Complex sentence: He is also the head of the World Health Organization Collaborating Centre for Research and Control of Opisthorchiasis, an infectious parasitic disease caused by the Southeast Asian liver fluke, which is endemic in northeastern Thailand and other portions of the Mekong River basin.
Split into simpler sentences: He is also the head of the World Health Organization Collaborating Centre for Research and Control of Opisthorchiasis, an infectious parasitic disease caused by the Southeast Asian liver fluke. The disease is endemic in northeastern Thailand and other portions of the Mekong River basin.