Koch travelled to South Africa to study Bovine Pleuropneumonia also known as Bovine Plague. The highly contagious disease was killing cattle and threatening the food supply of the region.

Koch conducted several expeditions to tropical regions to study diseases such as malaria, sleeping sickness (trypanosomiasis), and others. These expeditions took him to Africa, Asia, and Oceania.

Koch made significant contributions to the understanding of malaria transmission and control. He studied the life cycle of the malaria parasite ("Plasmodium") and demonstrated the importance of mosquito control in preventing the spread of the disease. His findings influenced public health strategies for malaria prevention.

Koch studied sleeping sickness (African trypanosomiasis) and identified the tsetse fly as the vector that transmits the disease. His research contributed to the development of strategies for controlling tsetse fly populations and preventing the spread of sleeping sickness.