Bacterial Meningitis

Bacterial meningitis

There are over 1500 cases of bacterial meningitis reported per annum in England and Wales [12]. It is estimated that one in ten people in the UK are carriers of one type of the bacteria within their nasopharynx capable of causing a form of meningitis or septicaemia, without becoming infected. However those whose immune system is compromised may be susceptible to the disease. Over fifty different types of bacteria can cause meningitis, below some of the most common pathogens are discussed further.

Meningitis, is where viable bacteria pass from the blood into the membranes surrounding the brain causing infection and therefore inflammation of the meninges. Septicaemia is caused by bacterial toxins destroying the blood vessels.

Neisseria Meningtidis is the most common cause of meningitis and septicaemia in the UK. There are five main meningococcal bacterial serogroups; A, B, C, W135 or Y[10]. The groups are defined by the differences between the polysaccharide capsules covering the cell wall of the bacteria. The capsules are also implicated in the bacteria’s ability to resist complement-mediated lysis [10].

Haemophilus influenzae type b (Hib) is the leading cause of meningitis in the US [10]. The type b capsule is a polymer of ribosyl-ribitol-phosphate and seems to be much more pathogenic than the sugar phosphate coated capsules found in the other five types of the bacteria.

Group B streptococcus can be found normally in the female genitourinary tracts. Up to 70% of infants born vaginally to an infected mother will show colonisation, however only 1-2% will actually develop an infection which can cause meningitis[10].

On infection Streptococcus pneumoniae initiates a large inflammatory response in the leptomeninges. A toxic neuraminidase is also produced which may be involved in the neurotoxicity of these infections and is likely to be the cause of lasting damage [10].

Vaccinations against Bacterial Meningitis

The vaccines against meningitis are focused around the ability to induce an immune response by injecting material from the capsule of the bacteria without actually causing meningitis. The hosts immune system will produce antibodies against this foreign polysaccharide and will lay down ‘memory’ antibodies which can multiply quickly in the event of future infection and destroy the bacteria by lysis or phagocytosis. The complement system within the body deals with infection and recurrent episodes of meningitis are often caused by an underlying deficiency of one of the late components of the complement system either C6, C7 or C8 [11]. Sickle Cell disease, thalassaemia and coeliac syndrome may also predispose an individual to bacterial meningitis.

Meningococcal bacteria vaccines

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