Microbiology

Microbial diseases affecting the nervous system tend to be serious because of the critical functions performed by the brain, spinal cord, and peripheral and cranial nerves. Infections can occur in the nervous tissue or in the covering membranes called meninges. Diagnostic tests for diseases of the nervous system often involve examination of the cerebrospinal fluid, and antibiotic therapy must use drugs that pass the blood‐brain barrier.

Meningococcal meningitis. Meningococcal meningitis is caused by the Gram-negative diplococcus Neisseria meningitidis. This organism is called themeningococcus. It is transmitted by respiratory droplets and often inhabits the nasopharynx without evidence of disease. The organism is believed to possess endotoxins that account for the symptoms associated with meningitis. Patients suffer severe and debilitating headache, as well as fever, chills, and blue-black skin spots. The neck is stiff, and seizures are possible. Examination of the cerebrospinal fluid reveals Gram-negative diplococci. The adrenal glands may by involved ( Waterhouse-Friderichsen syndrome). Aggressive therapy with penicillin and other drugs is required.

Haemophilus meningitis. Haemophilus meningitis is caused by Haemophilus influenzae type b. The organism is a Gram-negative, small rod that usually affects children during the first year or two of life. Nerve disorder, fever, and possible mental retardation result from the disease. The Hib vaccine is used to provide immunity, and rifampin and other antibiotics are used in therapy.

Listeriosis. Listeriosis is caused by a small, Gram-positive bacterium called Listeria monocytogenes. Also a blood disease, listeriosis can affect the meninges (listeric meningitis). The disease is transmitted by unpasteurized or improperly pasteurized milk and cheese products, as well as from animals. In a pregnant woman, the bacillus may affect the fetus and cause miscarriage.

Leprosy. Leprosy is considered a disease of the nervous system because the bacilli destroy the peripheral nerves in the skin. Thus affected, the patient cannot sense environmental changes, and injury to the skin tissues results. Deformed hands and feet and eroded bones, fingers, and toes are seen in the disease. In tuberculoid leprosy, skin pigments are lost. In lepromatous leprosy, skin nodules called lepromas disfigure the skin. The incubation time is roughly three to six years.

Leprosy is caused by an acid-fast bacillus called Mycobacterium leprae. The organism is cultivated with great difficulty in the laboratory. The disease is known by its preferred name Hansen's disease. Dapsone is used for therapy.

Tetanus. Tetanus is caused by the soilborne, anaerobic, Gram-positive rodClostridium tetani. Spores of this organism enter a wound, where they germinate to vegetative cells. The organisms produce a powerful exotoxin that interferes with the removal of acetylcholine from the synapses in the nervous system. This inhibition results in spasms affecting the muscles and causing clenched jaws and fists, paralysis of the respiratory muscles, disturbance of heart function, and death. The disease is prevented with immunizations of tetanus toxoid in the DPT vaccine. Established cases are treated with tetanus antitoxin (antibodies) and large doses of antibiotic such as penicillin.

Botulism. Botulism is caused by the anaerobic, Gram-positive, spore-forming rod known as Clostridium botulinum. The organism's spores enter food in vacuum-sealed, anaerobic environments, and they germinate to reproducing cells, which produce powerful exotoxins ingested with the food. The toxin interferes with the release of acetylcholine in the synapse between nerve and muscle cells. Without acetylcholine, nerve impulses cannot be transmitted, and paralysis soon begins. Respiratory arrest leads to death. No vaccine is available, but treatment with large doses of botulism antitoxin may prevent death. Infant botulism and wound botulism are also possible.