Veterinary practitioners and pathologists are sometimes asked to examine animals that have been found dead but were considered healthy by their owners when last seen. Based on the postmortem findings, it has been established that the leading underlying cause of sudden and unexpected death of dogs is heart disease. In fact, in many cases, sudden death is regarded as heart-related if no other cause of death is apparent. Heart diseases may be genetic, hereditary, or they can develop as a result of an infection or tumor.
Dilated cardiomyopathy is the most common form of chronic disease of the heart muscle in dogs. Sudden death caused by ventricular tachyarrhythmia-fibrillation (the most serious cardiac rhythm disturbance) occurs before the onset of congestive heart failure in at least 25 – 30% of affected Dobermans.1
Subvalvular aortic stenosis is one of the most common congenital heart defects in dogs and is an inherited defect of Newfoundlands and Golden retrievers. It is the most common congenital cardiac disease in the Boxer breed. Although dogs with a mild form of the disease may have a normal lifespan, severely affected dogs may experience life-threatening arrhythmias, congestive heart failure, endocarditis and sudden death.2
Arrhythmogenic Right Ventricular Cardiomyopathy
Arrhythmogenic right ventricular cardiomyopathy (ARVC) seen in Boxers and Great Danes. Many dogs do not have clinical signs of the disease and are diagnosed only following the discovery of irregular heartbeat during a routine examination. Affected dogs are at high risk for sudden cardiac death.3
Bacteria endocarditis and myocarditis in dogs infected with Bartonella vinsonii bacteria, important cardiac pathogens both in animals and humans. Heart disease developing after the infection is usually of short duration and may frequently lead to sudden death.4
Myocarditis associated with Trypanosoma cruzi, causative agent of Chagas disease. Infected dogs may have no signs and die suddenly. No vaccine is available for humans or dogs.
Myocarditis associated with Canine parvovirus. Within an infected litter, 70% pups will die in heart failure by 8 weeks of age, and the remaining 30% will have pathological changes which may result in sudden death many months or even years later. The most dramatic manifestation of CPV-2 myocarditis is the sudden death in young pups usually about 4 weeks of age. The collapsed dying pup may have cold extremities, pale gums and show gasping respiration or terminal convulsions.5
Degenerative mitral valve disease (DMVD), the most common heart disease and cause of heart failure in dogs. It causes severe backflow of blood back into the heart and ultimately, sudden death for millions of dogs around the world.
Doberman Pinschers with dilated cardiomyopathy (DCM) are at high risk of sudden cardiac death.
Heartworm disease (canine cardiopulmonary dirofilariasis) is a severe and life-threatening disease that affects the right chambers of the heart. It is caused by several species of roundworms. When heartworm disease is caused by species of Dirofilaria, sudden death is rare but can occur as a consequence of heart failure, respiratory disorder, severe weakness, or large blood clots.
Heartworm disease (canine angiostrongylosis) caused by Angiostrongylus vasorum, commonly known as the “French heartworm.” The parasite infects the right side of the heart and the pulmonary arteries and their branches, with potentially severe consequences for the host, including bleeding, respiratory diseases that do not respond to antimicrobial therapy and heart failure. The accumulation of adult and larval parasites is accompanied by thrombus formation, local inflammation, weakness of the artery wall followed by rupture of the thoracic aorta and sudden death.6,7,10
Certain cancers and tumors can produce severe bleeding. Hemangiosarcoma is a rapidly growing, highly invasive variety of cancer, often located in the right atrium of the heart, the spleen, or both. When a tumor in the right atrium is the site of bleeding, blood accumulated in the pericardial sac creates compression of the heart (cardiac tamponade) and contributes to death. When a site of hemangiosarcoma in the spleen is the source of bleeding, blood pools in the abdomen and sudden death results from blood loss.
Bilateral Adrenocortical Carcinomas
An important underlying cause of sudden and unexpected death of dogs is toxicity.
Most common rodent control agents include: cholecalciferol, bromethalin, strychnine, and zinc phosphide. The less common types include Pyriminil, Red squill, thallium, arsenic, phosphorus, a-naphthyl-thiourea (ANTU), norbormide, barium, and sodium monofluoroacetate (compound 1080). The onset of rodenticide poisoning signs is so quick as to find a dog dead. The sudden death may be caused by sudden catastrophic bleeding into the heart, lungs, abdomen, or brain.
Envenomation and poisoning by terrestrial animals (both vertebrate and invertebrate). The cane toad has a highly toxic paratoid (salivary gland) secretion that is particularly toxic to dogs. The effects of poisoning are so severe that it may cause sudden death. Dogs have been reported to be especially sensitive to tarantula envenomation, and death is reported to occur in 30 – 120 min for most dogs. Phlogiellus and Selenocosmia genus spider bites were reported to kill 7 dogs often within 2 hours of envenomation.
Ticks in the genus Ixodes are well known for their ability to induce paralysis during and after feeding. Sudden death has been reported in dogs with paralysis caused by Australian tick who experienced neuromuscular paralysis and heart failure.
Another important cause of sudden and unexpected death of dogs is gastrointestinal disease. Gastric dilation volvulus (bloat), liver or gallbladder torsion (twisting that interrupts the blood supply to those organs), gastric rupture due to peritonitis, parvovirus enteritis (which can cause severe enough disease without premonitory signs) may all cause sudden death.
Salmonella bacteria are known to cause severe gastrointestinal disease in dogs. Blood poisoning by bacterial toxins and sudden death is especially common in young, immuno-compromised or old animals.
Acute hemorrhagic gastroenteritis caused by Clostridium perfringens bacteria. An infected dog may be bright, alert, responsive, eating and drinking, be in good health and have no history of vomiting or diarrhea. He may be up-to-date on vaccinations and die suddenly in a pool of bloody feces.
Infection with Streptococcus canis may lead to severe respiratory diseases, such as aspiration pneumonia, a potentially fatal condition.
Hemoplasma infection which causes acute anemia.
Other causes of a sudden and unexpected death of dogs worth mentioning are tracheal obstruction by a foreign body, epilepsy, and pancreatic disease.
In today’s world, the shift towards dogs as a companion rather than working animals has resulted in changes in breed characteristics with breeding being focused on the appearance rather than working or cognitive abilities. The development of the breeds has been associated with the increasing prevalence of a large number of genetic diseases. There are more than 80 disorders that are either directly or indirectly associated with the requirements of the published breed standards which can have a detrimental impact on the dog’s health and welfare. Artificial selection of dogs for specific skeletal and other characteristics skirts Darwinian natural selection. None are more dependent on human intervention than breeds of extreme skull shapes and size.
Artificial insemination and Caesarean deliveries are widespread practices in the world of animal husbandry, and frequently the propagation of dog breeds comes at a cost. For example, brachycephalic airway syndrome (BAS) is a respiratory condition common to flat-faced breeds like the:
and others of similar skull conformation. In extreme examples, the BAS sufferers are simply unable to breathe and often undergo painful and costly surgeries which may eventually result in aspiration pneumonia and sudden death.
Giant dog breeds are also susceptible to growth-related problems. These large dog breeds are also prone to other diseases, such as osteosarcoma and gastric dilation volvulus. Finally, it is widely recognized that the average lifespan of giant breed dogs is shorter than that of smaller breed dogs.13 Responsible breeders will do everything possible to make sure their dogs live a disease-free life.
Spirocerca lupi, the dog oesophageal nematode, causes a potentially fatal disease in domestic dogs, and is currently clinically diagnosed by coproscopy and oesophagoscopy. The parasites cause lung lesions which results in pneumonia. Sudden death has been reported to occur in 7% of dogs infected with Spirocerca lupi.
Hemotropic mycoplasmas (hemoplasmas) are small epicellular parasites that adhere to the erythrocytes of infected animals. They are the causative agents of infectious anemia in several mammalian species, including dogs and cats. Blood-sucking arthropods like fleas and ticks have also been suggested to be possible vectors, but their ability to transmit the infection has not yet been experimentally confirmed. A role for mites in the mechanical transmission of infection has been proposed for dogs. The clinical picture can range from asymptomatic infection to acute hemolytic anemia and can induce anorexia, lethargy, dehydration, weight loss and sudden death.
Degenerative Valve Disease
Degenerative valve disease (DVD) usually affecting the mitral valve is the most common heart disease in dogs being responsible for 75–80% of all heart disease. Eventually, in some dogs, heart failure or sudden death occurs. Small breeds are predisposed, but many studies have shown an unusually high incidence and an early onset in the Cavalier King Charles Spaniel (CKCS) in many different countries, with a mortality of 37% for CKCS under 10 years.
In the UK, the Cavalier King Charles Spaniel Club developed breeding guidelines. These suggested that any dog used for breeding should be at least 5 years old and free from an audible murmur consistent with degenerative mitral valve (DMVD) disease. Dogs over 2½ years could be used for breeding if their parents were over 5 years before they developed a murmur. The first analysis of the UK CKCS database suggests that the advice given to breeders is having an important effect in decreasing the incidence of the disease. It is important that testing of young dogs and the “over 5” are performed by cardiologists to detect quiet murmurs. (Source: Degenerative Valvular Disease in the Cavalier King Charles Spaniel: Results of the UK Breed Scheme 1991–2010)
Sudden death is known to occur in dogs with previously undiagnosed heart diseases, including various cardiomyopathies, subaortic stenosis, myocarditis, and others. A major cause is cardiac ion channel dysfunction (channelopathy). Abnormally prolonged QT interval predisposes to potentially fatal ventricular arrhythmias. An apparently normal dog may die suddenly after activity. Affected puppies also may die during activity. An enlarged heart has been found to be the most important and single significant marker to identify Doberman Pinschers with dilated cardiomyopathy carrying a high risk to die of this heart diseases. Also a rare cancer, myxoma ventricular tumor may cause sudden death in dogs.
- N J Summerfield et al – Efficacy of Pimobendan in the Prevention of Congestive Heart Failure or Sudden Death in Doberman Pinschers with Preclinical Dilated Cardiomyopathy
- Stern et al. – A Single Codon Insertion In PICALM Is Associated With Development Of Familial Subvalvular Aortic Stenosis In Newfoundland Dogs
- Oyama et al. – Arrhythmogenic Right Ventricular Cardiomyopathy In Boxer Dogs Is Associated With Calstabin2 Deficiency
- Breitschwerdt et al. – Bartonella vinsonii subsp. berkhoffii and Related Members of the Alpha Subdivision of the Proteobacteria in Dogs with Cardiac Arrhythmias, Endocarditis, or Myocarditis
- Nandi et al. – Canine Parvovirus: Current Perspective
- Rinaldi et al. – Angiostrongylus Vasorum: Epidemiological, Clinical And Histopathological Insights
- Simón et al. – Human and Animal Dirofilariasis: the Emergence of a Zoonotic Mosaic
- Schlegel et al. – Clostridium Perfringens Type A Fatal Acute Hemorrhagic Gastroenteritis In A Dog
- Hülsmeyer et al. – International Veterinary Epilepsy Task Force’s Current Understanding Of Idiopathic Epilepsy Of Genetic Or Suspected Genetic Origin In Purebred Dogs
- Mozzer et al. – Rupture Of The Thoracic Aorta Associated With Experimental Angiostrongylus Vasorum Infection In A Dog
- Olsen et al. – Causes Of Sudden And Unexpected Death In Dogs: A 10-year Retrospective Study.
- Hardy et al. – Venomous and Poisonous Australian Animals of Veterinary Importance: A Rich Source of Novel Therapeutics
- Farrell et al. – The Challenges Of Pedigree Dog Health: Approaches To Combating Inherited Disease