Adverse Effects of Fever
The beneficial effects of fever during bacterial infections in rabbits have been shown to reverse at temperatures >5° F (3° C) above normal. Cytokine dysregulation may result in prolonged or extreme fevers with adverse effects on a variety of body functions in addition to the immune response.
Catabolic metabolic processes during fever are markedly different from catabolism of starvation. Protein loss occurs four times as rapidly in individuals with infectious or inflammatory diseases as compared with starvation-adapted individuals. Ketonemia is inhibited, resulting in the oxidation of large amounts of muscle- derived amino acids for energy. This cytokine-driven catabolism, combined with the decreased feeding behavior that accompanies fever, variable anorexia (even if feed is provided), and increased metabolic rate at higher temperatures, can result in rapid and severe muscle wasting, weakness, and atrophy. In humans, high fevers frequently cause seizures, especially in children,59 but this is rare in animals unless temperatures reach 108° F (42° C) in neonates. Prolonged high fevers in debilitated animals may lead to failure of the cardiovascular system.Fever is one of the earliest and most prominent manifestations of the acute phase reaction. Veterinarians have used the clinical thermometer to aid in diagnosis and to monitor the progress of illness in animals since 1770. With the increased knowledge of the pathogenesis of fever has come a better appreciation for the diverse causes of the febrile state. In ruminants and horses, however, infectious disease remains the most common reason for development of fever (Boxes 4.4 and 4.5). Careful evaluation for the presence of infectious disease is always indicated, especially when the onset of a fever is abrupt; the temperature is higher than 39.4° C (103° F); and the fever is accompanied by depression, variable loss of appetite, serous nasal exudate, epiphora, enlargement of lymph nodes, or diarrhea and a decreased or increased leukocyte count. Other causes of fever are neoplasia (Boxes 4.6 and 4.7), immune- mediated diseases (Boxes 4.8 and 4.9), noninfectious inflammation (Boxes 4.10 and 4.11), and certain drugs.