Uncovering the Cause of Fever in Dogs

30 The term fever of unknown origin (FUO) is often overused in veterinary medicine, as the number of patients in which a true cause of fever cannot be uncovered is relatively small. In 1961, Petersdorf and Beeson first defined FUO in humans as a fever ≥ 101°F (38.3°C) that persists for greater than 3 weeks, with the diagnosis uncertain after one week of study in the hospital. This definition has remained mostly intact today except for the requirement of in-hospital study.1,2 The duration of greater than 3 weeks was intended to eliminate cases of acute self-limited infectious disease (often viral) from the retrospective analysis of FUO cases.1 When describing FUO in dogs, fever is usually defined as greater than 103.5°F to 104°F (39.7– 40°C), with no duration of fever specified.3,4 In animals, the path to revealing the cause of persistent fever can be lengthy and expensive but, in most patients, an etiology can be eventually identified (see FUO in Animals: Often a Misnomer).