meningococcus

meningococcus, the bacterium Neisseria meningitidis, which causes meningococcal meningitis in humans, who are the only natural hosts in which it causes disease. The bacteria are spherical, ranging in diameter from 0.6 to 1.0 μm (micrometre; 1 μm = 10⁻⁶ metre); they frequently occur in pairs, with adjacent sides flattened. They are strongly gram-negative.

Meningococci are known to enter the nasopharynx and the bloodstream, and they can infect the lining of the brain and spinal cord. Meningococcal infections in the nasopharynx may cause no symptoms—up to 30 percent of the population may harbour the bacteria between epidemics. When the bacteria enter the bloodstream, however, infection can result in symptoms of bacteremia or septicemia. Infections of the lining of the brain and spinal cord in the central nervous system can result in meningococcal meningitis.

Meningococcus bacteria spread via contact with respiratory and throat secretions. Symptoms of infection initially resemble those of influenza, with fever, chills, nausea, and headache. In the case of meningococcal meningitis, other symptoms can include stiff neck, vomiting, confusion, and photophobia (increased sensitivity of the eyes to light). Symptoms of septicemia can include body aches, coldness in the extremities, fatigue, diarrhea, rapid breathing, and skin rash.