Infectious
INFEC'TIOUS, adjective Having qualities that may taint, or communicate disease to; as an infectious fever; infectious clothing; infectious air; infectious miasma.
1. Corrupting; tending to taint by communication; as infectious vices or manners.
2. Contaminating with illegality; exposing to seizure and forfeiture.
Contraband articles are said to be of an infectious nature.
3. Capable of being communicated by near approach.
Grief as well as joy is infectious