Telling Consumers, Gardeners, and Farmers about the Possible Risk of Rat Lungworm in the Local Food Supply in Hawai‘i

Abstract

The rat lungworm, Angiostrongylus cantonensis, uses various species of rats as its definitive hosts and a wide range of slug and snail species as its intermediate hosts.^1,2 When ingested by humans, this nematode is a major cause of eosinophilic meningitis.³ However, the risk of consuming the rat lungworm, is extremely low, especially when compared with other food-borne disease agents such as E. coli and Salmonella, or illegal pesticide residues. That said, ingesting a potentially harmful microscopic worm is an unpleasant thought, especially when consumers have seen the potential impact on television, which in serious cases can lead to coma and death, or to long-term neurological malfunction.

On July 8, 2009, the Discovery Channel (a US television channel) ran a 15 minute story on rat lungworm, calling it “one of the most feared parasites on the planet.”^4,5 The program covered the story of American tourists who had accidently eaten the parasite in a salad while on vacation in Jamaica in early 2000. While the victims eventually recovered, the story was seen by a large number of viewers. In late 2008 in Hawai‘i, two unrelated individuals had eaten insufficiently washed local produce and had developed the serious eosinophilic meningitis that results from ingesting harmful quantities of the parasite.⁶ Finally, a November 2011 story in Australia covered the death of an infant who had apparently consumed the rat lungworm parasites while in the family garden.⁷ The parents of the child were angry with public officials because they did not do more to notify the public of the potential risk in Sydney neighborhoods.

Alerting the public to the presence of a very rare non-communicable yet potentially serious disease is a double-edge sword, especially if it causes them to worry about potential risk associated with their fresh produce. Statistically speaking, consumers in Hawai‘i are much more likely, for example, to get hit by a car while walking across a street than to be infected by the rat lungworm. At the same time, there is a significant push to eat more fresh green vegetables, start school gardens, and bring the vegetables grown into the classroom and/or cafeteria, and for residents and visitors to buy more locally-grown produce. Reducing the use of pesticides that might kill rats and slugs and snails, seems also to be a priority for many. Large media campaigns to inform all consumers (residents and visitors) about a relatively small risk in the local food supply could have a significant economic impact on local produce growers. Health officials continue to struggle with this delicate situation, though the families of those who have been harmed by rat lungworm generally believe that all consumers should be informed of the potential risk as they have seen at first hand the devastating impact of the parasite on a family member.

While public policy should be left to policy makers and implementers, general advice for consumers and food growers can be shared via a range of media. Regarding consumers, first, all vegetables should be inspected for signs of snail or slug damage and discarded if there is any damage. If the plant is intact, for leafy vegetables, such as lettuce, Swiss chard, and celery, all leaves should be pulled apart and all surfaces inspected. This is important because slugs and snails, especially very small juvenile ones, can be found living deep among the leaves and stalks of the plant. Simply rinsing off the outer leaves of produce and then chopping the entire plant, for example for a fresh salad, might just lead to dicing up a live slug or snail, which may (or may not) be infected with rat lungworm. Once the plant has been disassembled and thoroughly inspected, all surfaces should be rinsed and rubbed with drinkable, running, cool water. This is the most effective way to reduce risk, but it is not an absolute guarantee. If a water sanitizing or produce “cleaning” product is used, it may or may not reduce the risk of a slug, snail, or the nematodes themselves being on the food that has been prepared and is about to be served.

As rat lungworms originate in the lungs of rats and undergo part of their development in snails and slugs before being re-ingested by rats in order to complete their development,³ the best way to control or eliminate the risk of infection is to control it at the source by killing the rats and controlling the snails and slugs in the production and processing areas. Unlike pesticides used against other crop and garden pests, which can be spread over an entire field or plant, pesticides for killing rats and slugs and snails are more targeted and come in bait forms. They are therefore generally less effective, and the baits can be highly susceptible to disintegrating in heavy rain. Thus, a methodical program to keep a farm or garden free of rats and slugs and snails needs to be in place.

Conflict of Interest

The author identifies no conflict of interest.