The nematode Angiostrongylus cantonensis is a rat lungworm, a zoonotic pathogen which causes a global, emerging infectious disease known as rat lungworm disease (RLWD). This nematode was first discovered in China in 1935 , but is now endemic in Asia, Australia, the Caribbean islands and Pacific islands; it has also spread to the American continents with more than 2,800 cases of human infection reported in 30 countries [2, 3]. Rats are the definitive host, primarily Rattus rattus and R. norvegicus . When rats eat infected slugs or snails, they ingest third stage (L3) larvae which eventually grow to sexual maturity and reproduce in the heart . Single-celled eggs hatch in the lung, and first stage larvae migrate up the bronchial tree, are swallowed, and 6-8 weeks after infection are excreted with feces . Slugs or snails then eat rat feces and acquire the first stage larvae. Slugs and snails are obligatory intermediate hosts which support parasite development from the first to the L3 larval stage.
Humans can become infected by ingesting intermediate or paratenic (passive carrier) hosts containing infective L3 larvae. The most important paratenic hosts are crustaceans (such as prawns and land crabs) and predacious land planarians, such as flatworms in the genus Platydemus . Once ingested by humans, larvae penetrate the intestinal mucosa and travel through the liver and lungs to the central nervous system (CNS) . RLWD can be a serious threat to human health. Angiostrongyliasis in humans can result in transient meningitis (inflammation of the meninges of the brain and the spinal cord) or a more serious disease involving the brain, spinal cord and nerve roots, with a characteristic eosinophilia of the peripheral blood and cerebrospinal fluid . Humans are a “dead-end” host, meaning the parasites do not reproduce in humans but remain in the CNS or can move to the eye chamber causing ocular angiostrongyliasis, where they remain until parasite death .
A. cantonensis has been documented as a parasitic disease of humans in Hawaiʻi and other Pacific islands since the early 1960’s . The flatworm Platydemus manokwari and the semi-slug Parmarion martensi (hereafter referred to as semi-slug) had recently immigrated to Japan and were thought to be the probable cause of an outbreak of angiostrongyliasis there in the year 2000 . The semi-slug is also a recent immigrant to the Hawaiian Islands  and is thought to be responsible for a recent outbreak of angiostrongyliasis cases on the Island of Hawaii .
In the district where the disease outbreak occurred (Puna district of the Island of Hawaii), >75% of P. martensi were found to be infected with A. cantonensis. In certain areas, semi-slugs were very numerous and some were heavily infected with L3 A. cantonensis larvae .
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