Skip to content


Reportable Disease Toolkit Badge

a) Primary, viral;

b) Post-infectious; Vaccine-related; Subacute sclerosing panencephalitis, and UnspecifiedAetiologic Agent

Reporting Obligations

Individuals who have or may have encephalitis shall be reported to the local Health Unit.

Reporting Form Button


Aetiologic Agent

Encephalitis is acute inflammation of the brain, typically with spinal cord involvement. The condition is mostly caused by an arbovirus infection (e.g., West Nile virus, Togavirus, Bunyavirus, Alphavirus) through a mosquito vector. Infections may result in St. Louis encephalitis (SLE), Western equine encephalitis (WEE), Eastern equine encephalitis (EEE) and California encephalitis (CE), however, most infections do not result in disease. Additionally, infections by enteroviruses, such as, coxsackie virus, ECHO virus and poliovirus may also lead to encephalitis. Inflammation of the brain can also be caused by bacteria, fungi, and protozoa.

Clinical Presentation

Most viral encephalitis infections are asymptomatic; mild cases often occur as febrile headache; severe infections are usually marked by acute onset, with headache, high fever, meningeal signs, stupor, disorientation, coma, tremors, occasional convulsions and spastic paralysis.

  • Primary encephalitis occurs when the disease condition is directly related to an infection of brain tissue.
  • Post infectious encephalitis is an adverse consequence of an infectious process elsewhere in the body e.g., chickenpox, influenza, or measles.
  • Encephalitis may also be caused by non-infectious processes e.g. lead, poisoning or hemorrhage.
  • Subacute sclerosing panencephalitis is an insidious onset of inflammation of the entire brain. It is thought to be caused by a slow latent measles virus post recovery from a past infection.

Note: Clinically, encephalitis involves abnormal brain function (e.g., change in mental status, motor or sensory deficits and speech or movement disorder). Comparatively, individuals with meningitis may experience discomfort, lethargy or headache, however, brain function is normal.

Modes of Transmission

Depends on causative agent.

Incubation Period

Depends on causative agent. For primary viral encephalitis the incubation period is usually 3–15 days.

Period of Communicability

Varies depending on the causative agent.

Risk Factors/Susceptibility

Susceptibility to clinical disease is usually highest for individuals at the extremes of age, however, risk by disease type varies across all the age groups.

Diagnosis and Laboratory Testing

Cases are confirmed if a patient has clinically compatible signs and symptoms of encephalitis along with isolation of organism from an appropriate specimen (e.g. cerebrospinal fluid or stool), detection of a specific antigen, or serologic confirmation of infection with an organism known to cause encephalitis. Given the variability of etiological organisms, consult with laboratory about appropriate specimens and testing methodologies.

Testing Information and Requisition Button

Treatment and Case Management

Educate the public and health care workers about reducing the spread of all types of infection by practicing proper hand hygiene, proper respiratory etiquette and using protection against vectors.

Treatment is mainly supportive and is under the care of the attending health care provider.

Obtain the following information during case management:

  • History of immunization in last 3 weeks, and
  • History of infectious illness in last 10 days

Patient Information

Patient Fact Sheet Button

Additional Resources

Centers for Disease Control and Prevention. “Eastern Equine Encephalitis, Symptoms and Treatment.”

Eastern Equine Encephalitis (EEE) Virus – Serology and PCR | Public Health Ontario


Ministry of Health and Long-Term Care, Infectious Diseases Protocol, 2022.