Why? Because rat lungworm disease, AKA neuro-angiostrongyliasis, is an emerging food-borne infection that can invade human brains and cause serious harm—even death. First discovered in rats in southern China in the 1930s, the parasite that causes neuro-angiostrongyliasis now thrives in tropical and subtropical regions of five continents, including Hawaii and the southeastern United States. Plus, the parasite was recently found on Mallorca, an island off the coast of Spain, and the city of Valencia, Spain. That means Europe is also threatened. Because of rat lungworm’s ongoing spread, many people who visit or live in the Asia-Pacific region, Latin America, Caribbean islands, Africa and beyond need to know about this parasite! Healthcare professionals also need to know about rat lungworm so they can recognize, diagnose and treat it as early as possible in order to prevent long-term harm.

Angiostrongylus cantonensis is a small, slender nematode first discovered in rats in southern China (then Canton, now Guangzhou) in 1933. Adult lungworms, which measure 1 to 1 ½ inches long, live and mate in the pulmonary arteries of rats. Since “angio” is a medical term for blood vessel and “strongylus” denotes the broader group of nematodes to which this parasite belongs, the words were combined to form the name of the parasite’s genus (“Angiostrongylus”). Its species name reflects the place (Canton, China) where it was originally found.

First, let’s review how the parasite survives in nature. After adult worms mate in rats’ pulmonary arteries, infected rats pass “first-stage” larvae in their droppings. Those pellets are eaten by snails and slugs, collectively called gastropods. Over time, the “first-stage” larvae in gastropods become “third-stage” larvae which are still invisible to the human eye but can now infect many animals, from humans to birds to rats. What animals in particular like to eat snails and slugs? RATS. In short, when rats eat A. cantonensis-infected snails and slugs OR gastropods eat rodent feces containing A. cantonensis larvae, the parasite is cycling through its normal hosts. Meanwhile, other creatures such as freshwater shrimp, crabs, frogs, toads and lizards can also eat gastropods and acquire larvae. As a result, humans have developed neuro-angiostrongyliasis by eating raw or undercooked snails or prawns, and curious toddlers have fallen ill after sampling snails in a garden. Occasionally, a raw snail, slug or other transfer host (see list above) is consumed on a dare, or by someone ’living off the land’ (for example, as a survival exercise), or for so-called “medicinal” reasons, thus triggering infection. Most importantly, today, many people probably contract neuro-angiostrongyliasis after eating poorly-washed, fresh, leafy greens and other uncooked produce—foods that may hide tiny snails or slugs containing thousands of larvae. A word to the wise? In high-risk settings, always think twice before eating raw, leafy salads, veggie wraps, and blended drinks such as ‘green smoothies.’ Or –even better—completely avoid them unless you know for sure that their ingredients have been carefully washed. No matter how tempting, adventurous travelers should also steer clear of exotic dishes containing raw, marinated snails, uncooked shrimp or freshwater crabs or other undercooked creatures that might contain A. cantonensis larvae.

After rat lungworm was discovered in a brown rat (AKA Rattus norvegicus) in southern China in 1933, roughly ten years later, A. cantonensis larvae were found in the spinal fluid of a teen-aged boy in nearby Taiwan. At the time, however, no one connected the dots between infection in a human and lungworms in rats. Nor had scientists described the unique migration of A. cantonensis larvae in rats. Then, in the 1950s, two Australian researchers made a stunning observation: not only did certain Angiostrongylus species live near and in rats’ lungs, they also invaded rats’ brains. The final piece of the puzzle fell into place in Honolulu in the 1960s. That’s when autopsies revealed rat lungworm larvae deep in the brain of two local residents who died of severe meningitis (an inflammation of membranes covering the brain). This confirmed that the same path traveled by the parasite in rats occurred in people as well.

According to Professor Robert Cowie of the University of Hawaii, following its initial discovery in China and Taiwan, the rat lungworm parasite spread west through Southeast Asia, east to various Pacific islands, north to Japan, and south to Australia, no doubt associated with military activity during and after World War II and increased travel and trade over subsequent decades. In addition to inhabiting the Australo-Asia-Pacific region, A. cantonensis has recently been reported in Africa, South America (Brazil, Colombia, Ecuador), Caribbean islands (Puerto Rico, Hispaniola, Cuba, Jamaica, Guadaloupe, Martinique), the Canary Islands off the northwest coast of Africa, Mallorca off the coast of Spain, and—in the U.S.—several southeastern states, most notably Florida, but also Louisiana, Oklahoma, Tennessee, Alabama, and possibly Mississippi. Do other tropical islands and nations have rats and snails harboring A. cantonensis? Most experts assume “yes.”

This question is difficult to answer because human infections are often missed. Here are some reasons why. 1) failure to diagnose A. cantonensis due to inadequate knowledge or diagnostic tests 2) insufficient surveillance for previous cases of mild to moderate infection in affected locales 3) a lack of simple, reliable tests using blood as opposed to spinal fluid to diagnose acute illness 4) a scarcity of doctors in certain places where the parasite now thrives One more caveat? Although medical articles and public health data databases have already documented several thousand patients with A. cantonensis infections (especially in Thailand, China, and French Polynesia, followed by the United States, where most infections have occurred in Hawaii), such reports only hint at the actual numbers and distribution of human cases worldwide.

No one has identified all of the snails and slugs that can harbor and transmit A. cantonensis, but the list probably numbers in the thousands, says Professor Rob Cowie of the University of Hawaii. “A lot of people have screened slugs and snails for rat lungworm over the last 50 years, and perhaps 50% contained larvae,” he says. “The parasite is not that selective. Therefore, if you’ve got snails in your garden and you live in a place where rat lungworm is present, you should assume your snails are infected.”

Over several centuries, both brown rats (Rattus norvegicus) and black rats (Rattus rattus) have traveled the seas and invaded new sites. In the 1700s, Norway rats boarded whaling ships; black rats mainly dispersed to new locales in the mid-1800s. Today, both rodent species are competent hosts that continue to spread A. cantonensis to new settings. Infected snails and slugs on tropical plants can also travel by ship and bring A. cantonensis larvae to places where previously-uninfected rats eat the gastropods, thus enabling the parasite to establish additional homes.

In a word, yes. Dogs are a good example. In high risk settings, puppies in particular may consume snails or slugs containing A. cantonensis larvae. Once infected, they often present with lethargy, weakness, or paralysis of their hind legs and tail. If left untreated, just like humans, dogs can suffer permanent neurologic damage, even death. On the other hand, when promptly diagnosed and treated with corticosteroids, de-wormers, and pain pills, many dogs recover after just a week or two of treatment, says veterinarian Alfred Mina of Hilo, Hawaii. Rat lungworm disease can also affect primates, birds and animals that graze in fields (horses, for example). In Sydney, Australia, rat lungworm is the leading cause of neurological illness in an owl-like bird called the tawny frogmouth; it is also an emerging disease in brushtail possums. In Miami, Florida, both a gibbon in a zoo and a privately-owned orangutan have died from neuro-angiostrongyliasis, as have squirrel monkeys in Hilo’s Panaewa Rainforest Zoo. On the island of Mallorca, hedgehogs were the first animals to alert local wildlife biologists to the arrival of A. cantonensis.

Signs and symptoms are diverse, varying from patient to patient. Early on, as third-stage larvae migrate from the intestine to other organs and tissues, low-grade fevers as well as abdominal pain, nausea, vomiting, cough, or shortness of breath may occur. In addition, skin rashes plus muscle and joint pains are also relatively common. Clinical symptoms are more specific once parasites reach the central nervous system and often include headaches and painful bodily sensations. In a severe infection, what may follow next are unremitting headaches, a stiff neck signaling meningitis, altered consciousness, or bowel and bladder dysfunction reflecting injury to the spinal cord. In rare cases, patients with overt neurologic symptoms have then progressed to complete paralysis and an inability to breathe, requiring emergency support in a hospital ICU.

Unlike what happens in rats, A. cantonensis cannot complete its life cycle in infected people. Therefore, after growing into “sub-adult” worms, migrating parasites typically die, either in the central nervous system or other tissues and organs. Nonetheless, those dying larvae can still trigger severe inflammation and scarring in the spinal cord and brain.

Once neuro-angiostrongyliasis is suspected, performing a lumbar puncture (AKA spinal tap) is key. The first goal is to look for inflammatory cells called “eosinophils.” In rare cases, spinal fluid may also reveal larvae, which proves the diagnosis. Finding parasite DNA in spinal fluid is another way to prove the diagnosis; in the U.S., such tests are usually run in state labs, at the Centers for Disease Control, or at the Laboratory for Parasitic Diseases at the National Institutes of Health. Even before spinal fluid is obtained, some patients receive treatment based on characteristic clinical findings and eosinophils in their blood as well as recent residence or travel to an affected area. Nonetheless, it is always best to confirm the diagnosis by obtaining spinal fluid. Seeking advice from a doctor with prior experience in the diagnosis and treatment of neuro-angiostrongyliasis is also highly recommended.

Following a confirmed diagnosis, acutely-infected patients typically receive high-dose corticosteroids to reduce inflammation in their brain or spinal cord. If their intracranial pressure is high, repeat lumbar punctures can also help to reduce pressure and relieve headache. Anti-helminthic (so-called “de-worming”) drugs are a final, important form of treatment, albeit more effective against younger, smaller larvae than sub-adult worms. Albendazole is the de-wormer currently recommended for humans. In an ideal world, corticosteroids plus albendazole would be started within two weeks of infection when larvae are still migrating. Nonetheless, it now appears that combined treatment using albendazole plus steroids is helpful not just before but after A. cantonensis larvae have entered the central nervous system. Another question? Should someone who bites into a slug or snail (for example, in a salad or sandwich) in a high-risk area take albendazole as immediate, post-exposure treatment? Although no one has ever compared post-exposure albendazole with “watching and waiting,” in this situation, many experts endorse a short course of albendazole.

Many simple measures can protect you from neuro-angiostrongyliasis. First, anyone living in or visiting an endemic area should thoroughly wash produce, especially lettuce and rough leafy greens, taking special care to dislodge tiny snails or slugs. Cooking vegetables to a temperature of 165 degrees F or freezing for 48 hours will also kill A. cantonensis larvae. Killing snails and slugs with baits and eliminating their outdoor hiding places are two more ways to limit one’s risk of exposure. More sensible advice?Don’t throw fresh leafy greens into a blender for a Kermit-colored smoothie. Don’t drink from a hose where a snail or slug might hide. Don’t let children play with snails! Finally, while traveling, avoid exotic foods containing raw or undercooked snails, crustacea or other creatures that could harbor A. cantonensis larvae.

Neither A. cantonensis parasites nor snails and slugs tolerate colder temperatures, which is why rat lungworms and neuro-angiostrongyliasis are currently confined to the tropics and sub-tropics. Nonetheless, if warming trends continue, even temperate areas could become more hospitable. Now that rat lungworm has gained a foothold in southern Europe and the southeastern United States as far north as Tennessee, monitoring its spread, both in animals and humans, is more important than ever. But the highest priority is raising general awareness among at-risk residents and travelers while--at the same time--educating healthcare professionals so that infected people are diagnosed and treated as quickly as possible.