DrBarchas.com

Animals Affected

Cats and dogs

Overview

Fever of unknown origin is a common syndrome in cats and dogs.  Affected animals experience an elevated body temperature, usually accompanied by lethargy, weakness, and lack of appetite.

As the name implies, the cause of fever of unknown origin is not determined in most cases.  However, most pets with the syndrome are treated for bacterial infections.  This treatment usually is successful.

Symptoms

• An elevated body temperature (usually above 103º F) is the most consistent symptom of fever of unknown origin.  Pets with fevers sometimes, but not always, will feel warm to the touch.  The normal temperature of cats and dogs ranges from 100.0- 102.5º F.
• Most pets with fever of unknown origin are weak and lethargic due to fever and dehydration.
• Lack of appetite is a common symptom of fever of unknown origin.
• Pets with the syndrome sometimes tremble.

Risk Factors

Due to the enigmatic nature of the syndrome, most cases of fever of unknown origin are not correlated with any known risk factors.  However, pets that are at increased risk of infection are at increased risk of the syndrome.  For instance, cats that go outdoors may develop infected wounds and a fever from fighting with other cats.  These wounds may be too small to detect, which may lead to a diagnosis of fever of unknown origin.

Young animals suffer from fever of unknown origin more often than older animals.

Complications

Most animals recover from fever of unknown origin when they are treated for infection and dehydration.  However, some cases do not respond to this therapy.  In these cases extensive testing, hospitalization, and intensive care may be required.  A very small number of pets do not survive fever of unknown origin.

Diagnosis

Diagnosis of fever of unknown origin is made when no cause can be found for a pet's elevated body temperature.   In most cases, basic blood and urine tests are performed prior to starting treatment for the syndrome.

Pets that do not respond to initial treatment may require comprehensive, advanced testing including diagnostic imaging (X-rays and ultrasound), cultures for bacteria and fungus, sampling of lymph nodes, joints, and organs, and blood tests for exposure to specific pathogenic organisms.

Treatment

Mild cases of fever of unknown origin may be treated with oral antibiotics such as doxycycline or Clavamox® and basic nursing care (including nutritional support) at home.  Rarely, anti-inflammatory medications such as prednisone or NSAIDs are used in the treatment of the syndrome.  Prednisone must be used cautiously because it can exacerbate some types of infection.

Severe cases of fever of unknown origin may require hospitalization for intravenous fluids, intravenous antibiotics, nursing care, and continuous veterinary supervision.

The most serious cases of fever of unknown origin require intensive management and supervision in a 24-hour veterinary facility.

Follow-up

In most cases, the symptoms of fever of unknown origin resolve within 48 hours of starting treatment.  Once treatment is complete, most pets do not suffer further episodes of the syndrome.

Pets that do not respond to treatment within 48 hours, or that suffer from recurring episodes of fever, should undergo more extensive treatment and diagnostics as outlined above.

Miscellaneous

Fever of unknown origin is by definition a mysterious syndrome.  Because of this, it is often frustrating for pet owners as well as veterinarians.  However, as mentioned above, most animals with the syndrome eventually make complete recoveries.

Copyright © Eric Barchas, DVM. All rights reserved.
The contents of this page are provided for general informational purposes only. Under no circumstances should this page be substituted for professional consultation with a veterinarian.