Most Dangerous Dog Diseases


There are thousands of known diseases that can affect canines of any breed, size or age. Some are contagious, some are transmitted by insects or other animals, and others are genetic. It is important to monitor your dog's behavior and speak to a veterinarian if your pet is exhibiting any unusual symptoms.

Zoonotic Diseases

Zoonotic diseases are those that can be transferred from animals to humans. According to the Centers for Disease Control, more than 6 out of every 10 infectious diseases in humans are spread from animals. Because people interact frequently with their pets, it is important to be aware of the ways zoonotic diseases can be spread. Coming into contact with the saliva, blood, urine or feces of an infected animal may result in transmission.


Rabies is a fatal viral infection of the nervous system that can affect all warm-blooded mammals, including humans. Rabies spreads through bodily fluids, such as saliva and blood and typically is transmitted through bites or open wounds. The virus travels through the canine nervous system to the brain, where it begins to multiply at a high speed. A rabid dog will often become:

  • Irritable
  • Aggressive
  • Depressed
  • Uncoordinated

This second stage is typically accompanied by excessive drooling. Symptoms appear between three and five months after the infectious bite, though they can appear sooner.

Rabies is not treatable in dogs and will always result in death. The American Kennel Club recommends that all exposed canines be euthanized immediately to prevent further transmission to other animals or humans. However, the disease can be prevented with a yearly vaccination.


Roundworms are the most common internal parasites in canines. Puppies can become infected through egg migration through the placenta or in the mother's milk. Young dogs are at the most risk for complications or death due to roundworm infection, though dogs of any age can be affected. Female worms lay hundreds of thousands of eggs each day, which can cause:

  • Stomach aches
  • Vomiting
  • Diarrhea
  • Coughing

The parasites also can be passed to humans, so infected dogs should visit a veterinarian as soon as possible. Treatment includes deworming medications and anti-parasitic drugs. Dogs who have been treated for infection should be monitored with follow-up visits to the vet.

Incurable Diseases

Incurable diseases are those that have no known treatment that can eliminate symptoms. The result is often death for infected dogs, or the canine likely will deal with symptoms for the rest of its life.

Canine Distemper

This contagious virus is spread through the air or contact with an infected animal. It first affects the tonsils and lymph nodes, then moves on to infect the respiratory, genital, gastrointestinal and nervous systems. Owners will notice:

  • High fever
  • Red eyes
  • Lethargic behavior
  • Lack of appetite
  • Continuous cough
  • Vomiting
  • Diarrhea

Once the brain and spinal cord are attacked, the dog may experience seizures, paralysis and hysteria. Because there is no cure, treatment focuses on mitigating the painful and dangerous symptoms. For dogs with diarrhea or lack of appetite, intravenous fluids can be administered. Antibiotics also may assist with secondary infections and potassium bromide is helpful to control seizures.

Infectious Canine Hepatitis

Hepatitis in dogs is caused by canine adenovirus type-1 and typically is transmitted through contact with the urine of an infected dog. The virus replicated in the tonsils and moves on to the lymph nodes. From here, it can enter the bloodstream and affect a variety of other organs, most importantly, the liver.

The results include:

  • Decreased liver functionality
  • Massive hemorrhage
  • Central nervous system trauma

It can be fatal and there is no known cure, so treatment focuses on alleviating symptoms. An intravenous catheter is important for keeping the dog hydrated and restoring blood sugar to proper levels. A blood transfusion may be required.


  • Owners can take preventive measure by having their dogs vaccinated for adenovirus beginning between 6 and 8 weeks of age and repeating once or twice a month until the puppy reaches 16 weeks.

Deadly Without Treatment


Canine parvovirus infection, better known as “parvo,” is extremely contagious and dangerous for puppies and unvaccinated adults. The disease infects cells lining the digestive tract and is spread by oral contact with infected fecal matter. Dogs who have contracted the illness will have contaminated stool before ever showing symptoms, which makes parvo especially easy to transmit.

Within 5 to 10 days of infection, symptoms include:

  • Gastrointestinal distress
  • High fever
  • Vomiting
  • Bloody diarrhea
  • Weight loss
  • Stomach pain

Many ultimately die without timely treatment. Veterinarians can work to reverse dehydration and treat secondary infections to restore the dog to a pain-free life. Most dogs will require hospitalization.


Heartworm is a dangerous parasite often found in dogs and is typically transmitted by mosquitoes. The disease is potentially fatal if not correctly treated. There are medications that can prevent infection.

If a dog does become a host for these long worms, there can be lasting damage to the heart, lungs and arteries. Death is often caused by inflammation of the blood vessels to the point of blocking blood flow, resulting in blood clots in the lungs or even heart failure.

Veterinarians will administer medication until it is determined that all of the parasites have been eliminated. During this time, exercise must be restricted to prevent the worms from multiplying or dying too quickly.


  • According to the Companion and Animal Parasite Council, 1 out of every 76 dogs tested positive for heartworm in 2015. The highest infection rate is in the southeastern United States.

Rare Diseases

Rare diseases are uncommon in dogs and there may not yet be much information about their causes or treatment.

Degenerative Myelopathy

Canine degenerative myelopathy is a progressive and rare disease that eventually causes the complete deterioration of the brain and spinal cord.

The disease is thought to be caused by a genetic mutation similar to that causing Lou Gehrig’s disease in people. It is incurable and fatal. Affected canines will experience:

  • Weakness in the hind legs
  • Gradual paralysis
  • Respiratory problems
  • Difficulty swallowing
  • Incontinence

To slow the progression of the disease, dogs should perform moderate exercise and physical therapy.

Glanzmann's Thrombasthenia

Glanzmann's thrombasthenia is a rare, genetic bleeding disorder. In affected canines, the blood platelets do not clot normally and put the dogs at risk of life-threatening bleeding and spontaneous hemorrhage. Otterhounds and Great Pyrenees are at higher risk.

Treatment includes oral and injected iron supplements. The spontaneous bleeding often subsides when the dog reaches adulthood for unknown reasons.

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