Pathophysiology and Treatment of Meningitis and Encephalitis
Description of the Diseases
Meningitis is an inflammation of the meninges, the tissue surrounding the brain and spinal cord. There are five types of meningitis: bacterial, viral, fungal, parasitic or non-infectious in origin. The most prevalent type being is viral (Centers for Disease Control and Prevention [CDC], 2014). The incidence of bacterial meningitis is about 1.3 in 100,000 whereas the estimated incidence of viral meningitis is about 11 in 100,000 (2014; Wan, 2013).
The first type of meningitis is bacterial. The two most prevalent organisms found are meningococcus and pneumococcus. Both are considered communicable. Meningococcal meningitis tends to affect males from the fall to spring season with epidemics in young children and adolescents which generally occur every 10 years. Pneumonoccal meningitis tends to be found in the young and those older than 40 years with these three predisposing conditions: sinusitis, a weak immune systems and pneumonia (Huether & McCance, 2012).
The second type of meningitis is viral. In the United States, non-polio enteroviruses are the most prevalent causative pathogens. Those most at risk are children less than 5 years old and the immunocompromised with the highest incidence during the summer and fall seasons. Herpesviruses, measles, mumps, influenza and arboviruses are also identified pathogens. Viral meningitis is considered contagious (CDC, 2014).
The third type of meningitis is fungal. It is usually found in immunocompromised persons infected with Cryptococcus and is not considered contagious (CDC, 2014). The disease also “develops insidiously” compared to bacterial and viral meningitis, both of which have rapid onset (2014; Huether & McCance, 2012, p. 394). However, it is “one of the most common causes of adult meningitis in Africa” (CDC, 2014).
The fourth type of meningitis is parasitic. It is usually caused by Naegleria fowleri, a microscopic ameba found in warm freshwater. The organism gains access to the brain through the nose and causes parasitic meningitis, a fatal but rare infection with only 31 reported cases from 2003 to 2012 (CDC, 2014). It is not contagious.
Lastly, noninfectious meningitis is associated with cancer, Lupus, certain drugs, neurosurgeries and traumatic brain injuries and is beyond the scope of this paper (Huether & McCance, 2014).
Encephalitis is characterized by inflammation of the brain and febrile illness similar to meningitis, but differs in that it presents with associated CNS involvement. It is usually viral in origin. Incidence is estimated at 20,000 per year in the United States (Whitley, 1990). The most common infectious viral agents are herpes simplex type 1 and arboviruses. A well-known arbovirus in Southern California is West Nile Virus. Post infectious encephalitis is a complication of a systemic viral infection, mainly poliomyelitis, rabies, mononucleosis or recovery from measles. It can also occur secondary to live attenuated MMR vaccinations (Huether & McCance, 2012).
Pathological Mechanisms Bacterial meningitis usually begins as a systemic infection, bacteremia or direct invasion from an infected area, such as the sinuses. The organisms invade the subarachnoid space and initiate an acute inflammatory process with neutrophil migration. The inflammation is compounded by bacterial toxins and cytotoxic agents which damage brain cells and increase vessel permeability. Increased intracranial pressure occurs due to the combination of swollen meningeal cells and bacterial exudate. Hydrocephalus occurs if excessive exudates block the arachnoid villi (Huether & McCance, 2012).
Fungal meningitis also invades the CNS via the bloodstream. However, it causes a granulomatous reaction in addition to inflammation. Formation of gelatinous masses and fibrosis damages cranial