Lassa Fever

Reporting Obligations

Suspected cases 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.


Aetiologic Agent:

Lassa fever is an acute illness caused by the lassa virus lasting 1-4 weeks. Lassa virus is an arenavirus, serologically related to lymphocytic choriomeningitis, Machupo, Juni, Guaanarito and Sabia viruses.

Clinical Presentation:

Onset is gradual, with malaise, fever, headache, sore throat, cough, nausea, vomiting, diarrhea, myalgia, chest and abdominal pain; fever is persistent or spikes intermittently. Inflammation and exudation of the pharynx and conjunctivae are common. Approximately 80% of human infections are mild or asymptomatic and the remaining have severe multisystem disease.

Modes of transmission:

Primarily through aerosol or direct contact with excreta of infected rodents deposited on surfaces such as floors, beds or in food and water.

It can also be spread person to person through sexual contact and in hospitals from infected persons’ pharyngeal secretions or urine or from contaminated needles, or in laboratory accidents.

Incubation Period:

Usually 6-21 days.

Period of Communicability:

Person to person spread may theoretically occur during the acute febrile phase when virus is present in secretions and excretions. Virus can be excreted in urine for 3-9 weeks from onset of illness and can be spread by sexual contact through semen for up to 3 months after infection.


Risk Factors/Susceptibility

All ages are considered susceptible. Risk factors include travelling to an endemic country (Guinea, Liberia, regions of Nigeria and Sierra Leone), or working in a laboratory or facility that handles lassa fever virus specimens or animals with lassa fever.


Diagnosis & Laboratory Testing

Consult Medical Microbiologist at 416-235-5726 or the local Public Health Ontario Laboratory before collecting any specimens. Any testing related to suspected lassa fever should be carried out under Level 4 containment facilities at the National Microbiology Laboratory in Winnipeg.

Approved tests for lassa fever include culture, nucleic acid amplification test (NAT), antigen detection, and IgM and IgG serology.

Special Pathogens Requisition



Treatment & Case Management

Treatment is under the direction of the attending health care provider in consultation with tropical disease specialist.

Strict isolation precautions for hospitalized cases with isolation room, preferably negative pressure room and precautions for body fluids and excreta maintained.

Contact management will need to be discussed with the Thunder Bay District Health Unit.


Patient Information

Patient Fact Sheet


  1. Ministry of Health and Long Term Care, Infectious Diseases Protocol, 2016.  Appendix A (2014) and Appendix B (2014)


Additional Resources

1. Public Health Agency of Canada. "Lassa Fever-Pathogen Safety Data Sheet."

2. Public Health Agency of Canada. "Travel Health Notices."

Last Updated: 26/04/2018