"In order to care for those affected, we have trained hospital staff in treatment methods and are working to keep the affected individuals isolated so as to avoid new spread," said Guido Sabatinelli, head of the WHO office in Sudan.

The epidemic has hit 12 communities in the eastern region of Southern Kordofan, including Habila, Dilling, Kurtala, Julud, Abu Gubeiha, Umbrembita and Alrigul towns. Cases of dengue fever also had been reported in Kassala and Blue Nile states to the east.

The illness is spread through the bite of a type of mosquito. "The key is ridding the area of these mosquitoes - so we are spraying the breeding area and also homes and surrounding areas," Sabatinelli explained.

Symptoms include sudden high fever, severe headache and pain behind the eyes and in the muscles and joints. Proper and early treatment can relieve the symptoms and prevent complications and death.

Dengue haemorrhagic fever is a more severe form of the disease, in which bleeding and shock sometimes occurs, leading to death. It is most serious in children. Bleeding usually occurs after three to five days of fever.

WHO, the UN Children's Fund (UNICEF), local and international NGOs as well as the Ministry of Health had begun distributing thousands of mosquito nets and large quantities of insecticides to people in the affected areas.

Sabatinelli pointed out that mass population movements following the signing early this year of the peace agreement ending civil war in southern Sudan and the movement of nomadic communities could cause the virus to spread to other regions.

The UN health agency had sent an epidemiologist and specialised doctor to Kadugli, Southern Kordofan's capital, to assess the situation.

"It is important to immediately assess if this type of mosquito is present in the north and the west to know whether or not the disease will spread," said Sabatinelli, adding that WHO had also hired an entomologist to evaluate the current risk factors in those areas.

The first recorded dengue fever outbreak in Sudan was reported in the mid-1980s in Red Sea state. Its case fatality rate was 25 percent.