Pyrexia in Dogs

Pyrexia in Dogs

Health & Safety

Pyrexia is a medical term that describes when a dog develops a fever which sees their body temperature rise a lot higher than it should. A dog's normal temperature should be between 99.5 and 102.5 F, but when this rises to 103.5 F, it becomes evident they have developed pyrexia and the underlying cause needs to be investigated sooner rather than later to prevent any further complications from developing.

The Causes

Why a dog develops a fever is not always that evident, but should they have a high temperature for longer than four days, it's important they be thoroughly examined by a vet. If the vet cannot find the reason why a dog has pyrexia, they often refer to it as being a “fever of unknown origin” or FUO for short. With this said, whenever a dog develops a higher than normal temperature, it is usually in response to a viral or bacterial issue that's attacking their system.

Although pyrexia is not a disorder as such, it is a good indication that a dog is suffering from some other health issue that needs investigating. It is worth noting that when dogs develop a fever, it is their natural defence system that’s kicking in which prevents bacteria from multiplying. When their body temperature is elevated, it also helps improve a dog's own immune system response. The problem starts to get extremely serious when a dog's body temperature gets too high and lasts for long periods of time. As such, any dog with a prolonged elevated body temperature needs to be seen by a vet sooner rather than later.

Symptom Associated with Pyrexia

As previously mentioned, when a dog develops pyrexia, there are specific symptoms associated with the condition which are as follows:

  • A higher body temperature (normal for a dog is between 99.5 and 102.5 F)
  • Shivers
  • Weakness
  • Loss of appetite
  • Rapid heart rate
  • Dehydration
  • Rapid breathing
  • Shock

The Causes

There are many reasons why a dog might develop pyrexia and this includes because they are suffering from the following health issues:

  • Bacterial infections
  • Viral infections
  • A parasite overload
  • An immune-mediated issues
  • Tumours
  • Metabolic disorders
  • Endocrine diseases
  • Inflammatory conditions
  • A reaction to certain drugs and medication
  • Contact with toxins
  • For unknown reasons, which is referred to as FUO - fever of unknown origin

Diagnosing the Problem

A vet would need to identify the underlying cause of the fever before deciding on a treatment option. However, if a dog is found to be severely dehydrated, they would need to be hospitalised and given vital fluid therapy to stabilise their condition. The vet would ideally need to know a dog's full medical history and be told how the onset of any symptoms first presented themselves. The more information a vet can be given, the better as it helps establish a diagnosis.

The vet would thoroughly examine a dog when they are suffering from pyrexia and would recommend carrying out the following tests which help confirm a diagnosis as well as identify the underlying cause of the fever:

  • A complete blood count
  • A full biochemistry blood profile
  • A urinalysis
  • X-rays which would help identify if a dog has developed a tumour, abscess or some kind of infection
  • Ultrasound
  • CT scan
  • MRI scan
  • Endoscopy to establish if there is some kind of internal obstruction or infection

Treatment Options

Treatment options would depend on the underlying cause of the problem. Severely dehydrated dogs would need to be hospitalised so they can be given vital fluids to rehydrate them and so the vet could carefully monitor their condition. Should it not be possible to identify why a dog has an elevated body temperature (FUO), the vet might refer them to a specialist, but this can prove extremely expensive and the tests needed are a lot more invasive.

Should the problem be caused by a bacterial infection, the vet would typically prescribe a course of appropriate antibiotics with the end goal being to kill off the damaging bacteria. It is essential that the complete course be finished for the treatment to be effective even if a dog shows signs of improvement after a couple of days.


The aftercare for dogs that suffered a high body temperature is all-important when it comes to their recovery time. This means limiting the amount of daily exercise they are given and making sure they are fed a correct, well balanced diet that contains the right levels of calories which again would help speed up their recovery. If a dog does not regain their appetite and is reluctant to eat solid food, the vet would recommend a high calorie liquid diet until they are back to normal again.

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