Download Activity 3 - Meningitis

Activity 3 - Meningitis
You have likely heard of meningitis too, another potentially life threatening “itis”. It is
inflammation or infection of the meninges.
What are the meninges?
The brain and the spinal cord are covered and protected by a series of membrane known as
the meninges. They are highly specialised, tightly controlling the things that can enter and
leave and also sealing the spaces that contain the fluid that bathes the brain; the
cerebrospinal fluid (CSF).
Question 1 what is the function of the CSF?
The meninges are actually
made up of three separate
layers known as:
1) The dura mater
2) The arachnoid mater
3) The pia mater.
The dura mater is the
thickest layer and is the first
layer of the meninges you
will reach if you open the
skull. The word “dura” is
derived from late 19th
century Latin meaning hard.
The arachnoid mater is the next layer and contains a lot of blood vessels creating a spiderweb like appearance. The word “arachnoid” is derived from the word arachnid which
pertains to spiders. The third and final layer beneath that is the pia mater. It is intimately
related to surface of the brain. The word “pia” is also derived from late 19th century Latin
and means tender.
What causes meningitis?
When these layers of the brain become inflamed, this is meningitis. Meningitis is most often
caused by an infection, typically a bacterial or viral infection. Rarely, it might be caused by a
fungus or tuberculosis or even by cancer cells (such as lymphoma). Alternatively chemical
meningitis (rare) can occur after surgery or other invasive treatments and procedures on the
brain or spine. The meninges are also irritated by blood in the CSF as occurs with a
subarachnoid haemorrhage. This may occur if one of the many vessels in the arachnoid
layer we discussed earlier rupture and bleed.
Meningitis can affect anyone of any age. Infective
meningitis is most common in babies and young
children or people with a compromised immune
system.
Viruses cause a greater number of cases of meningitis
than do bacteria. Viral meningitis is usually mild and
often clears up on its own. The main viruses
responsible are the enteroviruses, measles, mumps,
glandular fever, herpes and HIV.
Bacterial meningitis is less common than viral
meningitis but it potentially more serious. Acute
bacterial meningitis usually occurs when bacteria
enter the bloodstream and migrate to the brain and
spinal cord. It can also occur when bacteria directly
invade the meninges, as a result of an ear or sinus
infection, a skull fracture, or rarely, after some
surgeries.
A number of different types of bacteria can cause meningitis including:

Streptococcus pneumoniae (pneumococcus). This bacterium is the most common
cause of bacterial meningitis in infants, young children and adults. It more commonly
causes pneumonia or ear (otitis media, another “itis”) or sinus (sinusitis – yet another
“itis”) infections. There is a vaccine to help reduce the occurrence of this infection.

Neisseria meningitidis (meningococcus). Meningococcal meningitis commonly occurs
when bacteria from an upper respiratory infection enter your bloodstream. This
infection is highly contagious. It affects mainly teenagers and young adults, and may
cause local epidemics in college dormitories, boarding schools and military bases.
There is a vaccine to help reduce the occurrence of this infection.

Haemophilus influenza (Haemophilus type b - Hib). This used to be the leading
cause of bacterial meningitis in children. New Hib vaccines, as part of the routine
childhood immunization schedule, have greatly reduced the number of cases of this
type of meningitis.
Question 2 to find out what is causing the meningitis it might be necessary to take a sample
of the CSF. How would that be achieved?