Media playback is unsupported on your device Media caption Martin Cetron, CDC: "This would not necessarily have caught the patient in Dallas"

New York's JFK airport has started screening to try to stem the Ebola outbreak that has killed more than 4,000 people.

Passengers from Liberia, Sierra Leone and Guinea - the worst-hit countries - will have their temperatures taken and have to answer a series of questions.

Checks at O'Hare in Chicago, Newark, Washington's Dulles and Atlanta's airport will begin in the coming days.

This comes after the first person died of Ebola in Texas on Wednesday.

Thomas Duncan had travelled to the US from Liberia, and was only diagnosed with the disease once he arrived in Dallas.

The latest figures released by the World Health Organization show the number of deaths attributed to the the haemorrhagic fever has risen to 4,033.

The vast majority of the fatalities - 4,024 - were in the West African nations of Liberia, Sierra Leone and Guinea.

In other developments:

The UK should expect a "handful" of Ebola cases in the coming months, the government's chief medical adviser says

The Spanish nurse infected with Ebola at a Madrid hospital, Teresa Romero, improved overnight and is talking, medical sources say

The Confederation of African Football says it has no plans to change the January-February schedule of the African Nations Cup, after hosts Morocco called for a postponement over Ebola fears

The UN special envoy on Ebola, Dr David Nabarro, has warned that the world might have to live with the disease forever unless almost every country is mobilised to fight it

'Simulated patients'

The screening measures at JFK started on Saturday. Border agents will check passengers for signs of illness such as high temperatures.

Image copyright AP Image caption New York's authorities say the city is "particularly well prepared"

Passengers from the three African nations will also be asked about their travel history prior to coming to the US and also if they have been in contact with anyone suffering from Ebola.

If they answer "Yes" to any questions or are running a fever, a representative of the Centers for Disease Control and Prevention (CDC) will intervene and provide a public health assessment.

There are currently no scheduled direct flights from the three countries to the US, with most passengers from Africa travelling via Europe.

Media playback is unsupported on your device Media caption Infectious-disease specialist Dr Amesh Adalja said the measures did more for public confidence than preventing the spread of the virus

Gil Kerlikowske, commissioner of US Customs and Border Protection, said the new system provided an extra layer of assurance for the American public, and would cover 94% of travellers from the affected region.

Martin Cetron, director for the Division of Global Migration and Quarantine at the Centers for Disease Control, said that this was in addition to the 100% screening being carried out at the points of departure.

However, he cautioned that "we cannot get the risk to zero" and that the latest screening "may not have caught the Texas case".

Mr Duncan only developed symptoms a week after he entered the US.

Experts have warned that a person can carry the virus for up to three weeks before showing symptoms.

Ebola deaths: Confirmed, probable and suspected

Source: WHO

Note: figures have occasionally been revised down as suspected or probable cases are found to be unrelated to Ebola. They do not include one death in the US recorded on 8 October.

JFK and the four other airports account for 90% of air travellers arriving in the US. As many as 160 people enter the US from the worse-affected countries each day.

"There is no cause for alarm," New York Mayor Bill de Blasio said earlier, adding that the city was "particularly well prepared".

"Physicians, hospitals, emergency medical personnel are trained in how to identify this disease and how to quickly isolate anyone who may be afflicted."

To test the readiness of New York, people pretending to display Ebola symptoms - the so-called "simulated patients" - have been walking into hospital emergency rooms to see if there were any weaknesses in the new system.

How not to catch Ebola:

Avoid direct contact with sick patients

Wear goggles to protect eyes

Clothing and clinical waste should be incinerated and any medical equipment that needs to be kept should be decontaminated

People who recover from Ebola should abstain from sex or use condoms for three months

Why Ebola is so dangerous

How Ebola attacks

Ebola: Mapping the outbreak

Ebola facts People can catch Ebola if they are in direct contact with the bodily fluids of an infected person or animal Early symptoms include fever, muscle pain, headache and sore throat. This is followed by vomiting, diarrhoea and bleeding, sometimes from the eyes and mouth The current outbreak started in March in west Africa, where the worst-affected countries include Guinea, Sierra Leone and Liberia It is thought unlikely that the disease would spread if it did come to the UK because quarantine and communications are more developed than in parts of western Africa There is no licensed Ebola vaccine but treatments are in development