Answer
If humans were a host for a specific type of bacteria, the optimal temperature for this bacteria to live in would be the normal temperature for a typical human, which is 37.5$^{\circ}$C.
Work Step by Step
Because the human's body functions well in temperature of 37.5$^{\circ}$C, any parasite or bacteria that lives in the body also has to be able to live in the same temperature as the human body.
