Inflammation Of The Meninges Biology Essay

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Meningitis Research Foundation estimates that there are around 3,500 cases of bacterial meningitis and septicaemia every year in the UK and Republic of Ireland [1] . It affects more than 620 people in the United States each year. Five to ten percent of these people die from the disease and another eleven to nineteen percent suffers serious effects such as loss of limbs or deafness and brain damage. [2] In Africa major epidemics rates ranges from 100 to 800 per 100 000 population, but individual communities have reported rates as high as 1000 per 100 000 [3] .In endemic areas the highest attack rates are observed in young children. During epidemics, older children, teenagers and young adults are also affected. In other to understand why meningitis is such a global health issue, we need to first understand what meningitis is, the different types, and signs and symptoms. We can then analyse what causes meningitis and how it can be prevented and treated to reduce its incidence.

Meningitis is the infection or the inflammation of the meninges. The meninges are the protective membranes that surround the brain and spinal cord. They contain blood and supply nutrients to the brain. They consist of the dura, arachnoid, and the pia maters. When they become infected they swell as a defence mechanism and this can cause serious damages as less blood is available to them. Organisms that cause meningitis are bacteria, virus and fungi.

Bacterial meningitis occurs worldwide with an annual incidence of about 5 per 100 000 [4] . It affects people of all ages and of any ethnic group, it does not discriminate, although the organism responsible depends on age (table 1). It is also seen more frequently in people with a compromised immune system. From Table 1(see appendix) the common bacteria's are pneumococcus and Neisseria meningitidlis as it affects children from aged 3months to adults over 50years of age. In children younger than 3months group B streptococci, Escherichia coli and Listeria are the most common causes. In those over 50years of age pneumococcus, Listeria and gram negative bacilli are most common causes.

Neisseria meningitidlis causes illness sporadically in small clusters, either in isolated cases or epidemics worldwide (Figure 1). There are nine types of Neisseria meningitidis. Types A, B, C, Y and W-135 cause more than 95% of meningococcal disease globally [5] . Seasonal variations accounts for a variable proportion of endemic bacterial meningitis. In temperate regions, the number of cases increases in winter and spring. Types B and C of Neisseria meningitidlis cause majority of cases in Europe and America. In the past 10 years, the meningococcal meningitis infection has increased in New Zealand with an average of 500 cases occurring every year, and in most cases due to Neisseria meningitidlis type B [6] . In Africa and Asia most of the major epidemics are due to Neisseria meningitidis A and C.

Similarly Mongolia reported a large epidemic in the recent years (1994-95).There is increasing evidence of W135 being associated with outbreaks in considerable size. In 2000 and 2001 several hundred pilgrims attending the Hajj in Saudi Arabia were infected with Neisseria meningitidis W135 [7] . Then in 2002, W135 emerged in Burkina Faso, striking 13,000 people and killing 1,500. In 1996, Africa experienced the largest recorded outbreak of epidemic meningitis in history, with over 250 000 cases and 25 000 deaths registered. Between that crisis and 2002, 223,000 new cases of meningococcal meningitis were reported to the World Health Organization [8] . The most affected countries were Burkina Faso, Chad, Ethiopia and Niger.

In figure 1, below the major affected area, the Meningitis Belt in sub-Saharan Africa, this spans from Senegal in the west to Ethiopia in the east. This region has the highest case due to climate and social habits such high temperatures and overcrowding. Other region infected includes Asia and South America, within the epidemic zone. In the 1960s, China had a major outbreak affecting 3,000,000 people and killing 160,000 [9] . During this time there were no treatment and vaccines available. The incidence of meningitis in developing countries is reported to be ten-fold higher than in developed countries due to less access to preventive services such as vaccines.

Figure 1 Neisseria meningitidlis (meningococcal meningitis)

Demography of meningococcal meningitis

     Meningitis belt

     Epidemic zones

     Sporadic cases only

Clinical signs and symptoms of bacterial meningitis includes fever, photophobia, rapid onset of generalised headache which is a key feature, neck stiffness, skin rash purpuric in colour and does not fade away when pressed with a glass or when pressure is applied. This is caused as a result of bleeding into the skin (meningococcal septicaemia). Other symptoms includes epileptic seizures in children, irritability, confusion, nausea and vomiting, altered consciousness, muscle pain, anorexia and tachycardia. Bacterial meningitis is highly contagious; all suspected cases in contact should also be treated.

To diagnose bacterial meningitis a CT brain scan is done first to exclude raised intracranial pressure and a lumbar puncture to obtain the CSF. The CSF in bacterial meningitis would appear cloudy or yellow due to the high concentration of white blood cells, (usually more than 1000 neutrophils m/L) present and involved in phagocytosis of the bacteria [10] . Table 2(see appendix) below shows the features of the CSF in the bacterial and viral meningitis compared to normal which has no white blood cells in it and appears clear to the naked eye. The CSF would also contain low glucose content and a high protein level compared to normal. Staining of the CSF with stains to detect the organism will allow the species of bacteria causing the meningitis to be determined.

Bacterial meningitis is a serious disease with an overall mortality of about 10%; it requires prompt treatment with the appropriate intravenous antibiotic without delay [11] until the organism is identified. Once the bacterial causing organism is identified, the appropriate antibiotic should be given with consideration of allergies to the patient. The suggested treatment for the organisms that cause bacterial meningitis includes Penicillin G for pneumococcus, Neisseria meningitidis and Group B streptococcus, while Ampicillin and Gentamicin is used to treat Listeria. To treat Haemophilus influenzae type B meningitis in children steroids such as dexamethasone given intravenously is seen to reduce neurological consequences. Dexamethasone is also used to treat meningitis due to tuberculosis in adults but should not be used in other instances as it renders the white blood cells fighting infection less effective [12] . If patient is allergic to penicillin, Chloramphenicol should be used for Haemophilus influenzae and Neisseria meningitidis, Vancomycin for Pneumococcus bacteria and Trimethoprim to treat Listeria. Bacterial meningitis such as that caused by pneumococcal is very contagious so all those in close contact with those affected should be given prophylactic antibiotics. Analgesics such as oral dihydrocodeine should be used for headaches and antiepileptic drugs such as phenytoin should be used if seizures occur.

Associated with acute bacterial meningitis are septicaemia, hydrocephalus, and encephalitis as a result of an infection of the brain substance, or the spinal cord (myelitis) and vasculitis as a result of infection to the cerebral vessels. Prevention of bacterial meningitis is vital as it is a serious disease with a high mortality rate in young children, and even survivors of the disease may become mentally handicapped.

Haemophilus vaccine is available to children to prevent Haemophilus influenzae meningitis. Pneumococcal conjugate vaccine is given to prevent pneumococcal meningitis as part of routine vaccination programme for young children up to 2 years of age. It is also given to young children deemed to be at higher risk of contracting pneumococcal infection up to the age of 5years and especially for students and military recruits living in close proximity or in dormitories as it is very contagious. There is also a polysaccharide vaccine available for adults over the age of 65 years. The vaccine is recommended for those who are at increased risk of getting pneumococcal infection, for example, those with serious breathing conditions, heart disease and diabetes. Emphasis should be placed on overcrowding in developing countries to reduce the spread of meningitis. There is currently no vaccination to protect against meningococcal group B, the most common cause of bacterial meningitis in the UK, and in Africa [13] .

Viral meningitis is more common than bacterial meningitis with incidence of 10 cases per 100 000 people per year [14] . It is a mild disease with mild symptoms but can make people very unwell. It affects any age group, is more common and can be very serious in babies and young children where their bodies' defences are not fully developed as well as people with a compromised immune system and the very old people. Although most people make a full recovery some people are left with serious side effects. Most cases of viral meningitis are not severe enough to be diagnosed it is only when they cause serious neurological features that they are diagnosed.

Viral meningitis is caused when viruses beat the body's defences and spread to the meninges. The meninges become inflamed and the pressure around the brain causes nerve damage and produces symptoms such as headache, fever, neck stiffness, and drowsiness. The other symptoms caused such as enlarged lymph glands or enlarged salivary gland, or a rash depends on the specific virus involved. So many viruses can cause meningitis; the most common virus that causes viral meningitis is a group of virus called enteroviruses. Enteroviruses are estimated to cause approximately 75,000 cases of viral meningitis in the USA annually [15] . These viruses live in the stomach and intestine and causes colds, sore throats and diarrhoea, and on rare occasions spread through the body to the meninges. Over 80 types of the viruses are recognized but the commonest are coxsackie and echoviruses, and these virus accounts for 50-80% of all cases of viral meningitis. [16] Other common viruses include Arbovirus, Herpes simplex virus type 2, and Human immunodeficiency virus. Less common viruses include the Mumps virus which can cause meningitis and encephalitis about 1 case in a 1000, Herpes simplex virus type 1 and lymphocytic choriomeningitis [17] . Rare viruses that causes viral meningitis include Measles, Adenovirus, Rubella, Varicella-zoster, Influenzae, and Epstein-Barr virus which causes glandular fever symptoms, such as generalised headache, and also a faint red rash might occur, which could be made worse if treated with antibiotics, this virus leads to meningitis in about 1% of the case [18] .

Different viruses can cause meningitis, however the way in which the virus is spread will depend on its type. For example, enteroviruses are carried harmlessly in the intestines of both children and adults, and carriage of these viruses helps us to build up natural immunity to infection. Spread of these viruses is common and they can be passed from person to person by coughing, sneezing and on unwashed hands. Practising good hygiene, such as washing hands after going to the toilet, will help to prevent the spread of viruses that are passed away in faeces [19] . Viral meningitis is diagnosed clinically with no clinical tests done. If serious a lumbar puncture is done to examine the CSF and exclude bacterial meningitis.

The CSF of viral meningitis compared to a normal CSF and a CSF with bacterial meningitis is shown in Table 2 (see appendix). As seen from table 2 the CSF of viral meningitis will show a normal or slightly raised protein and glucose level as well as a raised lymphocyte cell count. Using Polymerase chain reaction on the CSF allows for the specific virus causing the meningitis to be identified. Viral meningitis is a mild disease and patients recover fully within a few days without treatment. Although in a few cases permanent damages can occur for example the mumps virus can cause deafness in about 1 in 15, and paralysis from acute polio caused by the enteroviruses [20] . If the virus spreads to the brain substance (encephalitis) it becomes a serious condition and antiviral agent such as Acyclovir should be given. Acyclovir is a pro-drug that stops replication of viral DNA. There are now routine (MMR) vaccines to protect against some viruses that cause meningitis such as mumps, measles and rubella. Mumps was the most common cause of viral meningitis in children before MMR was introduced. It is given at around 13 months of age with a booster dose before the age of five [21] .The spread of Herpes Simplex Virus type 2 and HIV can be reduced through education and enlightenment.

Fungal meningitis is rare and mostly occurs in immunocompromised individuals such as AIDS patients or those taking immunosuppressant, steroids or Cytotoxic drugs. Some Fungi that causes meningitis includes Candida albicans, Cryptococcus neoformans and mucormycosis. Fungal meningitis often develops slowly and can be difficult to diagnose and treat. However, sometimes the onset of the infection can be acute and symptoms may develop quickly. The symptoms of fungal meningitis are similar to other forms of meningitis. Brain abscess may form. It is also associated with encephalitis and Vasculitis thereby causing ischaemic or haemorrhagic strokes. Therefore, if not treated can be very life threatening. To diagnose fungal meningitis a lumbar puncture is also done to obtain a CSF, which would have a normal protein and glucose level. This would be examined for specific fungal antigen (repeated lumbar punctures may be done to culture the organism) or a biopsy of the brain abscess can be done or analysis of blood.

Fungal meningitis should be treated with intravenous amphotericin, although side effects of this drug include renal damage, which can limit effective doses being used. Flucytosine is another antifungal drug which can be used, as it inhibits fungal DNA synthesis. The overall duration of antifungal treatment will depend whether a person has problems with their immune system and the type of fungus causing the infection.  The treatment often takes 4-6 weeks in people who do not have problems with their immune system.  However, people with lowered immunity may require prolonged therapy and many also require long-term maintenance on antifungal therapy. Unlike some other meningitis infections (e.g. meningococcal), there is no risk of someone with fungal meningitis spreading the infection to other people as it is not contagious.  There is no vaccine for fungal meningitis.

In conclusion, meningitis occurs as a result of infection to the meninges that protect the brain, either by bacteria most common in Africa, virus most common in America or by fungi which is mostly seen in an individual with an immunocomprised system. Meningitis is a global issue affecting thousands of People every year; it can affect any age group and any race, although some bacteria affects people within a certain range, with effects ranging from minor to permanent such as deafness, paralysis, and brain damage and even fatal in some cases. Therefore, prevention by maintaining a good personal hygiene and the importance of overcrowding and living in well ventilated area to prevent spreading of viral and bacterial meningitis is essential. Prevention is also achieved by giving routine vaccinations in the meningitis belt. However, there are no vaccinations yet available for the meningococcal meningitis which is the most common type in the UK and in Africa.

Although the epidemiology of bacterial meningitis continues to evolve as preventive strategies are implemented.

Symptoms of meningitis includes onsets of generalised headache, neck stiffness, fever, purpuric rash which doesn't fade away when pressed with a glass, nausea and vomiting, should not be mistaken with a hangover and sometimes the symptoms are similar to that of the flu. If any of these signs persist one should visit a hospital where the patient should be administered intravenous antibiotics without delay and lumbar puncture will be done to obtain a CSF and examined to find out the particular organism causing the meningitis so as to be treated with the appropriate drugs.