One of the best perks of living in a tropical climate is having access to fresh produce year-round. However, a rare disease called rat lungworm has recently gained the attention of the medical community in Hawaii and elsewhere, and may make you think twice before you chop up a head of lettuce from your home garden.
You probably have never heard of rat lungworm disease, which is caused by a parasite, Angiostrongylus cantonensis. This tiny worm lives in southeastern Asia, the Pacific Islands (including Hawaii), Louisiana, Australia, Africa and the Caribbean. Although the parasite appears widespread in nature, fortunately the disease is rare with fewer than 3,000 cases reported worldwide since 1945. In Hawaii, 9 cases were reported in 2011 and a particularly severe case was documented in 2009.
Adult worms live in the pulmonary (lung) arteries of rats. Rats that are infected pass the parasitic larvae in their feces. When snails and slugs eat the feces, the larvae grow into the infective stage in their bodies. Humans become infected by eating raw or undercooked snails, slugs, shrimp, crabs, or frogs that contain the larvae. In western diets, this usually happens accidentally; small slugs or snails that feed on produce escape washing and are consumed. It’s easier than you might think to miss a small creature hiding out in the folds of a leafy vegetable. Once consumed by a human, the larvae cannot finish their lifecycle and bury themselves in the tissue of the nervous system, including the brain. This causes the body to mount an immune response that eventually kills the invaders. However, this response causes inflammation and swelling of the protective covering of the brain and the spinal cord, a condition known as meningitis. Common symptoms of meningitis include stiff neck, headache, a low-grade fever, pain or tingling in the skin, nausea, and vomiting. Eosinophilic meningitis (a form of meningitis characterized by eosinophils, a type of white blood cell) suggests rat lungworm disease because parasites are potent stimulators of this cellular immune reaction. The disease usually clears up on its own without medical intervention; however, in severe cases it can cause coma, brain damage, and even death. Diagnosis of the disease can be difficult and is usually based on the patient’s food history.
The State Laboratories Division of the Hawaii Department of Health is collaborating with the Centers for Disease Control and Prevention to establish performance characteristics of real-time PCR (a technique that allows a targeted DNA sequence to be amplified and quantified at the same time) to detect rat lungworm in patients. It is hoped that this assay may improve diagnostics inHawaiiand elsewhere. Treatment is non-specific and usually includes reducing central nervous system pressure, medications that reduce the body’s inflammatory response and pain management.
Fortunately, there are common-sense precautions that can prevent transmission of the disease. If you are in an area where this parasite is found, don’t eat raw or undercooked snails, slugs, frogs, shrimp, or prawns, as tempting as they may be. Always carefully wash fresh produce, and discard any that has damaged skin as this can indicate the presence of slugs or snails. The next time you are traveling go ahead and enjoy the local treats, but know the exposure risks and keep in mind that simple preventative measures can prevent a devastating disease from harming you and your companions.