silent killer
A metaphor for a disease or condition that progresses without obvious symptoms until it is serious. Often used in medical or public health contexts. Compare サイレントキラー, which is the direct loanword.
See also: サイレントキラー
High blood pressure is sometimes called a silent killer.
サイレントキラー is the direct loanword from English and is more common in casual or media contexts. 沈黙の殺人者 is a native Japanese translation with a slightly more formal or literary feel.
A calque from English 'silent killer', composed of 沈黙 (silence) + の (possessive particle) + 殺人者 (killer).