An outbreak of mosquito-borne yellow fever which has killed at least 165 people in Sudan's Darfur region is Africa's worst in decades, the World Health Organisation said on Thursday.
"Definitely, this outbreak now could be classed as the largest outbreak" since at least 1990, WHO country representative Anshu Banerjee told AFP.
Since September 2, there have been 732 suspected yellow fever cases in Darfur, including 165 deaths, said a separate report from WHO and Sudan's health ministry.
Outbreaks in other countries have been smaller because their routine vaccination programmes have started to include yellow fever, whereas Darfur had never had vaccinations for the virus until last month, Banerjee said.
That has left the population with no immunity.
"Anyone would be at risk," he said.
"The outbreak is very significant and the spread of the disease shows no signs of stopping," UN humanitarian coordinator Ali al-Za'tari said.
He said there was an urgent need for funds for more vaccine.
"The only way to stop its spread is to ensure vaccinations are administered to all people at risk," Za'tari said.
The death toll has now surpassed that of a 2005 yellow fever outbreak in Sudan's South Kordofan state which caused 163 deaths from 604 cases over about five months.
The yellow fever virus normally circulates among monkeys but could be linked to more mosquitoes breeding this year after heavy rains and flooding in the region.
Mosquitoes can become infected from the primates and transfer the virus to humans, Banerjee said, adding that the Darfur cases are concentrated among the region's nomads.
"It's spreading as the population is moving, and the mosquitoes are getting infected," he said.
The statement from Za'tari's office said that many more cases have likely not been reported to health authorities.
A vaccination campaign began on November 20 in the 12 most affected areas of Darfur.
The first phase targeting 2.2 million people is almost finished, and more than one million more doses are expected to arrive next week, Banerjee said.
Sudan's impoverished western Darfur region has been plagued by conflict since ethnic minority rebels rose against the Arab-dominated Khartoum government in 2003.
More than one million people are living in camps for the displaced.
There is no specific treatment for the illness found in tropical regions of Africa and the Americas but it can be contained through the use of bed nets, insect repellents and long clothing.
Vaccination is the most important preventative measure.