- A new comprehensive study of the rat lungworm parasite tallied 82 human cases between 2007 and 2017. Two of them were fatal.
- Scientists know the disease is spread through mollusks like snails and slugs, but it’s not clear how it gets from there into the human body.
- Once in the body, however, the parasite travels to the central nervous system. A healthy immune system can kill it, but makes you sick in the process.
A parasite found in rats, and spread to slugs and snails, has been making people in Hawaii sick for the past decade, according to a new study published in the American Journal of Tropical Medicine and Hygiene.
Since 2007, 82 people have reported serious illness, including nausea, headache, and partial paralysis or blindness, believed to be from the parasite Angiostrongylus cantonensis, better known as the rat lungworm.
The parasite enters the human body when people eat snails or slugs carrying it. But, except in one case where a victim ate a slug on a dare, most people aren’t intentionally eating slugs. So how do they get infected?
Researchers theorize that people eating unwashed produce are ingesting tiny slugs or snails hidden in their leafy greens or fresh fruits
The study found that the majority of patients with rat lungworm reported that they ate unwashed produce at least some of the time. Researchers also looked at other potential factors, including food sources and food storage. While only two patients said they stored food outside, more than half said they stored some food in unsealed containers.
Researchers noted that other activities such as home-growing food and keeping pets (whose food can attract the slugs) may also increase the risk of infection.
Most of the patients had observed snails or slugs on their property, and two-thirds had seen evidence of rats.
- Hawaii Department of Health
Researchers identified a particular species, known as a semi-slug, as an adept climber that seeks out food sources and carries a particularly high concentration of the parasite. The young of this species can be as small as 2 millimeters in length – about twice the width of the tip of a pencil. This would make them nearly impossible to spot lurking on a fresh bunch of leafy greens, and easy to swallow in a bite of raw apple or carrot.
Once inside the body, the parasite tries to attack the central nervous system.
The human body can kill the parasite before it reaches the brain, but the immune response causes serious illness
White blood cells flood the brain and spinal cord to fight off the invading rat lungworm, causing headache, stiff neck, and nausea. Sometimes, the parasite can lead to more serious symptoms like impaired vision and face or limb paralysis. In the most severe cases, it can lead to meningitis and, rarely, be fatal.
Symptoms vary by age group; the study included people who were between 9 months and 82 years old. Children are more likely to experience fever, vomiting, and fatigue, while people older than 10 often reported head and body aches.
In all but a few cases, the infection does not require treatment but dissipates on its own after the parasites die, according to the Centers for Disease Control and Prevention. In serious cases, medication can treat the symptoms of the parasite, which are caused by the body’s immune system and not the bug itself.
The study did not find a rise in cases over time. However, researchers noted that infections occurred mainly during the rainy season, and were concentrated in particular “hot spot” areas on the east side of the big island of Hawaii.