Ottawa is once again stepping up Canada's defences against Ebola, this time by ordering high-risk travellers from the West African countries ravaged by the viral disease to quarantine themselves at home or at a facility for 21 days after landing in Canada.

The new rules mark the first time Ottawa has threatened to force any asymptomatic travellers from the Ebola-affected countries into isolation.

However, Canada's new quarantine rules, which take effect immediately, do not extend to health-care workers who wore full protective gear while treating Ebola patients, as some in the Canadian aid community had feared they might.

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Instead, the policy classifies humanitarian workers as low-risk, unless the workers are aware of a gap in their personal protective equipment or a mistake in donning or doffing their head-to-toe suits that would put them at greater risk of catching the virus.

Low-risk travellers are being asked to take their temperatures twice daily, report symptoms to local public-health authorities and notify the same authorities of any planned travel. But they are not being asked to isolate themselves automatically.

Stephen Cornish, the executive director of Médecins Sans Frontières (Doctors Without Borders) in Canada said he was "reassured" by how Ottawa's new policy treats returning aid workers, especially compared to the more draconian policies enacted in some other countries.

In one high-profile case, an American nurse who volunteered with MSF in Sierra Leone fought quarantine orders in New Jersey and Maine before a judge in the latter state rejected the state's attempts to limit her movements, saying she posed no threat unless she began displaying symptoms.

"Having witnessed non-scientific measures adopted by some other jurisdictions already do a disservice to how people understand the disease, create fear and even create grave concern among our field workers, I'd say we were reassured that the measures adopted [Monday] largely reflect MSF's existing protocols of self-monitoring, checking symptoms [and] reporting symptoms immediately to health authorities," Mr. Cornish said.

Until now, Canada's policy has been to send travellers returning from Sierra Leone, Guinea and Liberia, the three countries hardest hit by the Ebola epidemic, to a quarantine officer for a health assessment, including a temperature check.

Under the new rules, anybody landing in Canada from the Ebola-affected countries who displays symptoms of the disease – such as fever, body aches, vomiting or diarrhea – would immediately be put into isolation and sent to hospital for a medical examination.

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Those who are not symptomatic are divided into two categories. High-risk travellers are defined as people who had direct, unprotected contact with Ebola patients, and they are the travellers who will be asked to self-isolate. It is not clear exactly what would happen if a high-risk traveller refused to quarantine him or herself.

Low-risk travellers are defined as all travellers from Sierra Leone, Guinea and Liberia who have no symptoms and have had no known contacts with Ebola patients.

The new rules do not affect Canada's earlier decision to stop processing visa applications from the three Ebola-affected countries, a decision that has been questioned by the World Health Organization and slammed by public-health experts.

The Ebola outbreak has killed nearly 5,000 people, almost all in Sierra Leone, Guinea and Liberia. A case of Ebola has never been diagnosed in Canada.