Encephalitis, including a) Primary, viral; b) Post-infectious; Vaccine-related; Subacute sclerosing panencephalitis, and Unspecified

Reporting Obligations

Suspected cases of viral encephalitis must be reported immediately by phone to the Thunder Bay District Health Unit at 625-8318 or toll-free 1-888-294-6630, ext. 8318 (Monday-Friday, 8:30am to 4:30pm). After hours and on weekends/holidays call Thunder Bay Answering Service at (807) 624-1280.

All other forms (post-infectious, vaccine-related, subacute sclerosing panencephalitis and unspecified) must be reported by the next working day by fax, phone or mail.

  • Fax: (807) 625-4822
  • Phone: 625-8318 or toll-free at 1-888-294—6630, ext. 8318
  • Mail: 999 Balmoral Street, Thunder Bay, ON P7B 6E7



Aetiologic Agent:

Encephalitis is an acute inflammatory disease involving parts of the brain, spinal cord and meninges caused by specific viruses, as well as bacteria, fungi, and protozoa. Post-infectious encephalitis can occur after vaccination or respiratory infections. The most common viruses implicated are measles, rubella, smallpox and chickenpox.

Clinical Presentation:

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

In post-infectious encephalitis, cases usually present with confusion, seizures, headaches, stiffness of the neck and fever

Modes of transmission:

Depends on causative agent.

Incubation Period:

Depends on causative agent. For primary viral encephalitis the incubation period is usually 5-15 days.

Period of Communicability:

Varies depending on the causative agent.


Risk Factors/Susceptibility

Susceptibility to clinical disease is usually highest in infancy and in old age.

  • Immunization in the last 3 weeks
  • Infectious illness in last 10 days
  • Exposure to certain vectors (e.g. mosquitos)


Diagnosis & 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.


Treatment & Case Management

Treatment is mainly supportive and is under the care of the attending Health Care Provider.


Patient Information

Patient Fact Sheet



  1. Ministry of Health and Long Term Care, Infectious Diseases Protocol - Appendix 1 (2022) a) Encephalitis, including Primary, viral; b) Post-infectious; Vaccine related; Subacute sclerosing  panencephalitis, and Unspecified.


Additional Resources

  1. PHAC. “Eastern Equine Encephalitis, Pathogen Safety Data Sheet Infectious Substances.”
  2. CDC. “Eastern Equine Encephalitis, Symptoms and Treatment.”
  3. PHO. “Eastern Equine Encephalitis Virus, History and Enhanced Surveillance in Ontario.”
  4.  National Institute of Neurological Disorders and Stroke - Information Pages
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