Meningitis is typically caused by an infection, most commonly viral or bacterial.
While many things can lead to meningitis, the root cause boils down to infectious agents invading the protective membranes (meninges) surrounding the brain and spinal cord. This invasion triggers inflammation, which characterizes the disease. The specific agent determines the type of meningitis and its severity.
Here's a breakdown of the common root causes:
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Viral Infections: These are the most frequent cause of meningitis, often resulting in milder symptoms. Common viruses include enteroviruses, herpes viruses (like herpes simplex virus - HSV), and the mumps virus.
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Bacterial Infections: Bacterial meningitis is less common but far more dangerous. Bacteria can enter the bloodstream and travel to the brain and spinal cord, or they may directly invade the meninges following a head injury or sinus infection. Common bacterial culprits include:
- Streptococcus pneumoniae
- Neisseria meningitidis (meningococcus)
- Haemophilus influenzae type b (Hib)
- Listeria monocytogenes
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Fungal Infections: Less common than viral or bacterial causes, fungal meningitis usually affects people with weakened immune systems. Examples include Cryptococcus species.
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Parasitic Infections: Rarely, parasites can cause meningitis.
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Non-Infectious Causes: In some instances, meningitis can result from non-infectious conditions, such as certain medications, cancers, inflammatory diseases (like lupus), and head injuries. These are less common than infectious causes.
Therefore, to summarize, the core problem is an agent (usually an infectious one) breaching the body's defenses and inflaming the meninges. This inflammation leads to the symptoms and potential complications associated with meningitis. The specific type of agent (virus, bacteria, fungus, parasite) dictates the specific cause of that particular case of meningitis.
