Meningitis is a dangerous inflammation of the meninges, the protective membranes that surround the central nervous system (brain and spinal cord).

Meningitis can produce numerous mild symptoms, including fever, nausea, headache, stiff neck, light sensitivity, and skin rash.

In more severe cases, it can cause confusion, seizures, stroke, brain damage, and death.

It's unknown exactly how many people suffer from meningitis each year.

However, in 2013 meningitis resulted in 303,500 deaths worldwide, according to a 2014 report in the medical journal The Lancet.

Meningitis isn't the same as encephalitis or myelitis, an inflammation of the brain or spinal cord, respectively (or encephalomyelitis, a simultaneous inflammation of the brain and spinal cord).

Infectious Causes of Meningitis

Most often, the meninges will become inflamed when the fluid surrounding the central nervous system is infected.

Viral meningitis is the most common form of the disease, according to the Centers for Disease Control and Prevention (CDC), and is most often caused by non-polio enteroviruses, such as echnoviruses and coxsackievirus A and B.

Numerous other viruses may cause it as well, however, including the mumps, measles, HIV, West Nile, and herpes viruses.

Bacterial meningitis is rare, but often severe and life threatening.

In the United States, the leading causes of bacterial meningitis are Haemophilus influenzae type b, Streptococcus pneumoniae (called pneumococcus meningitis), group B Streptococcus, Listeria monocytogenes, and Neisseria meningitidis (meningococcal meningitis).

Unlike viral and bacterial meningitis, fungal meningitis — generally caused by Cryptococcus, Histoplasma, Blastomyces, Coccidioides, or Candida fungi — isn't contagious.

It usually occurs when fungi travel through the blood to the spinal cord.

The microscopic ameba (a single-celled organism) Naegleria fowleri can cause a rare form of parasitic meningitis called primary amebic meningoencephalitis, in which the brain is also inflamed.

Other parasites, including Angiostrongylus cantonensis and Gnathostoma spinigerum, can also cause meningitis, particularly a form called eosinophilic meningitis, in which the cerebrospinal fluid contains a high amount of eosinophil white blood cells.

Non-Infectious Causes of Meningitis

There are also numerous non-infectious causes of meningitis.

For instance, various health issues, particularly inflammatory or autoimmune conditions, can lead to meningitis. These conditions include:

  • Lupus, and other autoimmune/inflammatory disorders
  • Cancers that can spread to the brain, such as leukemia, melanoma, breast cancer, and lung cancer
  • Rheumatoid arthritis
  • Behçet syndrome, an inflammation of the blood vessels
  • Sjögren syndrome, an autoimmune disease of the exocrine glands

A wide range of medications can also result in meningitis, such as:

Additionally, you can get meningitis after a head injury or brain surgery.

Risk Factors for Meningitis

Vaccines are available to prevent you from getting certain bacterial and viral infections that can cause meningitis, including meningococcus, pneumococcus, mumps, and measles.

Skipping your vaccinations increases your chances of getting these types of meningitis.

Spending time or living in close quarters with other people, such as in dorm rooms, day care settings, or military barracks, can also increase your risk of catching bacterial and viral meningitis from other people.

If you have a weakened immune system, such as from medications, HIV/AIDS, diabetes, pregnancy (especially for listeria), alcoholism, spleen removal, or recent organ or bone marrow transplants, you're also at an increased risk for infectious meningitis.

Infants are at an increased risk for bacterial meningitis, and children under 5 years old have a higher chance of contracting viral meningitis.

Premature babies with very low birth weights may be more prone to fungal meningitis — in particular, Candida blood stream infections that spread to the brain.

Exposure to the meningitis-causing parasite, Naegleria fowleri, which thrives in warm, freshwater locales such as hot springs, lakes, and poorly maintained swimming pools, can increase your chance of developing a very rare form of parasitic meningitis called primary amebic meningoencephalitis (PAM).

You can become infected with A. cantonensis and G. spinigerum parasites from eating certain raw or undercooked meat, such as snails, pigs, chickens, and freshwater fish, frogs, and shrimp, particularly while in Southeast Asian countries.