SYMPTOM
Fever
Owners may observe fever in their pet.
Various conditions
This symptom can occur in multiple conditions and warrants further assessment.
Localised Bacterial Infection
Infection contained within one area of the body, such as the kidneys, chest cavity, ear or mammary gland, triggers a systemic temperature rise before other signs become obvious. Pyelonephritis, pyothorax and mastitis are examples of this pattern, and the underlying site is usually identified through targeted investigation once fever is noted.
Immune-Mediated Inflammatory Disease
The immune system can drive inflammation and fever without any infection being present, and among dogs whose fever persists without an obvious cause on initial examination, immune-mediated disease is recognised as the single most common category identified. This group includes immune-mediated blood disorders and inflammatory conditions of the skin or joints, and fevers here often wax and wane rather than remaining constantly elevated.
Vector-Borne Infection
Organisms transmitted by tick bites, including Babesia, Ehrlichia and Anaplasma species, can cause fever alongside lethargy and reduced appetite. These infections are uncommon in dogs with no travel history but are relevant for dogs that have travelled or been imported from continental Europe or further afield.
Viral Infection
Viral illness produces fever as part of the wider immune response, and in cats feline herpesvirus is a frequent cause, often alongside sneezing, ocular discharge and reduced appetite. In dogs, viral components of the infectious respiratory disease complex can similarly cause a mild, self-limiting temperature rise.
Mild, Self-Limiting Pyrexia
A transient, low-grade temperature rise in the day or two following vaccination, or during a minor viral upper respiratory infection, reflects a normal and proportionate immune response rather than significant underlying disease. This pattern typically resolves without specific intervention and is not accompanied by the marked lethargy or inappetence seen with more significant causes of fever.
Why timing matters
Early observation
Early recognition allows prompt assessment and intervention if needed.
Later presentation
Persistent or worsening signs may indicate progression requiring attention.
The significance of this symptom depends on its context, duration, and associated findings.
Conditions commonly associated
Pneumonia
Elevated body temperature is common with active bacterial or viral pneumonia.
Pancreatitis in Dogs
Fever often accompanies pancreatitis as part of the inflammatory response within the pancreas and surrounding tissues. The elevation in body temperature tends to occur alongside abdominal pain and digestive signs in affected dogs.
Pneumonia
Fever is a common feature of pneumonia, reflecting the inflammatory and infectious processes within the lung tissue. The pyrexia typically occurs alongside respiratory signs such as coughing, increased breathing effort, and reduced exercise tolerance.
Otitis Externa in Dogs
Fever can occur in cases of otitis externa when bacterial infection within the ear canal becomes significant or spreads to deeper structures. The systemic response is more likely when the infection involves the middle ear or causes cellulitis of surrounding tissues.
Pancreatitis in Cats
Fever may accompany pancreatitis in cats, though the presentation in this species tends to be more subtle than in dogs. The pyrexia reflects pancreatic inflammation and can occur alongside vague signs such as lethargy and reduced appetite.
Feline Herpesvirus (FHV-1)
Fever can occur during acute flare-ups of feline herpesvirus infection, particularly in younger cats or those with compromised immunity. The elevated temperature typically accompanies upper respiratory signs such as sneezing, nasal discharge, and conjunctivitis.
Discospondylitis
The underlying infection driving discospondylitis commonly produces an intermittent or persistent raised temperature.
Anaplasmosis
Anaplasmosis triggers a systemic immune response to the tick-borne organism, commonly producing a raised body temperature.
Aspiration Pneumonia
The body's response to infection settling in the lungs commonly raises the temperature.
Babesiosis
The immune response mounted against the parasite commonly raises body temperature.
Ehrlichiosis
Ehrlichia infection triggers a systemic immune response in the days after a tick bite, producing a sustained rise in body temperature during the acute phase.
Endocarditis
An infected heart valve continually seeds bacteria into the bloodstream, maintaining a persistent or fluctuating fever.
Juvenile Cellulitis (Puppy Strangles)
A raised temperature can accompany the skin and lymph node inflammation typical of this condition in young puppies.
Mastitis
A raised temperature commonly accompanies the infection and inflammation within the affected mammary gland.
Pyelonephritis
Bacterial infection within the kidney tissue triggers a systemic inflammatory response that raises body temperature.
Pyothorax
An active bacterial infection filling the chest cavity drives a systemic rise in body temperature.
Salmonellosis
A raised body temperature commonly accompanies this bacterial infection as the immune system mounts a response.
Sterile Nodular Panniculitis
Active inflammation within the nodules can raise body temperature, producing an intermittent fever alongside the skin changes.
Toxic Epidermal Necrolysis
Extensive skin damage and the accompanying risk of secondary infection commonly raise body temperature.
Toxoplasmosis
The immune response mounted against this infection typically produces a raised body temperature during the acute phase.
When to explore further
When the symptom is persistent or worsening
When other signs are present alongside
When daily activities or quality of life are affected
When there is uncertainty about the cause
Noting when this symptom occurs, any triggers, and how it changes over time can provide useful information for veterinary discussions.
Last reviewed: 24 April 2026 · Dr Alastair Greenway MRCVS