Epidemiology & Risk Factors

Angiostrongylus cantonensis

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 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.