Rat Lungworm Overview
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. cantonensislarvae . Please see the current “RLW detection map” on this website for the most recent data on RLW detection in slugs and snails on the Island of Hawaii by the Big Island Rat Lungworm Working Group, College of Pharmacy, University of Hawaiʻi at Hilo.
Staff from the University of Hawaii-Hilo Daniel K. Inouye College of Pharmacy (DKICP) confirmed a collection of Parmarion martensi, an invasive slug, from the Kohala district of the Big Island. Inquiries of local residents further revealed multiple sightings in the area, indicating that this invasive pest has established in the Kohala district of the Big Island.
Commonly called the “semi-slug” for the partially formed shell on its back, the semi-slug has been associated with increased incidences of Angiostrongylus (rat-lungworm disease). The parasite, Angiostrongylus cantonensis, infects rats and snails or slugs at different times during its life cycle. Humans can contract the disease after accidentally consuming the parasite from a slug or snail. Cases range from severe discomfort and illness to permanent disability, or even death, depending on the amount of microscopic parasites consumed. Although all snails and slugs can carry the infective form of the parasite, semi-slugs are known to be carriers of a much heavier load of parasites.
The presence of the slug was confirmed through the efforts of students at Kohala Middle School, who are participating in a citizen science effort led by teacher Cristy Athan. Athan enrolled in a professional development class offered by UHH-DKICP and the Big Island Invasive Species Committee to learn more about rat lungworm and invasive rats and slugs. Teachers are taught safe handling protocols for the collection and disposal of snails and slugs, and are guided to develop an Integrated Pest Management Strategy to reduce slug and snail populations in school gardens. The students embraced the project and have enthusiastically committed to their roles as ambassadors for rat lungworm prevention. “They’re so into it,” says Athan. “Every single day, they’re telling me a new slug or snail story!”
Funded by the Hawaii Community Foundation’s Career Connected Learning STEM grant, the teacher professional development class offers standards-aligned lessons for teachers to use in their classrooms to increase awareness and safety in their school and at home, and to contribute to ongoing scientific efforts to develop a better understanding of slug/snail behavior. Kay Howe, DKICP education coordinator at UHH, was inspired to create the curriculum after her son contracted a serious case of the disease in 2008. Although she had worked at a school garden in Waimea the year before, she had never heard of rat lungworm disease. Over the years of supporting residents and visitors who contracted RLW, Howe often heard a similar sentiment: before diagnosis, many of them had never heard of it. “I was concerned because my mind kept coming back to that school garden. As school gardens were being put in at schools across the island I was so excited for the opportunity for the students to learn about agriculture and growing their own nutritious food, but I also worried – what are they doing about rat lungworm? Do they even understand the risk?”
Residents of Kohala are asked to be vigilant for this slug and to be extremely careful with washing garden vegetables. Slugs or snails should never be collected with bare hands – gloves or chopsticks can be used to dispose of slugs in heavily salted water. Slug baits can reduce populations around gardens and yards. Resources on RLW and on the teacher training can be found at www.biisc.org.