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Most Deadly Diseases in Dogs and Their Symptoms

María Besteiros
By María Besteiros, Expert veterinary assistant and canine/feline hairdresser.. Updated: February 28, 2024
Most Deadly Diseases in Dogs and Their Symptoms
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Any changes to your dog's well-being are a cause for concern. If we see certain symptoms, they can make it obvious something is seriously wrong. However, some of the deadliest diseases in dogs are slow to progress. For this reason, we need to be observant to even small changes and remember to take our dog for regular veterinary checkups, even when they seem otherwise fine.

AnimalWised provides you with a list of the 5 most deadly diseases in dogs. These include pathologies and disorders which occur relatively frequently in veterinary medicine, as well some rare conditions with high mortality, but low frequency.

You may also be interested in: Most Common Diseases in Rabbits


  1. Canine parvovirus
  2. Canine distemper
  3. Gastric torsion or dilation
  4. Hemolytic anemia
  5. Cancer

1. Canine parvovirus

Parvovirus is a highly contagious viral disease with an acute presentation, meaning it will develop relatively rapidly. Its inclusion in this classification of the five deadliest diseases in dogs is due to its high mortality rate if left untreated. The virus that causes it has a special affinity with cells that are in continuous reproduction, such as gastrointestinal mucosa. For this reason, it produces a clinical picture that includes the following symptoms:

  • Vomiting
  • Fever (although not exclusively)
  • Anorexia
  • Profuse diarrhea (may contain mucus or blood)
  • Dehydration
  • Depression
  • Abdominal pain

Infection of canine parvovirus occurs through contact with contaminated feces. The sick dog can shed the virus for weeks and the virus is only inactivated in the environment by cleaning with suitable products such as bleach. The virus can also be carried on feet, hair, shoes, etc. Although it affects dogs of all ages, it is most common in puppies between 6 and 12 weeks of age.

Parvovirus is diagnosed in the veterinary clinic using a rapid detection test, although false negatives can occur. Treatment involves hospitalization to give the dog IV fluids and medications to replenish fluid and electrolyte losses, as well as to control vomiting and diarrhea. Broad-spectrum antibiotics are also added to treat secondary bacterial infections that occur due to a weakened immune system. These are only measures as there is no specific treatment against parvovirus.

Prognosis will depend on the virulence of the strain, the age and immune status of the dog, and the rapidity of veterinary treatment. If we have had a dog with parvovirus we must disinfect the house and anything they touch with bleach. As prevention, it is important to vaccinate puppies. Before their vaccination schedule is completed, they must avoid contact with dogs whose immune status is unknown.

Most Deadly Diseases in Dogs and Their Symptoms - 1. Canine parvovirus
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2. Canine distemper

Distemper is another highly contagious canine disease caused by a virus. It can affect any dog, which is why immunization is so vital. It is spread by inhalation and is most common in puppies between 6 and 12 weeks. The virus attacks brain cells, skin, conjunctiva and mucous membranes of the respiratory and gastrointestinal tracts. For this reason, the symptoms can be very diverse. Some of the most common clinical signs include:

  • Fever
  • Anorexia
  • Pain
  • Apathy
  • Watery discharge from the eyes and nose (becomes thick, sticky, and yellowish in time)
  • Dry cough
  • Vomiting and diarrhea that can lead to dehydration
  • Encephalitis (see below)
  • Certain viral strains can cause hardening of the nose and callus formation on the pads

Encephalitis in dogs causes hypersalivation, head shaking, chewing movements or epileptic-like seizures. The so-called ‘distemper myoclonus’ is also characteristic. This is a disorder which causes rhythmic contractions of muscle groups in any part of the body, although it most commonly affects the head. It begins to appear during rest or sleep, but will eventually affect them during the day and night.

As one of the five deadliest diseases in dogs, treatment of canine distemper virus requires hospitalization. As with parvovirus, there is no treatment other than support. Antibiotics will be administered to prevent opportunistic bacterial infections, intravenous fluid therapy counteracts dehydration and medication may be used to control diarrhea, vomiting or seizures. It is essential to go to the veterinarian to start treatment immediately.

Survival will depend on factors such as the virulence of the strain, age and vaccination status.

Most Deadly Diseases in Dogs and Their Symptoms - 2. Canine distemper
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3. Gastric torsion or dilation

Gastric torsion or dilation is a veterinary emergency that can end the life of our dog. The high mortality it presents is the reason it is included in this list of the five deadliest diseases in dogs. As with parvovirus and distemper, it is really important to establish treatment immediately. Time is one of the factors that will most contribute to increasing the chances of survival.

When gastric torsion in dogs occurs, the stomach is distended by the presence of gas and fluid. Once this happens, it rotates on its longitudinal axis. This situation causes the stomach to be practically sealed. In doing so, it prevents the escape of air and accumulated liquid, as well as interfering with blood circulation. Although this disorder can occur in any dog, it is more common in large breeds.

Among the symptoms of gastric torsion in dogs are the following:

  • Restlessness and agitation
  • Hypersalivation
  • Nausea and retching (not vomiting)
  • Abdominal distention
  • Pale mucus membranes
  • Rapid breathing
  • Rapid heart rate
  • Weakness

Your vet will be able to confirm the diagnosis with an x-ray. In cases of torsion, surgery is usually required, but the dog must first be stabilized with fluids and intravenous medication. It often occurs in dogs which eat too quickly. To prevent this ailment we can divide the dog's food into several portions a day, prevent them from drinking or eating large quantities at once and avoid exercising on a full stomach.

Survival will depend on how quickly we go to the vet.

Most Deadly Diseases in Dogs and Their Symptoms - 3. Gastric torsion or dilation
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4. Hemolytic anemia

To understand canine anemia, specifically hemolytic anemia in dogs, we must know the process of hemolysis. This is the breakdown of red blood cells which turn into bile and hemoglobin. These substances accumulated in the body are the cause of jaundice in dogs (yellowing of the eyes and mucous membranes) and hemoglobinuria (orange-brown urine).

The dog will be weak, pale, and may have an enlarged spleen, liver, and lymph nodes. Various diseases can cause anemia, including lupus, leishmania, leptospirosis, ehrlichiosis or babesiosis. It has a high mortality rate, hence the inclusion in this list of the five most deadly diseases in dogs.

We will us babesiosis as an example for this whole group of disorders. Babesiosis in dogs is a disease caused by a protozoan (Babesia canis) that destroys red blood cells causing hemolytic anemia. Babesia reach the dog through the bite of an infected tick, hence the importance of keeping our dog dewormed throughout the year. It can also be contracted directly, without the presence of ticks.

The symptoms it produces are the following:

  • Fever
  • Yellow eyes and mucous membranes (due to increase in bilirubin)
  • Orange colored urine as a result of the rupture of red blood cells
  • Vomiting
  • Hemolytic anemia will be detected in a blood test

It is possible to observe the parasite under a microscope. Treatment should be started immediately and involves eliminating the parasite and controlling anemia. In the most severe cases, blood transfusions may be needed.

Survival will depend on the immune status of the dog, the detection of symptoms and the speed with which we go to the vet.

Most Deadly Diseases in Dogs and Their Symptoms - 4. Hemolytic anemia

5. Cancer

Cancer is an abnormal cell overgrowth that eventually invades surrounding tissue and continues to grow in an uncontrolled manner. This can even affect their bones. Cancer cells moving from an initial location to another part of the body is known as metastasis. If an organ is invaded, these malignant cells will not be able to fulfill the function that normal cells have been performing, causing organ failure.

The life expectancy of a dog with cancer will depend on multiple factors. This include as the virulence of the cancer, the age of the dog or the organ that is affected. It is essential to establish early diagnosis and treatment. Removal of the tumor and surrounding tissue is recommended whenever possible. Most cancers in dogs are detected through a simple physical examination. It is so important to schedule check-ups every 12 or 6 months at our veterinary clinic, as well as go to a consultation if we detect any lump, swollen limb or anomaly in our dog.

Cancer that affects internal organs such as the spleen or liver may take time to present symptoms. This will be observed in nonspecific signs such as weight loss, vomiting, diarrhea or constipation. Cancer most commonly affects middle-aged and geriatric dogs. As dogs are living longer due to a better quality of life, it is likely the incidence of cancer will increase. For this reason, and due to the high mortality of some types of cancer, we include this condition in the list of the five deadliest diseases in dogs, especially in older dogs. [1] [2]

Most Deadly Diseases in Dogs and Their Symptoms - 5. Cancer

This article is purely informative. AnimalWised does not have the authority to prescribe any veterinary treatment or create a diagnosis. We invite you to take your pet to the veterinarian if they are suffering from any condition or pain.

If you want to read similar articles to Most Deadly Diseases in Dogs and Their Symptoms, we recommend you visit our Other health problems category.

  1. Fleming, J. M., Creevy, K. E., & Promislow, D. E. (2011). Mortality in north american dogs from 1984 to 2004: an investigation into age-, size-, and breed-related causes of death. J Vet Intern Med, 25(2), 187-98.
  2. Eleni, C., Scholl, F., & Scaramozzino, P. (2014). Causes of death in dogs in the province of Rome (Italy). Vet Ital, 50(2), 137-43.
    doi: 10.12834/VetIt.13.07.01.
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