Eosinophilic meningoencephalitis

Angiostrongylus cantonensis is a parasitic nematode (roundworm) that causes angiostrongyliasis, the most common cause of eosinophilic meningitis in Southeast Asia and the Pacific Basin. The nematode commonly resides in the pulmonary arteries of rats, giving it the common name rat lungworm. Snails are the primary intermediate hosts, where larvae develop until they are infectious. Humans are incidental hosts of this roundworm, and may become infected through ingestion of larvae in raw or undercooked snails or other vectors, or from contaminated water and vegetables. The larvae are then transported via the blood to the central nervous system, where they are the most common cause of eosinophilic meningitis, a serious condition that can lead to death or permanent brain and nerve damage. Angiostrongyliasis is an infection of increasing public health importance, as globalization contributes to the geographic spread of the disease. First described by the renowned Chinese parasitologist Hsin-Tao Chen (1904–1977) in 1935, after examining Cantonese rat specimens, the nematode Angiostrongylus cantonensis was identified in the cerebrospinal fluid of a patient with eosinophilic meningitis by Nomura and Lim in Taiwan in 1944. They noted that raw food eaten by the patient may have been contaminated by rats. In 1955, Mackerass and Sanders identified the lifecycle of the worm in rats, defining snails and slugs as the intermediate hosts, and noting the path of transmission through the blood, brain, and lungs in rats. Some cases Texas, Tennessee and Alabama — occurred in people who hadn't traveled outside of the contiguous U.S., A. cantonensis is a helminth of the phylum Nematoda, order Strongylida, and superfamily Metastrongyloidea. Nematodes are roundworms characterized by a tough outer cuticle, unsegmented bodies, and a fully developed gastrointestinal tract. The order Strongylida includes hookworms and lungworms. Metastrongyloidea are characterized as 2-cm-long, slender, threadlike worms that reside in the lungs of the definitive host. Angiostrongylus costaricensis is a closely related worm that causes intestinal angiostrongyliasis in Central and South America. Following World War II, A. cantonensis spread throughout Southeast Asia and Western Pacific Islands, including Australia, Melanesia, Micronesia, and Polynesia. Cases were soon reported in New Caledonia, the Philippines, Rarotonga, Saipan, Sumatra, Taiwan, and Tahiti. In the 1960s, even more cases were reported from the region from locations such as Cambodia, Guam, Hawaii, Java, Thailand, Sarawak, Vietnam, and the New Hebrides (Vanuatu). In 1961, an epidemiological study of eosinophilic meningitis in humans was conducted by Rosen, Laigret, and Bories, who hypothesized that the parasite causing these infections was carried by fish. However, Alicata noted that raw fish was consumed by large numbers of people in Hawaii without apparent consequences, and patients presenting with meningitis symptoms had a history of eating raw snails or prawns in the weeks before presenting with symptoms. This observation, along with epidemiology and autopsy of infected brains, confirmed A. cantonensis infection in humans as the cause of the majority of eosinophilic meningitis cases in Southeast Asia and the Pacific Islands. Since then, cases of A. cantonensis infestations have appeared in American Samoa, Australia, Hong Kong, Bombay, Fiji, Hawaii, Honshu, India, Kyushu, New Britain, Okinawa, Ryukyu Islands, Western Samoa, and most recently mainland China. Other sporadic occurrences of the parasite in its rat hosts have been reported in Cuba, Egypt, Louisiana, Madagascar, Nigeria, New Orleans, and Puerto Rico. In 2013, A. cantonensis was confirmed present in Florida, USA, where its range and prevalence are expanding. In 2018, a case was found in a New Yorker who had visited Hawaii.