Angiostrongylus is a parasitic nematode that can cause severe gastrointestinal or central nervous system disease in humans, depending on the species. Angiostrongylus cantonensis, which is also known as the rat lungworm, causes eosinophilic meningitis and is prevalent in Southeast Asia, South America, and tropical Pacific islands. The recognized distribution of the parasite has been increasing over time and infections have been identified in other areas, including Africa, the Caribbean, and the United States. Angiostrongylus costaricensis causes eosinophilic gastroenteritis and is found in Latin America and the Caribbean.

Epidemiology & Risk Factors

Angiostrongylus cantonensis, also known as the rat lungworm, is a parasitic nematode (worm) that is transmitted between rats and mollusks (such as slugs or snails) in its natural life cycle. Other animals that become infected such as freshwater shrimp, land crabs, frogs, and planarians of the genus Platydemus, are transport 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. Most cases of infection are diagnosed in Southeast Asia, South America, 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. It 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). In addition, the semi-slug, Parmarion martensi (native of Southeast Asia)has spread in regions of Hawaii and is found to often be infected with A. cantonensis, and the freshwater snail Pomacea canaliculata (native of South America) has been introduced into Taiwan and China and has been implicated in outbreaks of disease in those countries.
Risk factors for infection with A. cantonensis 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.

Angiostrongylus costaricensis

Angiostrongylus costaricensis is a parasitic 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. Human 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 for infection with A. costaricensis are 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 contain A. costaricensis larvae. 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 to A. 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.

Disease

Angiostrongylus cantonensis

The incubation period of A. cantonensis averages 1 to 3 weeks, but has ranged from 1 day to greater than 6 weeks. Illness from A. cantonensis usually 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 of A. cantonensis resolve 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.

Angiostrongylus costaricensis

The 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. costaricensis is 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 system’s 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 spontaneously.

Diagnosis

Angiostrongylus cantonensis

Diagnosing A. cantonensis infections 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 costaricensis

Diagnosing A. costaricensis infections 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.

Treatment

Angiostrongylus cantonensis

There is no specific treatment for A. cantonensis infection. 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 costaricensis

There is no specific treatment for A. costaricensis infections. 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.

Prevention & Control

Angiostrongylus cantonensis

Prevention of A. cantonensis infections 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 costaricensis

Prevention of A. costaricensis infections 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.