Complex sentence: Relapsing fever is a vector-borne disease caused by infection with certain bacteria in the genus "Rickettsia" and "Borrelia", which are transmitted through the bites of lice or soft-bodied ticks (genus "Ornithodoros").
Split into simpler sentences: Relapsing fever is an infection caused by certain bacteria in the genus "Rickettsia" and "Borrelia". It is a vector-borne disease transmitted through the bites of lice or soft-bodied ticks (genus "Ornithodoros").