Types of Meningitis
Many people who carry bacteria associated with meningitis will never develop the disease. In some people, however, for reasons not fully understood, the bacteria will migrate through the body's outer immune defenses (for example, through nasal passages) and into the bloodstream (Pathan 2003).
Acute bacterial meningitis is dangerous and needs to be diagnosed and treated with antibiotics as quickly as possible. In the past, it was fatal in more than 50 percent of cases. However, with better and earlier treatment, fatality has dropped to 10 to 14 percent. Nevertheless, about 15 percent of survivors have long-term disabilities, including hearing loss and brain damage (CDC 2005 [meningococcal disease]). If acute bacterial meningitis is suspected, the person should see a physician and receive treatment immediately.
The most common strains of bacteria that cause meningitis are: Streptococcus pneumoniae (S. pneumonia) (about 50 percent of bacterial cases), Neisseria meningitidis (N. meningitidis) (about 25 percent of bacterial cases—and up to 60 percent in cases that involve children), and Listeria monocytogenes (about 10 percent of bacterial cases—almost exclusively in newborns and elderly) (Kasper 2004).
In recent years, common causes of bacterial meningitis have changed because of vaccines that targeted Haemophilus influenzae (H. influenza) and, to a lesser extent, N. meningitidis (Bilukha 2005). Previously, these two bacteria were responsible for most bacterial meningitis infections. H. influenzae type b used to be the most common cause of meningitis in infants; however, since the H. influenzae Serotype b (Hib) vaccine was introduced in 1985, the number of children in the United States who get meningitis from this organism has decreased by 95 percent (Beers 2005; CDC 2005 [Hib]). Today, S. pneumoniae accounts for about half of all bacterial cases.
Symptoms classically associated with bacterial meningitis include fever, headache, and stiff neck. In more than 75 percent of cases, changes in mental status occur, ranging from lethargy to coma, although some patients may become agitated and even combative. Nausea, vomiting, and sensitivity to light are also common symptoms. Seizures occur in up to 40 percent of patients.
There are several classes of drugs used to treat bacterial meningitis, including antibiotics, inflammation suppressors, and pain relievers. Antibiotics are used to kill the organism causing the infection. The other treatments are used to manage symptoms associated with the disease. If seizures occur, anti-seizure drugs (eg, phenobarbital and phenytoin) may be administered. When patients have trouble breathing, they may be administered oxygen, or may require assisted ventilation.
In the future, anti-inflammatory medications are expected to play a larger role in meningitis therapy (Pathan 2002). The inflammatory reaction associated with meningitis is at least partly modulated by proteins in the brain called tyrosine kinases (Angstwurm 2004; Sokolova 2004). They are involved in inflammatory reactions in the brain and in the movement of bacteria across the blood-brain barrier. Inhibitors of tyrosine kinases, including supplements such as genistein, may decrease the severity of inflammation and the ability of bacteria to cross the blood-brain barrier, which could possibly prevent infection and limit damage (Sokolova 2004).
Viral meningitis is the most common form of the disease (Romero 2003). About 90 percent of cases (in which the virus has been identified) are caused by enteroviruses, mostly coxsackieviruses and echoviruses (CDC 2005 [viral meningitis]).
It used to be difficult to identify which virus was causing viral meningitis; also, once bacteria were ruled out, further tests were not commonly done. However, because of the West Nile Virus (which can also cause meningitis), more tests using the polymerase chain reaction technique have been performed to identify the viruses. Epstein-Barr virus has also been found in the CSF of patients with meningitis (Volpi 2004). The viruses that cause measles, mumps, and chickenpox can also cause meningitis. Vaccines against these diseases may be partly responsible for the decrease in viral meningitis in children (Beghi 1984).
Mollaret's meningitis is a rare, recurrent viral meningitis that is painful but not generally life-threatening. The herpes simplex viruses, HSV1 and HSV2, have been associated with Mollaret's meningitis (Schmutzhard 2001).
Viral meningitis is generally treated with analgesics, bed rest, and fluids. Acyclovir or valacyclovir, drugs used to treat herpes, may be useful for treating Mollaret's meningitis (Schmutzhard 2001).
As with bacterial meningitis, the inflammatory cascade is an important contributor to damage caused by viral meningitis, and anti-inflammatory therapy will probably develop into an important part of therapy in the near future (Pathan 2003).
Other Types of Meningitis
Meningitis can also occur after certain medical procedures, such as catheter-based intervention for cerebral aneurysm (Meyers 2004). Chemical meningitis can occur as a result of drug use. In these nonbacterial or viral conditions, the disease is characterized chiefly by inflammation, making anti-inflammatory therapy potentially more important.
Chronic meningitis can occur after infections with tuberculosis, Lyme disease, AIDS, or syphilis, as well as in noninfectious disorders such as some cancers of the brain or blood (eg, leukemias and lymphomas) (Beers 2005).
Fungal infections are usually only a problem in people with weakened immune systems, such as people with AIDS or who have had their spleens removed. Usually the fungus responsible is a species of Cryptococcus, an encapsulated yeast (Beers 2005). These infections start when a person breathes in fungal spores from contaminated soil; the infection in the lungs is usually cleared by the immune system. Only when the immune system is weak do these infections progress to meningitis.