Deadly Lungworm Parasite Spread by Rats & Snails Is More Prevalent Than We Thought

Deadly rat lungworm parasites have found their way into Florida. The parasitic worm relies on snails and rats to complete its life cycle, but don't let this nematode's name fool you. This worm can cause meningitis and death in humans who inadvertently consume snails, frogs, or crustaceans harboring the infective parasite.

A study of rats in Florida conducted by scientists at the University of Florida and the Florida Museum of Natural History found the rat lungworm parasite in rats from Alachua, Leon, St. Johns, Orange, and Hillsborough counties, four of the ten countries they tested. It also has the potential to spread further.

Lead author Heather Stockdale Walden, of the UF department of infectious diseases and pathology, published the research report on May 18 in PLoS ONE.

A Deadly Life Cycle

Deadly Lungworm Parasite Spread by Rats & Snails Is More Prevalent Than We Thought — This rat lungworm larvae has reached the infective stage inside its snail host. When a rat eats the snail, it becomes infected with the parasite, which matures and reproduces inside the rat's pulmonary artery. *Image via Heather Stockdale Walden*

Snails acquire the rat lungworm, Angiostrongylus cantonensis, by eating the feces from an infected rat. The immature stage of the rat lungworm — the larval stage — develops within a snail host to its infective stage. When the snail is eaten by a rat, the larvae penetrates the rat's intestine and enters the bloodstream where it travels to the brain. Once there, the larvae develop into immature worms, re-enter the blood stream and end up in the rat's pulmonary artery, the vessel that goes from the rat's heart to its lungs. The pulmonary artery is where the worms complete their development and become sexually mature. Females lay eggs that hatch in the pulmonary artery. New larvae are coughed up from the lungs, then swallowed by the rats to leave the body in their feces. And the cycle continues.

Rats and snails are necessary parts of the nematode's life cycle, but humans can ingest the parasite by consuming infected snails or infected frogs and crustaceans, which can also pick up the nematode by eating rat feces. Once inside a human, if the parasite makes its way to the brain it causes eosinophilic meningitis — named for the white blood cell eosinophils that rush to the site of parasitic infections — and can cause coma or death.

Signs of infection in adults include a headache, stiff neck, fever, vomiting, nausea, and paralysis of the limbs and face. In children, the most common symptoms of infection are nausea, vomiting, and fever.

About 2800 humans have been infected with rat lungworm parasites worldwide. Since 2000, there have been 23 cases in Jamaica and snails contaminated with the parasite were implicated in over half of these cases. Two of those infections were fatal, and four people suffered nerve and brain damage. Fifteen people have been diagnosed with rat lungworm in Hawaii this year already.

And just because you don't live in Florida, Hawaii, or Louisiana, don't think you are safe. If the pokey snail can hitch a ride to Florida, it can move to other states.

"We expected the range of this nematode to be restricted to one part of the state because it's primarily a tropical species. But being within another organism could mean it's less impacted by cold weather," co-author John Slapcinsky said.

"The reality is that it is probably in more counties than we found it in, and it is also probably more prevalent in the southeastern US than we think. The ability for this historically subtropical nematode to thrive in a more temperate climate is alarming," Walden said.

The Threat in Florida

The first reports of rat lungworm, Angiostrongylus cantonensis in the US were in New Orleans, Louisiana in 1986. It is endemic — found commonly — in Hawaii.

Snails usually don't travel far, so the study authors believe they got to Florida on cargo containers and in potted plants. In a survey of 18 Florida counties evaluated by the research team for the presence of the parasite in rats, feces, and snails almost 23% of rats, about 16% of rat fecal samples, and nearly 2% of land snails tested positive for rat lungworm.

The researchers found the parasite in three native snails — the Florida amber snail, Succinea floridana; the perforate dome snail, Ventridens demissus; and the quick gloss snail, Zonitoides arboreus — and three non-native species of snails. By infecting multiple snail species, the rat lungworm has increased its chances of survival and ability to spread.

The only way to avoid infection with this potentially deadly nematode is to be careful what you eat. Wash produce and inspect leafy greens where small snails can hide. Instruct children not to eat or handle any snails they find and be sure to fully cook snails, frogs, or crustaceans before eating. Wash your hands after handling snails or produce. And give the greens you eat at a restaurant a quick check as well.