Doctors working in Sudan say they are concerned a deadly disease is sweeping through the population in the south.
The civil war exacerbates the spread of diseases
The medical emergency relief charity, Medecins Sans Frontieres, say thousands of people could already be suffering
Between 1985 and 1993, a similar epidemic in southern Sudan killed an estimated 100,000 people.
Kala-azar is a parasitic disease that weakens the immune system and is transmitted by the bite of the sandfly.
It is fatal if untreated.
Most people die from common infections the immune system can no longer handle, like pneumonia, diarrhoea and tuberculosis.
The spread of the disease has been exacerbated by the civil war, chronic food shortages and mass population movement.
MSF health advisor Kees Keus, who has just been in the upper Nile region of Bimbim, says the evidence points to this being a new epidemic in a population with little acquired resistance to kala-azar.
"We know from our experience in other places how devastating this can be. It is vital that we quickly discover the extent of the problem in this area."
The MSF say they have seen 150 new patients in the past week in the area. Twenty more arrive every day.
Most say they have already lost at least one member of their family to the disease.
There are reports of many more cases in the larger towns in the region but so far, doctors have been unable to get access.
MSF have called for a concerted effort by aid agencies working in the region to try and control the spread of the disease.
There is no vaccine, but it can be cured with drug injections and over 30 days of intense feeding.