Rat Lungworm FAQ

UH Hilo CoP Home > Rat Lungworm Home

This page holds responses to questions from the audience of the Rat Lungworm Forum held Nov 9, 2011 at the University of Hawaiʻi College of Pharmacy. Responses are provided by forum participants Drs. Rob Cowie, Rob Hollingsworth, Jon Martell and Sue Jarvi, and Jim Hollyer, Ann Kobsa and Kay Howe, and Dr. Will Pitt.

Q. Is the slime of the semi-slug dangerous too? I picked up 2 slugs to throw down the toilet and could not get the slime off my hand with water and soap, finally got it with gasoline.

It has been shown that slug slime may carry a very small number of parasites in comparison with the body of the slug itself. Ingestion of a few parasites could possibly cause an infection, but it would probably be relatively mild. There are no studies that support an infection could be caused by skin contact. However two victims of RLW from the Big Island claim to have gotten it through skin contact. Yes, the slime is very difficult to get off. Further studies would need to be done to determine the most effective and safe way of removing the slime. Direct handling of slugs is not advised. The use of gloves, baggies or picking up slugs with disposable chopsticks is preferable.


  • Heyneman D, Lim BL. Angiostrongylus cantonensis: proof of direct transmission with its epidemiological implications. Science, 1967; 158:1057-1058.
  • Qvarnstrom, Y., J.J. Sullivan, H.S. Bishop, R. Hollingsworth, and A.J. da Silva. 2007. PCR-based detection of Angiostrongylus cantonensis in tissue and mucus secretions from molluscan hosts. Applied and Environmental Microbiology 73(5): 1415–1419. aem.asm.org/content/73/5/1415.full
  • Jarvi SI, MEM Farias, K Howe, S Jacquier, R Hollingsworth, and W Pitt. 2012. Quantitative PCR estimates Angiostrongylus cantonensis (rat lungworm) infection levels in semi-slugs (Parmarion martensi). Molecular Biochemistry and Parasitology. Accepted.

Q. I have had rat lung symptoms for nearly 4 years. What can I expect for my future? What is the mechanism for the pain I still suffer?

Early cases of rat lungworm on the Big Island have shown that conditions and symptoms may persist for an indefinite length of time. To date, there have been no follow-up studies of long-term recovery rates of victims of rat lungworm on the Big Island. From meetings with rat lungworm victims from Hawaiʻi Island we have observed that some recoveries have been more successful than others. One case involved the long-term use of supplements that are antioxidants and support mitochondrial function. Other forms of alternative therapies have been reported, but many of these treatments can be prohibitively expensive as they are not covered by most insurance companies.

Reference: Kathleen Howe. Personal Communication.

Q. Can nerves become inflamed? Can damaged nerves become inflamed months or years later?

Nerve damage often occurs in more serious cases of rat lungworm. It can persist for months or years.

Reference: Wang et al. 2008. Human angiostrongyliasis. Lancet Infectious Diseases 8: 621–630. www.sciencedirect.com/science/article/pii/S1473309908702299

Q. Can rat worm larvae survive in the residual dried slime trails of slugs/snails? Example: a slime trail hours-days old?

A study would have to be done to absolutely confirm this, but probably not, especially if the trail was well dried. The parasite has been reported to live in water for up to 72 hours, and could possibly survive in slime under very moist conditions.

Reference: Cheng, T.C. & Alicata, J.E. 1964. Possible role of water in the transmission of Angiostrongylus cantonensis (Nematoda: Metastrongylidae). Journal of Parasitology 50 Section 2: 39-40.

Q. Can marine gastropods or other mollusk carry this parasite (e.g. opihi…)?

The Hawaiʻi Dept. of Health states that it is the fresh water opihi that can carry the parasite, as well as other aquatic organisms such as prawns, frogs, and water monitor lizards.

Q. Has there been any incidence of RLW in Oregon?

No, there have been no confirmed cases of rat lungworm in humans in Oregon. There has been one human victim reported in Louisiana. Most of the victims on the mainland have been vacationing in Hawaiʻi and have had symptoms present themselves once they returned to the mainland. The first reference below highlights the human case reported in New Orleans, LA. The second reference discusses the first report of the parasite, Angiostrongylus cantonensis in North America.


Q. Do you know if all 3 rat species in Hawaiʻi can be primary carriers? What about mice (Mus musculus)?

We know that Norways (Rattus norvegicus), black rats (Rattus rattus), and Polynesian rats (Rattus exulans) have been confirmed as carriers. House mice (Mus musculus) have not been confirmed.

Reference: Dr. William Pitt, USDA APHIS Wildlife Services. National Wildlife Research Center.

Q. Is there any reason to think that taking Pepto Bismol would prevent you from getting an infection?

We know of no studies that demonstrate that Pepto Bismol is preventative against this parasite.

Q. What are the best ways to cleanse vegetables (salad)? Are bleach, salt water, warm water, vinegar, and/or hydrochloric acid effective cleaning agents?

The best way to be sure your produce is free of slugs and snails is through careful washing and observation. We cannot yet recommend any products as the definitive studies have not been done. However, preliminary studies show vinegar, neem oil, grapefruit seed extract and food grade hydrogen peroxide to be ineffective as rinses that immobilize larvae. Bleach is not approved for use on food by the FDA and has carcinogenic byproducts. Studies are currently underway at UH Mānoa (R. Cowie and J. Hollyer) to determine what products will cause slugs and snails to drop off of produce in a wash.

Q. Why is there so little known about RLW? What is the history behind where it is thought to have come from?

The parasite is believed to have originated in Southeast Asia. This nematode was first discovered in China in 1935 (Chen HT, 1935), but is now endemic in Asia, Australia, the Caribbean islands and the Pacific Islands and has spread to the American continent and Brazil with more than 2,800 cases of human infection reported in 30 countries (Wang et al., 2008, 2011). A. cantonensis has been documented as a parasitic disease of humans in Hawaiʻi and other Pacific islands since the early 1960’s (Wallace and Rosen 1969). The flatworm Platydemus manokwari and the semi-slug Parmarion martensi had recently immigrated to Japan and were thought to be the probable cause of an outbreak of angiostrongyliasis there in the year 2000 (Asato et al. 2004). The semi-slug is also a recent immigrant to the Hawaiian Islands (Cowie, 1997) and is thought to be responsible for a recent outbreak of angiostrongyliasis cases on the Island of Hawaiʻi (Hollingsworth et al. 2007). In the area where the disease outbreak occurred (Puna district of the Island of Hawaiʻi), P. martensi were very numerous and some of them were heavily infected (>75% infected) with L3 A. cantonensis larvae (Hollingsworth et al., 2007). There are a number of studies that have been done on rat lungworm in China, Thailand and Taiwan, where most cases have originated. At this time, there is no medical research that has been done in Hawaiʻi.

References are available in the Overview section of the website.

Q. Why are 90% of RLW cases on the east side of the Big Island?

The east side of the Big Island has the conditions that support an environment favorable to slugs, snails and flatworms, it is wet, and there is a great deal of vegetation. Also, the semi-slug, a primary carrier of the parasite, made its arrival to the island in the area of Paradise Park in the Puna District, which is on the east side of Hawaiʻi Island. Our research includes tracking the range and spread of various mollusk species on Hawaiʻi Island, data is available on our website.

Reference: Hollingsworth et. al. 2007. Distribution of Parmarion cf. martensi (Pulmonata: Helicarionidae), a New Semi-Slug Pest on Hawaiʻi Island, and Its Potential as a Vector for Human Angiostrongyliasis. Pacific Science. 457-467. scholarspace.manoa.hawaii.edu/bitstream/handle/10125/22629/vol61n4-457-467.pdf?sequence=1

Q. Do rat predators (i.e. cats) contract the disease?

At this time there have been no reported cases of cats contracting the disease, in spite of the fact that they are predators of rats. There have been cases of dogs and horses getting the disease.

Q. Can slug-eating livestock get RLW, i.e. chickens or ducks? Can slug eating chickens pass it on to us through eggs or meat?

The parasite cannot be passed on through meat or eggs. It is not known at this time if chickens can get the disease from eating slugs. However, studies done in Australia have shown that parrots can contract the disease.

Q. Are sushi and poke safe?

There is no reason that the fish, in sushi and poke, would have the parasite. It would have to be contaminated from an outside source, i.e. a slug crawling onto the sushi/poke and a person accidentally ingesting said item.

Q. Can mongoose transmit?

The only people I know who have tested it are Ralph Robinson et al. in Jamaica. They tested approximately 150 mongooses (same mongoose species as here in Hawaiʻi) and found no evidence that mongoose are hosts of A. cantonensis.

Reference: Robert Cowie, Ph.D. Personal Communication.

Q. Are coqui paratenic hosts? Could coqui feces have nematodes?

We know of no studies determining if coquis could carry the nematode. Further studies would need to be done to determine if they can be paratenic hosts. However, it is known that frogs, prawns, and lizards can potentially become infected by eating infected snails.

Reference: Hollyer et. al. 2010. Best On-Farm Food Safety Practices: Reducing Risks Associated with Rat Lungworm Infection and Human Eosinophilic Meningitis. Food Safety and Technology 39::1-8. www.ctahr.hawaii.edu/oc/freepubs/pdf/FST-39.pdf

Q. I eat raw kale. A produce clerk said I should buy Hāmākua (Honakaʻa) kale rather than Puna kale. Is this a good idea?

It is up to the consumer where they buy their kale, it is also up to the consumer to wash and inspect it thoroughly. There have been cases reported from the Hamakua Coast as well as from the Puna District. Some lettuce growers are using hydroponic or aquaponic systems to grow as there is more of a barrier that might deter slugs. While a grower might be doing all they can to keep a slug population down, it is still important for the consumer to be responsible for the careful and thorough cleaning of all produce, especially the leafy greens that are to be eaten raw.

Q. What kind of cooking is necessary to kill the parasite on leafy greens, etc.?

The public Health Agency of Canada reports (www.phac-aspc.gc.ca/lab-bio/res/psds-ftss/acantonensis-eng.php):

Physical Inactivation: Inactivation can be achieved by exposure to -15°C for 12 to 24 hours or by boiling for 2–3 minutes. There has been some research on freezing as a way to totally eliminate the parasites in the bodies of giant African snails. It takes about 2 or 3 days before the animal is totally solid. However, that method is not very practical for lettuce.

This is based on the following study: Alicata, J. E. (1967). Effect of freezing and boiling on the infectivity of third-stage larvae of Angiostrongylus cantonensis present in land snails and freshwater prawns. Journal of Parasitology, 53(5), 1064-1066.

Q. Can I get RLW from noni juice that is raw, or does fermentation prevent the passing of the disease?

We know of no studies that have been done at this time on the effects of fermentation on the parasite. Fruits and any medicinal plants that are going to be consumed raw should be well washed. Neonate and young slugs are generally very small and difficult to see.

Q. During the 2005 survey of slugs, were the surveyors informing the people who called of the danger of RLW?

Yes, we explained the dangers of RLW to survey participants at the time that we visited each property to carry out the survey. We already knew as of late 2004 that the Asian semi-slug was potentially an important carrier of RLW in the survey area, based on information from our cooperators at the Centers for Disease Control in Atlanta.

Q. Are severe cases common or are most cases minor?

Approximately 2 to 3 years ago there was a very significant change in the nature of this disease as we’re seeing it in the state of Hawaiʻi. Severe cases were extremely rare before about 3 years ago. The severity of the disease probably relates to the severity of the infestation. The more worms ingested in the 3rd phase, the higher the parasite load, and the more severe the damage. Severe cases are being discussed because it marks a change in the nature of this disease. Severe cases aren’t common, but we run the very significant risk that they will become more common if the disease is not dealt with in a basic epidemiological way.

A thorough review of all cases, including those considered unconfirmed, would need to be done to completely answer this question. There have been a number of serious cases on Hawaiʻi Island, with most taking 6 or more months to begin to resolve themselves, and many reporting on going symptoms 6-10 years later.

Reference: Jon Martel, MD. University of Hawaiʻi, John A. Burns School of Medicine

Q. Is there any kind of immunity against RLW if you’ve been infected previously?

People have reported getting this disease two and three times or more on Hawaiʻi Island. This implies a lack of long-lasting immunity. However, a vaccine against A. costarisensis has been shown to be effective in mice and funding has been obtained by the Rat Lungworm Working Group to test this vaccine against A. cantonensis in wild Hawaiian rats (Rattus rattus). We are providing two recently published general reviews on immunity to helminthes as well as a reference to the vaccine.


  • Maizels, R. et al., 2009. Regulation of pathogenesis and immunity in helminth infections. The Journal of Experimental Medicine. 2059-2066.
  • Moreau, E. and Chauvin, A. 2010. Immunity against Helminthes: Interactions with the Host and the Intercurrent Infections. Journal of Biomedicine and Biotechnology. 1-9.
  • Solono-Parada, et al. 2010. Effectiveness of intranasal vaccination against Angiostrongylus
  • costaricensis using a serine/threonine phosphatase 2 A synthetic peptide and recombinant antigens. Vaccine (28) 5185-5196.

Q. What sort of antigen testing is currently available or in the works?

Currently available tests include:

Clinical Laboratories of Hawaiʻi works with Parasitic Disease Consultants in Georgia and offers an ELISA for the detection of antibodies against A. cantonensis. The cost is approximately $75.00 as of early 2012.

Other tests for detection of A. cantonensis antigens, antibodies or DNA under development are as follows:

Enzyme-linked immunosorbant assays (ELISA) detect antigens of or antibodies against A. cantonensis: are effective but not commercially available (Eamsobhana et al., 1997, 2003; Chen et al., 1986; Cross et al., 1982)

Dot-blot ELISA: based on blood dried on filter paper, epidemiological studies sensitivity and specificity of 100% (Eamsobhana et al., 2003)

A. cantonensis antigens (e.g. 39kD, 31kD, and 32kD) have been used in immunodiagnosis (Chen et al., 2005; Nuamtanong et al., 1996; Maleewong et al., 2001)

Jarvi SI, MEM Farias, K Howe, S Jacquier, R Hollingsworth, and W Pitt. 2012. Quantitative PCR estimates Angiostrongylus cantonensis (rat lungworm) infection levels in semi-slugs (Parmarion martensi). Molecular Biochemistry and Parasitology. Accepted.

Q. Who is responsible for keeping the danger of this disease and its understanding before professionals and the public? I Called the State Dept of Health in 2007 to question and report and was told that, “This is a life style choice disease” by the (State Epidemiologist).

Presumably much of the responsibility lies with the State Dept. of Health. While certain diet choices can put a person more at risk, we do not agree that it is a life style choice because of the broad range of conditions under which the disease has been contracted. The importance of eating fresh, and preferably locally grown greens is supported by health professionals and the greater Hawaiʻi community, and the Hawaiʻi Island Rat Lungworm Working Group (largely volunteer) supports this effort and is working to better educate the public.

Q. Is there any evidence that anti-helminth meds (mebendazole, albendazole, ivermectin) work in acute infection or is it all experimental/theoretical? Could these meds actually worsen clinical course due to acute die off?

The jury is still out on the use of the antihelmintics in treatment of rat lungworm disease. Physicians are concerned that the parasite die off might cause more inflammation in the brain, which could worsen a patient’s condition. However, these drugs have been used in very serious cases, where the patient was not expected to survive and evidence of worm tracks could be seen in brain MRIs. We have had serious cases here on the island where these drugs have been prescribed and the patients did recover. An early detection diagnostic is sorely needed on the Big Island and the RLW working group is in the early stages of testing in a rat model.

Q. Where were the 9 documented cases in 2010? Who gathered the data? Would you mention (for catchment users) that a 20 micron sediment filter will block the 3rd instar?

This data was collected by the Hawaiʻi State Dept. of Health. Most cases were from the island of Hawaiʻi.

The CDC suggests that a 20 micron filter would probably be adequate. However, the 20 micron size pressure will only flatten the larvae against the filter, making them wider, which could still allow them to stretch out thin and get through when there was no pressure being exerted. Use of at least a 15 micron filter is preferred.

If chlorine is being used as water treatment, then one should also be using a 1-micron filter anyway for protozoa. If using a UV system, then it is recommended to filter down to a 5 micron plus have the UV rated to inactivate nematodes. (Class A). A 20-micron filter alone is really just a sediment filter and not adequate treatment for anything else.

Reference: Patricia Macomber, MPH, CTAHR/University of Hawaiʻi. Komohana Research and Extension Center.

Q. Is a waterproof poster going to be made and posted around the community to inform people in the about RLW Disease?

There was a flyer available and it was laminated and waterproofed and taken out to farms and stores. Unfortunately, they do get taken down. Annually, we send out the sanitation branch to repost the posters. We are looking into other avenues to get information out there. We’re looking at private publications, private newspapers, social media networks, etc.

Reference: Marlena Castro Dixon, M.S., Epidemiological Specialist. Hawaiʻi State Department of Health, Disease Investigation Branch.

Q. Do copper barrier products work well? Rephrased: Can we prevent slugs and snails from getting to produce by using a copper band or some kind of spray on chemical like copper hydroxide?

Yes, copper does repel, but it’s not 100%. There have been tests in the laboratory with copper bands and semi-slugs as well as other slugs were tested to see if they would cross it, but it depends on the width of the band. They generally turn around and go the other way, but sometimes they got confused and went across the band; so it doesn’t always work.

Reference: Robert Hollingsworth, Ph.D., USDA.

Q. Will UV light kill slugs and snails and their nematodes?

We don’t think so; otherwise they would be dead in the environment. Studies would have to be completed using various intensities of UV light on isolated larvae to evaluate any effects.

Q. To what extent is the disease treatable?

There is no specific treatment for A. cantonensis infection. There is some evidence that certain supportive treatments may reduce the severity of headache and the duration of symptoms. Persons with symptoms should consult their health care provider for more information.

Reference: www.cdc.gov/parasites/angiostrongylus/treatment.html

Q. Can rat lungworm disease be contracted directly from rat urine/droppings?

We don’t think so. The first stage larvae have only been found in rat droppings and it is the third stage larvae that cause infection in humans. It is demonstrated that the larvae continue their development to the third stage when ingested by slugs and snails.

Q. Why aren’t people who have gotten RLW interviewed and followed-up with for research?

The RLW Working Group is attempting to obtain funding for public education and follow-up of RLWD cases. We recently initiated a Facebook page through which people can share their stories. We are working with school garden projects and agriculture programs in schools as well as the DOE in developing curriculum for integration of RLW education into public schools. We are hoping if funding becomes available to be able to document previous and ongoing cases to learn more about the long-term impacts of this potentially devastating disease.