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An Introduction to Rat Lungworm Disease

August 23, 2018
By: Joe Wat

If you’ve been watching the news or reading the newspaper you have probably been hearing about something called Rat Lungworm Disease. What is it? How did it come to Hawaiʻi? How can we keep ourselves and our families safe? After attending a training for educators run by the Oʻahu Farm to School Network and Kay Howe of the UH Hilo Jarvi research lab, we have some information to share.

Rat Lungworm Disease is caused by a small nematode (Angiostrongylus cantonensis), first identified by a researcher in Guangdong, China. Although it is indigenous to south-east Asia, rat lungworm parasites have established populations throughout many Pacific islands and the global tropics.

The life cycle of the rat lungworm parasite is complicated and involves many different players. First, an egg hatches in the lungs of an infected rat. These larval parasites migrate into the rat’s digestive tract and are expelled in the rat’s droppings. If the droppings are consumed by a slug or snail, the young parasites are able to molt two times as they grow into an adolescent infective stage. The rat lungworm life cycle is completed when a rodent eats infected snails or slugs, adolescent parasites travel through the gut to the central nervous system, and mature by molting two more times before mating in the pulmonary arteries and laying eggs in the rat’s lungs.

This is the ideal life cycle for the rat lungworm parasite, starting and restarting in the lungs of the common rat (Rattus norvegicus) with a quick visit to a mollusc. However, some rat lungworm parasites may find themselves in unfamiliar territory if a slug or snail is consumed by something other than a rat. In most other mammals the worm will not survive long enough to reproduce, however, regardless of their ultimate success, they try their best and travel through the gut and into the brain to mature. It is in this stage, as the worms travel along our nerves and through the brain, that they can cause the most damage to humans. 

Many cases of rat lungworm pass unnoticed. Although it is still under investigation, it is thought that the number of infective parasites consumed may determine the severity of symptoms which range from passing unnoticed, mild and flu-like, and rarely, all the way to coma, permanent neurological damage, and death.

What can we do about this? Humans have persisted in areas with endemic populations of rat lungworm for centuries. Carefully following a few simple steps can help to keep yourself and your family safe.

Address rodent infestations near your home. Because the worm is only able to reproduce in specific species, including the three species of rats common in Hawaiʻi, managing their population by properly storing refuse and setting traps may help decrease the parasitic load of slugs in your area.

Reduce slug and snail populations in the garden and around your home. Create a “slug jug” or other slug management kit which should include 1 part salt for every 7 cups of water. Schedule your slug hunts for early in the morning or in the evening when slugs and snails are most active. If the population is persistent, consider slug “traps” like damp tarps or cardboard where they will tend to accumulate. See our “How to… Practice Slug & Snail Removal in the School Garden Resource Guide” and CTAHR’s fantastic resource page on farm food safety practices for more details.

When preparing food, make sure that it is properly stored where slugs and snails cannot reach it. Any produce to be eaten raw, no matter where it is from, should be washed thoroughly, leaf by leaf, under running water to make sure no slugs or snails are present. There is no evidence that produce washes assist in removing or killing the parasites or slugs; carefully inspect the complete surface of anything to be eaten raw as you are washing. The parasite is also killed if it is left in the freezer overnight or cooked to 165 degrees.

If you are on catchment, make sure that you regularly maintain your system and replate filters to prevent access by slugs and snails. Using a 1 micron filter, small enough to catch a variety of infective protozoans, will also exclude the larval rat lungworm parasites.

References and Further Resources:

Hollyer, J. R., Troegner, V. A., Cowie, R. H., Hollingsworth, R. G., Nakamura-Tengan, L. C., Castro, L. F., & Buchholz, A. E. (2010, January). Best On-Farm Food Safety Practices: Reducing Risks Associated with Rat Lungworm Infection and Human Eosinophilic Meningitis. Retrieved August, 2018, from https://www.ctahr.hawaii.edu/oc/freepubs/pdf/FST-39.pdf
          Safety Information for Growers

Saulo, A. A. (2009, March). Avoid Contracting Angiostrongyliasis (Rat Lungworm Infection): Wash Fresh Fruits and Vegetables Before Eating! Retrieved August, 2019, from https://www.ctahr.hawaii.edu/oc/freepubs/pdf/FST-35.pdf
          Washing Instructions

Insights on PBS Hawaii [Television series episode]. (2017, June). In Rat Lungworm - What you Need to Know. What you Need to Do. Honolulu, HI. Retrieved August, 2018, from https://www.youtube.com/watch?time_continue=168&v=w8FUL8FT-RY
          HPBS interview with researchers and doctors about RLW

College of Tropical Agruiculture and Human Resources. (n.d.). Rainwater Catchment Solutions: Filters for Rainwater Catchment Systems [Brochure]. Hawaiʻi County, HI: Retrieved August 2018, from https://www.ctahr.hawaii.edu/hawaiirain/downloads/3_filters.pdf
          Filtration information

BARRATT, J., CHAN, D., SANDARADURA, I., MALIK, R., SPIELMAN, D., LEE, R., . . . STARK, D. (2016). Angiostrongylus cantonensis: A review of its distribution, molecular biology and clinical significance as a human pathogen. Parasitology,143(9), 1087-1118. doi:10.1017/S0031182016000652
          Description of disease history and pathology