infectivity ；

[例句] 这种病极易传染. It's a highly contagious infection.

[例句] 新城疫 ( NewcastleDisease,ND ) 是由新城疫病毒(NewcastleDiseaseVirus,NDV) 引起的极易传染的毁灭性疾病. Newcastle disease ( ND ) is regarded worldwide as one of the most devastating diseases of poultry.

--