Neuroangiostrongyliasis: Global Spread of an Emerging Tropical Disease

Abstract

Neuroangiostrongyliasis (NAS) is an emerging parasitic disease caused by the neurotropic nematode Angiostrongylus cantonensis. Since it was first discovered, in rats in southern China in the 1930s, this tropical to subtropical parasite has spread to much of Southeast Asia, the Pacific Islands (including Hawaii), Australia, Japan, South America, the southeastern United States, the Caribbean, Africa, the Canary Islands, and the Balearic Islands. The parasite completes its natural life cycle in snails and slugs (intermediate hosts), and rats (definitive hosts). Humans become accidental hosts after ingesting infective third-stage larvae contained within uncooked or undercooked intermediate or paratenic hosts, an event that sometimes results in NAS, also known as rat lungworm disease. Although A. cantonensis larvae cannot complete their life cycle in humans, their migration into the brain and spinal cord combined with a powerful inflammatory reaction often leads to eosinophilic meningitis and can, in rare instances, lead to coma, paralysis, and death or, in other cases, chronic, disabling neurologic sequelae. Symptoms of NAS are diverse, which often makes it difficult to diagnose. Treatment may include administration of analgesics, corticosteroids, anthelminthics, and repeat lumbar punctures to reduce intracranial pressure. Unfortunately, few medical providers, even in endemic areas, are familiar with A. cantonensis or its epidemiology, diagnosis, and treatment. As the parasite continues to spread and NAS affects more people, medical practitioners, as well as the general public, must become more aware of this emerging zoonosis and the potentially devastating harm it can cause.

Figure 1.

The global distribution, by country, of combined reported presence of Angiostrongylus cantonensis and cases of human or animal neuroangiostrongyliasis (red circles), with cases in returning travelers to nonendemic areas distinguished (blue circles).^,– If part of a country is distant from the main part of the country—Guam, Saipan, Hawaii, American Samoa, and Puerto Rico (United States); Ryukyu and Ogasawara Islands (Japan); New Caledonia, Tahiti, Mayotte, Réunion, Guadeloupe, and Martinique (France); and Canary Islands and Mallorca (Spain)—dots are placed on those locations in addition to the main part of country (if also present there). For most countries/territories, a single dot has been placed roughly where the greatest concentration of records occurs. For countries with records on multiple widespread islands, dots are placed on those areas with records—Malaysia (Peninsula Malaysia, Sarawak), Indonesia (Java, Sumatra, Flores, Sulawesi), and the Federated States of Micronesia (Chuuk, Pohnpei). For the continental United States, several dots for returning travelers are placed roughly where they were diagnosed. Note that the cases in the Bahamas may have originated in Louisiana, and the presence of A. cantonensis in Zimbabwe is unconfirmed.

Figure 2.

Angiostrongylus cantonensis completes its life cycle in various species of rats (definitive hosts) and snails (intermediate hosts).^,, Snails become infected by ingesting rat feces containing freshly hatched larvae (L1). The larvae develop into infectious third-stage larvae (L3) in the snail and remain as such for the life span of the snail or until the snail is eaten by a definitive, paratenic, or accidental host.

Figure 3.

Known distribution of natural infections of hosts of Angiostrongylus cantonensis^– and autochthonous human cases of neuroangiostrongyliasis in the United States^,,: orange circles, A. cantonensis in definitive (rats) and intermediate (snails and slugs) hosts; yellow circles, A. cantonensis in nonhuman accidental hosts (see text for details); red circles, numbers of human cases by state and year. AL = Alabama, FL = Florida, HI = Hawaii, LA = Louisiana, MS = Mississippi, OK = Oklahoma, TN = Tennessee, TX = Texas. The parasite is widespread in Florida. In Hawaii (orange and red), there have been human cases on all six largest islands (Table 1), although A. cantonensis has not been detected on the island of Lanai. The record in Oklahoma was a rat (Sigmodon hispidus), and one record in Louisiana was also a rat (Neotoma sp.), but it is unclear whether either of these species was a definitive or an accidental host.^,