What is Ebola virus disease?

Ebola virus disease (formerly known as Ebola haemorrhagic fever) is a severe, often fatal illness, with a  fatality rate of up to 90 per cent and, according to the World Health Organisation (WHO), one of the world's most virulent diseases.

The virus is systemic, which means it can move to and affect every part of the body causing direct damage to organs as well as internal bleeding. It causes shock, which drops a person's blood pressure and causes multi-system organ failure.

The natural host for Ebola remains unknown, but researchers say an outbreak is likely through contact with an infected animal, possibly bats.

The infection is transmitted by direct contact with the blood, body fluids and tissues of infected animals or people.

Severely ill patients require intensive supportive care. During an outbreak, those at higher risk of infection are health workers, family members and others in close contact with sick people and deceased patients.

Ebola virus disease outbreaks can devastate families and communities, but the infection can be controlled through the use of recommended protective measures in clinics and hospitals, at community gatherings, or at home.

The virus is named after the Ebola River in Zaire, in what is now the Democratic Republic of Congo, where the virus was discovered in 1976.

As of now, there's no vaccine or cure for Ebola virus disease. All that doctors can do is treat the symptoms and provide supportive care like monitoring heart rate, blood pressure, and breathing while making sure the patients' fluids are replenished.

Sometimes patients are given antibiotics to treat other possible infections in the hope of sustaining the patient through the infection so their immune system can eventually clear the virus. This is harder to achieve in the rural health systems of West Africa that are tasked with treating thousands of patients with insufficient resources.

When the body is infected with a virus, it starts creating antibodies to attack it. The people who survive Ebola-or any virus-have created enough antibodies to neutralise it.

The virus can get into the body through a wound, or even microabrasions in the skin that can't be seen easily. Additionally, the virus can get into the body through the eyes and mouth if those areas come into contact with something that contains the bodily fluids of an infected person. That's why health care workers are supposed to keep themselves completely covered while treating patients. The virus can be present even in the sweat of a patient.

The doctors and health care workers in West Africa are working in rural clinics, where the proper protections are scarce. Infected people may be quarantined with other people infected with the disease, making this kind of contact easier.

Although the virus has a two-to-21-day incubation period, it is unlikely that the disease spreads from someone who doesn't show symptoms. According to the United States Centre for Disease Control (CDC), people who are not symptomatic are not contagious.

Although there are several promising drugs and vaccines in development, since Ebola is less common - and research on it not well funded - there is no drug or vaccine that has been approved for use in humans.

One experimental serum was used by the two American patients, but there's not enough for widespread use yet. Another drug is still not ready for use on humans (See: WHO declares Ebola epidemic a global emergency).