Angiostrongylus spp

Angiostrongylus cantonensisAndAngiostrongylus costaricensis

TAXONOMY Class: Nematoda Around 19 species are recognized worldwide .

Two species infect humans widely: 1. Angiostrongylus cantonensis (Chen, 1935) causes eosinophilic meningitis 2. Angiostrongylus costaricensis (Morera & Cspedes, 1971) causes abdominal angiostrongyliasis, especially a problem in South America

Angiostrongylus cantonensisAngiostrongylus cantonensisis a parasitic worm of rats. It is also called the rat lungworm. The adult form of the parasite is found only in rodents. (Definitive Host).Snails and slugs get infected by ingesting the larvae. These larvae mature in snails and slugs but do not become adult worms. The life cycle is completed when rats eat infected snails or slugs and the larvae further mature to become adult worm.( Snails and slug : Intermediate Hosts )

Other animals that become infected such as freshwater shrimp, land crabs, frogs, and planarians of the genusPlatydemus, are transport hosts / paratenic hosts that are not required for reproduction of the parasite but might be able to transmit infection to humans if eaten raw or undercooked.Humans are accidental hosts who do not transmit infection to others.

EpidemiologyIt is likely that the parasite has been spread by rats transported on ships and by the introduction of mollusks such as the giant African land snail (Achatina fulica)/ bekicot. In addition, the semi-slug,Parmarion martensi(native of Southeast Asia)has spread in regions of Hawaii and is found to often be infected withA. cantonensis, and the freshwater snailPomacea canaliculata(native of South America) has been introduced into Taiwan and China and has been implicated in outbreaks of disease in those countries.

Angiostrongyliasis is widely distributed in regions where the rodents and marsupials known to carry the infection are known to exist. Most cases of infection are diagnosed in Southeast Asia and the Pacific Basin, but the parasite has also been found in Australia, some areas of Africa, the Caribbean, Hawaii and Louisiana. Outbreaks of human angiostrongyliasis have involved a few to hundreds of persons; over 2,800 cases have been reported in the literature from approximately 30 countries.

In Asia the highest numbers of human cases are found in Taiwan, Thailand, and in the Pacific Islands. The lowest numbers of human infections are found Vietnam, Malaysia, Indonesia, Japan, and Cuba.

The demographics of patients most frequently affected vary with country. In Tahiti, adults are affected more frequently than children, and the sexes have equal rates of infection, while in Thailand, males are nearly three times as likely to become infected as females and the majority of cases occur in individuals who are between the ages of twenty and thirty-nine. Alternatively, in Taiwan, the vast majority of cases, eighty percent, are children under the age of twelve who play with or eat raw Giant Africa Land Snails during the months of high rainfall when they are most abundant.

Risk factors include the ingestion of raw or undercooked infected snails or slugs; or pieces of snails and slugs accidentally chopped up in vegetables, vegetable juices, or salads; or foods contaminated by the slime of infected snails or slugs. It is possible that ingestion of raw or undercooked transport hosts (freshwater shrimp, land crabs, frogs, etc. ) can result in human infection, though this is less certain. In addition, contamination of the hands during the preparation of uncooked infected snails or slugs could lead to ingestion of the parasite.

MorphologyAdultAdult Angiostrongylus nematodes are slender worms that can grow to be25 mm - female : l : 21-25 mm, d : 0,30-0,36 mmFirst stage larvae are, on average, 0.27mm long and 0.014mm wide, while third stage larvae have mean dimensions of 0.557mm long and 0.025mm wide.

Adult female with characteristic red (gut) and white (uterine tubules) spiral appearance

Adult worms ofA. cantonensislive 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 passed 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 the pulmonary arteries where they become sexually mature. Of note, various animals 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.

Angiostrongylus cantonensisThe incubation period ofA. cantonensisaverages 1 to 3 weeks, but has ranged from 1 day to greater than 6 weeks. Illness fromA. cantonensisusually lasts between 2-8 weeks but can last longer. People present with symptoms of bacterial meningitis, such as nausea, vomiting, neck stiffness, and headaches that are often global and severe. Additionally, abnormal sensations of the arms and legs can occur.

Sometimes the eyes can be affected. When patients are tested for bacterial meningitis by taking a sample of the fluid that surrounds the brain, the fluid does not show high levels of the cells that help fight off bacterial infections (polymorphonuclear leukocytes) as one might expect. Instead, another cell type called eosinophils are found (this is called eosinophilic meningitis), though these cells may be absent early and late in the course of disease. Most infections ofA. cantonensisresolve spontaneously over time without specific treatment because the parasite cannot survive for long in the human body. However, serious complications can rarely occur, leading to neurologic dysfunction or death.

DiagnosisAngiostrongylus cantonensisDiagnosingA. cantonensisinfections can be difficult, in part because there are no readily available blood tests. Important clues that could lead to the diagnosis of infection are a history of travel to where the parasite is known to be found and ingestion of raw or undercooked snails, slugs, or possibly transport hosts (such as frogs, fresh water shrimp or land crabs) in those areas. A high level of eosinophils, a blood cell that can be elevated in the presence of a parasite, in the blood or in the fluid that surrounds the brain can be another important clue. Persons worried that they might be infected should consult their health care provider.

Angiostrongylus costaricensisparasitic nematode (worm) that resides in rodents and uses mollusks, such as slugs, as an intermediate host. Rats, such as the cotton rat, transmit the larvae through their feces. Slugs then ingest the larvae. Humans are accidental hosts of the parasite. The parasite is not able to complete its life cycle in humans and eventually dies in the abdomen.

EpidemiologyHuman infection principally occurs in Latin America and the Caribbean, with a few cases suspected in the United States and in the Republic of Congo. The organism is also found in animals in the Southern U.S. (Texas).

Risk factors Risk factors for infection withA. costaricensisare not well established but are likely to be ingestion of infected slugs or raw vegetables or vegetable juices contaminated with slugs or their slime, which can containA. costaricensislarvae. The infection of transport hosts, which are not essential to the lifecycle of the parasite, has not been identified and any role in human infection is not known, in contrast toA. cantonensis. Some reports have shown the case rate to be higher in children 6 to 12 years of age, males, and in persons of higher socioeconomic status. There has been one food-related outbreak in Guatemala that affected primarily adults.

There is some question whether or not larvae can exit the infected mollusks in slime (which may 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 in the lungs, where the worms ultimately die. The life cycle ofAngiostrongylus (Parastrongylus) costaricensisis similar, except that the adult worms reside in the arterioles of the ileocecal area of the definitive host. In humans,A. costaricensisoften reaches sexual maturity and release eggs into the intestinal tissues. The eggs and larvae degenerate and cause intense local inflammatory reactions and do not appear to be shed in the stool.

Angiostrongylus costaricensisThe incubation period is not specifically known, but is thought to usually range from several weeks to several months, possibly even up to 1 year.A. costaricensisis usually found in the intestine (especially the ileocecal region) and can cause abdominal pain, fever, nausea and vomiting. Abdominal findings can often mimic appendicitis, and infection is identified after surgical removal of the appendix. In rare cases, the larvae enter the mesenteric arteries found in the abdominal cavity where they mature into adults and can cause arteritis, infarction, thrombosis, and gastrointestinal hemorrhage.

Eggs produced by adult worms lodge in capillaries and cause an inflammatory reaction as they degenerate. The immune systems response to the adults, larvae, and eggs can result in a massive eosinophilic inflammatory reaction, with eosinophilic invasion of the intestinal wall and eosinophilic vasculitis. Intestinal obstruction and perforation can occur, and deaths have been reported. Recurrent episodes of illness may occur over several months. Most cases resolve spontaneousl

Angiostrongylus costaricensisDiagnosingA. costaricensisinfections can be difficult, in part because there are no readily available blood tests. Important clues that could lead to the diagnosis of infection are a history of travel to where the parasite is known to be found and ingestion of raw or undercooked slugs or food contaminated by infected slugs or their slime. A high blood level of eosinophils, a blood cell that can be elevated in the presence of a parasite, can be another important clue. Persons worried that they might be infected should consult their health care provider.

The two factors that contribute most greatly to the diagnosis of angiostrongyliasis is a history of ingestion of known hosts in endemic regions and evidence of antibodies and antigens in cerebral spinal fluid or eyes. There are four main diagnostic tests that can be used in order to detect these things. enzyme-linked immunoabsorbent assay (ELISA):detects serum antibodies against the antigen prepared from the parasite. Serum is considered to be positive if it has more than twice the normal antibody levels. False negatives are not uncommon. spinal tap:patient assumes sitting position for a minimum of 30 minutes prior to puncture with a 19 or 21 gauge needle while in a flat position. Initial fluid is observed for presence of parasites. others:often produce inconsistent and/or unreliable results - indirect immunofluorescent antibody (IFA): - indirect hemagglutination (IHA): - counterimmunoelectrophoresis (CIE):

TreatmentAngiostrongylus cantonensisThere is no specific treatment forA. cantonensisinfection. There is some evidence that certain supportive treatments may reduce the severity of headache and the duration of symptoms. Persons with symptoms should consult their health care provider for more information.Angiostrongylus costaricensisThere is no specific treatment forA. costaricensisinfections. Most infections resolve spontaneously though sometime surgical treatment is necessary to removed portions of inflamed intestine. Persons with symptoms should consult their health care provider for more information.

Management and Therapy Despite the fact that there is no specific therapy for the Angiostrongyliasis because of its short course, there are a number of treatments for symptoms. analgesics and corticosteroids:alleviate radicular symptoms and headache spinal tap:reduces intracranial pressure and associated headache general and neurologic care:for patients suffering from complications such as infections thiabendazole:anthelminthic drug determined to have insignificant effect on clinical course of angiostrongyliasis mebendazole:100mg, twice daily for five days for anthelminthic treatment

Prevention & ControlAngiostrongylus cantonensisPrevention ofA. cantonensisinfections involves educating persons residing in or traveling to areas where the parasite is found about not ingesting raw or undercooked snails and slugs, freshwater shrimp, land crabs, frogs, and monitor lizards, or potentially contaminated vegetables, or vegetable juice. Removing snails, slugs, and rats found near houses and gardens should also help reduce risk. Thoroughly washing hands and utensils after preparing raw snails or slugs is also recommended. Vegetables should be thoroughly washed if eaten raw.

Angiostrongylus costaricensisPrevention ofA. costaricensisinfections involves educating persons residing in and traveling to areas where the parasite is known to be found about not ingesting raw or undercooked slugs or potentially contaminated vegetables or vegetable juices. Removing slugs and rats found near houses and gardens should help reduce risk. Thoroughly washing hands and utensils after preparing raw slugs is also recommended. Vegetables should be thoroughly washed if eaten raw.

Humans are accidental or incidental hosts of A. cantonensis and may become infected after ingesting infected mollusks or crustaceans, the paratenic hosts, that are raw or improperly cooked. Humans may also be infected by ingesting fresh vegetables contaminated with the worm by carnivorous planarians that have fed on infected snails or slugs. Alternatively, vegetables may also be infected with the liquids secreted by the mollusks that are not removed by proper washing before human ingestion.