The high proportion of health workers infected with the Ebola virus in West Africa is "unprecedented" and is hampering efforts to curb the epidemic, the World Health Organization (WHO) said Tuesday, according to dpa. More than 240 health care workers have developed the disease in Guinea, Liberia, Nigeria and Sierra Leone while treating patients and more than 120 have died, the UN agency said. The causes of the high infection rate among medical personnel included lack of protective equipment - not even gloves and face masks - and its improper use, it said. Other problem are a severe lack of medical staff and health care professionals working in isolation wards for more hours than are considered safe, the WHO said. Staff who are exhausted are more prone to make mistakes. The high death toll of health workers was hindering efforts to bring the outbreak under control, the WHO warned. Even before the outbreak, the number of physicians was low in the region, which has 1.5 doctors to every 100,000 patients, and doctors are concentrated in urban areas.