Liberian President Ellen Johnson Sirleaf says the whole world has a stake in the fight against Ebola.

In a "letter to the world" broadcast on the BBC, she said the disease "respects no borders", and that every country had to do all it could to help fight it.

President Johnson Sirleaf added that a generation of Africans were at risk of "being lost to economic catastrophe".

The Ebola outbreak has killed more than 4,500 people across West Africa, including 2,200 in Liberia.

International donations have so far fallen well short of the amounts requested by UN agencies and aid organisations.

In the worst-affected countries - Guinea, Liberia and Sierra Leone - about 9,000 people have been found to have the Ebola virus, which kills an estimated 70% of those infected.

Fragile states

The letter, commissioned by the BBC and read out on the World Service's Newshour programme, starts with the words "Dear World".

She goes on to say that the fight against Ebola "requires a commitment from every nation that has the capacity to help - whether that is with emergency funds, medical supplies or clinical expertise".

"We all have a stake in the battle against Ebola," she says. "It is the duty of all of us, as global citizens, to send a message that we will not leave millions of West Africans to fend for themselves."

She said it was not a coincidence that Ebola had taken hold in "three fragile states... all battling to overcome the effects of interconnected wars".

Liberia, she noted, had about 3,000 qualified doctors at the start of the civil war in the late 1980s - and by its end in 2003 it had just three dozen.

"Ebola is not just a health crisis," she added. "Across West Africa a generation of young people risk being lost to an economic catastrophe."

Donation shortfall

The latest crisis in West Africa is the worst-ever Ebola outbreak.

The virus spreads between humans by direct contact with infected blood, bodily fluids or organs, or indirectly through contact with contaminated environments.

Donors have given almost $400m (£250m) to UN agencies and aid organisations, short of the $988m requested.

Separately, the UN has also appealed for donations to a $1bn Ebola trust fund, intended to act as a flexible source of back-up money to contain the disease.

UN chief Ban Ki-moon said on Friday that the fund, which was launched in September, had received just $100,000 (£62,000) in donations so far.

Former UN Secretary General Kofi Annan told the BBC he was "bitterly disappointed" with the international community's response.

"If the crisis had hit some other region it probably would have been handled very differently," he said in a BBC interview.

How not to catch Ebola:

• Avoid direct contact with sick patients as the virus is spread through contaminated body fluids
• Wear goggles to protect eyes
• Clothing and clinical waste should be incinerated and any medical equipment that needs to be kept should be decontaminated
• People who recover from Ebola should abstain from sex or use condoms for three months

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Uncertainty over figures