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 dogs 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
Diagnosis
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
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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