This is the 5133rd most frequent Chinese word.
infectious
The Chinese word for "infectious" (传染的) means capable of spreading disease or emotion from one person to another.
The word '传染性' here describes the disease's ability to spread from one individual to another biologically.
这种疾病具有很高的传染性。
This disease is highly infectious.
The word '感染力' is used metaphorically here to describe an emotionally impactful quality that spreads among people.
他的笑容富有感染力，让所有人都心情变好。
His smile is infectious and makes everyone feel better.
'感染了' indicates the spreading effect of the teacher's positive energy to others psychologically.