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Rat Lungworm

Angiostrongylus cantonensis

Reproduction

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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.

Average age at sexual or reproductive maturity (female): 6 weeks.

Average age at sexual or reproductive maturity (male): 6 weeks.

Key Reproductive Features: gonochoric/gonochoristic/dioecious (sexes separate); sexual ; fertilization (Internal ); oviparous

Parental Investment: pre-fertilization

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Syed, S. 2001. "Angiostrongylus cantonensis" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Angiostrongylus_cantonensis.html
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Sofia Syed, University of Michigan-Ann Arbor
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Barry OConnor, University of Michigan-Ann Arbor
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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.

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Syed, S. 2001. "Angiostrongylus cantonensis" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Angiostrongylus_cantonensis.html
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Sofia Syed, University of Michigan-Ann Arbor
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Behavior

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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).

Communication Channels: tactile ; chemical

Other Communication Modes: pheromones

Perception Channels: tactile ; chemical

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Syed, S. 2001. "Angiostrongylus cantonensis" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Angiostrongylus_cantonensis.html
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Sofia Syed, University of Michigan-Ann Arbor
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Barry OConnor, University of Michigan-Ann Arbor
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Life Cycle

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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.

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Syed, S. 2001. "Angiostrongylus cantonensis" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Angiostrongylus_cantonensis.html
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Sofia Syed, University of Michigan-Ann Arbor
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Barry OConnor, University of Michigan-Ann Arbor
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Renee Sherman Mulcrone
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Benefits

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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.

Negative Impacts: injures humans (causes disease in humans )

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Syed, S. 2001. "Angiostrongylus cantonensis" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Angiostrongylus_cantonensis.html
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Sofia Syed, University of Michigan-Ann Arbor
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Barry OConnor, University of Michigan-Ann Arbor
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Renee Sherman Mulcrone
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Associations

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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.

Ecosystem Impact: parasite

Species Used as Host:

  • Rattus norvegicus
  • Achatina fulica
  • Pila spp.
  • Viviparus javanica
  • Veronicella alte
  • Veronicella siamensis
  • some snails, Gastropoda
  • some mammals, Mammalia
  • some freshwater prawns, Decapoda
  • some land crabs, Pleocyemata
  • some frogs, Anura
  • Rattus rattus
  • Homo sapiens
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Syed, S. 2001. "Angiostrongylus cantonensis" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Angiostrongylus_cantonensis.html
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Sofia Syed, University of Michigan-Ann Arbor
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Barry OConnor, University of Michigan-Ann Arbor
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Renee Sherman Mulcrone
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Trophic Strategy

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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.

Animal Foods: body fluids

Primary Diet: carnivore (Eats body fluids)

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Syed, S. 2001. "Angiostrongylus cantonensis" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Angiostrongylus_cantonensis.html
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Sofia Syed, University of Michigan-Ann Arbor
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Barry OConnor, University of Michigan-Ann Arbor
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Distribution

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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.

Biogeographic Regions: nearctic ; palearctic ; oriental ; ethiopian ; neotropical ; australian ; oceanic islands (Native )

Other Geographic Terms: cosmopolitan

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Syed, S. 2001. "Angiostrongylus cantonensis" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Angiostrongylus_cantonensis.html
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Sofia Syed, University of Michigan-Ann Arbor
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Barry OConnor, University of Michigan-Ann Arbor
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Habitat

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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.

Habitat Regions: temperate ; tropical ; terrestrial ; saltwater or marine ; freshwater

Terrestrial Biomes: forest ; rainforest

Aquatic Biomes: lakes and ponds; rivers and streams; temporary pools; coastal

Wetlands: marsh ; swamp

Other Habitat Features: urban ; suburban ; agricultural ; riparian ; estuarine ; intertidal or littoral

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Syed, S. 2001. "Angiostrongylus cantonensis" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Angiostrongylus_cantonensis.html
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Sofia Syed, University of Michigan-Ann Arbor
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Barry OConnor, University of Michigan-Ann Arbor
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Renee Sherman Mulcrone
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Life Expectancy

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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.

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Syed, S. 2001. "Angiostrongylus cantonensis" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Angiostrongylus_cantonensis.html
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Sofia Syed, University of Michigan-Ann Arbor
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Barry OConnor, University of Michigan-Ann Arbor
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Morphology

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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.

Range length: 15.9 to 25 mm.

Other Physical Features: ectothermic ; homoiothermic; bilateral symmetry

Sexual Dimorphism: female larger; sexes shaped differently

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Syed, S. 2001. "Angiostrongylus cantonensis" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Angiostrongylus_cantonensis.html
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Sofia Syed, University of Michigan-Ann Arbor
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Barry OConnor, University of Michigan-Ann Arbor
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Associations

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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.

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Syed, S. 2001. "Angiostrongylus cantonensis" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Angiostrongylus_cantonensis.html
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Sofia Syed, University of Michigan-Ann Arbor
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Brief Summary

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The nematode (roundworm) Angiostrongylus cantonensis, the Rat Lungworm, is the most common cause of human eosinophilic meningitis, a meningoencephalitis characterized by eosinophils in the cerebrospinal fluid. Humans are accidental hosts for these parasites. Most cases of eosinophilic meningitis have been reported from Southeast Asia and the Pacific Basin, although the infection is spreading to many other areas of the world, including Africa and the Caribbean.

Adult A. cantonensis live in the pulmonary arteries of rats. The females lay eggs that hatch, yielding first-stage larvae, in the terminal branches of the pulmonary arteries. The first-stage larvae migrate to the pharynx, are swallowed, and pass in the feces. They penetrate, or are ingested by, an intermediate host (snail or slug). After two molts, third-stage larvae are produced, which are infective to mammalian hosts. When the mollusk is ingested by the definitive host, the third-stage larvae migrate to the brain where they develop into young adults. The young adults return to the venous system and then to the pulmonary arteries, where they become sexually mature. A variety of animals can act as paratenic (transport) hosts: after ingesting the infected snails, they carry the third-stage larvae, which can resume their development when the paratenic host is ingested by a definitive host. Humans can acquire the infection by eating raw or undercooked snails or slugs infected with the parasite; they may also acquire the infection by eating raw produce that contains a small snail or slug, or part of one. There is some question regarding whether or not larvae can exit the infected mollusks in slime (which might be infective to humans if ingested, for example, on produce). The disease can also be acquired by ingestion of contaminated or infected paratenic animals (crabs, freshwater shrimps). In humans, juvenile worms migrate to the brain, or rarely to the lungs, where they ultimately die.

(Centers for Disease Control Parasites and Health website)

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Angiostrongylus cantonensis

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Angiostrongylus cantonensis is a parasitic nematode (roundworm) that causes angiostrongyliasis, the most common cause of eosinophilic meningitis in Southeast Asia and the Pacific Basin.[2] The nematode commonly resides in the pulmonary arteries of rats, giving it the common name rat lungworm. Snails are the primary intermediate hosts, where larvae develop until they are infectious.

Humans are incidental hosts of this roundworm, and may become infected through ingestion of larvae in raw or undercooked snails or other vectors, or from contaminated water and vegetables.[3] The larvae are then transported via the blood to the central nervous system, where they are the most common cause of eosinophilic meningitis, a serious condition that can lead to death or permanent brain and nerve damage.[4] Angiostrongyliasis is an infection of increasing public health importance, as globalization contributes to the geographic spread of the disease.[5]

History

First described by the renowned Chinese parasitologist Hsin-Tao Chen (1904–1977) in 1935, after examining Cantonese rat specimens,[1] the nematode Angiostrongylus cantonensis was identified in the cerebrospinal fluid of a patient with eosinophilic meningitis by Nomura and Lim in Taiwan in 1944. They noted that raw food eaten by the patient may have been contaminated by rats. In 1955, Mackerass and Sanders identified the lifecycle of the worm in rats, defining snails and slugs as the intermediate hosts and noting the path of transmission through the blood, brain, and lungs in rats.[citation needed]

Infectious agent

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Male A. cantonensis
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Tail of adult male of A. cantonensis, showing copulatory bursa and long spicules (arrows), scale bar is 85 µm

A. cantonensis is a helminth of the phylum Nematoda, order Strongylida, and superfamily Metastrongyloidea. Nematodes are roundworms characterized by a tough outer cuticle, unsegmented bodies, and a fully developed gastrointestinal tract. The order Strongylida includes hookworms and lungworms. Metastrongyloidea are characterized as 2-cm-long,[6] slender, threadlike worms that reside in the lungs of the definitive host.[7] Angiostrongylus costaricensis is a closely related worm that causes intestinal angiostrongyliasis in Central and South America.

Epidemiology and pathogenesis

Following World War II, A. cantonensis spread throughout Southeast Asia and Western Pacific Islands, including Australia, Melanesia, Micronesia, and Polynesia. Cases were soon reported in New Caledonia, the Philippines, Rarotonga, Saipan, Sumatra, Taiwan, and Tahiti. In the 1960s, even more cases were reported from the region from locations such as Cambodia, Guam, Hawaii, Java, Thailand, Sarawak, Vietnam, and the New Hebrides (Vanuatu).[8]

In 1961, an epidemiological study of eosinophilic meningitis in humans was conducted by Rosen, Laigret, and Bories, who hypothesized that the parasite causing these infections was carried by fish. However, Alicata noted that raw fish was consumed by large numbers of people in Hawaii without apparent consequences, and patients presenting with meningitis symptoms had a history of eating raw snails or prawns in the weeks before presenting with symptoms. This observation, along with epidemiology and autopsy of infected brains, confirmed A. cantonensis infection in humans as the cause of the majority of eosinophilic meningitis cases in Southeast Asia and the Pacific Islands.[9]

Since then, cases of A. cantonensis infestations have appeared in American Samoa, Australia, Hong Kong, Bombay, Fiji, Hawaii, Honshu, India, Kyushu, New Britain, Okinawa, Ryukyu Islands, Western Samoa, and most recently mainland China. Other sporadic occurrences of the parasite in its rat hosts have been reported in Cuba, Egypt, Louisiana, Madagascar, Nigeria, New Orleans, and Puerto Rico.[8]

In 2013, A. cantonensis was confirmed present in Florida, USA, where its range and prevalence are expanding.[10] In 2018, a case was found in a New Yorker, who had visited Hawaii.[11]

In recent years, the parasite has been shown to be proliferating at an alarming rate due to modern food consumption trends and global transportation of food products. Scientists are calling for a more thorough study of the epidemiology of A. cantonensis, stricter food safety policies, and the increase of knowledge on how to properly consume products commonly infested by the parasite such as snails and slugs that act as intermediate hosts or those that act as paratenic hosts such as fish, frogs, or freshwater prawns.[12][13][14] Ingestion of food items that can be contaminated by the mucus excretions of intermediate or paratenic hosts, such as snails and slugs or by the feces of rats that act as definitive hosts, can lead to infection of A. cantonensis.[15] The most common route of infection of A. cantonesis in humans is by ingestion of either intermediate or paratenic hosts of the larvae.[16] Unwashed fruits and vegetables, especially romaine lettuce, can be contaminated with snail and slug mucus or can result in accidental ingestion of these intermediate and paratenic hosts. These items need to be properly washed and handled to prevent accidental ingestion of A. cantonensis larvae or the larvae-containing hosts.[17] The best mechanism of prevention of A. cantonesis outbreak is to institute an aggressive control of snail and slug population, proper cooking of intermediate and paratenic hosts such as fish, freshwater prawn, frogs, mollusks, and snails along with proper food handling techniques.[18] The common prevention techniques for diarrheal illness is very effective in preventing A. cantonensis infection.[19] Not much is known about why it targets the brain in humans, but a chemical induced chemotaxis has been implicated recently. Acetylcholine has been previously reported to enhance motility of this worm via nicotinic acetylcholine receptors.[20] Experimental assays in animal model are needed to validate a chemical induced chemotaxis by use of anticholinergic drugs to prevent cerebral infection following infections by A. cantonesis.[21]

Hosts

Intermediate hosts of larvae of for A. cantonensis include:

Definitive host of A. cantonensis include wild rodents, especially the brown rat (Rattus norvegicus) and the black rat (Rattus rattus).[22]

Paratenic hosts of A. cantonensis include: predatory land flatworm Platydemus manokwari and amphibians Bufo asiaticus, Rana catesbeiana, Rhacophorus leucomystax and Rana limnocharis.[26]

In 2004, a captive yellow-tailed black cockatoo (Calyptorhynchus funereus) and two free-living tawny frogmouths (Podargus strigoides) suffering neurological symptoms were shown to have the parasite. They were the first avian hosts discovered for the organism.[32]

Pathogenesis of human angiostrongylosis

The presence of parasitic worms burrowed in the neural tissue of the human central nervous system will cause obvious complications. All of the following will result in damage to the CNS:[citation needed]

  1. Direct mechanical damage to neural tissue from the worms' motion
  2. Toxic byproducts such as nitrogenous waste
  3. Antigens released by dead and living parasites

Eosinophilic meningitis

Although the clinical disease caused by Angiostrongylus invasion into the central nervous system is commonly referred to as "eosinophilic meningitis", the actual pathophysiology is of a meningoencephalitis with invasion not just of the meninges, or superficial lining of the brain, but also deeper brain tissue. Initial invasion through the lining of the brain, the meninges, may cause a typical inflammation of the meninges and a classic meningitis picture of headache, stiff neck and often fever. The parasites subsequently invade deeper into the brain tissue, causing specific localizing neurologic symptoms depending on where in the brain parenchyma they migrate. Neurologic findings and symptoms wax and wane as initial damage is done by the physical in-migration of the worms and secondary damage is done by the inflammatory response to the presence of dead and dying worms. This inflammation can lead in the short term to paralysis, bladder dysfunction, visual disturbance and coma and in the long term to permanent nerve damage, mental retardation, nerve damage, permanent brain damage or death.[33]

Eosinophilic meningitis is commonly defined by the increased number of eosinophils in the cerebrospinal fluid (CSF). In most cases, eosinophil levels rise to 10 or more eosinophils per μl in the cerebrospinal fluid, accounting for at least 10% of the total CSF leukocyte (white blood cell) count.[34] The chemical analysis of the CSF typically resembles the findings in "aseptic meningitis" with slightly elevated protein levels, normal glucose levels and negative bacterial cultures. Presence of a significantly decreased glucose on CSF analysis is an indicator of severe meningoencephalitis and may indicate a poor medical outcome. Initial CSF analysis early in the disease process may occasionally show no increase of eosinophils only to have classical increases in eosinophils in subsequent spinal fluid analysis. Caution should be advised in using eosinophilic meningitis as the only criterion for diagnosing angiostrongylus infestation in someone with classic symptoms as the disease evolves with the migration of the worms into the central nervous system.[citation needed]

Eosinophils are specialized white blood cells of the granulocytic cell line which contain granules in their cytoplasm. These granules contain proteins that are toxic to parasites. When these granules degranulate, or break down, chemicals are released that combat parasites such as A. cantonensis. Eosinophils, which are located throughout the body, are guided to sites of inflammation by chemokines when the body is infested with parasites such as A. cantonensis. Once at the site of inflammation, Type 2 cytokines are released from helper T cells, which communicate with the eosinophils, signaling them to activate. Once activated, eosinophils can begin the process of degranulation, releasing their toxic proteins in the fight against the foreign parasite.[citation needed]

Clinical signs and symptoms

According to a group case study, the most common symptoms in mild eosinophilic meningitis tend to be headache (with 100% of people in the study suffering from this symptom), photophobia or visual disturbance (92%), neck stiffness (83%), fatigue (83%), hyperesthesias (75%), vomiting (67%) and paresthesias (50%).[35][19] Incubation period is often 3 weeks, but can be 3–36 days[8] and even 80 days.[36]

Possible clinical signs and symptoms of mild and severe eosinophilic meningitis are:

Treatment

The severity and clinical course of Angiostrongylus disease depends significantly on the ingested load of third-stage larvae,[38] creating great variability from case to case, making clinical trials difficult to design, and effectiveness of treatments difficult to discern. Typical conservative medical management including analgesics and sedatives provide minimal relief for the headaches and hyperesthesias. Removing cerebrospinal fluid at regular 3- to 7-day intervals is the only proven method of significantly reducing intracranial pressure and can be used for symptomatic treatment of headaches.[39] This process may be repeated until improvement is shown.[34] There is growing evidence of moderate quality that suggests corticosteroid therapy using prednisolone[40] or dexamethasone[41] has beneficial effect in treating the CNS symptoms related to A. cantonensis infections.[42][43] Although early research did not show treatment with antihelminthic agents (parasite killing drugs) like thiobendazole or albendazole effective in improving the clinical course of the illness,[44][35] a number or recent studies out of Thailand and China show that the combination of glucocorticoids and antihelminthics are safe and decrease the duration of headaches and the number of patients who had significant headache.[41][40][45][46] Although the addition of antihelminthic agents for management of A. cantonensis infection has a theoretic risk of precipitating a neurologic crisis by releasing an overwhelming load of antigens though simultaneous death of the larvae,[39] no study has shown this to exist in the clinical setting.[47][41][46][40] Additionally, the failure to kill parasites before they attempt to migrate out of the CNS increases the risk of mechanical damage by migrating larvae. Although combination therapy using albendazole and prednisolone has no significant advantage compared to treatment using prednisolone alone in mild cases,[48] the treatment with antihelminthics is demonstrably safe and may have significant benefit for patients with high parasite loads at risk for permanent disability or death.[33] Further studies to better define treatment regimens for mild, moderate, and severe disease would be extremely useful, but have not yet been performed due to the technical difficulties mentioned above.

Diagnosis

The diagnosis of disease caused by A. cantonensis infestation is often difficult and relies heavily on the history of a likely ingestion of a commonly infested host and the presence of typical features of the disease. The presumptive diagnosis is particularly strong when eosinophilic meningoencephalitis can be confirmed. The diagnosis of eosinophilic meningitis can be arrived at through detection of elevated cranial pressure and increased numbers of eosinophils. The diagnosis of the cause of eosinophilic meningitis and the presence of A. cantonensis is remarkably more difficult. A spinal tap, or a sample of CSF, must be taken to search for A. cantonensis worms or larvae. A. cantonensis is undetectable in the CSF of more than half of the infected individuals. Current methods of detecting specific antigens associated with A. cantonensis are also unreliable. Consequently, alternative approaches to detect antigen-antibody reactions are being explored, such as Immuno-PCR.[49] A rapid dot-blot ELISA test is also available for quick, effective and economical on-site diagnosis of A. cantonensis.[50]

References

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Angiostrongylus cantonensis: Brief Summary

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Angiostrongylus cantonensis is a parasitic nematode (roundworm) that causes angiostrongyliasis, the most common cause of eosinophilic meningitis in Southeast Asia and the Pacific Basin. The nematode commonly resides in the pulmonary arteries of rats, giving it the common name rat lungworm. Snails are the primary intermediate hosts, where larvae develop until they are infectious.

Humans are incidental hosts of this roundworm, and may become infected through ingestion of larvae in raw or undercooked snails or other vectors, or from contaminated water and vegetables. The larvae are then transported via the blood to the central nervous system, where they are the most common cause of eosinophilic meningitis, a serious condition that can lead to death or permanent brain and nerve damage. Angiostrongyliasis is an infection of increasing public health importance, as globalization contributes to the geographic spread of the disease.

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