On Dec. 31, 2019, 31-year-old Chaunda Rodrigues of Hilo, Hawaii bought an avocado-and-lettuce sandwich from a local market. But when Rodrigues started to eat, something stuck to her teeth. Horrifyingly, it was part of a mucinous, 2.5-inch slug. Then came the aftershock. A few days later, a lab at the University of Hawaii confirmed that the creature Rodrigues bit into contained , a foodborne parasite that can invade human brains.
Ever since A. cantonensis, also called "rat lungworm," was first discovered in southern China in the mid-1930s, the neurotropic nematode has slowly but inexorably spread. Today it inhabits tropical islands and warm, humid areas of . Although rats are the parasite's definitive host, humans most often fall ill after ingesting infective larvae within snails and slugs, many of which are invasive species. A classic example is the Asian semi-slug Parmarion martensi. Ever since it was first identified on Oahu in 1996, on the Big Island in 2004, and on Maui in 2017, P. martensi has often entered human habitats bearing heavy larval loads. Once inside humans, those same larvae head for the central nervous system where they typically grow and die, sometimes leaving deadly inflammation and neurologic harm in their wake.
Rodrigues was not a passive person. Once her dilemma became clear, she quickly obtained an anti-helminthic drug called albendazole (Albenza). She also posted on Facebook, publicly sharing her saga and a vivid photo of her gooey, severed gastropod. Finally, 2 weeks after biting the slug, Rodrigues and her husband against Island Naturals Market for negligence in failing to clean ingredients of the sandwich it made and sold and thus prevent exposure to a potentially fatal parasite.
What's the Risk? Hard to Say
Although many illnesses due to A. cantonensis go undiagnosed or are never reported, in 2019, nine official cases occurred among local residents and visitors to the Big Island of Hawaii. Did a few pills of albendazole protect Rodrigues from the same fate? No one knows for sure, but thankfully she stayed well. The bad news, on the other hand, is that, every year, millions of people visit Hawaii knowing nothing about rat lungworm, including answers to such basic questions as: What the heck is it? How can I avoid it? How is it diagnosed? Are there early warning signs that will allow me to receive prompt, effective treatment before developing complications? The same ignorance holds true for most of their doctors back home.
One patient who learned this the hard way is a 56-year old woman from Seattle who, like many others right now, couldn't wait to enjoy some sultry sun and balmy trade winds after life under more restrictive COVID lockdowns and protocols. Never guessing that a dangerous parasite might contaminate local produce, Julie Packard blithely ate several salads and a veggie wrap during her 8-day stay on Hawaii Island in December 2021. Her early symptoms -- a strange tightness in her chest and sporadic tingling -- began before she left. Days later, Packard also suffered myalgias, burning pains, and a truncal rash followed by altered vision and balance. Bottom line? It wasn't until after 5 weeks of worsening symptoms that Packard finally had a spinal tap and a small sample of her cerebrospinal fluid was shipped to the Laboratory of Parasitic Diseases at NIH. There, an for A. cantonensis DNA proved strongly positive, but her brain was already injured. Even 3 months later -- despite 2 weeks of albendazole and ongoing treatment with Decadron -- the once-athletic social worker still had double vision and an unsteady gait.
Other telltale signs and dire consequences of neuroangiostrongyliasis include severe, unremitting headaches, paraesthesias, bowel and bladder dysfunction due to radiculomyelitis, hydrocephalus, and coma -- and even death.
The Biologic Backstory and Foodborne Transmission
As any medical student can attest, you can't talk "parasite" without mentioning "life cycle." Rat lungworm's earthy cycle first became clear in the 1950s and 1960s. In brief: adult A. cantonensis worms live and mate in rats' pulmonary arteries, fertilized eggs hatch in rats' lungs, and baby larvae pass in rats' feces. After snails and slugs eat those feces and their larvae mature, the cycle begins anew when a new gang of rats eat the mollusks.
How do people enter the picture? In the first few decades following rat lungworm's discovery, most human cases (often presenting as eosinophilic meningitis) were linked to eating raw or undercooked freshwater snails or prawns. In the 1960s, however, research in Hawaii and Polynesia suggested that fresh leafy greens hiding snails or flatworms could also transmit infection. A , in which 12 medical students from Chicago suffered rat lungworm meningitis after sharing a large Caesar salad in Jamaica, left no further doubt that produce could also transmit the neuro-invasive nematode.
A Globalizing Parasite That Needs More Attention
Many lessons can be gleaned from the modern saga of the rat lungworm, from its ongoing global spread (today, the parasite happily thrives in Southeast Asia, the Pacific islands, Japan, Australia, South America, the Caribbean, and the southeastern U.S. as well as parts of Africa and the Canary and Balearic Islands) to the need to weigh healthy eating against a genuine foodborne hazard in these and other endemic sites. Fortunately, thorough washing of produce removes infected A. cantonensis-infected mollusks, cooking and freezing outright kill larvae, and mitigates illness. At the same time, if residents and tourists in affected areas are not warned, how can they practice self-protective measures?
While still remain in controlling A. cantonensis, one thing is clear. As it continues to move and establish new homes, widespread education of people at risk and their doctors will be key to reducing harm -- and, even better, preventing infection in the first place.
Claire Panosian Dunavan, MD, is a professor of infectious diseases at the David Geffen School of Medicine at UCLA, and a past president of the American Society of Tropical Medicine and Hygiene. She recently produced a documentary about rat lungworm disease, called "," which will air in the fall.