April 8 (Reuters) - At least 50 hippos and other large animals have been killed by anthrax poisoning in eastern Congo’s Virunga National Park and have been spotted floating along a major river that feeds one of Africa’s great lakes, the head of the park said on Tuesday.

Tests confirmed anthrax poisoning, said Virunga Park director Emmanuel De Merode, adding that buffalo have been killed too. The exact cause of the poisoning was not yet clear.

Park guards noticed there was a problem when the dead animals started to appear about five days ago along the river, which forms Congo’s border with Uganda and runs through an area under the control of rebel fighters.

Anthrax is a serious disease usually caused by bacteria found naturally in soil. Wild animals can become infected if they inhale anthrax spores in contaminated soil, plants, or water.