A rare outbreak of mosquito-borne yellow fever which has killed 165 people in Sudan's Darfur region in the past three months continues to spread, the UN warned on Thursday.
"The outbreak is very significant and the spread of the disease shows no signs of stopping," the United Nations resident and humanitarian coordinator, Ali al-Za'tari, said in a statement.
He said there is an urgent need for more funds for additional vaccines.
"The only way to stop its spread is to ensure vaccinations are administered to all people at risk," Za'tari said.
Since September 2 there have been 732 suspected yellow fever cases including 165 deaths, said a separate report from the UN's World Health Organization (WHO) and Sudan's Ministry of Health.
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.
"It is likely that many more cases of yellow fever have not been reported to health authorities," the statement from Za'tari's office said.
A vaccination campaign began on November 20 in the 12 most affected areas of Darfur.
So far, 1.3 million people have been inoculated, the statement said, adding that health workers have been able to reduce the death rate to about 24 percent from 40 percent earlier in the outbreak.
Sudan's impoverished western Darfur region has been plagued by conflict since ethnic minority rebels rose against the Arab-dominated Khartoum government in 2003.
This is the first yellow fever outbreak in Darfur in 10 or 20 years, WHO country representative Anshu Banerjee said last month.
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.
There is no specific treatment for the illness found in tropical regions of Africa but it can be contained through the use of bed nets, insect repellents and long clothing.
Vaccination is the most important preventative measure.