Uganda, currently battling an Ebola epidemic in a western district, said Saturday it has registered four new cases involving a doctor and three nurses, according to dpa. The news brings the total number of those infected by the deadly virus to 55, out of which 16 have died so far. "The medical staff, including the doctor, are in Bundibugyo hospital isolation unit," the chairman of the Ebola National Task Force, Dr Sam Okware, told Deutsche Presse-Agentur dpa. The health ministry has issued an order to all medical staff in the district who have been in contact with Ebola patients to be quarantined, Okware said. Aggressive measures are being put in place to contain the epidemic which has spread in over 10 villages in Bundibugyo district on the border with the Democratic Republic of Congo since September. "This Ebola strain is different from other strains found in Sudan and the Congo. We are taking precautions and we have told any health worker who feels unwell to be quarantined. We have one doctor and three nurses and they have been isolated," Okware said. This latest outbreak of the fast-spreading killer disease in the East African country is the second since late 2000 when Ebola hit the northern region, leaving 224 people dead out of the total of 425 who were infected. Deputy Health Minister Dr Emmanuel Otala told dpa Saturday night that "we are containing the spread of the disease and we have provided protective gear to all the health workers in the district. Fifteen people have been isolated in the hospitals and the rest have recovered and gone back home." The World Health Organization (WHO) said Friday it was particularly concerned by a new strain of the deadly virus. A WHO spokesman told journalists in Geneva: "Anytime we are looking at Ebola and a new strain of Ebola, this presents a new challenge and we are very concerned." The usual signs of Ebola are fever, intense weakness, muscle pain, headache and sore throat. Vomiting may follow and in some cases there is both internal and external bleeding. It is transmitted by direct contact with blood and other bodily fluids.