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Fever in Cats

By: PetPlace Veterinarians

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A fever is defined as abnormally high body temperature resulting from internal controls. It is believed that fever is a method of fighting infection. The body resets the temperature control area of the brain to increase the body temperature – probably in response to invasion of foreign matter such as bacteria or viruses. Since many invaders do not thrive in hot environments, by increasing the temperature of the body, these invaders can be destroyed.

This is different from hyperthermia, which is an increase in body temperature due to external influences such as hot weather, inability to pant or sweat. The brain does not intend for the body temperature to increase.

Fever is usually differentiated from hyperthermia based on the animal's recent environment, for example if he was in a hot car, as well as the animal's response to the increased temperature. Animals that pant excessively and have increased heart and respiratory rates are typically victims of overheating (hyperthermia). Fever animals do not exhibit significant distress.

The normal temperature in cats is 100.5 to 102.5 degrees Fahrenheit.

Causes of Fever

  • Infection
  • Inflammation
  • Cancer
  • Drug related
  • Immune system disease
  • Idiopathic – cause not determined. This is also referred to as fever of unknown origin.

    What to Watch For

  • Lethargy
  • Behavior changes such as "crankiness"
  • Not eating or drinking
  • Hiding
  • Swellings or lumps (abscesses or tumors)
  • Draining wounds


    Fever is easily diagnosed based on a rectal temperature. A body temperature over 103F is considered a fever. Diagnosing the underlying cause of the fever, which is usually related to an infection, can be challenging. Sometimes, history and physical exam findings can indicate the cause of the fever or source of infection. Unfortunately, diagnosis may require various tests if the cause is not easily determined. Some recommended tests may include:

  • CBC – complete blood count or hemogram. This will determine white blood cell count, red blood cell count and platelets. Many animals with fever have an elevated white blood cell count

  • Chemistry profile to help determine the overall health of the animal and to detect any organ impairment

  • Blood smear to detect blood parasites

  • Serologic testing for uncommon sources of fever such as tick transmitted diseases

  • Blood evaluation for immune system diseases

  • Feline leukemia and feline immunodeficiency virus testing

  • Urinalysis to detect a urinary tract infection

  • X-rays to determine if there are any internal masses, pneumonia or other abnormalities that may lead to a fever

  • Abdominal and/or cardiac ultrasound to detect a source of infection such as liver, kidney, heart valves

  • Exploratory surgery with various organ biopsies in prolonged fever cases without diagnosis


    Treatment for a fever is based on the underlying diagnosis and severity of the fever. Some mild fevers may not be treated since mild fevers can help destroy invading bacteria or viruses.

    If a diagnosis is not readily apparent based on history and physical exam findings, it is quite common for your veterinarian to try a course of antibiotics before progressing to diagnostic testing. For temperatures over 104.5 - 105 F, medication is recommended initially to break the fever. Ketoprofen is commonly used to treat fevers. Commonly prescribed antibiotics are:

  • Amoxicillin
  • Ampicillin
  • Cephalexin
  • Doxycycline

    If the fever continues or recurs despite antibiotic treatment, additional diagnostic testing is recommended.

    If a cause for the fever is determined, treatment is specific for the cause. Since there are so many different causes of fever, a full discussion of each cause is beyond the scope of this article.

    Home Care

    For mild fevers, less than 104.5F, monitoring your pet at home may result in spontaneous recovery. Make sure your pet continues to eat and drink. Take your pet's temperature one to two times daily. If the temperature rises above 104.5F, this should prompt you to contact your veterinarian.

    Also, look for any areas of infection such as abscesses, skin lumps, blood in urine or straining to urinate, sneezing or breathing difficulty. In addition, lack of appetite or lethargy should prompt an examination and treatment by your veterinarian.

    Preventative Care

    Many causes of fever are not preventable and are associated with infections. Keeping your pet and the environment clean as well as avoiding exposure to ill pets or animal fights can reduce the chance of infections and fevers.

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