WASHINGTON - A Texas health-care worker who treated a man who later died of Ebola has tested positive for the disease in a preliminary test, as countries around the world scramble to stem the deadly outbreak which is outpacing efforts to fight it.

If the preliminary test results are confirmed, the Texas patient's case would mark the first known transmission of Ebola in the United States and the second diagnosis in the country, CNN said.

The case, which officials announced yesterday, has dealt a blow to the worldwide battle to stem the outbreak and underlines the United Nations' fears and growing concerns about Ebola, for which there is no vaccine or widely available treatment.

"The virus is far ahead of us and every day the situation gets worse," the head of the UN's emergency Ebola mission, Mr Anthony Banbury, told UN leaders after a tour of Liberia, Guinea and Sierra Leone, the West African nations hardest hit by the worst- ever outbreak of the disease.

The health-care worker, who has not been named, reported a low-grade fever last Friday night and was isolated and referred for testing, Texas health services said in a statement.

She was from Texas Health Presbyterian Hospital in Dallas, the hospital which treated Mr Thomas Eric Duncan, the Liberian man who died last Wednesday.

"We knew a second case could be a reality, and we have been preparing for this possibility," said Dr David Lakey, commissioner of the Texas Department of State Health Services.

"We are broadening our team in Dallas and working with extreme diligence to prevent further spread."

More than 4,000 people have died from Ebola in seven countries since the start of the year, according to the World Health Organisation. The news came a day after US airports began screening travellers from epidemic-hit West Africa.

"No matter how many of these procedures are put into place, we can't get the risk to zero," said Dr Martin Cetron, director of the Centres for Disease Control and Prevention's Division of Global Migration and Quarantine of the screenings. Professor Lawrence Gostin, who teaches global health law at Georgetown Law School, believes such monitoring "had virtually no effectiveness" when used in Canada and Asia during the Sars outbreak in 2002. He said travellers with fever can evade detection by taking over-the-counter medication.

In Asia, 14 health ministers, including Singapore's Mr Gan Kim Yong, and several experts will meet from today to Friday for the 65th session of the World Health Organisation's regional committee for the Western Pacific to discuss cross-border measures to tackle the virus.

Singapore itself is taking a multi-pronged approach which includes taking effective measures to protect against importation of cases, carrying out enhanced surveillance to detect and isolate suspect or real cases, and to quarantine and monitor those exposed.

In Britain, Health Secretary Jeremy Hunt declared that the country is ready to cope with an Ebola outbreak, following a nationwide exercise to test its readiness.

The eight-hour exercise featured actors pretending to have Ebola, with doctors, nurses and the ambulance service treating them around the country.

In Latin America, Peru and Uruguay have announced airport measures, and Mexico and Nicaragua plan to tighten controls of migrants heading for US soil.

Meanwhile, International Monetary Fund chief Christine Lagarde on Saturday pleaded with people to remember that not all of Africa has been hit with the deadly Ebola epidemic.

"We should be very careful not to terrify the planet in respect of the whole of Africa."

AGENCE FRANCE-PRESSE, BLOOMBERG