meningitis

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meningitis

(mĕnĭnjī`tĭs) or

cerebrospinal meningitis

(sĕr'əbrōspī`nəl), acute inflammation of the meningesmeninges
, three membranous layers of connective tissue that envelop the brain and spinal cord (see nervous system). The outermost layer, or dura mater, is extremely tough and is fused with the membranous lining of the skull.
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, 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, HIVHIV,
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.
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, 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 1996–7, an epidemic centered in the Sahel region of W Africa killed 25,000. In the United States it is seen most often in children and teens.

Streptococcus 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 group B streptococcusstreptococcus
, any of a group of gram-positive bacteria, genus Streptococcus, some of which cause disease. Streptococci are spherical and divide by fission, but they remain attached and so grow in beadlike chains.
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, tuberculosistuberculosis
(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, lymphatic, and
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, leptospirosisleptospirosis
, febrile disease caused by bacteria of the genus Leptospirae. The disease occurs in dogs, cattle, pigs, sheep, goats, and horses and is transmissible to humans.
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, and Lyme diseaseLyme disease
or Lyme borreliosis,
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
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.

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; separate vaccines have been developed against serogroup B meningococcus. Development of an inexpensive meningococcal vaccine for the strain most common in Africa's meningitis belt, which stretches from Senegal and Guinea in the west to Ethiopia in the east, led beginning in 2010 to a mass vaccination drive in the region under the sponsorship of the World Health Organization (WHO) and the Program for Appropriate Technology in Health (PATH).

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 coccidioidomycosiscoccidioidomycosis
, systemic fungus disease (see fungal infection) endemic to arid regions of the Americas, contracted by inhaling dust containing spores of the fungus Coccidioides immitis.
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 and histoplasmosis.

Meningitis

Inflammation of the meninges. Certain types of meningitis are associated with distinctive abnormalities in the cerebrospinal fluid. With certain types of meningitis, especially bacterial, the causative organism can usually be recovered from the fluid. See Central nervous system

Meningeal inflammation in most cases is caused by invasion of the cerebrospinal fluid by an infectious organism. Noninfectious causes also occur. For example, in immune-mediated disorders antigen-antibody reactions can cause meningeal inflammation. Other noninfectious causes of meningitis are the introduction into the cerebrospinal fluid of foreign substances such as alcohol, detergents, chemotherapeutic agents, or contrast agents used in some radiologic imaging procedures. Meningeal inflammation brought about by such foreign irritants is called chemical meningitis. Inflammation also can occur when cholesterol-containing fluid or lipid-laden material leaks into the cerebrospinal fluid from some intracranial tumors.

Bacterial meningitis is among the most feared of human infectious diseases because of its possible seriousness, its rapid progression, its potential for causing severe brain damage, and its frequency of occurrence. Most cases of bacterial meningitis have an acute onset. Common clinical manifestations are fever, headache, vomiting, stiffness of the neck, confusion, seizures, lethargy, and coma. Symptoms of brain dysfunction are caused by transmission of toxic materials from the infected cerebrospinal fluid into brain tissue and the disruption of arterial perfusion and venous drainage from the brain because of blood vessel inflammation. These factors also provoke cerebral swelling, which increases intracranial pressure. Before antibiotics became available, bacterial meningitis was almost invariably fatal. See Antibiotic

Most types of acute bacterial meningitis are septic-borne in that they originate when bacteria in the bloodstream (bacteremia, septicemia) gain entrance into the cerebrospinal fluid. Meningitis arising by this route is called primary bacterial meningitis. Secondary meningitis is that which develops following direct entry of bacteria into the central nervous system, which can occur at the time of neurosurgery, in association with trauma, or through an abnormal communication between the external environment and the cerebrospinal fluid.

Many viruses can cause meningeal inflammation, a condition referred to as viral aseptic meningitis. The most common viral causes include the enteroviruses, the various herpesviruses, viruses transmitted by arthropods, the human immunodeficiency virus type I (HIV-1), and formerly, the mumps virus. If the virus attacks mainly the brain rather than the spinal cord, the disorder is termed viral encephalitis. See Animal virus, Arboviral encephalitides, Enterovirus, Herpes

Fungal, parasitic, and rickettsial meningitis are less common in the United States than are bacterial and viral. These infections are more likely to be subacute or chronic than those caused by bacteria or viruses; in most cases, the meningeal inflammation is associated with brain involvement. An acute form of aseptic meningitis can occur in the spirochetal diseases, syphilis and Lyme disease. See Lyme disease, Medical mycology, Medical parasitology, Rickettsioses, Syphilis

Meningitis

 

inflammation of the meninges of the brain and spinal cord; inflammation of the pia mater is called leptomeningitis; of the dura mater, pachymeningitis.

Meningitides are classified according to their causative agent (viral, bacterial, fungal, tubercular, syphilitic) and course (acute, subacute, chronic) and according to the nature of the changes in the cerebrospinal fluid (purulent and serous). Primary meningi-tides are those that arise as independent diseases, secondary meningitides develop either as a complication to injuries or by infection traveling from a suppurative focus somewhere else in the body (for example, inflammation of the middle ear may lead to otogenic meningitis).

Meningitis is most often found in children. It sets in with a sudden rise in temperature, headache, and vomiting. Sensitivity to light and noise increases. Infants often have convulsions. The fontanel swells from increased intracranial pressure (edema of the inflamed meninx), the head is thrown back because of convulsive tonic contraction of the occipital muscles, and complete unconsciousness may ensue. Meningococcic (epidemic cerebro-spinal) meningitis is marked by pustular (herpetic) eruptions on the face and lips and by a stellate rash on the extensor surfaces of the arms. Some forms of meningitis (for example, adenoviral) may be accompanied by muscular pain and intestinal disturbances. The cranial nerves are sometimes involved.

Tubercular meningitis develops gradually, manifested by pro-longed malaise (weakness, headaches, slightly elevated temperature) and often an expression of miliary tuberculosis.

Treatment of meningitis is comprehensive and carried out in a hospital. The main therapeutic principle is a combination of antibiotics with sulfanilamides. Antituberculosis and antisyphilis treatment are used in tubercular and syphilitic meningitis, respectively. Dehydrating agents are used to reduce edema. Sedatives and vitamins are also prescribed. The patient must be carefully monitored and provided a balanced diet. Prompt treatment usually results in complete recovery.

Meningitis can be prevented by hospitalizing patients with the meningococcic and pneumococcic forms of the disease and by the detection and treatment of healthy carriers of the infection. Suppurative foci should be eliminated promptly, and specific primary diseases (tuberculosis, syphilis) prevented or effectively treated.

REFERENCE

Reznik, B. la., and S. F. Spalek. Meningity u detei. Moscow, 1971.

L. O. BADALIAN

meningitis

[‚men·ən′jīd·əs]
(medicine)
Inflammation of the meninges of the brain and spinal cord, caused by viral, bacterial, and protozoan agents.

meningitis

inflammation of the membranes that surround the brain or spinal cord, caused by infection