Rat Lungworm is a Thing

Rat lungworm infection actually is a real thing. If you think the name sounds odd, that is nothing compared to how this infection gets around and what it does.

What is rat lungworm?

Rat lungworm is caused by Angiostrongylus cantonensis, a parasite of rats. When rats ingest Angiostrongylus larvae, they migrate from the rat's gut to their lungs where they mature into adult worms. Adult worms can lay 15,000 eggs per day! The eggs hatch in the rat and become first stage juvenile larvae, which are passed out into the environment in the rat's feces. The juvenile larvae mature into third stage larvae and typically infest slugs and snails. They may also be picked up by frogs, freshwater prawns, some lizards and land crabs.

Slugs and snails travel and shed larvae as they go. They can contaminate vegetables in the field or garden, or even be washed into drains and contaminate water (which in turn may be used to irrigate crops).

How is rat lungworm spread?

Humans can get infected by accidental ingestion of third stage larvae by directly eating the Angiostrongylus larvae that may be on salads, in the water, or in undercooked prawns, land crabs and snails.

Once ingested by humans, the third stage larvae migrate from the gut to the central nervous system and develop into an adult worm. Not surprisingly, growing and developing larvae and adult worms in the central nervous system can result in typical symptoms of meningitis, such as intense headaches and neck stiffness. Other symptoms of rat lungworm may include tingling or painful feelings in the skin, low-grade fever and sleepiness (especially in children). Gastrointestinal signs and symptoms are more common in children but often also occur in adults and include abdominal pain, nausea and vomiting.

So, one might say that rat lungworm is the cause of human brain worm! This type of meningitis is notable for being associated with increased number of eosinophil white blood cells, and is called eosinophilic meningitis.

Is rat lungworm contagious?

Angiostrongylus infection, or angiostrongyliasis, in humans is not contagious. That means one person who is infected with rat lungworm cannot transmit infection to another person. Clusters of infection in a household are not attributable to person-to-person spread of infection. Instead, people eating the same contaminated food – such as a shared salad or undercooked shrimp – might all get infected.

Where is rat lungworm found?

Previous cases of Angiostrongylus cantonensis were reported from China, Southeast Asia and the South Pacific islands. However, widespread travel and shipping have resulted in the spread of the infection to other areas of the world. Cases are increasingly being reported in the United States – and angiostrongyliasis is now the most common infective cause of eosinophilic meningitis in the U.S.  The infection is believed to be established in parts of the western hemisphere, including the southern United States, the Caribbean, and the Amazon basin. In fact, cases have been reported in Hawaii and New Orleans. And, recent research has confirmed that the A. cantonensis parasite has infected many Florida rats and snails.

How is rat lungworm diagnosed?

Direct detection of A. cantonensis (young adults or larvae) in cerebrospinal fluid (CSF) is the gold standards for diagnosis of human angiostrongyliasis. However, it is rare that we actually see the parasites in the CSF. Typically, direct identification of the worm is successful in less than 10% of samples. Also, because there are no readily available blood tests for rat lungworm, diagnosing A. cantonensis infections can be difficult.

Important clues that raise suspicion and may help lead to the diagnosis of infection are a history of travel to where the parasite is known to be found and a history of eating (potentially poorly washed) salad or raw or undercooked snails, slugs, frogs, fresh water shrimp or land crabs in, or from (if produce is shipped) those areas. Another important clue is finding a high level of eosinophil white blood cells (that may increase in number in the setting of a parasitic infection). If you are concerned that you may have been infected by rat lungworm contact a medical professional.

What are the symptoms of rat lungworm?

The good news is that mild cases of angiostrongyliasis are most often self-limiting and resolve spontaneously without specific therapy. Typically the parasite just dies over time, even without treatment. It is somewhat unpredictable how long or how severe symptoms may be, and they may last for several weeks or months.

How is rat lungworm treated?

Treatment is directed at the symptoms and primarily consists of pain medication for headache. Sometimes steroids are added for increased anti-inflammatory effect. Antiparasitic medications directed at the worms usually are not recommended for treatment of A. cantonensis infections. This is because dying worms can increase inflammation and exacerbate symptoms. Thus, it is ill advised to give medication that may lead to the simultaneous killing of multiple rat lungworms in the brain.

How can I prevent rat lungworm?

Ultimately, the key to avoid getting infected with this parasite is prevention. Wash produce. Wash hands, especially if you handle snails. Be aware of the potential risks associated with eating salads, snails and raw or undercooked frogs, shrimp and crabs. Of course, rat and snail/slug control is also essential. If you think you have a pest problem, contact your local pest control professional.