Local health officials and the World Health Organization are facing numerous challenges containing the spread of Ebola in West Africa. On Thursday, the WHO said the outbreak could exceed more than 20,000 cases, six times the current confirmed figure, before it’s brought under control.

Liberia and Sierra Leone have been the hardest-hit, while Nigeria is still trying to contain a handful of cases stemming from one airline passenger who brought the virus into the country in July.

The WHO said last week that Liberia and Sierra Leone have underestimated the virus the most of all the affected countries, particularly in terms of how their populations are reacting to the outbreak.

On Thursday, the WHO said that the actual number of cases in the hardest-hit areas may be two to four times higher than currently reported figures.

The agency has issued a new plan for halting the spread of the virus within six to nine months, which public health officials say is possible because Ebola is actually simple to contain with basic infection control practices. Here are some of the barriers preventing health officials from getting the outbreak under control.

1. Initial symptoms look like the flu

Ebola patients don't turn bright pink or develop spots, so it's difficult to spot someone who's just contracted the virus. In fact, patients in the early throes of Ebola exhibit many of the same symptoms associated with the more common (and less deadly) influenza virus, as well as a number of other diseases that are prominent in Africa, such as malaria or typhoid fever. This can lead to Ebola patients being housed with the general sick population at a hospital, where everyone is exposed to the infection.

The WHO says one of the biggest problems with containing Ebola is that families are hiding any relatives they suspect of having the disease, for fear of the social stigma that comes with admitting a case of infection.

Containment of confirmed patients is key to stopping the virus’s spread, says Earl Brown, professor of virology at the University of Ottawa. The most obvious place to contain patients is at a hospital, he told CTV News Channel.

“So if you have people fleeing the method of containment, then that’s a problem.”

Others have been denying that an infected person is sick with Ebola, and will send that person to an isolation ward, the WHO says. The WHO calls these isolation wards "an incubator of the disease," in a news release issued last week. Ebola patients are cared for in the same communal room where patients with other diseases are being treated, and the Ebola virus can easily spread to the entire ward.

2. Ebola is easy to transmit

Ebola patients become walking human-to-human virus transmitters as soon as they begin to show symptoms, and remain contagious even after death. The virus spreads through all bodily fluids, including blood, vomit, feces, saliva and sweat. Male patients who've recovered from the virus can also pass it on through their semen up to seven weeks after recovery.

Patients must be isolated immediately, but many caregivers have been infected while diagnosing and treating the disease, making it more difficult to enforce quarantine and stop the virus from spreading.

Authorities believed they'd properly quarantined the airline passenger who brought Ebola to Nigeria last July, but 13 more cases have been reported in the country since then. On Friday, two new cases were discovered in the spouses of doctors who came in contact with the airline passenger. They were the first two cases outside the group of caregivers who treated the patient.

The WHO warns that even lab technicians testing blood samples must take extra precautions, as contact with a blood sample can be enough to cause infection.

Dead Ebola victims must be burned, but the WHO says some rural villages are burying their dead instead. Rural areas have also been reluctant to report their Ebola cases.

3. The outbreak is in an area with poor public health infrastructure

This latest outbreak has been so difficult to get a handle on because it is occurring in a part of the world that does not have the necessary expertise or infrastructure to deal with it.

Health care facilities in West Africa are facing massive shortages of necessary protective equipment, such as gowns, masks and gloves, “the thing we take for granted in our hospitals” in North America, says University of Pittsburgh infectious disease specialist Dr. Amesh Adalja.

Getting the outbreak under control does not require any new or novel protocols, he added. Once donor countries step up with money and manpower, it is basic infection control practices that will stem the tide of infections.

4. Some people are resisting healthcare efforts

Some West African countries are having difficulty containing Ebola because members of the population think the virus is a hoax. That's made it tough for countries to get full co-operation from their citizens.

The issue came to a head last week, when a group of Liberian non-believers attacked and looted a clinic in Monrovia's West Point slum where up to 30 patients were being held in quarantine with the virus. The attackers freed the Ebola patients and looted the clinic of its soiled sheets, mattresses and bedclothes, many of which were stained with infected blood and other bodily fluids.

Officials are still searching for many of the escaped patients in Monrovia, a city of nearly 1 million people.

Health officials are also dealing with what the WHO calls "shadow zones," Ebola-affected areas where the locals will not allow doctors to visit or help the infected. Officials don't know how many people have been infected in these shadow zones.

5. Ebola is difficult to treat or control

It can take between two and 21 days for someone infected with the virus to begin showing symptoms, and it's been difficult for officials to convince some patients to stay in quarantine for that length of time.

The WHO says every time a new clinic opens in Liberia, a flood of previously unreported Ebola patients arrives, suggesting there is a large population of undiagnosed Ebola cases in the country.

At the same time, many clinics and treatment centres have closed their doors because doctors and patients are too afraid to expose themselves to the virus, the WHO says.

There is currently no WHO-approved vaccine for the Ebola virus, although some experimental vaccines have been produced and tested in an effort to stem the outbreak. However, the vaccines have already run out.

Patients infected with Ebola require intensive supportive care, which can be taxing on hospital resources and poses a risk to healthcare workers who can be easily infected. There is no specific treatment for Ebola patients, other than to keep them constantly hydrated.

6. Ebola hides in animals

Africa has faced more than a dozen Ebola outbreaks since the virus was first reported in 1976. Ebola is usually slightly different from outbreak to outbreak, meaning it can behave in unpredictable ways.

Ebola has survived through the last 38 years by hiding in "reservoir" animals that can support the virus without dying from it. The virus will multiply and mutate while it lives in the reservoir animal, thus giving rise to multiple strains of the same Ebola.

This current strain is believed to have come from fruit bats that passed it on when they were eaten by primates or humans.

The WHO says pig farms may also play a role in transmitting the virus, as pigs can come in contact with fruit bats and pass on the infection to farmers.