Authorities have deployed medics to Uganda's Bundibugyo district, on the border with the Democratic Republic of Congo, where the strain was first reported, said Sam Zaramba, director of medical services.
Laboratory tests have ruled out the lethal haemorrhagic Marburg fever, but patients are complaining of abdominal pains, severe diarrhoea and fever, although none suffered from bleeding, he said.
"My team has been on the ground for the past week trying to establish what the disease is. But its symptoms are not similar to those of the known haemorrhagic fevers," Zaramba told AFP.
Health authorities said last month they had contained an outbreak of Marburg fever that killed a gold mine worker in western Uganda.