Not much gets to the brain.
But meningitis manages, with sometimes deadly results.
The command center in your skull is a citadel, wrapped in a tough membrane, and cushioned in fluid. It is further protected by the special architecture of its blood vessels. While capillaries elsewhere in the body let all sorts of things slip in and out with relative ease, not much squeezes past the tight fortress of cells that line the brain's vessels.
But somehow, the bacteria that cause meningitis slip through this protective barrier and set off havoc in the layers of tissue enfolding the brain. The result is swelling that can lead to headache, seizures, damage to the brain, and, in one in five cases, death.
In fact, specialists say a healthy person with a sudden onset of headache, fever, and pain in the neck should be treated immediately with antibiotics. Other symptoms include nausea, sensitivity to light, and drowsiness.
Last week, three teenagers in Alliance, a city of 22,846 northeast of Canton, were struck by meningitis. Two died. A third is hospitalized in serious condition.
Meningitis is an inflammation in the outer layer of the brain known as the meninges. Bacteria and virus are capable of causing the swelling, but it is the bacterial infection that is life threatening, said Dr. Haig Donabedian, an infectious disease specialist at the Medical College of Ohio.
“Like most bacterial infections, it rarely causes anything wrong,'' Dr. Donabedian said. “For every one person with meningitis, you'll find about 100 that have the bacteria in their nose and throat.''
It's not known why bacteria that sit quietly in most people become life threatening in about 2,600 people each year, Dr. Donabedian said. CDC statistics show there is one case of meningococcal disease for every 100,000 people. Nor is much known about how the bacteria cross the blood-brain barrier and enter the three layers of the meninges, said Dr. David Fisk, a fellow in infectious disease at University of Michigan Medical School.
“It lives only in humans, and it must be passed from human to human. The real question is, why was there an outbreak in Alliance? Was there a high infection rate, or was it just pure chance?'' Dr. Donabedian said.
A number of bacteria can cause meningitis. In Alliance, the causative agent is called Neisseria meningitidis. But bacteria such as Streptococcus pneumoniae can cause the swelling in the brain lining. Before the development of infant vaccines, the respiratory tract infection, Haemophilus influenzae was the leading cause of meningitis in children under 5.
The Neisseria bacteria can cause a lethal septic reaction, during which blood pressure plummets and leads to shock. “Lack of blood supply to fingers and toes can cause them to die off in hours. It's incredible,'' Dr. Fisk said.
A spokesman for the Ohio Health Department said 130 to 150 bacterial meningitis cases occur in Ohio each year. About 20 percent of those end in death.
When the bacteria hits the brain, parts of the immune system, including cells called neutraphils, respond to the presence of the foreigner. The neutraphils attempt to fight the invader and produce pus. The build up of pus increases pressure on the brain, bringing disability, and death.
A vaccine is available against Neisseria, and it's effective 70 percent of the time.