An outbreak of Lassa fever in northern Liberia has already claimed at least seven lives and rural health workers say they lack drugs to treat further illness, health authorities said Thursday.

"Right now, we have clinical reports of about 10 confirmed cases of Lassa fever in Nimba County out of which seven died," Dr. Moses Pewu, Liberia’s chief acting medical officer, told IRIN.

Nimba is a densely populated county that lies between Guinea and Cote d'Ivoire, where more than 10,000 returning refugees and internally displaced people (IDP) have been resettled, according to the United Nations refugee agency (UNHCR).

Lassa is a viral haemorrhagic fever known to be endemic in Liberia, Guinea, Sierra Leone and parts of Nigeria. It probably exists in other West African countries as well, according to the UN World Health Organisation (WHO).

Humans become infected with Lassa from contact with infected rodents. The virus can also be transmitted from one human to another through direct contact with body fluids. Rural dwellers, especially those living in areas of poor sanitation or crowded living conditions, are at greatest risk of contracting the illness.

Symptoms include headache, sore throat, muscle pain, chest pain, nausea, vomiting, diarrhoea and cough. Severe cases may progress to bleeding from the mouth, nose, vagina or gastrointestinal tract.

WHO says some studies indicate that 300,000 to 500,000 cases of Lassa fever and 5,000 deaths occur yearly across West Africa. The overall case-fatality rate is 1 percent to 15 percent among hospitalised patients, WHO says. The illness is especially severe late in pregnancy, with fetal loss and sometimes maternal death occurring in more than 80 percent of cases.

Pewu said rural health workers in Nimba County do not have the capacity to deal with the disease. "The drugs for treatment for Lassa fever are in short supply," he said.

The humanitarian coordination section of the UN Mission in Liberia (UNMIL) in its situation report early this week noted the poor state of health infrastructure to deal with the illness.

"Some of the problems in tackling the disease include weak or non-existent surveillance, monitoring and supervision, poor diagnosis of the disease at some health facilities, and lack of adequate drugs and treatment facilities," the report said.

The report, which quoted a joint team of the Ministry of Health and WHO that visited villages in Nimba County, said "there is a high presence of Lassa fever" in those areas.

Liberia’s recent National Human Development Report said the country's health facilities were in ruins. It said the country’s 14-year civil war destroyed 95 percent of health facilities, and that the number of trained government doctors in the country had dropped from 400 to less then 20 at the war's end in 2003.