For health professionals: Lassa fever

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What health professionals need to know about Lassa fever

Public health authorities in Canada are advised to be vigilant. There must be recognition, reporting and prompt investigation of patients with symptoms of Lassa fever and other viral haemorrhagic fevers.

Person-to-person transmission of Lassa virus is mainly associated with direct contact with blood and bodily fluids. Health care providers caring for patients with suspected or confirmed Lassa virus should apply infection control precautions.

Health care providers are advised to avoid:

  • any exposure to blood and bodily fluids
  • contact with possibly contaminated environments that is:
    • direct
    • unprotected

They should also always use:

  • safe burial practices
  • safe injection practices
  • personal protective equipment

Clinical manifestations

Lassa viral haemorrhagic fever is an acute viral illness lasting 1 to 4 weeks. There’s a gradual onset of symptoms, which include:

  • fever
  • myalgia
  • headache
  • sore throat and cough
  • chest and abdominal pain
  • nausea, vomiting or diarrhea
  • generalized weakness or malaise

Fever may be persistent or intermittent. Inflammation and exudation of the pharynx and conjunctivae is commonly observed. Many cases are mild or asymptomatic.

Severe cases may result in:

  • shock
  • seizures
  • hypotension
  • hemorrhage
  • pleural effusion
  • encephalopathy
  • proteinuria, which can result in edema of the face and neck

During the second week of illness, there may be:

  • ascites
  • pleural effusion
  • edema of the head and neck

Renal and circulatory failure may occur, aggravated by vomiting and diarrhea. In the severest cases, bleeding into the skin, mucosae and deeper tissues occurs, usually leading to death.

In non-fatal cases, the fever subsides and the patient’s condition improves rapidly, although tiredness may persist for several weeks. There is usually a leucopaenia, although a high polymorphonuclear leucocytosis is encountered occasionally. Late complications include sensorineural deafness in around 25% of patients.

Pregnant women may suffer more severe infections, particularly in the third trimester. Up to 95% of infected mothers lose their fetuses.

Symptoms in children are similar to those in adults. However, infant infection can result in swollen baby syndrome, which can be fatal and includes symptoms such as:

  • edema
  • bleeding
  • abdominal distension


The National Microbiology Laboratory (NML) is the only facility in Canada permitted to work with live haemorrhagic fever viruses like Lassa. The laboratory offers the world’s highest level of containment. It meets or exceeds all national and international guidelines for safety and security.

Any testing related to a suspected Lassa fever infection must be carried out in a containment level 4 (CL4) laboratory. CL4 laboratories ensure maximum containment through:

  • HEPA filtration of supply air
  • decontamination of all waste
  • complete sealing of the laboratory
  • isolation of personnel from viruses through the use of positive pressure suits
  • double HEPA (high-efficiency particulate absorption) filtration of exhausted air

Shipping of samples

If a sample requires testing, immediately contact the 24-hour emergency line at 1-800-545-7661.

An expert will assist you in developing an Emergency Response Assistance Plan. This will help ensure the safe shipping of the sample to the NML.


Treatment with the antiviral drug ribavirin is most effective when started within the first 6 days of illness. It should be given intravenously for 6 days. This drug does not prevent deafness associated with Lassa fever.

Patients should receive supportive care to maintain appropriate:

  • oxygenation
  • blood pressure
  • fluid and electrolyte balance

In severe cases, a blood transfusion may be needed.

Prevention and control

Those who have been in close contact with an infectious patient must be identified. This should take place within 3 weeks of the patient’s onset of illness.

Individuals should be monitored and their temperature taken daily for 21 days after their last exposure to the patient. If a high temperature (above 38ºC) develops, the person should contact a physician immediately.

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