It took international experts some time to decide that the animal disease Rift Valley fever was the primary cause of death in the epidemic, but the outbreak is still puzzling.

Unusually, whole herds of animals are said to have been killed by the disease, and human victims are commonly suffering bleeding from orifices, a symptom which in previous outbreaks has only affected 5% of patients.

The disease was first reported at the regional centres of Garissa and Wajir, but a disease with similar symptoms of bleeding is now also being seen in towns near the border with Somalia and Ethiopia. Dr Saade Abdallah of the Red Cross says far greater resources need to be devoted to investigate the outbreak, and to get access to flooded areas.

No-one can be too sure how many people have been affected. Relief organisations are hoping that the Kenyan army will provide a helicopter - something that's not happened since the alarm was raised nearly a month ago. The Ministry of Health says around 350 people, mostly nomads, have died so far, but local MPs are claiming that 5,000 people in the area have died because of the disease and starvation.