Red Cross workers carry away the body of a person suspected of dying from the Ebola virus, in the Liberian capital Monrovia, on October 4, 2014
Monrovia (AFP) - Doctors and nurses across Liberia went on strike on Monday to demand danger money to care for Ebola patients, as the World Health Organization called the health crisis the worst in modern times.
Health care workers in west Africa are on the frontline of the worst-ever Ebola outbreak, which has killed more than 4,000 people this year, mostly in Guinea, Sierra Leone and the hardest-hit, Liberia.
The Liberian walkout came as US officials said the United States must "rethink" its approach to Ebola after a female nurse in Texas contracted the tropical virus, in the first case of contamination on US soil and the second outside Africa.
As the US case fuelled global jitters, President Barack Obama and his French counterpart Francois Hollande issued a joint call for "stepped-up" global efforts to combat the disease.
And European Union ministers called a meeting for Thursday to discuss screening travellers from Ebola-hit west Africa, in line with steps taken by Britain, the United States and Canada.
In the face of panic that was "spreading faster than the virus", the WHO issued a stark warning that the Ebola crisis was "the most severe acute public health emergency in modern times".
"I have never seen a health event threaten the very survival of societies and governments in already very poor countries," said WHO chief Margaret Chan in a statement delivered on her behalf at a Manila conference.
"I have never seen an infectious disease contribute so strongly to potential state failure."
In Liberia, the chairman of the national health workers' union, Joseph Tamba, said his strike call had been heeded.
"Health workers across the country have downed tools as we asked them to do," Tamba told AFP.
In the capital Monrovia, a patient quoted on local radio described scenes of desolation with the sick deserted by staff.
"We are at the Ebola Treatment Unit and no one is taking care of us," the unnamed man said. "Last night several patients died. Those who can walk are trying to escape by climbing over the fence."
Journalists have been banned from Liberia's Ebola clinics, making the situation there difficult to ascertain.
But a nurse at the capital's JFK medical centre said staff had shown up for work there even though they supported the strike action. "We are here to help the patients. They could be our parents too," said the nurse, who did not wish to be named.
- Risk bonus -
Ninety-five Liberian health workers have died so far in the epidemic, and their surviving colleagues want pay commensurate to the acute risk of dealing with Ebola, which spreads through contact with bodily fluids and for which there is no vaccine or widely available treatment.
Danger money aside, Tamba said many workers were not even being paid their regular wage to combat an epidemic that has killed more than 2,300 in Liberia and overwhelmed its skeletal health service.
He said that at the Island Clinic -- which is backed by the WHO -- staff were promised a monthly wage of $750 (595 euros) for nurses and lab technicians, and $500 for other carers.
A union representative earlier said wages were as low as $250 a month.
Tamba indicated that workers were open to talks to find a solution. "If she (President Ellen Johnson Sirleaf) can tell us plain blank 'Look, there is no money for you people', we will sit down. We don't have to fight her," he told AFP.
The WHO's Chan has warned of "many more cases" to come for Guinea, Sierra Leone and Liberia without radical action by the international community.
In a telephone call on Monday, Hollande and Obama stressed the need for "a stepped-up mobilisation of the international community and the European Union, in close coordination with the United Nations, the WHO and the countries concerned," Hollande's office said in a statement.
Both cases of contamination reported so far outside Africa -- in Spain last week and now in the United States -- have involved health workers who fell ill despite stringent safety protocols surrounding Ebola.
- Human trials -
In the United States, health authorities said a female nurse -- identified by local media as 26-year-old Nina Pham -- tested positive after caring for a Liberian Ebola patient, Thomas Eric Duncan, who died on Wednesday.
The nurse at Texas Health Presbyterian Hospital in Dallas is in isolation and said to be in stable condition.
Experts still do not know exactly how the woman was infected, the Centers for Disease Control and Prevention said.
"We have to rethink the way we approach Ebola infection control because even a single infection is unacceptable," said CDC director Tom Frieden.
Meanwhile, Canada announced it would begin testing an experimental vaccine, VSV-EBOV, on humans. The first results will be available in December, according to Health Minister Rona Ambrose.
In Spain, a crisis cell set up when Madrid nurse Teresa Romero fell sick after caring for two missionaries with Ebola said the nurse remained in a "very serious condition".
Fifteen other people are under observation in a Madrid hospital for symptoms of the disease, which include fever, diarrhoea, vomiting and bleeding.