What causes your dog to have a fever?

While there are many different causes of fever in dogs, the most common causes of fevers include:

Infections (Bacterial, Viral or Fungal)

By far the most common cause of fever in dogs, infections can be caused by any number of bacteria, viruses, and fungi. Common bacterial infections in dogs include pneumonia, liver or kidney infections, and infected wounds (ie: dog bites). Tick-borne diseases such as Lyme and Ehrlichia will also often trigger a fever in dogs. 

Infections are diagnosed through a combination of blood and urine tests, x-rays, and performing specific cultures or titres. Treatment will include the appropriate antibiotic or antifungal medication. In many cases, supportive care like IV fluid therapy will be required as well. Prognosis will depend on the type of infection, and is always better when treatment is sought early in the disease process.

Inflammatory Conditions

Inflammation and fever can sometimes occur without an underlying infectious cause. The most common presentation of this in veterinary practice is a condition called pancreatitis. This literally means ‘inflammation of the pancreas’ and typically causes vomiting, loss of appetite, abdominal discomfort and sometimes fever.

Previously thought to only happen after exposure to a high fat meal, pancreatitis can occur out of nowhere and should always be on your radar for a dog with a fever. 

Diagnosis of pancreatitis is most commonly made via blood tests and ultrasound. Treatment involves fluid therapy, pain management, and nutrition. Prognosis is usually good when treatment is sought early on. 

Autoimmune Disease

Another cause of fever in dogs is autoimmune disease. This occurs when a dog’s own immune system is stimulated inappropriately and starts to attack its own cells. Common examples include polyarthritis, meningitis, immune-mediated hemolytic anemia (IMHA) and immune-mediated thrombocytopenia (ITP). 

These conditions can be quite serious. They can occur as a primary disease or secondary to another issue like infection or cancer. Diagnosis is made via blood and urine tests, and sometimes other lab samples (ie: joint taps, cerebrospinal fluid taps). The mainstay of treatment is typically immunosuppressive doses of steroids along with supportive care.

Neoplasia (Cancer)

A less common cause of fever, certain cancers can trigger the immune system to react inappropriately. For example, dogs with leukemia, lymphoma, or cancer of the bone marrow may present with a fever.

In older dogs with auto-immune disease like immune-mediated hemolytic anemia (IMHA) or immune-mediated thrombocytopenia (ITP), there is often an underlying cancerous cause. 

Fever of Unknown Origin

In rare cases, even after running all the correct diagnostic tests (blood, urine, imaging, cultures, joint taps, etc), we cannot find an explanation for a dog’s fever. These cases are diagnosed as ‘Fever of Unknown Origin’ and are treated with supportive care. This condition appears to be far more common in cats than in dogs.