Meningitis is caused by inflammation of the meninges, the protective membranes covering the brain and spinal cord, primarily due to infections. The main causes of meningitis include: Infectious Causes:
- Bacterial infections: These are less common but more severe and life-threatening. Common bacteria causing meningitis are:
- Neisseria meningitidis (meningococcus)
- Streptococcus pneumoniae (pneumococcus)
- Haemophilus influenzae type b (Hib)
- Listeria monocytogenes
- Group B Streptococcus
- Mycobacterium tuberculosis Bacteria can reach the meninges via the bloodstream or direct spread from infections like ear or sinus infections, skull fractures, or surgeries
- Viral infections: The most common cause of meningitis, especially in the United States. Viruses include:
- Enteroviruses
- Herpes simplex virus
- Varicella zoster virus
- Mumps virus
- HIV
- Arboviruses (transmitted by insects)
- Influenza virus Viral meningitis is generally less severe than bacterial
- Fungal infections: Less common, usually affecting people with weakened immune systems. Examples include Cryptococcus neoformans and Coccidioides species
- Parasitic infections: Rare causes include certain parasitic worms and amoebae like Naegleria fowleri (causing amebic meningitis)
Non-infectious Causes:
- Physical injuries (head trauma)
- Brain surgery
- Certain cancers
- Autoimmune diseases such as systemic lupus erythematosus
- Drug reactions (e.g., to NSAIDs or antibiotics)
These cause inflammation without infection
. Transmission and Risk Factors:
- Meningitis-causing infections can spread through respiratory droplets (e.g., sneezing) or close contact
- People living in close quarters (dormitories, military barracks) are at higher risk.
- Weakened immune systems, pregnancy, young children, and elderly individuals are more susceptible
In summary, meningitis is caused by various infectious agents-primarily bacteria and viruses-and less commonly fungi and parasites, as well as by non- infectious factors like injury or autoimmune conditions
