The Discovery of Humans in Hawai‘i Infected with Angiostrongylus cantonensis, and Early Epidemiological Findings

An epidemic of eosinophilic meningitis occurred in Hawai‘i in 1958, and was presumed to have been caused by a parasitic infection. There were no fatal cases and the source of the infection was not known. In the course of investigating the epidemic, it was learned that two patients who had died at the State Mental Hospital on O‘ahu in December 1959 and January 1960 had eosinophilic meningitis. The preserved brain of one patient yielded a number of young adult nematodes identified as Angiostrongylus cantonensis; the other contained possible nematode remnants.1 Surveys of rats around the State Mental Hospital showed that 23% were positive for A. cantonensis, and, knowing that the life cycle of this parasite involved snails as intermediate hosts, it seemed likely that the two patients had eaten snails.1 Was this parasite also the cause of the thousands of cases of eosinophilic meningitis then recently reported in French Polynesia? Surveys of rats in the Society Islands showed them to be heavily infected with A. cantonensis,2 and while snails were not eaten raw in the Society Islands, freshwater prawns, which can act as paratenic hosts, were eaten raw and were thought to be the source of infection.3 Fish were also suggested as possible paratenic hosts that might provide a pathway for human infection.4 Infected rats were found on many other Pacific islands and cases of eosinophilic meningitis had been reported from some of them. No cases were found on islands where the parasite was absent, consistent with A. cantonensis as the etiological agent.1,3 This early epidemiological research established the association between the presence of rat lungworm (A. cantonensis) and cases of human eosinophilic meningitis.