Pathophysiology of Meningitis and Encephalitis
Meningitis and encephalitis are two similar infections of the central nervous system that often lead to fatality of the host organism. Both diseases occur when pathogens enter the blood stream and gain access into the central nervous system. Stimulating inflammation within the cranial cavity, the pathogens continue to multiply and take harmful effects on the host. Inflammation, the body’s response to infection, ultimately causes all of the symptoms and complications of meningitis and encephalitis. The pathophysiology of meningitis and encephalitis aids in the explanation and understanding of the symptoms, effects, and underlying agendas of the two infections.
Meningitis is the inflammation of the meninges, membranes that encase the brain and spinal cord. Although meningitis can result from protozoal or fungal infections, bacteria and viruses typically cause the often fatal disease. Known for its sudden onset of flu-like symptoms, the infection rapidly progresses into an agonizing cascade of high fever, chills, nausea, vomiting, light sensitivity, purpura (dark discolorations of the skin caused by bleeding beneath the skin), and possibly seizures. In severe cases of meningitis, limbs or extremities must be amputated due to the appearance of purpura.
Viral meningitis, the most common form of the disease, often resolves itself without treatment within a few days. However, bacterial meningitis, somewhat rare in the United States but rampant in West Africa, requires immediate attention in order to prevent fatality. The bacteria that cause meningitis include Streptococcus pneumoniae, Neisseria meningitidis, Streptococcus agalactiae, and Listeria monocytogenes. The severity of the body’s response to the bacteria depends on the “virulence of the strain, host defenses, and bacteria-host interactions” (Lazoff, par. 5). For example, S. pneumoniae (pneumococcal meningitis) has a mortality rate of 40% of infected patients, while N. meningitidis (meningococcal meningitis) kills only 5-10% of its victims (Phillips, par. 14). Although the bacteria commonly live
harmlessly in the mouth and throat, they occasionally overcome the body’s immune system, thus infecting the host. One can acquire meningitis through direct contact with the bacteria during trauma or neurosurgery.
The infectious bacteria enter into the body through the nasopharynx. Numerous bacteria contain pili, structures on the surface of the cell wall, that adhere to receptors on mucosal cells within the nasopharynx. In the nasopharynx, the bacteria colonize and invade nearby tissues (Phillips, par. 3). Next, they enter the central nervous system by way of the blood stream or respiratory tract. Because the bacteria have a capsule composed of polysaccharides, they easily evade phagocytosis by the neutrophils and the complement system (a component of the immune response).
The bacteria then travel to the meninges, the membranes that encase the...