Causes of Encephalitis
The causes of encephalitis are most often viral, but bacterial, fungal, autoimmune, or parasitic infections can also be responsible. In all cases, encephalitis results from inflammation of the brain, which disrupts normal nerve function and leads to potentially life-threatening symptoms.
Viral Causes
Viruses are the leading cause. Common culprits include:
Herpes simplex virus (HSV-1) – one of the most dangerous and common causes of severe encephalitis in adults
Enteroviruses, including coxsackievirus and echovirus
Arboviruses, such as West Nile virus, Japanese encephalitis virus, and tick-borne encephalitis virus
Measles, mumps, and rubella – particularly in unvaccinated individuals
Rabies virus, although rare, is almost always fatal if not treated before symptoms appear
HIV-related encephalitis, due to weakened immunity or co-infections
In South Africa, mosquito-borne viruses, HIV complications, and opportunistic infections like cytomegalovirus (CMV) in people with AIDS can also trigger encephalitis.
Bacterial and Other Infections
Bacteria like Mycoplasma pneumoniae or Borrelia burgdorferi (Lyme disease) may rarely cause encephalitis. In infants, group B streptococcus and Listeria infections can be responsible. Tuberculosis is another known cause in South Africa, especially in rural or high-burden areas.
Fungal encephalitis is uncommon but can occur in people with compromised immunity. Fungi such as Cryptococcus or Aspergillus may spread to the brain in such cases.
Autoimmune Encephalitis | Causes of Encephalitis
In autoimmune encephalitis, the immune system mistakenly attacks the brain. This type may be triggered by cancer, infections, or may occur without a clear cause. Anti-NMDA receptor encephalitis is one recognised form, especially in young women.
Post-Infectious or Parainfectious Encephalitis
This occurs when the body’s immune response to an infection—such as measles or influenza—causes inflammation in the brain after the initial infection has cleared. It is more common in children and is sometimes referred to as acute disseminated encephalomyelitis (ADEM).
Understanding the causes of encephalitis helps doctors choose the right tests and treatments quickly. Early identification is vital, especially in regions like South Africa where TB and HIV may complicate the clinical picture.
[Next: Symptoms of Encephalitis →]
