Fever (Pyrexia):

• Fever is elevation of core body temperature above that normally maintained by an animal and is independent to effects of ambient conditions on body temperature.
• It is combination of hyperthermia and infection or inflammation.
• Fever is general reaction of animals to action of harmful and most frequent infectious agent known as pyrogens.
• Pyrogens may be endogenous or exogenous.

Etiology:

Fever may be septic, most common or aseptic depending on presence or absence of infection.

Septic Fever:

• These fevers are caused by infection with bacteria, virus, fungi, protozoa
  • Localized infection such as abscess
  • Intermittently systemic as in bacteremia, endocarditis
  • Consistently systemic as in septicemia

Aseptic Fever:

• Chemical fevers caused by injection of foreign protein, intake of dinitrophenols
• Surgical fever due to breakdown of tissues
• Fever from tissue necrosis
• Severe hemolytic crisis (hemoglobinemia)
• Extensive infarction
• Extensive necrosis in rapidly growing neoplasm
• Immune reactions- anaphylaxis, angioneurotic edema