Toothbrushes can harbor bacteria, viruses, and other disease-causing organisms. Toothbrushes can also become contaminated with saliva and blood. In fact, the parainfluenza virus can survive on toothbrush bristles for over 24 hours. Atmore et al. Your brush is most likely to act as a disease vector if you share it with another person or if the brush is not permitted to dry completely after each use.
Most bacteria thrive in warm, moist environments.
Proper oral hygiene is extremely important. Label your toothbrush so it does not get mixed up with other brushes. Rinse your brush with clean water before and after each use. Shake it dry after rinsing. It is best to alternate between two or three brushes.