(CNN)-- The deadliest outbreak of Ebola virus on record has sparked fears that the killer virus could spread from West Africa to other regions and continents.
The outbreak began with just a handful of cases in Guinea in March. Since then, that number has grown to909 confirmed cases and another 414 probable or suspected in that country, Sierra Leone and Liberia and Nigeria,according to the World Health Organization.
Some729 people of the 1,323 total confirmed and possible infections have died, reports WHO as of July 27.
The WHO says "drastic action is needed" to contain Ebola, warning that previously undetected chains of transmission are boosting the numbers of sick and increasing the chances that the disease spreads from Africa.
"This epidemic is without precedent," said Bart Janssens, director of operations for Médecins Sans Frontières, also known as Doctors Without Borders. "It's absolutely not under control, and the situation keeps worsening. ... There are many places where people are infected but we don't know about it."
What's the latest?
The Ebola outbreak has been centered in Guinea, Sierra Leone and Liberia, where authorities have been working to contain the virus.
In Liberia, President Ellen Johnson Sirleaf announced Wednesday that, "without exceptions, all schools are ordered closed pending further directive from the Ministry of Education." She also declared Friday a nonworking day "to be used for the disinfection and chlorination of all public facilities."
On the same day, the Peace Corps said it was temporarily removing its 340 volunteers from Liberia, Sierra Leone and Guinea due to the outbreak.
The announcement comes as two Peace Corps volunteers were isolated after coming in contact with someone who ended up dying of Ebola, a spokeswoman for the group said. She said these two Americans "are not symptomatic," and the Peace Corps will work to return them to the United States once they get medical clearance to travel.
Concerns about Ebola aren't confined to those three countries.
Patrick Sawyer, a naturalized American citizen who worked in Liberia, flew to Nigeria intending to attend a conference. After exhibiting symptoms upon arrival July 20, he was hospitalized and died on July 25. He's the first American to die in the outbreak, though two other U.S. aid workers in Liberia have contracted Ebola and are being treated.
Sawyer's was the only known case in Nigeria, WHO said.
And the British government convened an emergency meeting to discuss the threat of Ebola to the UK, even though no case has been reported there. Officials discussed what measures could be taken if UK nationals in West Africa should become infected, Foreign Secretary Philip Hammond said.
Why was someone infected with Ebola allowed on a plane?
It is unknown whether Sawyer was displaying symptoms before he flew from Monrovia, Liberia's capital, to Ghana and then to Togo to switch planes to fly to Lagos.
His Minnesota-based widow, Decontee Sawyer, told CNN that he had cared for his ill sister in Liberia, though she said he didn't know at the time that his sister had Ebola. When he arrived in Nigeria, he told officials that he had no direct contact with anyone who had the disease.
Mindful of this, Nigeria-based airline companiesASKYandArik Airsuspended operations at the end of July into Monrovia and Freetown, the capitals of Liberia and Sierra Leone, respectively. ASKY said passengers departing from Conakry, Guinea, would be screened for signs of the virus.
Cetron says it is unlikely the virus would spread on an airplane unless a passenger were to come into contact with a sick person's bodily fluids.
Stressing the key role that those working at airports play in keeping Ebola in check, the CDC spokesman said: "Being educated, knowing the symptoms, recognizing what to do, having a response to protocol, knowing who to call -- those are really, really important parts of the global containment strategies to deal with threats like this."
What elseis being done to stop the spread of the disease?
Ebola patients are being isolated by health officials in West Africa, and those who have come into contact with them are being told to monitor their temperatures.
President Sirleaf hasclosed most of Liberia's borders with neighboring countries, and the few points of entry that are still open will have Ebola testing centers. The President also placed restrictions on public gatherings and ordered hotels, restaurants and other entertainment venues to play a five-minute video on Ebola safety.
The CDC has issued an alert to health workers in the United States to watch out for any patients who may have recently traveled to West Africa and could have contracted the virus.
"It is a highly infectious virus that can kill up to 90% of the people who catch it, causing terror among infected communities," it says. The death rate in this outbreak has dropped to roughly 55% because of early treatment.
There is also no vaccination against it.
Of Ebola's five subtypes, the Zaire strain -- the first to be identified -- is considered the most deadly.
Carers are advised to wear impermeable gowns and gloves and to wear facial protection such as goggles or a medical mask to prevent splashes to the nose, mouth and eyes.
MSF says it contained a 2012 outbreak in Uganda by placing a control area around its treatment center. An outbreak is considered over once 42 days -- double the incubation period of the disease -- have passed without any new cases.
How does it spread?
The WHO says it is believed that fruit bats may be the natural host of the Ebola virus in Africa, passing on the virus to other animals.
Humans contract Ebola through contact with the bodily fluids of infected animals or the bodily fluids of infected humans.
MSF says that while the virus is believed to be able to survive for some days in liquid outside an infected organism, chlorine disinfection, heat, direct sunlight, soaps and detergents can kill it.
MSF epidemiologist Kamiliny Kalahne said outbreaks usually spread in areas where hospitals have poor infection control and limited access to resources such as running water.
"People who become sick with it almost always know how they got sick: because they looked after someone in their family who was very sick -- who had diarrhea, vomiting and bleeding -- or because they were health staff who had a lot of contact with a sick patient," she said.
Ebola Facts: How Many Patients Are Being Treated Outside of West Africa?
least 16 Ebola cases have been treated outside of West Africa in the
current outbreak, including a Dallas hospital worker who tested positive
for Ebola on Saturday. Most of these involve health and aid workers who
contracted Ebola in West Africa and were transported back to their home
country for treatment. Three cases were diagnosed outside of West
Africa: A Liberian man who began showing symptoms four days after
arriving in Dallas,a Spanish nurse who became illafter treating a missionary in a Madrid hospital and theDallas hospital workerwho
was involved in the treatment of a Liberian patient infected with
Ebola. These cases are compiled from reports by the federal Centers for
Disease Control and Prevention, the World Health Organization, Doctors
Without Borders and other official agencies.
Nebraska Medical Center
A Spanish nurse contracted Ebola while treating
a missionary who died in a Madrid Hospital.
Emory University Hospital
SundayA hospital worker involved in the treatment of an Ebola patient from Liberia has tested positive for the disease.
The Centers for Disease Control and Prevention has sent experts to Texas to trace anyone who may have come incontact with Thomas E. Duncan, a Liberian who traveled to Dallas, while he was contagious.
Health officials usecontact tracingto
identify and monitor everyone who might have been exposed to the
patient during the time he was contagious. If infected, most people
develop symptoms within eight to 10 days of being exposed. Anyone who
starts running a fever or having symptoms is isolated and tested for
Ebola. If the test is positive, that person is kept in isolation and
treated, and his or her contacts are then traced for 21 days. The
process is repeated until there are no new cases.
Federal officials announced on Oct. 8 that passengers from West Africa arriving atfive American airportswill
be screened for fever. About 90 percent of the people arriving from the
main countries stricken with Ebola come through the five airports:
Kennedy International, Washington Dulles International, O’Hare
International, Hartsfield-Jackson International and Newark Liberty
International. Screenings began at Kennedy Airport in New York on Oct
11. The new procedures will begin at the other four airports later this
Ebola spreads throughdirect contact with body fluids.
If an infected person’s blood or vomit gets in another person’s eyes,
nose or mouth, the virus may be transmitted. Although Ebola does not
cause respiratory problems, a cough from a sick person could infect
someone who has been sprayed with saliva. Because of that, being within
three feet of a patient for a prolonged time without protective clothing
is considered to be direct contact. Specialists at Emory University
Medical Center in Atlanta have also found thatthe virus is present on a patient’s skin after symptoms develop, underlining how contagious the disease is once symptoms set in.
virus can survive for several hours on surfaces, so any object
contaminated with bodily fluids may spread the disease. According to the
C.D.C., the virus can survive for a few hours on dry surfaces like
doorknobs and countertops and can survive for several days in puddles or
other collections of body fluid. Bleach solutions can kill it.
the current outbreak, most new cases are occurring among people who
have been taking care of sick relatives or who have prepared an infected
body for burial. Health care workers are at high risk.
Mr. Duncan, who traveled toDallas from Liberia,was diagnosed with Ebola on Sept. 30. Hedied on Oct. 8.So far, none of the nearly 50 people who may have been exposed to the virus in Dallas have shown signs of illness.
Man arrives in
Dallas to visit
care at Dallas
is sent home.
Man is admitted to Dallas hospital and is placed in isolation.
are currently no drugs or vaccines approved by the Food and Drug
Administration to treat or prevent Ebola, and in past outbreaks the
virus has been fatal in 60 percent to 90 percent of cases. An
experimental drug called ZMapp might help infected patients, but the
drug is unproven and only available in limited quantities. The World
Health Organization suggests thatblood from Ebola survivors might be used to treat others, but there is no proof that such a treatment alone would work.
The United States government plans tofast-trackdevelopment
of a vaccine shown to protect macaque monkeys, but there is no
guarantee it will be effective in humans. Beyond this, all physicians
can do is try to nurse people through the illness, using fluids and
medicines to maintain blood pressure, and treat other infections that
often strike their weakened bodies. A small percentage of peopleappear to have an immunityto the Ebola virus.
The Ebola virusinfects
cells by punching into the cell and injecting a small piece of viral
RNA. The RNA hijacks the machinery of the cell and uses it to create
more copies of the Ebola virus, which in turn infect other cells.
antibodies against the Ebola virus in their blood. Antibodies are
Y-shaped proteins that can latch on to a specific virus and prevent it
from infecting cells. Plasma extracted from the blood of Ebola survivors
might be transfused into infected people, possibly helping them fight
The drug ZMappis
a mixture of three different antibodies that were developed in mice and
modified to work in humans. The drug was first tested in humans during
the current outbreak, but it is unclear if the drug is effective. ZMapp
is made in tobacco plants and there is only limited manufacturing
An earlier version of this graphic referred incorrectly to the
structure that encloses human cells. It is the cell membrane, not the
Symptoms usually begin about eight to 10 days after exposure to the virus, but can appear as late as 21 days after exposure,according to the C.D.C.At
first, it seems much like the flu: a headache, fever and aches and
pains. Sometimes there is also a rash. Diarrhea and vomiting follow.
in about half of the cases, Ebola takes a severe turn, causing victims
to hemorrhage. They may vomit blood or pass it in urine, or bleed under
the skin or from their eyes or mouths. But bleeding is not usually what
kills patients. Rather, blood vessels deep in the body begin leaking
fluid, causing blood pressure to plummet so low that the heart, kidneys,
liver and other organs begin to fail.
American health workers, Dr. Kent Brantly, Nancy Writebol and Dr. Rick
Sacra, contracted Ebola in Liberia, were treated in the United States
and later released. Another American, who has not been identified,
contracted Ebola in Sierra Leone and is being treated at Emory
University Hospital in Atlanta. The fifth American,Ashoka Mukpo,is a freelance cameraman for NBC who was filming in Liberia. He arrived at the Nebraska Medical Center on Monday.
than 8,000 people in Guinea, Liberia, Nigeria, Senegal and Sierra Leone
have contracted Ebola since March, according to the World Health
Organization, making this the biggest outbreak on record.More than 3,800 peoplehave died.
The Centers for Disease Control and Preventionsaid on Sept. 23that
in a worst-case scenario, cases could reach 1.4 million in four months.
The centers' model is based on data from August and includes cases in
Liberia and Sierra Leone, but not Guinea (where counts have been
Estimates are in line with those made by
other groups like the World Health Organization, though the C.D.C. has
projected further into the future and offered ranges that account for
underreporting of cases.
Cumulative cases in Liberia and Sierra Leone
11,000-27,000 cases through Jan. 20
537,000-1.4 million cases through Jan. 20
70 percent of patients are treated in settings that confine the illness
and that the dead are buried safely. About 18 percent of patients in
Liberia and 40 percent in Sierra Leone are being treated in appropriate
the disease continues spreading without effective intervention. Dr.
Thomas R. Frieden, the C.D.C. director, said, “My gut feeling is, the
actions we’re taking now are going to make that worst-case scenario not
come to pass. But it’s important to understand that it could happen.”
Source: Centers for Disease Control and Prevention
16 an expansion of military and medical resources to combat the
outbreak, including the deployment of as many as 4,000 American military
personnel to Liberia and Senegal. He said the United States would help
Liberia in the construction of more than 17 Ebola treatment centers in
the region, with about 1,700 beds, and would also open a joint command
operation to coordinate the international effort to combat the disease.
But military planners say construction of thecenters have been delayedbecause of the difficulty in getting heavy equipment to the areas.
epidemic is growing faster than efforts to keep up with it, and it will
take months before governments and health workers in the region can get
the upper hand,according toDoctors Without Borders.
some parts of West Africa, there is a belief that simply saying “Ebola”
aloud makes the disease appear. Such beliefs have created major
obstacles for physicians trying to combat the outbreak. Some people have
evenblamed physicians for the spread of the virus,
opting to turn to witch doctors for treatment instead. Their skepticism
is not without a grain of truth: In past outbreaks, hospital staff
members who did not take thorough precautions became unwitting travel
agents for the virus.
Ahmed Jallanzo/European Pressphoto Agency
Liberian health workers on the way to bury a woman who died of the Ebola virus.
Ebola wasdiscovered in 1976,
and it was once thought to originate in gorillas, because human
outbreaks began after people ate gorilla meat. But scientists have since
ruled out that theory, partly because apes that become infected are
even more likely to die than humans.
Scientists now believe thatbats are the natural reservoir for the virus,
and that apes and humans catch it from eating food that bats have
drooled or defecated on, or by coming in contact with surfaces covered
in infected bat droppings and then touching their eyes or mouths.
biggest headlines have tended to involve outbreaks of deadly viruses
that medical workers have few, if any, tools to combat. The four most
prominent are compared below. No cure is known for any of them, nor has
any vaccine yet been approved for human use.
Emerged / identified
1976; latest outbreak in 2014
1967; latest major outbreak in 2005
Originally, Congo Basin and central Africa; latest strain, West Africa
Originally, central Europe; latest major outbreak, Angola
Fruit bats, by way of monkeys and other animals
Fruit bats, sometimes by way of monkeys
Bats, by way of camels
Bats, by way of civets
Type of virus
Type of illness
Fatality rate in outbreaks
50% to 90%
24% to 88%
Readily by close contact or fluids; not by aerosol
Readily by close contact or fluids; not by aerosol
Not very readily; mechanism unclear
Very readily by aerosol, fluids or close contact
On Sept. 30, officials with the federal Centers for Disease Control and
Prevention said Mr. Duncan first went to the hospital on Sept. 26. On
Oct. 1, the Texas Health Presbyterian Hospital issued a statement that
he first arrived there after 10 p.m. on Sept. 25.