Meningitis - Causes 

Causes of meningitis 

Meningitis can be caused by bacteria or a virus.

Bacterial meningitis

Vaccination programmes have helped reduce the number of different types of bacteria that can cause meningitis. However, there are currently a number of bacteria that do not have effective vaccines yet. Some bacterial causes are described below.

Neisseria meningitidis bacteria

Neisseria meningitidis bacteria are often referred to as meningococcal bacteria. There are several different types of meningococcal bacteria called groups A, B, C, W, X, Y and Z.

There is a vaccination that provides protection against group C meningococcal bacteria. Read more information about the Men C vaccination. There is also a quadruple vaccine that provides protection against group A, C, W and Y meningococcal bacteria.

In the UK, most cases of meningococcal meningitis are caused by the group B bacteria. A vaccine for group B disease is being tested in clinical trials but is not yet available for general use.

Streptococcus pneumoniae bacteria

Streptococcus pneumoniae bacteria are often referred to as pneumococcal bacteria. Pneumococcal bacteria tend to affect babies and young children because their immune systems (the body's defence system) have not built up immunity (protection) to these bacteria.

Spreading the bacteria

The meningococcal bacteria that cause meningitis do not live long outside the body, so are usually only spread through prolonged, close contact. Possible ways to spread the bacteria include:

  • sneezing
  • coughing
  • kissing
  • sharing utensils, such as cutlery
  • sharing personal possessions, such as a toothbrush or cigarette

As most people  particularly adults above 25 have a natural immunity to the meningococcal bacteria, most cases of bacterial meningitis are isolated (single cases). However, there is a chance of a small outbreak of cases occurring in environments where a lot of young people live close together. For example:

  • a boarding school
  • a university campus
  • a military base
  • student housing

Pneumococcal bacteria are much easier to catch than meningococcal bacteria, and are spread through coughing and sneezing. However, in most cases they only cause mild infection, such as a middle ear infection (otitis media).

Read about pneumococcal infections for more information about the type of infections these bacteria can cause.

Viral meningitis

As in the case of bacterial meningitis, vaccination programmes have successfully eliminated the threat from many viruses that used to cause viral meningitis.

For example, the measles, mumps and rubella (MMR) vaccine provides children with immunity against mumps, once a leading cause of viral meningitis in children. 

Read more information about the MMR vaccination.

There are still a number of viruses that can cause viral meningitis. These include:

  • enteroviruses - a group of viruses that usually only cause a mild stomach infection, and can be spread through coughing, sneezing or not washing your hands after touching a contaminated surface
  • the herpes simplex virus - which can cause genital herpes and cold sores 

During a meningitis infection

In most meningitis infections, bacteria or viruses spread through the blood. An infection can begin in one part of the body, such as your throat or lungs, before moving through the tissue and into the blood.

The brain is usually protected from infection by the blood-brain barrier, which is a thick membrane that filters out impurities from the blood before allowing it into the brain.

However, for reasons that are not entirely clear, in some people the infection is able to pass through the blood-brain barrier and infect the meninges (brain membrane). The immune system responds to the infection by causing the meninges to swell in an attempt to stop the spread of infection. The swollen meninges may then damage the brain and the rest of the nervous system (nerves and spinal cord).

Bacteria or viruses can also infect the cerebrospinal fluid (CSF), which is the fluid that surrounds and supports the brain and spinal cord. An infection of the CSF can cause further swelling of the meninges, leading to increased pressure in the skull and pressing on the brain. This is known as intracranial pressure.

Page last reviewed: 14/06/2012

Next review due: 14/06/2014

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