Russian expresses 'aches' with the preposition
у, the person who aches in the genitive case, and the part of the
body that aches in the nominative case.
У Сергея болит голова. Sergei's head hurts.
У Антона болят ноги. Anton's legs hurt.
To indicate the illness that someone has, in Russian we use 'to
have' expressions with the preposition у, without the word есть.
У Володи аппендицит. Volodya has appendicitis.
У профессора температура 38,5. The professor has temperature of
38.5.