Abstract
Eosinophilic meningitis caused by infection with Angiostrongylus cantonensis, a parasitic nematode, is an emerging infectious disease of humans and other animals, known as angiostrongyliasis or rat lungworm disease. Symptoms range from headache and muscle spasms in mild cases to coma and even death. Many human cases have been recorded around the world, with the majority in tropical and subtropical locations. The increase in numbers of human cases and the expansion of the geographic distribution of cases make this parasite and its hosts important research foci. Definitive hosts include various rat species such as Rattus norvegicus, R. rattus, and R. exulans, and a number of land and freshwater snails and slugs have previously been identified as intermediate hosts.1 Both definitive and intermediate hosts are obligate to the life cycle of A. cantonensis. Paratenic hosts span a wide range of fauna and are not needed in the nematode's life cycle, but act as reservoirs in which different larval stages of the parasite can persist but not develop further; they include freshwater shrimp, flatworms, and frogs.2–4 Accidental hosts, including humans and other mammals, as well as birds, permit development from the third larval stage to the subadult (fifth) stage but are then dead ends for the parasite.5,6 These hosts are infected primarily through consumption of raw or undercooked intermediate or paratenic hosts, either intentionally or accidentally via contaminated produce.7
In Hawai‘i, there have been recent outbreaks with cases of infection on four of the main islands. Since there is currently a limited consensus on appropriate therapy, steps to prevent infection should be taken. The first step to facilitate this and to lay the groundwork for future management of the hosts is to identify the intermediate hosts of A. cantonensis and to determine its geographic distribution within the Hawaiian Islands. To do this over 1000 specimens of 37 terrestrial and freshwater snail and slug species (30 introduced, 7 native) from the six largest Hawaiian Islands were screened using a molecular approach.8 Total DNA was extracted from foot tissue of each specimen and was amplified using Angiostrongylus-specific primers.8 Amplicons were visualized on agarose gels to determine if specimens were positive or negative for A. cantonensis. All of the positive specimens and a random sample of all other specimens tested were also reamplified using species-specific primers.9 All positive samples were still positive with the newer primers. The parasite was present in 16 (14 alien, 2 native) of these species, from five of the six largest Hawaiian Islands. These species represent 10 phylogenetically diverse terrestrial pulmonate families and 2 more distantly related caenogastropod families (one terrestrial and one freshwater). This broad phylogenetic representation demonstrates that this parasite is not host specific, to the extent that perhaps even any snail or slug species could act as an intermediate host.
Keywords: Angiostrongyliasis, Eosinophilic meningitis, Hawai‘i, Nematodes, Rat lungworm disease, Slugs, Snails
Acknowledgements
We thank JK's thesis committee members Kenton Kramer and Chris Lepczyk for advice and support, the various people involved in collecting specimens from the field, and the American Malacological Society, Hawaiian Malacological Society, and University of Hawai‘i Ecology, Evolution and Conservation Biology program (Watson T. Yoshimoto scholarship) for funding. This article is an extended and updated abstract of a contribution to the Rat Lungworm Disease Scientific Workshop held at the Ala Moana Hotel, Honolulu, Hawai‘i in August 2011. Funding for the workshop and for this publication was provided by the National Institute of Food and Agriculture, United States Department of Agriculture, through Award No. 2011-65213-29954.
Conflict of Interest
None of the authors identifies any conflict of interest.
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