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List of the Most Deadly Dog Diseases

↯ Key takeaway points

  • Knowing the signs of common and deadly dog diseases is important for pet parents
  • In 2011, gastrointestinal, musculoskeletal, and nervous systems were most commonly affected by deadly diseases
  • Certain breeds are more commonly affected by specific diseases
  • Veterinary research has helped us identify and track dangerous dog diseases
  • Knowing the signs of deadly diseases and seeking veterinary care is crucial for the well-being of our pets.
Written by Jay
BsC (Hons) Animal Behaviour & Welfare graduate with a passion for advocating for misunderstood animals.
Zoo and wildlife doctor in veterinary medicine passionate about animal welfare and preventive medicine.
Published on
Saturday 9 January 2021
Last updated on
Tuesday 6 June 2023
most deadly dog diseases
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As a pet parent, it is important to know the signs of both common and the most deadly dog diseases. In 2011, it was found that the gastrointestinal, musculoskeletal, and nervous systems were most commonly affected by a disease that caused death. It was also found that certain breeds were more commonly affected by certain diseases than others.

With advances in veterinary research, we now have statistics on a range of dangerous diseases. So what makes a deadly dog disease? How many dogs get them each year? What signs should you look for? Read on to find out more!

Top 12 Most Deadly Dog Diseases

By researching which body systems are the most affected by a deadly disease, we have compiled a list of deadly dog diseases. Amongst these diseases are canine distemper, heartworm, canine parvovirus, cancer, obesity, rabies, Lyme disease, kidney disease, infectious canine hepatitis, leptospirosis, and fungal diseases.

1. Canine Distemper

Canine distemper (Canine morbillivirus) is a highly destructive viral illness. But just how dangerous is it? In adult dogs, the mortality rate is as high as 50 percent. In puppies, the rate exceeds 80 percent. With the disease’s high mortality rate and destructive nature, it is by far one of the most deadly dog diseases in the world today. In canines, distemper attacks several body systems. These include the digestive, respiratory, and central nervous systems. Because the virus affects multiple systems, canine distemper is highly contagious via inhalation. And, despite extensive vaccination across the USA, canine distemper remains a major threat for our furry friends.

The symptoms of canine distemper vary widely and can be indistinguishable from kennel cough or as severe as rabies. If severe, the infection causes high fever, coughing, vomiting, diarrhea, and hardening of the footpads. In some cases, the illness allows for secondary bacterial infections that result in serious neurological symptoms. CNS signs include muscle twitches, seizures, sensitivity to light, circling, blindness, and paralysis. Even after overcoming this virus, many dogs continue to show serious signs of illness for the rest of their lives. Dogs who have overcome canine distemper may present with hard pad disease, enamel hypoplasia, and degeneration of the nervous system. When CNS degeneration becomes too advanced to support a good quality of life, most vets will recommend euthanasia.

2. Heartworm

Dog heartworm (Dirofilaria immitis) is a type of parasitic roundworm that causes dirofilariasis. Spread from host to host through mosquito bites, this type of worm causes mortality when left untreated. As well as this, the treatment itself can result in mortality. Both of these factors combined make dog heartworm disease one of the most deadly dog diseases on this list. While 98 percent of heartworm treatment is successful, exerting a dog who is undergoing treatment can cause serious complications. Dead worms may break loose from the heart and travel to the lungs. In rare cases, this causes respiratory failure and sudden death.

In the beginning, infected dogs show few or no signs of infestation. This is because the worms spend six months maturing within the heart. Even after the worms mature a sedentary dog may show no signs. Active dogs, however, will show the classic symptoms of heartworm disease. These include a cough, exercise intolerance, weight loss, and fainting. As the infestation worsens, infected dogs have difficulty breathing and show signs of heart failure. Finally, dogs with heavy infestation develop caval syndrome. Caval syndrome is fatal without surgical intervention from a vet.

3. Canine Parvovirus

Canine parvovirus (CPV) is a highly contagious virus. In untreated cases, the mortality rate exceeds 91 percent. Untreated dogs with severe parvovirus can die within 48 to 72 hours. Also, CPV infections are most dangerous to puppies between the time of weaning and six months, leading to many puppy deaths each year. Perhaps most dangerous to puppies is cardiac CPV. Within a litter, more than 70 percent of puppies die of heart failure by eight weeks of age. The remaining 30 percent die months or years later. In the most severe cases, puppies around four weeks old die suddenly of cardiogenic shock. With its high mortality rate and contagious nature, CPV is one of the most deadly dog diseases in the world today.

Dogs with CPV show signs of disease within three to seven days. The symptoms include lethargy, fever, vomiting, and bloody diarrhea. Because the intestinal lining is damaged by CPV, dogs often present with anemia and endotoxemia. These factors combined lead to shock and death. Aggressive early treatment is necessary for a dog’s survival. Dogs with CPV require fluid therapy, antiemetics, and antibiotics to overcome the disease.

deadly dog diseases
Canine Parvovirus is a contagious deadly disease.

4. Cancer

Cancer develops in one in three dogs, making it the leading cause of death for our pets. Just like in humans, dogs can develop carcinomas, sarcomas, lymphomas, and leukemias. Unfortunately, chemotherapy is only partially effective in many cases, according to a 2014 study.

The symptoms of cancer include lumps, swellings, halitosis, lameness, weight loss, lethargy, lack of appetite, and black stools. Some breeds are more predisposed to certain types of cancer than others. Boxers, Boston Terriers, and Golden Retrievers most commonly suffer from mast cell tumors. Great Danes, Rottweilers, and Greyhounds are more prone to bone cancer than small breeds. Owners need to be aware of what types of cancer their breed is prone to for early treatment. For dogs, the most common treatments are surgery, chemotherapy, and radiation therapy. If your dog is diagnosed with cancer, don’t panic – be sure to talk to your vet about all of your options as soon as possible.

5. Obesity

Obesity and being overweight affects more than 56 percent of dogs in the USA. This equals a whopping 50 million dogs, according to the American Pet Products Association (APPA). In comparison with non-obese dogs, obese dogs are at higher risk of osteoarthritis, diabetes, surgery complications, and urinary incontinence. As well as this, dogs who are obese have a shorter lifespan. Studies suggest that the lifespan of an overweight dog is 2.5 years shorter. While a 2.5-year difference may not seem like a huge amount to humans, it is important to consider this number in perspective. If converted to human terms, this number translates to 10 to 15 years less. These worrying statistics make obesity one of the most deadly dog diseases in the USA.

Obesity in dogs occurs with excessive food intake and a lack of exercise. But how can you tell if your dog is overweight? Most vets will recommend using the “Body Condition Score” system. Using this system, a score of 3 is healthy. If your dog scores a 3, their ribs can be felt without excess fat, and your dog has an obvious waist when viewed from above. Meanwhile, a score of 5 suggests that your dog has obvious fat deposits over the neck, limbs, and backbone. There is also obvious abdominal distention.

6. Rabies

The rabies virus is fatal in over 99 percent of cases. Worryingly, 98 percent of these cases are caused by the canine rabies virus variant (CRVV), despite the virus being eliminated from the USA in 2004. Globally, 59,000 people die of rabies each year despite rabies control efforts. While there are isolated cases of humans and dogs surviving clinical rabies, these are not well-documented and these cases are difficult to replicate. This makes rabies one of the world’s deadliest diseases, for both humans and dogs alike.

Most cases of rabies begin with a bite. In dogs, the virus incubation period varies from one week to several months. During this time, an infected dog may be able to infect other dogs and humans. Next, the prodromal phase is marked by a change in temperament. While a quiet dog might become agitated, an outgoing dog might become nervous. This phase persists for two to three days. Following this prodromal phase are two forms of clinical disease. Furious rabies occurs when the infected dog becomes aggressive, displays extreme hunger, pica, and paralysis. The infected dog usually dies in a violent seizure. Dumb rabies is the most common form. This form involves progressive paralysis and difficulty swallowing. Ultimately, the infected dog falls into a coma and dies. Both forms of the virus are deadly for dogs.

7. Lyme Disease

At least four tick species transmit Lyme disease. Although these ticks prefer certain species to feed upon, they are willing to feed on humans and dogs. Once the tick is attached, it takes one or two days for it to transmit the Borrelia bacteria. Thus, prompt removal of ticks is extremely important for the prevention of Lyme disease. Without prompt treatment, Lyme disease can go on to damage the kidneys and heart, causing the most severe complications.

Dogs with acute Lyme arthritis are responsive to antibiotics. However, Lyme nephritis does not carry the same prognosis. The mortality rate of this disease is not clear, however, this rare renal form is usually fatal. The clinical signs of Lyme nephritis may be acute or chronic. Anorexia, dehydration, vomiting, weight loss, and polyuria are just a few of the main symptoms of this devastating complication. Lyme nephritis progresses rapidly, and while some dogs may live for a few months, the end result is usually death. Similarly, Lyme disease that damages the heart can lead to heart failure. Current research suggests that this form of illness is uncommon but possible for dogs to experience.

8. Chronic Kidney Disease

Kidney disease is one of the leading diseases affecting dogs worldwide. While chronic kidney disease only affects between 0.5 and 1.0 percent of dogs worldwide according to one study, the devastating effects make it one of the most deadly dog diseases to date. Chronic kidney disease (CKD) is incurable and causes mortality within months or years. Rather than a cure, your vet will attempt to delay disease progression and to improve your pet’s quality of life.

Chronic kidney disease comes with a huge variety of symptoms. These range from drinking too much, vomiting, and weakness, to sudden blindness, bone fractures, and bleeding into the stomach. CKD is also associated with periodontitis and cardiac disorders, both of which can be dangerous if not addressed by a vet.

9. Infectious Canine Hepatitis

Infectious canine hepatitis (ICH) is a liver condition caused by canine mastadenovirus A. With a mortality rate of 10 to 30 percent, ICH causes several serious problems to dogs, especially young puppies. The different forms of this disease can cause death within 24 hours or months depending on the severity of the disease. This disease is spread through the blood, urine, saliva, and feces of infected dogs. So, when outbreaks of this deadly disease occur in shelters and kennels, the results are devastating.

In rare cases, dogs develop circulatory collapse and fall into a coma after 24 to 48 hours of suffering ICH. In acute cases, the disease is characterized by a high fever, increased heart rate, blood clotting problems, abdominal pain, enlarged tonsils, and bruising in the mouth. Severely affected dogs may develop brain damage that causes seizures, partial paralysis, head pressing, and circling. Dogs with the acute form of ICH either recover or die within two weeks. Finally, the chronic form results in hepatic failure and death weeks or months after the initial infection.

10. Kennel Cough

Kennel cough is the name of several upper respiratory infections in dogs. While not usually deadly, kennel cough can become fatal in rare cases. The causative agents include Bordetella bronchiseptica, canine parainfluenza virus, and canine coronavirus. Kennel cough is highly contagious. It is easily spread from one dog to another, making it a huge problem in kennels and shelters across the USA. When a dog coughs, the causative agent becomes airborne and spreads rapidly to other dogs. The disease can also be spread through dog toys, blankets, and other shared objects.

In most cases, kennel cough causes a dry cough, vomiting, and retching. In severe cases, however, dogs may develop fever, depression, and emaciation. While these causative agents are not normally deadly by themselves, the secondary infections can be. Secondary infections from Streptococcus, Pasteurella, and Pseudomonas can quickly lead to pneumonia, sepsis, and lung collapse.

kennel cough in dogs
Kennel cough can be deadly.

11. Leptospirosis

When treated by a vet, leptospirosis has a survival rate of 80 to 90 percent. This gives the disease a fatality rate of 10 to 20 percent. While these statistics may not sound concerning, it should be noted that clinical signs of leptospirosis can be mild or extreme. The mild form is most common, but the severe form is extremely deadly. For this reason, leptospirosis is one of the most deadly dog diseases on our list.

In severe cases, leptospirosis causes organ failure, internal bleeding, and death. This is because the bacterium infects a dog’s major organs and damages them. Thus, the prognosis in these cases is guarded. With the overwhelming damage to the organs, some dogs rapidly deteriorate and die despite receiving treatment.

12. Fungal Diseases

Some fungal diseases are extremely deadly and difficult to diagnose. Geotrichosis is a rare and often fatal disease. Geotrichum candidum is a fungus of soil and decaying organic. The signs of infection may include coughing, poor appetite, increased thirst, difficulty swallowing, and jaundice. Histoplasmosis is another potentially fatal fungal disease. Found in river valleys, this fungus infects the lungs, lymph nodes, and gastrointestinal tract of dogs. Similar to geotrichosis, the signs of histoplasmosis are non-specific. The signs include diarrhea, weight loss, coughing, and difficulty breathing. Sudden infection can cause death within two to five weeks.

There are plenty of dangers lurking out there for your dog. But, by arming yourself with the knowledge of the most deadly dog diseases, you can help to keep your pooch safe from harm.

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