He could be infectiously enthusiastic and extraordinarily charming: whenever we talked, his eye contact bordered on hypnotic.
"catching, having the quality of spreading from person to person," 1540s of diseases, 1610s of emotions, actions, etc.; see infect + -ous.
infectious in·fec·tious (ĭn-fěk'shəs)adj.
Capable of causing infection.
Caused by or capable of being transmitted by infection.
Caused by a pathogenic microorganism or agent.