Brain-Invading Rat Lungworm Found in Georgia

Another parasite is threatening to wiggle its way into human brains.

A few weeks ago, the journal Emerging Infectious Diseases published a case study describing an Australian woman who presented with a perplexing array of neuropsychological and physical symptoms over the course of a year. A biopsy revealed a live, 80mm (approximately three inch) nematode worm squirming its way through her brain tissue. Subsequent PCR sequencing identified the worm as Ophidascaris robertsi, a parasite that until now, was only known to infect python snakes.

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Atlanta Outbreak

The latest parasitic neuro-invader is the subject of a new paper from the same journal, which is published by the Centers for Disease Control and Prevention (CDC). Researchers discovered the presence of Angiostrongylus cantonensis, commonly known as rat lungworm, in brown rats in Atlanta, Georgia between 2019 and 2022. They warned that rats can transmit the parasite to humans and other mammals.

Rat lungworm can cause eosinophilic meningoencephalitis, an infection that affects the brain. Severity of the infection ranges from mild to life-threatening, depending on various factors such as the number of larvae that reach the brain and the effectiveness of an individual’s immune response. Doctors often treat the condition with anti-parasitic medications and steroids to reduce inflammation. In severe cases, they may perform surgery to alleviate pressure on the brain.

How They Live

The parasite has an elaborate life cycle that involves multiple hosts. Rodents, primarily rats, serve as the definitive hosts where the parasite reaches maturity. The journey to the brain begins when a rat ingests food contaminated with the third-stage larvae of the parasite, usually found in snails or slugs. 

Once inside the rodent’s body, larvae migrate through the circulatory system to the central nervous system and into the brain. After undergoing two molts in the brain, they mature into adult nematodes. It’s in this cerebral location where they can cause eosinophilic meningoencephalitis. 

Eventually, the adult worms wind their way into pulmonary arteries of the lungs, where they lay eggs that hatch into first-stage larvae. These larvae travel to the rat’s throat, where they are swallowed. Then the rat expels them through its feces and they are ready to infect another host.

Adult Angiostrongylus cantonensis nematodes are relatively small. The males typically measure around 10–19 mm (three quarters of an inch) in length. The females are generally larger, measuring between 21–25 mm (about an inch). Individuals are flimsy and slender, with a simple mouth and no lips or buccal cavity. 

A Growing Problem

Researchers initially identified rat lungworm in Asia. It has made its way to the United States through various trade routes, establishing itself in states like Hawaii, Texas, and Florida. The study is particularly worrisome because it confirms that the parasite has now crept into Georgia.

The researchers collected and examined tissue samples from brown rats found dead at a zoo in Atlanta. Through histological evaluation and genetic analysis, they found the parasitic infected about 21 percent of the sampled rats. Importantly, the parasite’s genetic markers matched those previously identified in Louisiana, indicating that it’s the same strain that’s been inching across the southern United States.

The study raises public health concerns, not just for Georgia but for the broader Southeast. As infected hosts spread through the country, there’s an increasing chance of transmission to humans and domestic animals. The authors underscored the need for heightened medical vigilance and ongoing research to mitigate the health concerns posed by this increasingly pervasive parasite.

Although the paper doesn’t reference any human deaths or infections in Georgia thus far, the mortality rate for people contaminated with the nematode hovers at just over two percent, with severe consequences observed in nearly six percent of cases, according to CDC statistics.