New York and New Jersey have ordered a mandatory quarantine for medics who treated victims of Ebola in west Africa.

The new measures have been ordered by governors Andrew Cuomo and Chris Christie a day after an American doctor tested positive for Ebola in New York on returning from working in hard-hit Guinea.

Craig Spencer, 33, was in stable condition in isolation at Bellevue Hospital Center on Friday as he underwent treatment for the illness, which has killed nearly 4900 people – most of them in west Africa.

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The New York case revived fears about the possible spread of the virus in US cities but a glimmer of hope came with the news two Texas nurses infected while treating a Liberian man are now free of the virus.

In Manhattan, Cuomo and Christie announced additional screening protocols at JFK and Newark international airports at a joint press conference.

Steps include mandatory quarantine for up to 21 days of any individual who has had direct contact with an Ebola patient while in Guinea, Liberia or Sierra Leone, including medics who treated Ebola patients.

Additionally, anyone who has travelled to the affected regions but not had direct contact with an Ebola patient will be actively monitored by public health officials and quarantined if necessary.

Christie said a health care worker who arrived at Newark with a recent history of treating patients with Ebola in west Africa but who had no symptoms had been placed in quarantine.

Spencer was rushed to the hospital with fever and gastrointestinal symptoms on Thursday, a week after returning from a stint with the charity group Doctors Without Borders.

His live-in fiancee and two of his close friends are in quarantine but healthy, officials said.

New York Mayor Bill de Blasio, Cuomo and other officials sought to allay fears Spencer had put New Yorkers at risk by using the subway, going bowling and eating out before falling ill.

“There is no cause for alarm,” de Blasio said.

“New Yorkers need to understand the situation is being handled and handled well.”

President Barack Obama has been vocal in calling on Americans not to give in to fear or hysteria, stressing that Ebola does not spread easily and that the US is well-equipped to deal with new cases.