There is a book published by philologist Pavlo Chuchka from Uzhhorod State University “Surnames of Transcarpathian Ukrainians: The Historic-Etymological dictionary” (2005). Title: Прізвища закарпатських українців: історико-етимологічний словник П. Чучка.
As per him , there are several variations of this surname both mentioned in Lemko and Boyko villages located in present day Lviv region. Surname in Litus form first mentioned in 1819 in Бусовисько на Бойк (Lviv region). Surname is originated from old Czech name Letoň, which in turn originated from early Slavic name Лѣто.