An uptick in meningitis cases from the Rat Lung Worm on Maui and the Big Island of Hawaii have sparked widespread fear through the community recently. Fourteen cases of RLW have been reported this year, following 11 cases in 2016. Media outlets have jumped on the stories and coconut wireless has misled many. Having studied this particular parasite for three years and conducted independent research on it during my undergraduate career at the Pacific Biosciences Research Center, I’ve been concerned about the lack of understanding of the parasite’s transmission and its impact on my community. Rat Lung Worm is a serious disorder and steps should be taken to avoid transmission, but, compared to many other pathogens, it is also relatively difficult to contract the parasite. Like shark attacks, the possibility of contracting Rat Lung Worm doesn’t necessarily warrant the fear elicited by the media. So let’s look at the facts:
Angiostrongylus cantonensis is the tiny parasitic worm responsible for the eosiniphilic meningitis disorder. First documented in China, the parasite has since spread to North America, Australia, Africa, Oceania, the Caribbean, and South America. Rats are the parasite’s definitive host, which contract the mature worms by feeding on intermediate hosts such as snails and slugs infected with third stage larvae. These juveniles then enter the bloodstream from the intestine of the rat and mature in the central nervous system. Adult worms mate in the pulmonary artery and females lay eggs in the lungs. The eggs are then ingested through the trachea, and non-human infective first stage larvae are excreted in the rat’s feces. During this first life stage, the larvae contained in the rat’s feces are consumed by snails, where the parasites develop into their third, human infective life stage in the snail’s tissue.
Human infection is caused by the consumption of undercooked snails or passive carrier hosts like frogs and crustaceans (crabs, prawns), improperly washed vegetable produce as well as water supplies contaminated with snail tissue. Snail trails have been shown to have traces of the parasites but appear to be species specific and the number is so low in the slime that it is a transmission of lesser concern. Humans cannot contract the parasite through the skin or through the bloodstream, it must be ingested. As we are not a primary host for the species, once ingested, the parasite becomes disoriented and finds its way to the cerebrospinal fluid (CSF) and infects the casing around the spinal cord and brain, eventually dying and thereby eliciting a harmful immune response.
Most common symptoms of the infection include headache, neck stiffness, paraesthesia, vomiting, and nausea. The eosinophilic meningitis condition itself is defined by an increase of eosinophils (specific white blood cells that attack parasites) in the CSF. The eosinophils gather in the CSF and release their granular contents on the parasite’s surface, inadvertently causing damage to surrounding tissue through inflammation. As a result, high rate of human A. cantonensis infection can result in blindness, coma, and even death. There is no cure for RLW but anti-inflammatory medication and pain-killers can alleviate the symptoms.
Though the chances of getting RLW are smaller than being attacked by a shark in Hawaii, one should take the precautions to avoid contact. If you have a garden, make sure to wash your produce thoroughly with running water; soaking it is inadequate and may expose even more parasites. Cooking or freezing produce and escargot is the sure fire way to kill the parasites. Keep children and animals away from snails and slugs as they are most likely to try and ingest a raw infected mollusk. It has been recommended that households with water catchment should switch to a 1-micron filter and regularly inspect their holding tanks for slugs and snails.
Most importantly, rid yourself of fear and use common sense. It has been sad to hear the impact on local Maui farmers due to the lack of fact checking done by individuals. Incidents like shark attacks and worms in your brain get plenty of media attention but are often of least concern. Ironically, there have been 20 confirmed mumps cases in Hawaii this year, which is a disease that’s easily avoidable through vaccination, but has returned due to the same lack of fact checking and misleading information. Knowledge is power.