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Snails, Slugs, and Semi-slugs: A Parasitic Disease in Paradise

Categories: General

Parmarion martensi: a semi-slug commonly found in Hawaii.

CDC plays a vital role supporting state health departments, particularly with management of rare or lesser-known pathogens. Recently, CDC’s Division of Parasitic Diseases (DPD) was contacted by the Hawaii Department of Health (HI DOH) for advice regarding three cases of presumed Angiostrongylus cantonensis (AC) infection. AC, commonly called the rat lungworm, is a parasitic worm and the most common infectious cause of eosinophilic (a type of white cell) meningitis in humans worldwide.

AC has an interesting life cycle. Infected rodents carry the adult worm and pass immature worms in their feces. Mollusks (i.e., snails, slugs, or semi-slugs) become infected by ingesting immature worms in the rat feces. Humans become infected by ingesting raw or undercooked mollusks (these guys can be tiny enough to hide on a nickel; – check it out[PDF, 1 page]! infected with the worms or contaminated raw produce. Transmission might also occur through ingestion of raw or undercooked freshwater shrimps/prawns, crabs or frogs. In humans, AC causes eosinophilic meningitis, the symptoms of which can include headache, stiff neck, nausea, vomiting, low-grade fever, fatigue, and abnormal skin sensations (e.g., tingling or pain). In most cases, the symptoms disappear in weeks to months and most patients recover completely, although rare cases of blindness, paralysis, and death have been reported.

A picture from differential interference contrast microscopy showing A. cantonensis. This larva was obtained from a P. martensi slug collected in Hawaii. Infective, third-stage larvae measure 0.425 mm – 0.523 mm in length

A picture from differential interference contrast microscopy showing A. cantonensis. This larva was obtained from a P. martensi slug collected in Hawaii. Infective, third-stage larvae measure 0.425 mm – 0.523 mm in length

Armed with this information, a team of scientists from USDA (HI), HI DOH and DPD began testing mollusks collected near the case-patients’ homes in Hilo Puna. We used morphologic and molecular techniques to test and document infection in slug samples sent from Hawaii. HI DOH has determined that many patients live in communities outside of the municipal water/sewage system and consume home-grown produce. The DPD molecular diagnostic parasitology lab, which I lead, continues to collaborate on testing of environmental samples and the development of methods to evaluate the effectiveness of interventions to eliminate infected rodents and mollusks. In this new phase of the collaboration, a real-time PCR assay developed in-house at DPD to detect A. cantonensis is being used to analyze mollusk samples collected in Hawaii. Future efforts will involve the transferring of this real-time PCR test and other molecular methods to Hawaii so testing can be performed in-state.

Since initial contact with Hawaii, four more cases of presumed AC infection have been reported. In response, we are helping to educate the public in Hawaii on how to prevent the infection. Information has also been developed for the healthcare community in Hawaii because many physicians may not consider AC when evaluating patients with eosinophilic meningitis. AC can be prevented by avoiding the consumption of raw/undercooked snails, slugs, freshwater shrimp/prawns, crabs and frogs; by washing raw produce thoroughly prior to eating; and by wearing gloves and washing hands after handling mollusks.

Public Comments

Comments listed below are posted by individuals not associated with CDC, unless otherwise stated. These comments do not represent the official views of CDC, and CDC does not guarantee that any information posted by individuals on this blog is correct, and disclaims any liability for any loss or damage resulting from reliance on any such information. Read more about our comment policy ».

  1. October 3, 2009 at 8:51 pm ET  -   David Schroeder

    Interesting. Thanks for the information regarding the certain foods. I’ll remember this next visit to Hawaii.

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  2. October 6, 2009 at 7:30 am ET  -   blaine stevens

    05 October 09 My wife purchased organic romaine hearts from the military on post commissary on Ft Benning Ga. I often have it for lunch, this time (the First spotting) I found a (I believe) semi-slug the heart was loaded with what I assumed to be feces from the slug… the slug was similar in appearance to the one in the picture of this site… though its back end mangled or decaying. so I removed the slug rinsed the leaves removed any browned or obviously eaten areas and consumed the lettuce as I was i a rush to eat and get back to work. Am I in any danger from eating the lettuce?

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  3. AUTHOR COMMENT October 15, 2009 at 8:44 am ET  -   Alex da Silva

    Dear Mr. Stevens,
    Thank you for your inquiry about the risk of acquiring Angiostrongylus infection after eating lettuce on which you found a semi-slug. Angiostrongylus cantonensis infection occurs mostly in Asia, the Pacific (including Hawaii), and the Caribbean, and can cause eosinophilic meningitis. Sporadic cases have also occurred in South America and Africa. Angiostrongylus costaricensis occurs mostly in Central and South America and causes eosinophilic enteritis, a gastrointestinal disorder. A handful of cases of Angiostrongylus cantonensis infection have occurred in the continental United States, one in Louisiana from an ingested snail found locally, but other cases may have been due to imported snails, slugs, semi-slugs, or rats harboring Angiostrongylus larvae. Imported produce may be contaminated with snails, slugs, semi-slugs, or their slime containing Angiostrongylus larvae. Imported snails, slugs, and rats harboring larvae may also result in contamination of local produce. While there is likely less risk of infection from produce grown in the continental United States, the occurrence of Angiostrongylus species in the United States is not well defined, and the risk from imported produce is unknown. Washing produce thoroughly should theoretically reduce the risk of Angiostrongylus infection.

    For more information, please call 1-800-CDC-INFO or 1-770-488-7775, or refer to the CDC website regarding Angiostrongylus: http://www.cdc.gov/ncidod/dpd/parasites/angiostrongylus/

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  4. June 13, 2013 at 10:24 pm ET  -   Lynn

    I noticed slugs around my lettuce plants. What precautions should I take before eating my lettuce. I first of all dipped my lettuce a couple of times in hot water. I then rinsed it several times is cool water, and also as a precaution. I put a little dish washing liquid in my water and dipped the lettuce in it, then I dipped my lettuce several times in clean water. Have I taken enough precautions in order to eat my lettuce. I know there have been a few cases of people getting seriously sick from eating home grown lettuce, and I don’t want to get sick. I am trying to grow my own basil, lettuce, rosemary, and tomatoes since produce is so expensive.

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