The Ebola epidemic¹ threatens the "very survival" of societies and could lead to failed states, the World Health Organization has warned.

世界卫生组织发出警告，埃博拉病毒的蔓延威胁到社会的“生存”并可能导致国家衰亡。

The outbreak, which has killed some 4,000 people in West Africa, has led to a "crisis for international peace and security", WHO head Margaret Chan said.

She also warned of the cost of panic "spreading faster than the virus".

Meanwhile, medics have largely ignored a strike call in Liberia, the centre of the deadliest-ever Ebola outbreak.

Nurses and medical assistants had been urged to strike over danger money and conditions. However, most were working as normal on Monday, the BBC's Jonathan Paye-Layleh in Monrovia said.

A union official said the government had coerced² workers - but the government said it had simply asked them to be reasonable.

In a speech delivered on her behalf at a conference in the Philippines, Ms Chan said Ebola was a historic risk.

"I have never seen a health event threaten the very survival of societies and governments in already very poor countries," she said. "I have never seen an infectious disease contribute so strongly to potential state failure."

She warned of the economic impact of "rumours³ and panic spreading faster than the virus", citing a World Bank estimate that 90% of the cost of the outbreak would arise from "irrational⁴ attempts of the public to avoid infection".

Ms Chan also criticised pharmaceutical⁵ firms for not focusing on Ebola, condemning⁶ a "profit-driven industry [that] does not invest in products for markets that cannot pay".