy with little light reaching the ground. Epiphytes and climbing plants are also abundant. Precipitation is typically not limiting, but may be somewhat seasonal.

riparian

Referring to something living or located adjacent to a waterbody (usually, but not always, a river or stream).

saltwater or marine

mainly lives in oceans, seas, or other bodies of salt water.

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

suburban

living in residential areas on the outskirts of large cities or towns.

swamp

a wetland area that may be permanently or intermittently covered in water, often dominated by woody vegetation.

tactile

uses touch to communicate

temperate

that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).

terrestrial

Living on the ground.

tropical

the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.

urban

living in cities and large towns, landscapes dominated by human structures and activity.

References

Aguiar, P., P. Morera, J. Pascual. 1981. First record of Angiostrongylus cantonensis in Cuba. American Journal of Tropical Medicine and Hygiene, 30 (5): 963-965.

Anderson, D., L. Fitzgerald, C. Gardiner, A. Gutter, R. Harris. 1990. Eosinophilic meningoencephalitis due to Angiostrongylus cantonensis as the cause of death in captive non-human primates. American Journal of Tropical Medicine and Hygiene, 42 (1): 70-74.

Barnes, R. 1987. Invertebrate Zoology. Orlando, Florida: Dryden Press.

Brusca, R., G. Brusca. 2003. Invertebrates. Sunderland, Massachusetts: Sinauer Associates, Inc..

Center for Disease Control and Prevention, 2004. "Angiostrongylus cantonensis Infection" (On-line). CDC, Division of Parastitic Diseases, Parasitic Disease Information. Accessed August 23, 2004 at http://www.cdc.gov/ncidod/dpd/parasites/angiostrongylus/factsht_angiostrongylus.htm.

Cross, J. 2000. "Central Nervous System Parasites, Phasmidea, Order: Strongylida. Angiostrongylus cantonensis" (On-line). Atlas of Medical Parasitology. Accessed August 23, 2004 at http://www.cdfound.to.it/HTML/ang.htm.

Ishih, A., T. Lakwo, M. Sano, M. Terada. 1998. Effects of Albendazole against larval and adult Angiostrongylus cantonensis in rats. Parasitology International, 47 (4): 281-288.

Janovy, J., L. Roberts. 2000. Foundations of Parasitology 6th Edition. Boston: McGraw-Hill.

Jitpimolmard, S., J. Kanpittaya, E. Mairiang, S. Tiamkao. 2000. MR findings of eosinophilic meningoencephalitis attributed to Angiostrongylus cantonensis. American Journal of Neuroradiology, 21 (6): 1090-1094.

Prociv, P., D. Spratt, M. Carlisle. 2000. Neuro-angiostrongyliasis: unresolved issues. International Journal for Parasitology, 30 (12-13): 1295-1303.