An estimated 500,000 people in west Africa are infected with lassa fever every year, the World Health Organisation (WHO) said Wednesday, amid calls for more money to be spent on preventing its spread. \"The disease remains an epidemic in Liberia, Sierra Leone, Guinea and Nigeria with evidence of its presence in Ghana, Ivory Coast and Mali,\" the WHO\'s representative in Sierra Leone, Dr Wondimagegnehu Anemu told delegates at a conference on infectious diseases. Anemu said he hoped the four-day meeting \"will create an opportunity to examine the potential impact of the epidemic in the region and the world.\" Sierra Leone\'s Health Minister Zainab Bangura said that eradicating the rodent that carries the virus was \"almost impossible.\" Instead he argued that countries \"should embark on adequate measures to prevent the spread of the disease and all available resources should be spent on those access that promote good health as well as personal and environmental hygiene.\" The acute viral haemorrhagic fever causes some 5,000 deaths annually in west Africa, according to World Health Organisation figures.