Former South African President Nelson Mandela was admitted to the hospital late Wednesday due to his recurring lung infection, the South African President's office today.
"Doctors are attending to him, ensuring that he has the best possible expert medical treatment and comfort," the government's statement said.
Mandela, 94, spent 18 days in the hospital in December for a lung infection and gallstones.
"We appeal to the people of South Africa and the world to pray for our beloved Madiba and his family and to keep them in their thoughts. We have full confidence in the medical team and know that they will do everything possible to ensure recovery," South African President Jacob Zuma said in the statement.
The anti-Apartheid activist was admitted to a Pretoria hospital on March 10 for routine medical tests and to "manage existing conditions in line with his age," a spokesman for the South African President's office said.
Despite rare public appearances, Mandela, who is credited with changing race relations in South Africa, remains hugely popular in the country.
In November 2012, banknotes featuring Mandela's image were printed and entered into circulation in South Africa.
After enduring nearly three decades of prison, much of it at hard labor in a lime quarry, Mandela emerged as a gentle leader who was elected South Africa's first black president in 1994.
He was awarded the Nobel Peace Prize for his leadership in ending apartheid without violence, and later became a global statesman who inspired millions people around the world.
The move was announced in a statement sent Wednesday to South Korea from North Korea's chief delegate to inter-Korean military talks.
North Korea recently cut a Red Cross hotline between the Koreas, but there's still a hotline linking aviation authorities in both Koreas.
The hotline mentioned Wednesday is important because the Koreas use it to communicate as hundreds of workers travel back and forth to the Kaesong industrial complex. Officials say more than 900 South Korean workers were in Kaesong on Wednesday.
North Korea is angry over routine U.S.-South Korean drills and recent U.N. sanctions punishing it for its Feb. 12 nuclear test.
"CDC reported the incident to the FBI and we understand that the FBI will initiate an investigation concerning the reported incident," Dr. Rob Weyant, director of the CDC's Division of Select Agents and Toxins, told ABCNews.com in an email. "Since the investigation is just underway, the agency will not comment further regarding details of this incident."
The FBI would not confirm it was investigating the incident at the Galveston National Laboratory.
"The FBI does not confirm nor deny the existence of investigations" as a matter of policy, said Shauna A. Dunlap, a media coordinator for the FBI Houston Division.
A lab spokesman said he did not think the FBI was investigating, but rather that the FBI was monitoring the lab's ongoing investigation.
The CDC can make a referral to the FBI if it finds "possible violations involving criminal negligence or a suspicious activity or person to the FBI for further investigation," according to 2007 congressional testimony from Dr. Richard Besser, who directed the CDC's Coordinating Office for Terrorism Preparedness and Emergency Response at the time. He is now ABC News' chief health and medical editor.
The biolab realized the vial went missing on March 21 because it was preparing for its annual CDC inspection for the week of March 25, Weyant said. Prior to the inspection, the CDC visited in January 2012.
The last time the vial was used was November 2012, University of Texas Medical Branch spokesman Raul Reyes told ABCNews.com. The University of Texas Medical Branch owns the $174 million biolab, which was designed with the strictest security measures to hold the deadliest viruses in the country.
Only one scientist worked with the virus, and Reyes said the lab suspects that scientist accidentally threw the vial away in November.
"We have determined, and the CDC has agreed, that this never was a public health risk," Reyes told ABCNews.com, adding that people who accessed the lab underwent intense background checks and had to go through many layers of security each day.
"If a bad person were intent on weaponizing this type of virus," Reyes said, "it would be much simpler to fly down to Venezuela, go into the field and collect a specimen."
Violation of the Public Health Security and Bioterrorism Preparedness and Response Act of 2002 can result in up to five years imprisonment, up to a $250,000 penalty for an individual or up to $500,000 for a group, Weyant said.
"As of March 26, 2013, CDC has referred 18 entities to the HHS inspector general for failure to comply with the select agent regulations resulting in over $2 million in monetary penalties," Weyant said.
Like Ebola, the missing Guanarito virus causes hemorrhagic fever, which involves "bleeding under the skin, in internal organs or from body orifices like the mouth, eyes, or ears," according to the Centers for Disease Control and Prevention.
"This is clearly an incident that is very discomforting and embarrassing to the University of Texas Medical Center and their national biosecurity lab that they have there," said Dr. William Schaffner, chairman of preventive medicine at Vanderbilt University Medical Center in Nashville, Tenn. "You can be sure there are a lot of sweating people down the chain at that institution."
Fortunately, losing a vial of Guanarito is not as threatening as losing a vial of anthrax, said Schaffner, a former president of the National Foundation for Infectious Diseases. The virus could theoretically spread between humans, but it usually only spreads between rodents in Venezuela.
Researchers don't believe the virus can survive in rodents in the U.S., according to a statement from David Callender, president of the University of Texas Medical Branch.
Still, the virus has caused "at least several hundred cases" of human disease in regions where it is common, said NIH's director of the Office of Biodefense Research Affairs, Michael Kurilla.
"The mortality is anywhere from at least 10 to 20 percent or slightly more," Kurilla told ABCNews.com, adding that there is no treatment or cure for Guanarito. "That is considered very, very severe if you have a 1 in 5 chance of dying without anything to do for the person other than provide supportive hospital care."
Kurilla said the Galveston biolab requires the most stringent safety measures because it studies biosafetly level BSL-4 materials, or dangerous infectious diseases that have no vaccines or cures. BSL-4 materials include Guanarit, Ebola and smallpox.
The Galveston researchers were conducting a routine inspection on March 20 and 21 when they noticed there were only four Guanarito vials instead of five. They announced the lapse on March 23.
The university does not believe this was the result of a security breach or any wrongdoing, but it notified the Centers for Disease Control and Prevention.
All solid waste in BSL-4 labs is typically disposed of via a pressurized heating process that destroys hazardous materials without allowing the liquid to boil away, Kurilla said. As such, it's unlikely that investigators will be able to determine and prove whether this is what actually happened to the vial.
It's possible investigators will find the clerical error that led to the accidental disposal, but with computerized record keeping, it's less likely that vial numbers were transposed and the error can be easily traced, Kurilla said.
"I suspect that they may not ever be able to account for it if it was that kind of human error," Schaffner said. "This is a record-keeping issue, which means it was a human issue, which means doing that kind of tedious, important work, there was just a momentary slip up."