Eosinophilic meningitis: Meningitis with a high percentage of eosinophils (a type of white blood cell) in the cerebrospinal fluid (CSF). The usual cause is the parasite Angiostrongylus cantonensis, also known as the rat lungworm.
People become infected with this parasite by ingesting its larvae in raw or insufficiently cooked snails, slugs, freshwater prawns, frogs, or fish. Infection may also occur by consumption of fresh produce such as contaminated lettuce. When the larvae are ingested, they penetrate the intestinal tract, go into blood vessels, and eventually reach the meninges (the covering of the brain and spinal cord). The larvae usually die there shortly thereafter. An eosinophilic reaction develops in response to the dying larvae. It is manifested by an outpouring of eosinophils in the CSF.
Most cases of eosinophilic meningitis due to A. cantonensis have been reported in SE Asia and the Pacific Basin. However, in 2002 an outbreak of eosinophilic meningitis was reported in the US. The outbreak struck 12 young adults after they had returned from a trip to Jamaica. Symptoms included headache, neck pain, visual disturbances, and hyperesthesias. Nine of the travelers required hospitalization. A case-control study showed that consumption of a Caesar salad at one dinner was strongly associated with the development of the eosinophilic meningitis.
Most cases of eosinophilic meningitis due to A. cantonensis are self-limited and resolve without complications. However, neurologic sequelae do develop in some cases, and deaths have been reported from the disease.