Infections of the central nervous system affect the brain and spinal cord, usually causing swelling. The consequences of this can be serious but with rapid treatment most cases of central nervous system infection can resolve without long-term neurological damage.

Many pathogens can infect the central nervous system

Infection of the central nervous system can occur when a pathogen, such as a virus or bacteria, enters the brain. Pathogens can get to the brain via the blood, the nerves, or through a skull fracture.

Once inside the central nervous system, bacteria and viruses multiply, and the body responds by triggering inflammation and swelling:

  • Meningitis develops when a bacterium, virus, or fungus infects the meninges, the membranes that line the brain and spinal cord. Bacterial meningitis is generally more life-threatening than viral meningitis, but is not as infectious.
  • Encephalitis involves general swelling of the brain and is usually caused by a viral infection. Herpes simplex virus, which is the virus responsible for cold sores, and human herpes viruses, including the chicken pox and measles viruses, can live in the nerves for years after infection, before travelling to the brain and causing encephalitis. Other viruses can be spread by insect bites and include the West Nile fever virus and the Japanese encephalitis virus.
  • Brain abscesses can develop as a result of an infection with bacteria or fungi that spreads into the brain, causing a build up of pus that destroys healthy nerve cells.

Types of meningitis

Neisseria meningitidis, Streptococcus pneumonia and Haemophilus influenza type b are common causes of bacterial meningitis. The bacteria infect the meninges by spreading from the ears or sinuses, or by moving from the nose or mouth into the blood stream.

Meningitis can also be spread by person-to-person contact but it is usual for people to have the bacteria that can cause the infection on their skin and in their nose as a harmless commensal organism.

A second form of meningitis, called aseptic meningitis, or viral meningitis, is caused by enteroviruses that can travel from the digestive tract or are spread by insect bites.

Other viruses that can cause aseptic meningitis are the herpes simplex virus, Epstein–Barr virus, HIV, varicella zoster virus and mumps virus.

Central nervous system infection and inflammation

Central nervous system infections, like most infections, stimulate an immune response. This involves white blood cells moving to the area of infection to attack the pathogens, which inevitably leads to excess fluid and plasma in the area. This causes inflammation and swelling, which is in itself highly dangerous when this raises fluid pressure inside the skull. In central nervous infections, most of the symptoms are caused by the body’s response.

Meningitis is commonly associated with:

  • A headache, which can be very severe
  • A stiff neck that aches and feels tender
  • Fever
  • Nausea and vomiting
  • Feeling confused, and having seizures
  • Photophobia: an aversion to bright light

Some types of infection in the central nervous system can be distinguished by specific symptoms and the severity of symptoms:

  • Bacterial meningitis can cause a rash of red and purple spots on the chest, arms, and legs.
  • Viral meningitis tends to cause less severe symptoms.
  • Encephalitis usually begins with a headache, fever and malaise. This can quickly develop into symptoms that resemble meningitis.
  • Brain abscesses can cause headaches, vomiting and drowsiness. Patients can also fall into a coma.