Eosinophilic meningitis is a rare form of meningitis. Meningitis is inflammation of the fluid and membranes (also called meninges) in your brain and spinal cord.

Eosinophilic meningitis most often develops from certain parasites that normally infect animals, not people. Because of that, it’s much less common than viral or bacterial meningitis.

Even though it’s rare, some people may be at risk of eosinophilic meningitis because of where they live, travel, or work.

Continue reading to learn more about this condition, including its causes, symptoms, treatment, and whether you might be at risk.

Eosinophilic meningitis is also called eosinophilic meningoencephalitis or EM. Several types of helminth worms cause EM. According to the Centers for Disease Control and Prevention (CDC), the most common of them are:

  • Angiostrongylus cantonensis (rat lungworm)
  • Baylisascaris procyonis (a raccoon roundworm)
  • Gnathostoma spinigerum

The specific infections these worms can cause are named after them:

  • angiostrongyliasis
  • baylisascariasis
  • gnathostomiasis

These parasites can enter your body when you drink contaminated water or interact with the stool or droppings of an infected animal. It can eventually spread to your brain or spinal cord, where it can cause EM.

Rarer causes of EM include:

Symptoms of EM usually begin within 24 hours to several days after ingestion of the parasite. Sometimes it can take up to several weeks for symptoms to show.

The most common symptoms and signs of EM are:

A doctor will diagnose EM based on your symptoms and lab tests.

They will ask you about your health history and conduct a physical exam. They may also ask where you live and what you do for work. Make sure to tell the doctor:

  • about any recent travel
  • if you work in a garden or sandbox
  • if you recently ate raw (never frozen) fish

Discussing these or other unusual experiences might help them identify the cause of your symptoms.

During the physical exam, your doctor will look for:

If your doctor suspects EM based on your symptoms and a possibility of a parasitic infection, they will run some tests to confirm it.

They may collect your blood or cerebrospinal fluid. In addition, they will likely order imaging tests of your brain, like a CT scan or MRI.

There’s no specific treatment for EM caused by helminth worms.

A doctor may prescribe over-the-counter (OTC) pain relievers or corticosteroids (such as prednisone or prednisolone) to reduce pain and inflammation.

Doctors rarely treat the infection itself because researchers haven’t observed a clear benefit of this approach. However, some reports indicate that antiparasitic drugs (such as albendazole) can help treat the infection.

EM can cause very severe complications, such as:

Because of the life threatening complications, it’s essential to seek immediate medical attention if you suspect EM in yourself or someone else.

Because EM caused by helminth worms is very rare, researchers don’t have enough data to estimate the general outlook for people with EM. Here’s what they do know.

Mild cases of EM are more common. They usually resolve on their own within a few weeks.

In some cases, EM can have severe complications. According to some research, more than 90% of people who entered a coma due to rat lungworm infection eventually died.

Generally speaking, neurological (brain-related) symptoms of EM are usually associated with a poor outlook.

Although EM is rare, some people may be at risk because of where they live, where they travel, and what they do for work.

Rat lungworm infections are the most frequent causes of EM. Rat lungworms are common in:

  • Southeast Asia
  • the Pacific Islands, including Hawaii
  • Australia

Doctors have also observed rat lungworm infections in the Americas (North, Central, and South America) and the islands of the Indian Ocean.

Rat lungworms can infect people who eat raw:

  • snails
  • slugs
  • frogs
  • freshwater prawns
  • crabs
  • fish

Less commonly, it can exist in contaminated vegetables, water, and fruit juice.

Babies, toddlers, and young children can contract an infection after playing with snails or other animals and then touching their mouths.

A raccoon roundworm, Baylisascaris procyonis, infects raccoons in the United States, especially in the:

  • Midwest
  • Northeast
  • Mid-Atlantic
  • West Coast

People living in these areas who work or spend time with raccoons are at risk of EM. As with rat lungworm, children are more at risk of Baylisascaris procyonis infections because of how often they touch their mouths.

Gnathostoma spinigerum infections are most common in Southeast Asia, particularly in Thailand, and Japan. Most infections come from insufficiently cooked freshwater fish.

People who regularly work in the soil in the southwestern United States or northern Mexico may be at risk of coming in contact with fungi that can also cause EM.

Can a household pet transmit eosinophilic meningitis?

Whether you can contract EM from your pet depends on the type of pet you have.

Although cats and dogs can sometimes develop EM from Gnathostoma spinigerum, they don’t transmit it to humans. This is because of the complicated life cycle of this parasite. Humans can only contract it from undercooked fish infected with the parasite.

However, if you have other animals as pets, there can be a risk of EM. Animals that can infect humans include:

  • raccoons
  • snails and slugs
  • frogs
  • snakes
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Here are a few things you can do to prevent contracting the parasites that cause EM:

  • Don’t eat raw or undercooked snails, slugs, frogs, or shrimp.
  • If you handle live snails, slugs, frogs, or shrimp, wear gloves and wash your hands.
  • Always thoroughly wash fresh produce.
  • Avoid eating uncooked or undercooked vegetables, fish, and meat when traveling in areas where parasites are common.
  • Avoid contact with raccoons.
  • Always wash your hands after being outdoors.
  • Discourage your children from touching their mouths.

Eosinophilic meningitis (EM) is a rare type of meningitis usually caused by an infection with helminth worms. Rat lungworms cause the most common EM infections.

Although EM usually resolves on its own without treatment, it can sometimes cause dangerous complications, including coma and death.

You can prevent EM by avoiding eating raw or undercooked snails, slugs, frogs, or shrimp and thoroughly washing your hands after being outdoors and before each meal.