JUN 30, 2017 11:09 AM PDT

Brain-infecting Parasite Rises at 'Alarming' Rate in Florida

WRITTEN BY: Xuan Pham

Health officials are warning Florida residents to be especially cautious given the “alarming” spread of a brain-infecting parasite known as the rat lungworm.

Image credit: Heather Walden

The rat lungworm (Angiostrongylus cantonensis) is so named because the parasite matures in the pulmonary arteries of rats. But the feces of infected rats can transmit the parasite to garden-variety slugs and snails, which become the parasite’s intermediate hosts. When humans consume these infected gastropods, either accidentally or on purpose, the parasite hitches a ride to the brain and spinal cord.

In a recent study, epidemiologists collected samples from over 1,500 rats and snails across 18 Florida counties. They found that almost 23 percent of rats, 16 percent of rat feces, and 2 percent of snails were infected with the parasite. The infected hosts were found in five counties: Alachua, Leon, St. Johns, Orange and Hillsborough.

Although only five counties showed presence of the parasite, the team suspects that the infection is more widespread than their results show. "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 U.S. than we think. The ability for this historically subtropical nematode to thrive in a more temperate climate is alarming,” said Heather Walden, an assistant professor in the department of infectious diseases and pathology at the University of Florida. “The parasite is here in Florida and is something that needs to be taken seriously,” she added.

"What happens is that the parasite gets into humans -- humans are not the host that it can complete its life cycle in, as opposed to being in a rat -- so when it gets in a human, it can get lost, and it will go to the brain, and it'll stay there," said Walden. "When it gets to the brain, you can have eosinophilic meningitis.” Meningitis is inflammation and swelling of the meninges. In the best-case scenario, infected patients have zero or very mild symptoms that resolve in a few weeks. In the worst-case scenario, infection can lead to coma or even death.

The researchers also think the rise in global temperatures could have contributed to the spread of the rat lungworm. "We expected the range of this nematode to be restricted to one part of the state because it's primarily a tropical species," said John Slapcinsky, a curator at the Florida Museum, and one of the study co-authors. "But being within another organism could mean it's less impacted by cold weather."

Slapcinsky also noted that the parasite "doesn't seem to be picky" about snail hosts, a trait that could endanger the native snail species and allow the parasite to further expand its range, all at once. "There are a lot of snail species endemic to South Florida that don't occur anywhere else, and the last thing you want to do is throw one more problem their way," he said. "Rat lungworm is finding a whole new pool of animals to infect. The more species it infects, the larger its population can be, which could make transmission even easier."

To avoid brain encounters with the rat lungworm, experts obviously recommend against consuming live or raw snails and slugs. In addition, they also urge people to carefully prepare lettuce and other produce, as these may hide a snail or two. It’s also worth noting that the infection isn’t contagious from person to person. Just mind what you eat. And finally, humans make terrible hosts for the parasite and these worms will eventually die out in our system.

Additional source: Florida Museam of Natural History

About the Author
  • I am a human geneticist, passionate about telling stories to make science more engaging and approachable. Find more of my writing at the Hopkins BioMedical Odyssey blog and at TheGeneTwist.com.
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