A top U.S. health official urged swift action Thursday to prevent the deadly Ebola virus from becoming the next AIDS epidemic, while a Spanish nurse was at "serious risk" of dying.

Teresa Romero, 44, is "very ill and her life is at serious risk as a consequence of the virus," Madrid's regional president Ignacio Gonzalez told parliament.

Tens of thousands of English schoolchildren will be given a lie-in or more rigorous sports classes as part of a major trial announced on Thursday to assess how advances in neuroscience can affect learning.

There is evidence that tailoring the school day to reflect the delayed sleep cycle of teenagers improves their learning and that aerobic exercise boosts brain function, but how and to what extent will now be tested on a large scale.

The serious-faced physicians practice pulling on bulky white suits and helmets that make them look more like astronauts than doctors preparing to fight a deadly enemy. These training sessions at U.S. hospitals on Ebola alert and for health workers heading to Africa can make the reality sink in: Learning how to safely put on and take off the medical armor is crucial.

"When you're in the real deal, remember to take your time," biosafety expert John Bivona told doctors during a course this week at the University of Chicago's medical center. Suits splashed with patients' vomit or blood must be removed carefully, he explained.

Some people may retain awareness after they have technically died, according to an unusual study published on Wednesday into hospital patients who went into deep cardiac arrest.

In a boost for the long and frustrating quest for an AIDS vaccine, researchers on Wednesday unveiled molecular imaging of an elusive feature that helps HIV infect immune cells.

Haiti's cholera epidemic is still an emergency and a let up in response based on the decreasing number of cases could have "tragic consequences," a U.N. special envoy said Wednesday.

"I fear that the enormous progress we have made leads people to believe that the problem has been resolved. It is not resolved," Pedro Medrano, the U.N. coordinator overseeing cholera response in Haiti, told Agence France Presse in Washington.

The United States and Canada announced stepped-up airport screening measures Wednesday to look for passengers carrying Ebola, as the deadly virus killed a man in Texas and the worldwide toll neared 3,900.

The spillover of the virus -- with the first diagnosis in United States and the first case of infection in Spain -- has raised fears of contagion in the West.

The United Nations mission in Liberia announced on Wednesday a second infection among its employees of the deadly Ebola epidemic ravaging the impoverished west African nation.

France will introduce plain cigarette packaging in 2016, Health Minister Marisol Touraine said on Wednesday, as the country seeks to stub out high smoking rates in under-16s.

The United States will announce tightened controls on international travelers in the coming days to prevent Ebola from spreading on U.S. soil, health officials said Tuesday.