Angiostrongyliasis (ann-gee-o-stronge-uh-luss) is an infection caused by the internal parasites Angiostrongylus cantonensis and Angiostrongylus costaricensis. These worms are transmitted as eggs or larvae from rats to other animals such as snails, slugs, and some crustaceans. Humans become infected when they ingest immature parasites, usually after eating undercooked or raw mollusks, crustaceans, and especially snails. Angiostrongyliasis infection often has no symptoms, or mild symptoms, although some cases result in the development of meningitis. Infection disappears as the worms die in the body.
The majority of outbreaks of angiostrongyliasis occur in Southeast Asia and the Pacific Islands, although cases have been reported in other countries. The first appearance of the parasites in humans was noted in 1944 and since then, there have been numerous reported infections.
Angiostrongyliasis is caused by the ingestion of one of two parasites, Angiostrongylus cantonensis or Angiostrongylus costaricensis. Both are parasites of rats and are transmitted to snails and slugs when they eat rat feces. Crustaceans such as prawns can also carry the parasite. Transmission to humans occurs when humans eat undercooked or raw intermittent hosts containing the parasite. Most humans become infected after eating in restaurants that do not cook the animals properly, or when they accidentally ingest a snail or slug attached to a salad item that has not been washed properly.
Infection by A. cantonensis, which travels to the brain or lungs and eventually dies there, usually results in mild symptoms, or no symptoms, although eosinophilic meningitis can develop. Meningitis is usually accompanied by headaches, a stiff neck, fever, nausea, and vomiting. Infection by A. costaricensis, which travels to the digestive tract and dies there, can result in abdominal pain as the dying parasites cause inflammatory pain in the abdomen.
WORDS TO KNOW
HELMINTHIC DISEASE: Helminths are parasitic worms such as hookworms or flatworms. Helminthic disease is infectious by such worms. A synonym for helminthic is verminous.
PARASITE: An organism that lives in or on a host organism and that gets its nourishment from that host. The parasite usually gains all the benefits of this relationship, while the host may suffer from various diseases and discomforts, or show no signs of the infection. The life cycle of a typical parasite usually includes several developmental stages and morphological changes as the parasite lives and moves through the environment and one or more hosts. Parasites that remain on a host's body surface to feed are called ectoparasites, while those that live inside a host's body are called endoparasites. Parasitism is a highly successful biological adaptation. There are more known parasitic species than nonparasitic ones, and parasites affect just about every form of life, including most all animals, plants, and even bacteria.
The Angiostrongylus parasites were first discovered in rats in China in 1933 and in humans in Taiwan in 1944. Infection of rats first spread throughout the Indo-pacific basin and through Madagascar, Cuba, Egypt, Puerto Rico, and New Orleans. Following the end of World War II in 1945, infected rats spread to Micronesia, Australia, and Polynesia. During the 1950s, infected rats were reported in the Philippines, Saipan, New Caledonia, Rarotonga, and Tahiti; during the 1960s, infected rats had spread to Thailand, Cambodia, Java, Sarawak, Guam, and Hawaii.
During 2000, students from Chicago traveling through Jamaica became infected with eosinophilic meningitis. The cause of infection was pinpointed to a salad that was eaten by all the students and that most likely contained secretions from infected slugs or snails.
In August 2006, a number of cases of angiostrongyliasis infection were reported in Beijing, China. Over the course of two months, an outbreak occurred during which the number of infected people rose to 132. The cause of this outbreak was linked to a restaurant chain that served Amazonian snails, known hosts of the parasites. These snails were most likely undercooked, causing the parasite to infect humans.
Angiostrongyliasis parasites die within weeks to months. Sometimes the body reacts to the dying parasites, which causes mild symptoms such as abdominal pain. Infected humans usually recover fully without treatment, although treatment may be administered to treat symptoms. Eosinophilic meningitis can also develop and is characterized by neck pain, headaches, and nausea. Although there is no specific treatment for angiostrongyliasis, analgesics, corticosteroids, and certain anti-helminthic drugs may be administered.
Infections can be prevented by cooking snails, crustaceans, and slugs thoroughly so that the parasite is killed. In addition, careful washing of salad items will prevent infected snails and slugs from being present in salads and potentially being ingested. Although some cases have been attributed to the ingestion of mucus and secretions, some scientists insist that it is still unknown whether transmission can occur following ingestion of mucus from infected snails and slugs. Ingestion of mucus may occur when people who collect snails touch their mouths or nasal passages. Infection can also be prevented by wearing gloves while collecting snails.
The main mode of transmission of the parasites that cause angiostrongyliasis is through poor preparation of food. Therefore, infection is more likely to occur in countries with soft regulations on food preparation. People traveling through countries in which rats are infected by the parasites need to be aware of the risks associated with eating food in these countries. Reducing the rodent population in endemic countries also reduces the available population for the initial reservoir of the parasite, and thus, minimizes the opportunity for infection.
IN CONTEXT: HAVE CASES OCCURRED IN THE CONTINENTAL UNITED STATES?
The Centers for Disease Control and Prevention (CDC) states that “In 1993, a boy got infected by swallowing a raw snail ‘on a dare.’ The type of snail he swallowed isn't known. He became ill a few weeks later, with muscle aches, headache, stiff neck, a slight fever, and vomiting. Although he had eosinophilic meningitis, his symptoms went away in about 2 weeks, without treatment of the infection.”
The CDC specifically recommends that to avoid infection: “Don't eat raw or undercooked snails or slugs. If you handle snails or slugs, wear gloves and wash your hands. Always remember to thoroughly wash fresh produce.”
SOURCE: Centers for Disease Control and Prevention (CDC)
The type of snails eaten and the methods used to cook these snails also impact infection. Therefore, restaurants that sell certain snails could potentially contribute towards spreading the infection. Furthermore, as the proper cooking of snails can render the parasites harmless, thorough cooking of snails would prevent infection.
Giant African land snails are frequent hosts of the angiostrongyliasis parasite. In Taiwan, angiostrongyliasis occurs most often among children who play with (and sometimes eat) the giant African land snail during the rainy months of June to October when they are most abundant. In the islands of French Polynesia, most infections occur in adults.
In the United States, Giant African land snails are illegal to import as pets. They are considered an invasive species capable of supporting the emergence of angiostrongyliasis in the United States, as well as an agricultural pest. In 2004, authorities seized the snails in over 100 U.S. exotic pet shops and among private owners. Additionally, several schools that kept Giant African land snails as projects turned them over to public health authorities.
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Centers for Disease Control and Prevention (CDC). “Fact Sheet: Angiostrongylus cantonensis Infection.” May 13, 2004 <http://www.cdc.gov/ncidod/dpd/parasites/angiostrongylus/factsht_angiostrongylus.htm> (accessed Jan. 25, 2007). International Society for Infectious Diseases.
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