What happens in meningitis, exactly?

What is it?

Meningitis is an acute inflammation of the membranes covering the brain and the spinal cord. Typical symptoms include fever, headache, and neck stiffness. Small children, however, often show instead very unspecific symptoms, such as irritability and drowsiness. There are many causes for meningitis, and therefore many different sets of symptoms.

The mortality rate of meningitis depends very much of the underlying cause and the age of the patient. Untreated bacterial meningitis is almost always fatal, while untreated viral meningitis tends to be resolved with time. 20-30% of newborns with bacterial meningitis die, but in older children the number is 2%, and in adults 19-37%.

While the exact rate of incidence is unknown, in 2013 meningitis resulted in 303 000 deaths worldwide. Bacterial meningitis occurs yearly in about 3 people per 100 000 in Western countries, while in some areas of Sub-Saharan Africa the rate has been suggested to be as high as 800 cases per 100 000 people each year.

What causes it?

Meningitis is typically caused by an infection with microorganisms: most commonly viruses, followed by bacteria, fungi, and protozoa. The pathogen often comes from someone who is carrying it but is not ill. It can be spread through, for example, sneezing, coughing, kissing, and using the same things, such as toothbrushes.

What happens during it?

It’s hardly news to anyone that our central nervous system (the brain and spinal cord) is both crucial to us and rather fragile. Without it we wouldn’t be able to think, perceive, move, or metabolize. It makes sense to protect the CNS, and among various other mechanisms, we have three different membranes called meninges that enclose it.

In most cases of meningitis, pathogens reach the meninges trough the bloodstream. We have a system that prevents harmful things from entering the CNS through vessels, but in some places this blood-brain barrier can be weak, and the pathogens can enter the space between the innermost and middle meninges.

Cytokines are molecules that our immune system produces when it encounters an invader. Their job is to provoke inflammation, so that blood vessels dilate and become more permeable, which in turn leads more immune cells being transported to the infected area to fight the pathogen.

In meningitis the brain’s immune cells detect the pathogen and release large amount of cytokines. The blood-brain barrier becomes more permeable to allow immune cells to enter the CNS. This also lets more blood to get trough, which makes the meninges swell. When swelled, they obviously take more space and cause the CNS to be under more pressure. The laws of physics dictate that blood prefers to flow to areas of low pressure: in meningitis, this means that the CNS doesn’t get enough blood (and, crucially, oxygen) and the neurons begin to die.

How can it be treated?

Vaccines are an important method of preventing meningitis. There are several of them offered in different stages of life. Vaccines work by introducing a pathogen to our immune system under safe circumstances, so that our cells can create a memory of it and respond to a future invasion quickly and effectively. Vaccines have proved to be very effective in eliminating different meningitis-causing pathogens in populations. Antibiotics can be useful in preventing meningitis in those who have a temporarily high risk of contraction, such as a skull fracture.

Because of the high mortality rate, introducing antibiotics to someone suspected to have the condition is often recommended, even if there isn’t yet a definite knowledge of whether the symptoms are caused by bacteria and, hence, whether antibiotics will help. Intravenous fluids can help to heighten blood pressure, and oxygen can be administered through a face mask. Bringing the patient to care immediately is crucial, especially so in bacterial meningitis: while the condition is potentially fatal, most of those treated quickly make a full recovery.


Sources: https://en.wikipedia.org/wiki/Meningitis, http://www.nhs.uk/conditions/Meningitis/Pages/Introduction.aspx, http://www.news-medical.net/health/Meningitis-Mechanism.aspx





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