The CDC this week reports finding the spread of Angiostrongylus cantonensis, (Rat Lungworm) into Georgia. Originally described in Asia, where most human infections are reported, is now endemic in different regions of the world. In the United States, A. cantonensis was initially reported in Hawaii, and later in Texas, Louisiana, Alabama, and Florida, likely introduced by infected rats and gastropods through trade routes, such as on merchant ships.
In Hawaii, where severe human illnesses have been reported over the last decade, public health officials have released a stark warning:
“This is a serious disease that can be acquired on any of our islands because slugs and snails throughout the state carry the parasite responsible for the illness,” said Keith Kawaoka, deputy director of Environmental Health. “This is a grim reminder that we all need to take precautions when working in our gardens and on farms, and eliminate slugs, snails and rats from our communities to reduce the risks posed by this parasitic disease.”
Angiostrongyliasis, also known as rat lungworm, is a disease that affects the brain and spinal cord. It is caused by a parasitic nematode (roundworm parasite) called A. cantonensis. The adult form of A. cantonensis is only found in rodents. However, infected rodents can pass larvae of the worm in their feces. Snails, slugs, and certain other animals (including freshwater shrimp, land crabs, and frogs) can become infected by ingesting this larvae; these are considered intermediate hosts. Humans can become infected with A. cantonensis if they eat (intentionally or otherwise) a raw or undercooked infected intermediate host, thereby ingesting the parasite.
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This infection can cause a rare type of meningitis (eosinophilic meningitis). Some infected people don’t have any symptoms or only have mild symptoms; in some other infected people the symptoms can be much more severe. When symptoms are present, they can include severe headache and stiffness of the neck, tingling or painful feelings in the skin or extremities, low-grade fever, nausea, and vomiting. Sometimes, a temporary paralysis of the face may also be present, as well as light sensitivity. The symptoms usually start 1 to 3 weeks after exposure to the parasite, but have been known to range anywhere from 1 day to as long as 6 weeks after exposure. Although it varies from case to case, the symptoms usually last between 2–8 weeks; symptoms have been reported to last for longer periods of time.
You can get angiostrongyliasis by eating food contaminated by the larval stage of A.cantonensis worms. In Hawaii, these larval worms can be found in raw or undercooked snails or slugs. Sometimes people can become infected by eating raw produce that contains a small, infected snail or slug, or part of one. It is not known for certain whether the slime left by infected snails and slugs are able to cause infection. Angiostrongyliasis is not spread person-to-person.
Diagnosing angiostrongyliasis can be difficult, as there are no readily available blood tests. In Hawaii, cases can be diagnosed with a polymerase chain reaction (PCR) test, performed by the State Laboratories Division, that detects A. cantonensis DNA in patients’ cerebrospinal fluid (CSF) or other tissue. However, more frequently diagnosis is based on a patient’s exposure history (such as if they have history of travel to areas where the parasite is known to be found or history of ingestion of raw or undercooked snails, slugs, or other animals known to carry the parasite) and their clinical signs and symptoms consistent with angiostrongyliasis as well as laboratory finding of eosinophils (a special type of white blood cell) in their CSF.
There is no specific treatment for the disease. The parasites cannot mature or reproduce in humans and will die eventually. Supportive treatment and pain medications can be given to relieve the symptoms, and some patients are treated with steroids. No anti-parasitic drugs have been shown to be effective in treating angiostrongyliasis, and there is concern that they could actually make the symptoms worse because of the body’s response to potentially more rapidly dying worms. Persons with symptoms should consult their health care provider for more information.
To prevent angiostrongyliasis, don’t eat raw or undercooked snails or slugs, and if you handle snails or slugs, be sure to wear gloves and wash your hands. Eating raw or undercooked freshwater shrimp, land crabs and frogs may also result in infection, although, there has not been any documented cases in Hawaii. You should also thoroughly inspect and wash fresh produce and vegetables, especially if eaten raw. Eliminating snails, slugs, and rats founds near houses and gardens might also help reduce risk exposure to A. cantonensis.
When preparing food for cooking, any suspect food products should be boiled for at least 3 to 5 minutes, or frozen at 5°F (15°C) for at least 24 hours; this will kill the larval stage of the worm.