Dogs are susceptible to a wide range of infectious diseases, many of which are preventable through vaccination, and non-infectious conditions that affect virtually every organ system. This comprehensive reference covers the most common dog diseases owners need to know, organized by category, with symptoms and urgency guidance for each.
Highly Contagious Infectious Diseases
These viral and bacterial diseases spread readily between dogs and range from treatable to life-threatening. Vaccination is the most effective prevention for the viral diseases listed below.
Canine Parvovirus (CPV-2)
One of the most dangerous infectious diseases in dogs, parvovirus attacks the gastrointestinal lining and immune system. It spreads via contact with infected feces and can survive in the environment for over a year. Symptoms: Severe bloody diarrhea, profuse vomiting, extreme lethargy, fever or hypothermia, rapid dehydration, collapse. Primarily affects unvaccinated puppies 6 weeks to 6 months old, though unvaccinated adults are also susceptible. Mortality in untreated cases exceeds 90%. With aggressive veterinary treatment (IV fluids, anti-nausea medication, antibiotics to prevent secondary infection), survival rates reach 70-90%.
Canine Distemper
A multi-systemic viral disease affecting the respiratory, gastrointestinal, and central nervous systems. Symptoms progress in stages: Initial fever, discharge from eyes and nose, coughing, and vomiting give way to neurological signs: seizures, muscle twitching, paralysis, and behavioral changes. Surviving dogs often suffer permanent neurological damage. No specific antiviral treatment exists; supportive care manages symptoms. Vaccination is highly effective.
Canine Infectious Respiratory Disease Complex (Kennel Cough)
A multifactorial upper respiratory infection caused by several pathogens, most commonly Bordetella bronchiseptica bacteria and canine parainfluenza virus. Spreads via airborne droplets in kennels, dog parks, and grooming facilities. Symptoms: Harsh, honking cough (often described as something stuck in the throat), gagging, retching, nasal discharge. Most dogs recover in 1 to 3 weeks without treatment. Severe or persistent cases, particularly in puppies or immunocompromised dogs, can progress to pneumonia. Bordetella vaccine (intranasal or injectable) is recommended for socially active dogs.
Leptospirosis
A bacterial disease (genus Leptospira) transmitted through contaminated water, urine of infected wildlife, and direct contact with infected animals. Found worldwide and increasingly common in urban and suburban environments. Symptoms: Sudden fever, muscle pain, vomiting, excessive thirst and urination, jaundice (yellow tinge to skin and eyes), kidney and liver failure in severe cases. Antibiotic treatment (doxycycline) is effective when started early. Vaccination covers the four most common serovars.
Parasitic Diseases
Heartworm Disease (Dirofilaria immitis)
Transmitted by mosquitoes, heartworm larvae develop into adult worms (up to 30cm long) living in the heart and pulmonary arteries. The American Heartworm Society reports that heartworm disease has been diagnosed in all 50 US states. Symptoms (early): Mild persistent cough, reduced exercise tolerance. Symptoms (advanced): Severe coughing, difficulty breathing, cardiovascular signs, caval syndrome (sudden cardiovascular collapse). Treatment with melarsomine exists but is expensive, prolonged, and carries risk. Monthly prevention with ivermectin, milbemycin, or moxidectin-based products is vastly preferable.
Intestinal Parasites
- Roundworms (Toxocara canis): Most puppies are born with roundworms or acquire them through nursing. Symptoms: pot-bellied appearance, poor coat, failure to thrive, visible worms in vomit or feces. Zoonotic - can infect humans, particularly children.
- Hookworms (Ancylostoma caninum): Blood-feeding parasites causing anemia, dark or bloody diarrhea, and weight loss. Can penetrate human skin causing cutaneous larva migrans.
- Giardia (Giardia duodenalis): Protozoal parasite causing foul-smelling, watery diarrhea. Spread via contaminated water. Responds to metronidazole or fenbendazole treatment.
- Tapeworms: Acquired by eating infected fleas or prey animals. Segments visible as rice-grain-sized pieces around the anus or in feces. Praziquantel treatment is highly effective.
Endocrine and Metabolic Diseases
Hypothyroidism
Deficient thyroid hormone production - the most common endocrine disorder in dogs. Most common in middle-aged to older dogs, particularly Golden Retrievers, Dobermans, Irish Setters, and Cocker Spaniels. Symptoms: Weight gain without increased appetite, lethargy, cold intolerance, hair loss (symmetrical, non-itchy bilateral alopecia, particularly on the trunk), thickened or "tragic" facial expression, dry coat. Treated with daily oral levothyroxine - prognosis is excellent with medication.
Cushing's Syndrome (Hyperadrenocorticism)
Excessive cortisol production, most commonly caused by a pituitary tumor (pituitary-dependent, 85% of cases) or an adrenal tumor. Affects middle-aged to older dogs. Symptoms: Dramatic increase in thirst and urination, increased appetite, pot-bellied appearance (muscle wasting and fat redistribution), bilateral hair loss, darkened and thickened skin (calcinosis cutis), panting, recurrent skin or urinary infections. Diagnosed via ACTH stimulation or low-dose dexamethasone suppression tests.
Diabetes Mellitus
Insufficient insulin production (Type 1 analog) or insulin resistance (Type 2 analog) leading to impaired glucose metabolism. More common in intact females and middle-aged to older dogs. Symptoms: Marked increases in thirst and urination, increased appetite with concurrent weight loss, cloudy eyes (diabetic cataracts), recurring urinary tract infections. Managed with twice-daily insulin injections, consistent diet, and regular glucose monitoring.
Orthopedic and Musculoskeletal Conditions
Canine Hip Dysplasia (CHD)
Abnormal hip joint development causing laxity, secondary osteoarthritis, and chronic pain. Strongly heritable. Responsible breeding programs include OFA or PennHIP screening. Most prevalent in German Shepherds, Labradors, Golden Retrievers, Rottweilers, and Saint Bernards. Symptoms: Bunny-hopping gait, reluctance to rise, exercise intolerance, swaying hindquarters, muscle atrophy over the hindquarters. Management includes weight optimization, controlled exercise, joint supplements, NSAIDs, and in severe cases, surgical options (TPO, FHO, total hip replacement).
Intervertebral Disc Disease (IVDD)
Herniation or extrusion of the intervertebral disc material compressing the spinal cord. Chondrodystrophic breeds (Dachshunds, Beagles, Corgis, Shih Tzus, Basset Hounds) are at dramatically elevated risk due to early disc degeneration. Symptoms range by severity: Neck or back pain and muscle spasm, knuckling of paws, paraparesis (weakness in hindlimbs), to complete paralysis with loss of pain sensation. Treatment ranges from strict rest for mild cases to emergency surgery for acute paralysis. Outcome is significantly better when treated before complete loss of pain sensation occurs.
Common Cancers in Dogs
Cancer is the leading cause of death in dogs over 10 years of age. Early detection is critical for treatment success.
- Lymphoma: Cancer of lymphocytes affecting lymph nodes, bone marrow, and organs. Most common canine cancer. Presents as painless, enlarged lymph nodes (often under the jaw, in front of the shoulders, behind the knees). Many forms respond well to multi-agent chemotherapy (CHOP protocol).
- Mast Cell Tumor (MCT): Skin tumor that can also affect internal organs. Highly variable behavior: some are benign, others aggressively malignant. Any skin lump in a dog warrants fine-needle aspiration at a minimum. Boxers, Bulldogs, and Pugs are at elevated risk.
- Osteosarcoma: Aggressive primary bone cancer, accounting for 85% of all canine bone tumors. Large and giant breeds (Great Danes, Saint Bernards, Rottweilers, Greyhounds) are disproportionately affected. Presents as focal lameness and bony swelling, most commonly at the distal radius or proximal humerus. Highly painful. Treated with amputation plus chemotherapy.
- Hemangiosarcoma: Malignant tumor of blood vessel cells, most commonly affecting the spleen, heart, and skin. Golden Retrievers and German Shepherds are at elevated genetic risk. Often presents without warning as sudden internal bleeding (pale gums, collapse, distended abdomen).
Preventable Diseases: The Core Vaccine Protocol
The American Animal Hospital Association (AAHA) recommends the following core vaccines for all dogs regardless of lifestyle: rabies (legally required in most jurisdictions), canine distemper virus, canine parvovirus, and canine adenovirus (hepatitis). Non-core vaccines recommended based on lifestyle and geography include Bordetella (kennel cough), leptospirosis, Lyme disease, and canine influenza. Discuss your dog's specific vaccination needs with your veterinarian annually.