The Daniel K. InouyeCollege of Pharmacy

Rat Lungworm

Frequently Asked Questions

I have had Rat Lungworm 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 disease (RLWD) contracted in Hawaiʻi 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. From meetings with RLWD victims we have observed that some recoveries have been more successful than others.

Supplements and other treatments may be useful in gradually restoring health over the long term. Some victims have reported benefits from acupuncture and Chinese herbal formulas along with therapies such as intravenous vitamin and glutathione administrations, however these treatments can be prohibitively expensive as they are not covered by most insurance companies. It is generally reported by those who have had serious cases of rat lungworm disease that recovery is slow and very often incomplete. Pain management therapy can be helpful. A support group to provide an avenue for victims to communicate with each other about recoveries and methods for relief from long-term symptoms is recommended.

References

  • Reports from survivors and caregivers of rat lungworm disease survivors during Rat Lungworm Support Group meetings hosted by the Hilo Medical Center, and from personal communications with survivors and caregivers.
  • Howe, K. 2013. A severe case of rat lungworm disease in Hawaiʻi. Hawaii Journal of Medicine and Public Health. 72:(supp. 2): 46-48.

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

Nerve damage often occurs in more serious cases of rat lungworm disease (RLWD). It can persist for months or years, becoming chronic. One RLWD expert in the medical field reports the following:

“…Tissue damage resulting from a combination of direct mechanical and chemical disruption increases with time. Many larvae do succumb to the host immuno-inflammatory response, stopping dead in their tracks, but this leads to the formation of dense, fixed inflammatory foci. The more advanced the larva, the bigger the lesion, and the longer it will take to resolve; it’s very likely that the remains of an immature adult worm (L5) could persist in the CNS for months or possibly years, with surrounding chronic inflammation causing the deposition of permanent scar tissue. Many patients suffer prolonged, sometimes permanent, clinical sequelae. While some become convinced the parasite has survived, even multiplied, in their brain, the simple explanation is that their CNS lesions have been too extensive for complete resolution. They may be affected by irritating and debilitating symptoms indefinitely, with the only treatment available being non-specific, as offered by physiotherapy and pain clinics.”

Parasthesia, or extreme skin sensitivity, has been frequently reported as pain, numbness, itching, or a sensation fo worms crawling under the skin. Skin sensitivity, particularly on extremities (arms, legs) and similar in sensation to a very bad sunburn, has been reported to persist for years by some who have had rat lungworm disease.

References:

  • Personal Communication: Hilo Medial Center, Rat Lungworm Support Group.
  • Wang et al. 2008. Human angiostrongyliasis. Lancet Infectious Diseases 8: 621–630.
  • Jarvi S., P. Prociv. 2020. Angiostrongylus cantonensis and neuroangiostrongyliasis (Rat lungworm disease). Parasitology (accepted for publication).

Has there been any incidence of RLW in Oregon?

There have been no confirmed cases of rat lungworm disease (RLWD) in humans or other animals that have been contracted in Oregon, however there may be cases that were diagnosed or treated in Oregon but the infection originated in Hawaiʻi; we know of one infection where this was the case (personal communication).

We know as well of cases of RLWD reported in the U.S. where the infection was contracted in Hawaiʻi or another location but were diagnosed, or were not diagnosed but had symptoms of RLWD, when the traveler(s) returned home. The parasite is endemic on the U.S. mainland in the Gulf States from Florida through and into Texas, and is beginning to move north with infection found in cotton rats in Oklahoma.

The first human case of RLWD on the U.S. mainland was reported in Louisiana in 1993. Twelve additional cases reported from the continental U.S. (excludes Hawaiʻi) were discussed in a study that examined confirmed cases of RLWD reported from 2011-2017. Of these 12 cases, six had no travel history outside of the continental U.S. and were deemed to have originated in the state of residence. Four were from Texas and one each from Tennessee and Alabama. And in 2019 the Alaska Division of Public Health reported a case of RLWD acquired by an Alaskan resident who had vacationed in Hawaii.

References below highlight the first report of the rat lungworm Angiostrongylus cantonensis in North America, it range expansion, and human cases of rat lungworm disease acquired on the U.S. mainland, in Hawaiʻi, and in Jamaica.

References:

  • New, D., M.D. Little, J. Cross. 1995. Angiostrongylus cantonensis Infection from Eating Raw Snails. New England Journal of Medicine. 332:1105-1106.
  • Campbell, B. G. and M.D. Little. 1988. The finding of Angiostrongylus cantonensis in rats in New Orleans. American Journal of Tropical Medicine and Hygiene 38::568–573.
  • Flerlage, T., Y Qvarnstrom, J Noh, JP Devincenzo, A Madni, B Bagga, N Hysmith. 2017. Angiostrongylus cantonensis eosinophilic meningitis in an infant, Tennessee USA. Emerging Infectious Diseases. 23(10): 1756-1758. DOI: 3201/eid2310.170978.
  • Hammoud, R.A., S.L. Nayes, J.R. Murphy, G.P. Heresi, I.J. Butler, N. Perez. 2017. Angiostrongylus cantonensis meningitis and myelitis, Texas, USA. Emerging Infectious Diseases. 23(6): 1037-1038. DOI:https:..dx.doi.org/10.3201/eid2306.161683.
  • Kim, D.Y., T.B. Stewart, R.W. Bauer, M. Mitchell. 2002. Parastrongylus (=Angiostrongylus) cantonensis now endemic in Louisiana wildlife. Journal of Parasitology. 88(5): 1024-1026. https://doi.org/10.1645/0022-3395(2002)088[1024:PACNEI]2.0.CO;2
  • Lindo, J.F., C.T. Escoffery, B. Reid, G. Codrington, C. Cunningham-Myrie, M.L. Eberhard. 2004. Fatal autochthonous eosinophilic meningitis in a Jamaican child caused by Angiostrongylus cantonensis. American Journal of Tropical Medicine and Hygiene. 70: 425-428.

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

The rat lungworm (RLW) Angiostrongylus cantonensis is believed to have originated in Southeast Asia. This nematode was first discovered in China in 1935 but is now endemic in Asia, Australia, the Caribbean islands and the Pacific Islands and has spread to the Americas where it is reported in the southern United States, Brazil, Ecuador, and the Guiana Shield on the northern coast of South America.

A paper from China in 2008 states more than 2,800 cases of human infection have been reported in 30 countries and certainly that number has grown in the past twelve years. A. cantonensis has been documented as a parasitic disease of humans in Hawaiʻi and other Pacific islands since the early 1960’s. Numerous studies were conducted in Hawaiʻi from 1960 to 1970 after which research dropped off, only to be resumed after the year 2000. It is certain there were cases of rat lungworm disease (RLWD) that occurred in the interim but it was only in 2007 that the Hawaiʻi Department of Health made angiostrongyliasis (RLWD) a reportable disease.

The flatworm Platydemus manokwari, a paratenic host for the parasite, and the semi-slug Parmarion martensi, immigrated to Japan and were thought to be the probable cause of an outbreak of angiostrongyliasis in the year 2000. The semi-slug, a relatively recent arrival to the Hawaiian Islands, is thought to be responsible for outbreaks of disease cases on the Island of Hawaiʻi that began around 2005 and continue to the present. In the Puna District, where outbreaks first occurred, P. martensi were numerous and some were heavily infected (>75% infected) with L3 A. cantonensis larvae.

The semi slug has since spread as have cases of rat lungworm disease in Hawaiʻi. In 2016 the Governor created a task force to assess the threat of the disease. Until 2017, P. martensi had only been reported on Hawaiʻi and Oahu, however, investigations following an outbreak of human cases on Maui confirmed its presence on that island.

In 2019 a case of RLWD was reported in the North Kohala District on Hawaiʻi Island and reports of the arrival of P. martensi were made and confirmed. The RLW parasite is known to be present on all of the Hawaiian Islands with the possible exception of Molokaʻi, however the lack of findings there may be due to the lack of thorough investigation. Human cases of RLWD have been reported from Kauai, Oahu, Maui, Lanai, and Hawaiʻi Island.

There are a number of studies that have been done on RLW in China, Thailand and Taiwan, where the majority of human cases have originated globally. Recently in Hawaiiʻi, the collaborative efforts of researchers and educators have made advancements in the prevention and treatment of RLWD.

References:

  • Asato, R., K. Taira, M. Nakaurma, J. Kudaka, K. Itokazu, M. Kawanaka. 2004. Changing epidemiology of Angiostrongylus cantonensis in Okinawa Prefecture, Japan. Japan Journal of Infectious Disease 57:184-186.
  • Chen H.T. 1935. A new pulmonary nematode of rats, Pulmonema cantonensis ng, nsp from Canton. Annals of Parasitology 13: 312–17.

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

The east side of the Big Island (Hawaiʻi Island) has ideal conditions that support an environment favorable to slugs, snails and flatworms; it is wet, and there is a great deal of vegetation. The semi-slug Parmarion martensi, a primary carrier of the rat lungworm (RLW), made its arrival to the island in the area of Paradise Park in the Puna District on the east side of Hawaiʻi Island sometime around the year 2000.

Studies published in 2007 showed that this newly arrived invasive pest carried extremely high numbers of infective stage RLW larvae and the slug has unusual behavior; it is relatively fast, will climb easily, and seems to like to get into dwellings, food, and beverages. Juvenile slugs are small, can be infected, and can easily be missed when cleaning greens such as lettuces etc.

The Puna District stands out as one of the most impoverished districts in the state. The primary industry is agriculture and many people residing in this area grow their own food for household consumption, sometimes without adequately inspecting or washing it.

It is very easy for a small slug or snail to hide in leafy greens and headed vegetables that are eaten raw, and this is one source of disease transmission. Juvenile semi slugs and neonates, which are newly hatched slugs and about the size of a grain of rice, have been found to be infected with RLW larvae and this is why it is stressed that careful cleaning, drying, peeling, or cooking (3-5 minutes)/freezing (48 hours or more) produce, are the best methods of prevention of rat lungworm disease (RLWD).

Another possible reason for the majority of cases originating in that area is the large number of households using rainwater catchment systems for their primary water supply. In the 1950ʻs and 60ʻs very large subdivisions in the Puna District were approved by Hawaiʻi County and were constructed with no infrastructure for water.

As there is no state or federal oversight for individual rainwater catchment systems, residents are responsible for the design and maintenance of their own systems. Many people have reported finding slugs and snails in their catchment tanks, often drowned, and preliminary studies at the Jarvi Lab have shown the potential for infected, drowned slugs, especially the semi slug, to shed large numbers of infective RLW larvae. The larvae can survive for some time in water and have been observed passing through a range of filters, including 20, 10, and 1 micron filters.

More studies to determine the likelihood of catchment systems as a source of transmission need to be done. The Jarvi Lab has also been conducting research to determine infection rates for slugs/snails on Hawaiʻi Island and compares the information collected with data from other islands in the Hawaiian Island chain. The Jarvi Lab research also includes tracking the range and spread of various mollusk species, especially Parmarion martensi, on Hawaiʻi Island.

The compiled data is shown in a presentation given by L. Kaluna from the UHH Jarvi Lab at Hawaii Invasive Species Council, Brown Bag Lunch Presentation #30 and is available for viewing online.

Other studies have been done at UH Manoa to look at the distribution of the RLW, slug and snail hosts that have been found to be carriers, and the potential for expansion of the range of RLW in Hawaiʻi with expected climate change.

References

  • 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.
  • Howe, K., L. Kaluna, A. Lozano, B .Torres Fischer, Y. Tagami, R. McHugh, S. Jarvi. 2019. Water transmission potential of Angiostrongylus cantonensis: Larval viability and effectiveness of rainwater catchment sediment filters. PLoS ONE 14. e0209813–20. doi:10.1371/journal.pone.0209813.
  • Kim, J.R., T.M. Wong, P.A. Curry, N.W. Yeung, K.A. Hayes, R.H. Cowie. 2108. Modelling the distribution in Hawaii of Angiostrongylus cantonensis (rat lungworm) in its gastropod hosts. Parasitology 1-8. DOI.org/10.1017/S0031182018001026
  • Hawaii Invasive Species Council. April 1, 2020. Brown Bag #30: Rat lungworm update (Lisa Kaluna, UH Hilo). https://dlnr.hawaii.gov/hisc/news/brown-bag-30-rat-lungworm-update-lisa-kaluna-uh-hilo/