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

Pathogenesis:

Fig: Pathogenesis of Fever

Classification of Fever:

Fever can be classified as follows:

Aetiological:

• Protein fever: Fever occurs due to administration of foreign protein, damaged tissue following necrosis, hemorrhage and fracture
• Salt fever: Fever caused due to administration of hypertonic saline
• Neurogenic Fever: Damage of brain cells following injury, trauma, hemorrhage, tumor causes fever
• Transitory Fever: Fever caused due to over dehydration in animals. It is also known as thirst fever
• Drug Fever: Fever caused due to administration of some drugs like adrenaline, thyroxin, nicotine, caffeine
• Idiopathic Fever: Specific fever against specific diseases, ex; Anthrax, Ephemeral fever, etc.

Clinical:

• Acute fever: There is sudden sharp elevation of body temperature to level of 104°F or above. This type of fever is recorded in acute bacterial or viral disease.
• Sub-acute fever: Temperature doesnot goes too high and remains within range of 103°F. This type of fever is recorded in mild inflammatory reactions; metritis, nephritis, cystitis, etc.
• Chronic fever: In this type of fever, temperature doesnot exceeds above 1-2°F beyond normal range. Course is usually prolonged. It is seen in pulmonary tuberculosis, chronic pyometritis, etc.

Types of Fever:

1. Simple Fever: In this type of fever, temperature doesnot touch normal limit in 24 hours and variation of temperature donot exceed 2-4 °F. It is noted in lobar pneumonia, enteric fever, etc.
2. Remittent Fever: In this type of fever, temperature doesnot touch normal limit in 24 hours and variation of temperature is above 2°F in 24 hours
3. Intermittent Fever: In this type of fever, fever persist for few period of time followed by drop to normal temperature and again temperature starts to rise. This type of fever is seen in human malaria, Surra, canine distemper (biphasic fever)
4. Irregular Fever: This type of fever doesnot get fixed pattern. There is daily fluctuation of temperature without any pattern. It is seen in veterinary practice as in CD, Louping ill, swine erysipelas, strangles in horse
5. Transient fever: Fever subsides within 24 hours after its development.
6. Continuous fever: Fever persist for longer period of time than simple fever. Ex; Tick-borne fever
7. Periodic fever: Periodic attack of fever alternate with febrile period.
8. Sthenic fever: High rise of temperature is accompanied with strong bounding pulse. It is observed in acute inflammatory conditions
9. Asthenic fever: There is moderate temperature with weak and quick pulse. Ex; fever in pulmonary tuberculosis

Stages of Fever:

There are 3 stages in fever:

• First stage:
  • In this stage, temperature of body rises as a result of spasm of blood vessels in skin
  • Ratio of heat production increases to heat loss.
  • This phase of rapidly rising temperature is accompanied by chills (feeling of cold) and shivering (rigors).
  • As internal temperature remains high, but extremities remains cold.
  • As result of shivering, there is more heat production due to spasm of muscles.
  • Chills are due to stimulation of cutaneous nerve endings following fall in body temperature caused by spasm of superficial blood vessels.
• Second stage:
  • In this stage, temperature remains highest
  • Ratio of heat production to heat loss remains at definite level
  • There is cessation of shivering
• Third stage:
  • In this stage, there is decline in body temperature.
  • Heat loss is increased compared to heat production
  • Heat loss occurs as profuse sweating or dilatation of blood vessels.
  • Body regains its normal temperature.

Clinical Findings in Different Stages of Fever:

1^st stage:

• Dullness, drowsiness
• Disinclination to move
• Inappetance
• Erection of hairs, arched back
• Rapid respiration, shivering
• High colored urine

2^nd stage:

• Profound dullness
• Drooping of ears
• Lowering of head
• Frequent respiration
• Rapid pulse
• Congested mucus membrane
• Hot breath, dry muzzle, anorexia
• Drop in milk yield
• Increased thirst, constipation, scanty urine

3^rd stage:

• Respiration less frequent
• Regain of appetite
• Skin coat appears normal
• Muzzle becomes moist
• Urine turns normal

Treatment/ Management of Fever:

• Management of fever should be aimed at removing its causes.
• Antibiotics are recommended if bacterial infection is present. Penicllin, cephalosporins, oxytetracycline should be administered either orally or parenterally depending on severity of infection
• Antipyretics drugs; Meloxicam @0.2-0.5 mg/kg, b.wt., IV/IM/SC for 3-5 days is recommended. Paracetamol can also be used @ 10mg/kg, b.wt.
• Supplemental therapy should be provided. Vitamin B-complex injection can be given to stimulate appetite.
• Vitamin-C injection or tablet should be given to improve immune function.