A medical mystery reveals a new host for the rat lungworm parasite

When a 78-year-old woman went to a hospital in Guangzhou, China, in November 2012 complaining of a headache, drowsiness and a stiff neck, doctors initially were puzzled. The patient had meningitis, but no signs of bacteria or viruses that can cause the illness. Then a cerebrospinal fluid test revealed she had a high number of white blood cells called eosinophils, a clue that she was fighting a parasitic infection. That helped the doctors zero in on a culprit: a thin, swirly-patterned worm called Angiostrongylus cantonensis. The woman was suffering from rat lungworm disease. So was her adult son.

But how were the pair infected? Rat lungworm disease, which gets its name from the fact that the worm eggs hatch in the lungs of rats, is commonly associated with ingesting snails or slugs (SN Online: 7/21/16). Infected rats poop out the worm larvae, which the mollusks can then pick up and pass on to humans if eaten. Yet the patients had eaten no slugs or snails.

Painful parasite

This Angiostrongylus cantonensis larva was found inside a centipede. It’s at the stage in its life cycle when, if ingested, it can infect humans, potentially migrating to the human brain and causing meningitis.

An investigation of the pair’s diet revealed they had eaten Chinese red-headed centipedes bought at the market. “Centipede is a common traditional Chinese medicine,” usually consumed in a dried powder, says Lingli Lu, a neurologist at Zhujiang Hospital in Guangzhou. The two patients, however, had eaten them raw.

Lu and her colleagues confirmed the source of the infection by testing 20 centipedes they bought from the same market. The team discovered A. cantonensis larvae that could infect humans in seven of the centipedes. The infected worms had an average of 56 larvae each. The case is the first evidence that eating raw centipedes contaminated with worm larvae can transmit rat lungworm disease, the researchers report July 30 in the American Journal of Tropical Medicine and Hygiene.

The discovery adds to a growing list of hosts that can pass this parasite to humans. While the worm needs snails to complete its life cycle, other animals, called paratenic hosts, can eat the snails and then infect humans. Humans have gotten rat lungworm disease by eating freshwater shrimp, frogs, crabs and monitor lizards. Once inside the human body, the worms migrate to the brain, where they eventually die. While symptoms can be mild, infection can cause damage to the central nervous system, including brain inflammation, paralysis and even death. Infected humans cannot pass the disease to other people.

Rat lungworm is still considered rare (there have been about 3,000 recorded cases around the world), and the disease is most prevalent in tropical and subtropical regions, says Heather Stockdale Walden, a parasitologist at the University of Florida College of Veterinary Medicine in Gainesville. In the United States, the parasites are endemic in the Hawaiian Islands, and cases of rat lungworm have been reported as far north as Oklahoma.

Most cases in the United States occur from eating snails and slugs, which hide in unwashed produce. People should be aware of this parasite, Walden says, but not alarmed. “As long as you’re cooking your food [and] washing your produce, the likelihood of infection with the parasite is pretty low.”

Leave a Reply