meningitis (mĕnĭnjī`tĭs) or cerebrospinal meningitis (sĕr'əbrōspī`nəl), acute inflammation of the meninges meninges (mĭnĭn`jēz), three membranous layers of connective tissue that envelop the brain and spinal cord (see nervous system ).
..... Click the link for more information. , the membranes that cover and protect the brain and spinal cord. It can be caused by bacteria, viruses, fungi, or other organisms, usually introduced via the bloodstream from infections elsewhere in the body.

Viral meningitis

Viral meningitis, sometimes referred to as nonbacterial or aseptic meningitis, is milder and more common than bacterial forms. It can be caused by any of a number of viruses, including enteroviruses, the mumps virus, herpesviruses, HIV HIV (Human Immunodeficiency Virus), either of two closely related retroviruses that invade T-helper lymphocytes and are responsible for AIDS . There are two types of HIV: HIV-1 and HIV-2. HIV-1 is responsible for the vast majority of AIDS in the United States.
..... Click the link for more information. , and several mosquito-borne viruses (Bunyavirus and flavivirus) usually associated with encephalitis. Viral meningitis is usually seen only in individual cases rather than in outbreaks. Those not vector-borne are usually spread from person to person by the fecal-oral route. Symptoms include headache, fever, stiff neck, and tiredness, sometimes accompanied by a rash. There is no specific treatment.

Bacterial meningitis

A variety of organisms can cause bacterial meningitis, a serious form that can be fatal, especially in children. Symptoms include high fever, headache, chills, vomiting, stiff neck or back, and confusion, sometimes accompanied by a purplish rash. Serious cases can quickly lead to delirium, coma, or convulsions. It is spread by oral or nasal secretions.

The leading cause of bacterial meningitis is the ill-named bacterium Haemophilus influenzae b (Hib), originally thought to be an influenza virus. It commonly affects infants and children. The second most common bacterial cause of meningitis is Neisseria meningitidis (meningococcus). Meningococcal meningitis affects people of all ages and tends to occur in epidemics, especially among those who live in crowded conditions. An outbreak in the slums of Brazil in 1974–75 killed 11,000 people and left over 75,000 with permanent neurological complications. In 1996, an epidemic centered in the Sahel region of W Africa killed 16,000. In the United States it is seen most often in children and teens.

Strepococcus pneumoniae, also referred to as pneumococcus, is another cause of serious meningitis cases. It is the most common cause of meningitis in adults. It often accompanies pneumococcus infections in other parts of the body, such as the ear or sinuses. Other bacterial causes of meningitis include tuberculosis tuberculosis (TB), contagious, wasting disease caused by any of several mycobacteria. The most common form of the disease is tuberculosis of the lungs (pulmonary consumption, or phthisis), but the intestines, bones and joints, the skin, and the genitourinary,
..... Click the link for more information. , leptospirosis leptospirosis (lĕp'təspīrō`sĭs), febrile disease caused by bacteria of the genus Leptospirae.
..... Click the link for more information. , and Lyme disease Lyme disease, a nonfatal bacterial infection that causes symptoms ranging from fever and headache to a painful swelling of the joints. The first American case of Lyme's characteristic rash was documented in 1970 and the disease was first identified in a cluster at
..... Click the link for more information. .

Bacterial meningitis calls for emergency medical care and the administration of antibiotics. Close contacts of patients with bacterial meningitis may receive prophylactic antibiotics, such as rifampin. Definitive diagnosis can be made by laboratory tests of cerebrospinal fluid obtained by a lumbar puncture (spinal tap). Twenty to thirty percent of children who survive bacterial meningitis sustain permanent neurological damage such as deafness, mental retardation, or convulsions. Since the late 1980s, routine vaccination of young children against Hib has virtually eliminated Hib disease in the United States. Routine vaccination against meningococcal meningitis is recommended for pre-adolescents, and vaccination is also recommended for persons in the military or traveling to parts of Africa where the disease is endemic. The meningococcal vaccine does not provide protection against all meningococcus strains.

Fungal meningitis

Fungal meningitis has been on the rise in the United States due to opportunistic infection with Cryptococcus neoformans in people weakened by AIDS. In these patients, it is often fatal. It can be treated with the antifungals amphotericin B and fluconazole. Other causes include coccidioidomycosis coccidioidomycosis (kŏksĭd'ēoi'dōmīkō`sĭs)
..... Click the link for more information. and histoplasmosis.

meningitis

Inflammation of the meninges. Bacteria (including meningococcus, among others), often from infection elsewhere, produce the most dangerous forms. Symptoms develop rapidly: vomiting, then severe bursting headache, then stiff neck. Young children may have convulsions. The patient may die within hours. Pus in cerebrospinal fluid can block brain passages and spinal spaces, leading to life-threatening hydrocephalus. Speedy diagnosis (by lumbar puncture) and treatment (with antibiotics) can prevent brain damage and death. Viral meningitis usually has a short course and requires no therapy.