Demystifying Rat Lungworm (How to safely enjoy your CSA bag without anxiety)

Carried by even the tiniest of slugs, rat lungworm is sheathed in enough fear and unease to deter many of us from eating fresh, locally grown veggies. You've likely heard a horror story or two about the brain-invading parasite, especially if you’re a resident of the rainy, east side of Hawai’i. But what exactly is it, and how can we prevent it?  Here’s what you need to know to safely enjoy your CSA bag, without freaking out. 

The Worm 

Angiostrongyliasis cantonensis (pronounced an-gee-o-stron-guh-luss can-tun-en-sis), is a tiny, parasitic nematode (roundworm), commonly referred to as the rat lungworm. The parasite’s preferred host animals are rats (hence the name), who harbor the adult worms in their lungs and pass the larvae through their feces. Mollusks (like snails and slugs) ingest the infected rat feces and become secondary hosts for the parasite. Normally, A. cantonensis larvae grow into young adults inside the mollusks before they are passed back to the rats, where they reproduce and complete their life cycle. However, this cycle is sometimes interrupted when an unsuspecting mammal (like a human) accidentally ingests the parasite through an infected slug. Thankfully, the human body is not a good host for the worms; because they cannot mature and reproduce, they will eventually die.

The Disease 

Even though the worms do not prefer to live in the human body, they can still cause a serious illness called eosinophilic meningitis. This is a rare form of meningitis and is probably what you think of when you hear “rat lungworm.” The symptoms usually include headaches, nausea, vomiting, stiff neck, pain in the limbs, and sometimes visual impairment. In some cases, the illness can cause life threatening complications, while in other cases, the infected person may have no symptoms at all. Either way, there is no true treatment for the condition because the parasite will die on its own.  

The Slugs 

Various species of slugs and snails can be carriers of A. cantonensis (rat lungworm). The biggest culprit seems to be the invasive semi-slug, Parmarion martensi (that’s the one that has the little yellow oval on its back). As mentioned before, humans can ingest A. cantonensis by eating a slug or part of a slug. It is not yet known by the scientific community whether you can get sick from ingesting worm larvae through slug/snail slime, but it’s probably better to err on the side of caution. Slugs love to feed on leafy greens, making them easily ingestible by someone wanting to enjoy some fresh lettuce or kale. However, you don't need to stop eating fresh veggies! Let’s talk about prevention. 

The Greens 

Our Da Box producers use best practices to prevent transmission of the rat lungworm parasite, including growing greens hydroponically. Even so, slugs can easily go undetected, and it is important to carefully clean your produce before consuming. Here are some tips from CTAHR (UH Manoa’s College of Tropical Agriculture and Human Resources): 

1. Always wash your produce!! Running water is the #1 most effective method for ensuring safe produce. Do not try to soak your produce in water with additives like soap, bleach, or food-grade hydrogen peroxide, etc.  

1. For things like cabbages, remove the outer leaves. Inspect for slugs. Cut the cabbage and inspect the insides for slugs.  

1. For root crops like carrots and beets, wash the veggie under running water and scrub with your hands or a brush.  

1. For salad mix and herbs that are pre-washed and bagged, rinse before eating.  

1. For lettuce and other leafy greens that are not pre-washed/pre-bagged, take apart each leaf. Rinse each individual leaf under running water and lightly rub. Once each leaf is rinsed, rinse them all together one more time and drain.  

1. For veggies with very intricate leaves, like curly kale, we recommend cooking before eating to kill the parasite (unless you feel up to thoroughly inspecting every leaf crevice). Freezing for 48 hours will also kill the parasite. 

1. If you don’t have the patience for washing, you can’t go wrong with cooking your veggies (fully/to 165 degrees) before eating! 

Rat lungworm should be taken seriously, but not feared. It is easily preventable with awareness and safe practices, like the ones listed above. For more information, please see: 

Rat Lungworm: Causes and How It Spreads | Rat Lungworm Disease (Angiostrongylus) | CDC 

Angiostrongyliasis (Rat Lungworm) | Disease Outbreak Control Division 

Rat Lungworm – CTAHR Farm Food Safety: Good Agricultural Practices Education