Common Dog Diseases | Symptoms, Prevention & Treatment Guide

*Disclaimer: The following information is for reference only. If your dog shows one or more of these symptoms, please consult a veterinarian immediately. Do not delay treatment.

Dogs are our most loyal companions, and as responsible pet owners, understanding common dog diseases and their warning signs is crucial. Early detection and prompt veterinary care can significantly improve treatment outcomes. This comprehensive guide covers the symptoms, causes, prevention methods, and treatment options for various canine health conditions to help you protect your beloved pet.

Parasitic Diseases in Dogs

Ticks

Dog ticks are among the most common external parasites in Hong Kong, particularly when dogs spend time outdoors in grassy areas or country parks. Ticks attach to a dog's skin to feed on blood, causing skin irritation and potentially transmitting serious blood-borne diseases such as Ehrlichiosis and Babesiosis, which can lead to acute anemia and even death.

Symptoms:

• Visible blood-sucking parasites attached to the skin (ranging from sesame seed to pea size)
• Red, swollen, or inflamed skin at attachment sites
• Anemia symptoms: pale gums, weakness, lethargy
• Fever and decreased appetite
• Enlarged lymph nodes
• Severe cases may show jaundice and bleeding tendencies

Prevention: Regular use of tick prevention products is the most effective preventive measure, including topical spot-on treatments (such as Frontline, NexGard), tick collars, or oral preventatives. Thoroughly check your dog's entire body after outdoor activities, especially ears, between toes, armpits, and groin areas. Avoid taking dogs into areas with dense vegetation.

Treatment: Remove ticks using specialized tick removal tools to ensure the mouthparts are completely extracted. If your dog has contracted tick fever, antibiotic treatment is required, and severe anemia cases may need blood transfusions. Early treatment has a good prognosis; delayed treatment can be fatal.

Fleas

Dog fleas are the most common external parasites. They feed on your dog's blood, then jump into the environment to mate and lay eggs. A single flea can lay up to 50 eggs per day, leading to rapid population growth. Flea saliva contains allergenic substances that commonly cause Flea Allergy Dermatitis (FAD), resulting in intense itching.

Symptoms:

• Frequent scratching and biting at the body
• Red, inflamed skin and hair loss (especially on lower back and tail base)
• Visible small black specks on skin (flea dirt/feces)
• Restlessness and agitation
• Severe infestations can cause anemia
• Possible tapeworm infection (fleas are intermediate hosts for tapeworms)

Prevention: Use flea prevention products year-round, including topical treatments, oral medications, or flea collars. Regularly wash your dog's bedding and blankets. Vacuum your home frequently, especially carpets, sofa crevices, and other areas where flea eggs may hide.

Treatment: Use vet-recommended flea treatment products on your dog. Simultaneously, thoroughly clean the home environment using environmental insecticide sprays on carpets and furniture. Since the flea life cycle can span several months, continue prevention for at least 3 months to completely eliminate the infestation.

Heartworm Disease

Canine heartworm disease is a potentially fatal parasitic disease transmitted through mosquito bites. After heartworm larvae enter a dog's body via mosquito, they gradually develop into adult worms up to 30cm long, residing in the right ventricle and pulmonary arteries, severely affecting heart and lung function. Hong Kong's humid, mosquito-prone climate makes dog heartworm infection risk considerably high.

Symptoms:

• Early stages may show no obvious symptoms
• Lethargy and fatigue
• Reduced exercise tolerance, becoming winded with minimal activity
• Persistent cough, severe cases may cough blood
• Difficulty breathing
• Weight loss
• Abdominal swelling (ascites)
• Congestive heart failure
• Sudden death in severe cases

Prevention: Prevention is far more important than treatment! Monthly heartworm preventative medication is the most effective prevention method, with various oral or topical products available. A heartworm test is recommended before starting prevention to confirm your dog is not already infected. Continue prevention year-round without interruption.

Treatment: Heartworm treatment is high-risk and expensive. Treatment requires injection of adulticide medication (Melarsomine), during which dogs must strictly limit activity for several weeks, as dead worms can cause vascular blockage and embolism. Some severe cases may require surgery to remove heartworms. Treatment success rates depend on the severity of infection.

Skin Diseases in Dogs

Sarcoptic Mange (Scabies)

Dog scabies is a highly contagious skin disease caused by Sarcoptes scabiei mites, which can spread to other animals and even humans. These mites burrow into the skin's surface layer, digging tunnels to lay eggs and causing intense itching. Infection typically starts on ear edges, elbows, and abdomen, and will spread throughout the body if untreated.

Symptoms:

• Intense itching with almost constant scratching
• Hair loss in affected areas
• Crusty, thickened skin
• Red, inflamed skin
• Secondary bacterial infections from scratching
• Pus formation and foul odor in infected areas
• Crusting on ear margins is a classic sign

Prevention: Avoid contact with infected animals. Quarantine and examine new dogs before introducing them to your household. Maintain a clean living environment for your dog. Some flea and tick prevention products also protect against scabies mites.

Treatment: Your vet will prescribe mite-killing medications, either as medicated baths, topical treatments, or oral medication (such as Ivermectin). Treatment typically takes 4-6 weeks. All animals in the household should be treated simultaneously. Thoroughly clean and disinfect your dog's bedding and living environment.

Demodectic Mange (Demodex)

Dog demodectic mange is caused by Demodex canis mites. These mites normally exist in dog skin follicles, but when a dog's immune system is weakened, the mites overpopulate and cause skin disease. Puppies and immunocompromised dogs are most susceptible. Demodectic mange is not contagious to humans or other animals.

Symptoms:

• Localized form: mild patchy hair loss on face, around eyes, and mouth corners
• Generalized form: hair loss spreads across the entire body
• Red, crusty skin
• Secondary bacterial infection causing pyoderma
• Thickened skin with pigmentation changes
• Foul odor
• Usually not very itchy (unless secondary infection present)

Treatment: Localized forms in puppies often resolve spontaneously. Generalized forms require longer treatment, including oral mite-killing medications (such as Ivermectin or Isoxazoline-class drugs), medicated baths, and antibiotics for secondary bacterial infections. Regular skin scrapings are needed during treatment to monitor progress.

Infectious Diseases in Dogs

Rabies

Rabies is one of the most deadly dog infectious diseases, transmissible to humans and other animals through infected animal saliva. The virus attacks the central nervous system, and once symptoms appear, it is almost 100% fatal. Hong Kong law requires all dogs to be vaccinated against rabies.

Symptoms:

• Behavioral changes (gentle dogs becoming aggressive or vice versa)
• Pupils dilated in early stages, constricted in later stages
• Changes in bark/vocalization
• Progressive throat paralysis
• Dropped jaw, inability to close mouth
• Excessive drooling
• Hydrophobia (fear of water)
• Loss of coordination, unsteady gait
• Eventually paralysis, seizures, and death

Prevention: Regular rabies vaccination is the only effective prevention method. Hong Kong requires dogs to receive their first vaccination at 5 months of age, with boosters every 3 years thereafter. Avoid contact with wildlife or stray animals.

Treatment: There is currently no effective treatment for rabies. Once symptoms appear, the fatality rate approaches 100%. Prevention is the only solution.

Canine Distemper

Canine distemper is a highly contagious viral disease that primarily attacks a dog's respiratory, digestive, and nervous systems. Puppies and unvaccinated dogs are most susceptible, with mortality rates exceeding 50%. This is one of the most serious viral infections in dogs.

Symptoms:

• High fever (may reach 39.5-41°C/103-106°F)
• Loss of appetite and lethargy
• Increased eye discharge, purulent ocular secretions
• Runny nose, nasal discharge progressing from clear to thick
• Coughing and difficulty breathing
• Vomiting, diarrhea, bloody stool
• Hardening of paw pads and nose (hard pad disease)
• Later stage neurological symptoms: seizures, muscle twitching, epileptic fits
• Loss of coordination, paralysis

Prevention: Vaccination with the DHPP vaccine (which includes distemper) is the most effective prevention. Puppies should begin vaccination at 6-8 weeks of age, with boosters every 3-4 weeks until 16 weeks old, then annually or every 3 years thereafter. Avoid contact with dogs of unknown origin or sick dogs.

Treatment: There is no specific antiviral medication for canine distemper. Treatment is primarily supportive, including IV fluids, antibiotics for secondary infections, anti-vomiting and anti-diarrheal medications, and anti-seizure drugs. Dogs that recover may have permanent neurological damage.

Canine Parvovirus (Parvo)

Canine parvovirus is an extremely dangerous dog gastrointestinal infection, primarily transmitted through contact with contaminated feces. The virus attacks rapidly dividing cells, including intestinal lining and bone marrow, causing severe gastroenteritis and immune system damage. Unvaccinated puppies have mortality rates up to 90%.

Symptoms:

• Intermittent vomiting, progressively worsening
• Complete loss of appetite
• Mild fever or low body temperature
• Severe depression
• Severe diarrhea, feces pale orange or gray
• Distinctive foul-smelling feces
• Bloody stool, projectile watery diarrhea
• Severe dehydration
• Abdominal pain
• Dramatic white blood cell count drop

Prevention: DHPP vaccination is key to preventing canine parvovirus. Puppies should avoid public places or contact with dogs of unknown origin until vaccination series is complete. Parvovirus is extremely hardy in the environment; bleach solution is required for thorough disinfection of contaminated areas.

Treatment: There is no medication to kill the virus; treatment focuses on aggressive supportive care. Dogs require hospitalization for IV fluids to correct dehydration, anti-nausea medication, antibiotics to prevent secondary infections, and nutritional support. Hospital stays typically last 5-7 days, and treatment costs are substantial. Early treatment can improve survival rates to 70-90%.

Infectious Canine Hepatitis

Infectious canine hepatitis is caused by Canine Adenovirus Type 1 (CAV-1), primarily transmitted through contact with infected dogs' feces, urine, or saliva. The virus mainly attacks the liver, kidneys, and eyes, with severe cases potentially fatal within 24-48 hours. This is another dog infectious disease requiring serious prevention.

Symptoms:

• Fever and elevated body temperature
• Loss of appetite and lethargy
• Vomiting, diarrhea, or soft stool
• Abdominal pain, resistance when palpated
• Enlarged tonsils
• Swollen lymph nodes
• Jaundice (yellowing of skin and whites of eyes)
• "Blue eye" during recovery (corneal edema appearing bluish-white)
• Bleeding tendencies in severe cases

Prevention: The DHPP vaccine includes the canine adenovirus component; regular vaccination provides effective protection. Avoid contact with sick dogs and their excretions.

Treatment: No specific treatment exists; supportive care is the mainstay, including IV fluids, liver-protective medications, antibiotics for secondary infections, and blood transfusions if bleeding tendencies occur. Survival rate is approximately 10-30%; survivors may become carriers, shedding virus for months.

Leptospirosis

Canine leptospirosis is a serious disease caused by Leptospira bacteria, transmitted through contact with contaminated water sources, soil, or urine from infected animals. This is a zoonotic disease – both dogs and humans can be infected. Infection risk is higher during Hong Kong's rainy season.

Symptoms:

• High fever
• Loss of appetite and lethargy
• Increased eye discharge
• Vomiting and diarrhea (gastroenteritis symptoms)
• Liver inflammation and jaundice (yellowing skin)
• Dark, concentrated urine (brownish or greenish-brown)
• Kidney failure
• Bleeding tendencies: subcutaneous and mucosal hemorrhage
• Enlarged lymph nodes and spleen
• Muscle pain and stiff movement

Prevention: Vaccination against leptospirosis (usually included in annual vaccines). Prevent dogs from drinking or contacting standing water or sewage. Avoid areas with standing water after rain. Control rodent populations around your home.

Treatment: Early antibiotic treatment (such as Doxycycline or Penicillin) has good results. Severe cases require hospitalization, including IV fluids, dialysis (for kidney failure), and supportive care. Recovered dogs may continue shedding bacteria for months, requiring hygienic precautions.

Kennel Cough (Infectious Tracheobronchitis)

Kennel cough is a highly contagious respiratory disease caused by multiple pathogens, including Bordetella and canine parainfluenza virus. It's common in places where dogs congregate, such as pet shops, dog parks, and boarding facilities. While usually not fatal, it can be more serious in puppies and senior dogs.

Symptoms:

• Sudden onset of strong, dry cough sounding like "honking"
• Coughing may be followed by gagging or producing white foam
• Body temperature usually normal
• Appetite and energy often unaffected
• May develop fever if secondary bacterial infection occurs
• Runny nose
• Severe cases can progress to pneumonia

Prevention: Vaccination against Bordetella and canine parainfluenza. Ensure vaccines are current before your dog visits boarding facilities or groomers. Avoid contact with coughing dogs.

Treatment: Mild cases typically resolve within 1-3 weeks on their own. Vets may prescribe cough suppressants for symptom relief; antibiotics are needed if secondary bacterial infection occurs. Allow your dog to rest fully and avoid irritating the trachea (use a harness instead of collar).

Internal Organ Diseases in Dogs

Gastrointestinal Disease

Dog gastrointestinal disease is one of the most common health problems in dogs, caused by various factors including dietary indiscretion, bacterial or viral infections, parasites, food allergies, and foreign body ingestion. Improperly managed GI issues can lead to dehydration, malnutrition, and other serious consequences.

Symptoms:

• Vomiting (food, bile, or foam)
• Diarrhea (loose or watery stool)
• Blood or mucus in stool
• Straining to defecate or inability to pass stool (constipation)
• Weight loss
• Decreased appetite
• Abdominal bloating or pain when touched
• Increased intestinal sounds
• Dehydration (decreased skin elasticity)

Prevention: Maintain regular feeding schedules and avoid sudden food changes. Don't feed human food or spoiled food. Deworm regularly. Prevent your dog from eating things off the ground. Keep water and food bowls clean.

Treatment: Mild GI upset may be managed by fasting for 12-24 hours to rest the digestive system, then feeding easily digestible food. Severe vomiting or diarrhea requires veterinary attention, potentially including anti-nausea medication, anti-diarrheal medication, IV fluids, and further diagnostics to identify the underlying cause.

Liver Disease

Dog liver disease can result from various causes, including infections, toxins, medication side effects, tumors, and congenital problems. The liver is a vital metabolic organ responsible for detoxification, protein production, and energy storage; compromised liver function affects overall health.

Symptoms:

• Loss of appetite
• Weight loss
• Increased water intake and urination
• Vomiting and diarrhea
• Abdominal swelling (ascites)
• Jaundice (yellowing of skin, whites of eyes, gums)
• Lethargy and listlessness
• Neurological symptoms (hepatic encephalopathy in severe liver disease)
• Bleeding tendencies
• Dark-colored urine

Prevention: Prevent dogs from accessing toxic substances (certain plants, chemicals, human medications). Maintain a balanced diet and avoid high-fat foods. Regular health check-ups can detect liver problems early.

Treatment: Treatment depends on the underlying cause. Options may include prescription liver diet, liver-protective medications, antibiotics (if infection present), diuretics (if ascites present), and supportive therapy. Some liver diseases can be well managed if detected early.

Kidney Failure

Dog kidney failure can be acute or chronic. Acute kidney failure is usually caused by toxins, infections, or urinary obstruction – it has rapid onset but may be reversible with prompt treatment. Chronic kidney disease is more common in senior dogs; it's irreversible but can be slowed with proper management.

Symptoms:

• Decreased appetite
• Excessive thirst and dramatically increased water intake
• Frequent urination or decreased urine output
• Rough, dull coat
• Lethargy and fatigue
• Vomiting
• Mouth ulcers and ammonia-smelling breath
• Weight loss
• Anemia (pale gums)
• Seizures in advanced stages

Prevention: Ensure your dog has access to plenty of clean drinking water. Avoid exposure to kidney-toxic substances (grapes, raisins, certain medications). Middle-aged and senior dogs should have regular blood tests to monitor kidney function. Promptly treat urinary tract infections.

Treatment: Acute kidney failure requires aggressive IV fluid therapy and supportive treatment; some cases can recover. Chronic kidney disease treatment aims to slow progression and maintain quality of life, including prescription kidney diet, phosphate binders, erythropoietin (if anemic), blood pressure control, and subcutaneous fluid therapy.

Heart Disease

Dog heart disease is quite common in middle-aged and senior dogs. Small breeds are more prone to mitral valve disease, while large breeds more commonly develop dilated cardiomyopathy. Heart disease progressively affects the heart's pumping ability, eventually leading to heart failure.

Symptoms:

• Decreased appetite
• Reduced stamina and easy fatigue
• Coughing (especially at night or after exercise)
• Rapid breathing and difficulty breathing
• Exercise intolerance
• Abdominal swelling (ascites)
• Pale or bluish mucous membranes
• Weight loss
• Fainting episodes

Prevention: Maintain a healthy weight; avoid obesity which strains the heart. Have regular health check-ups including cardiac auscultation by your vet. Medium to large breed dogs may consider periodic cardiac ultrasound examinations. Avoid excessive strenuous exercise.

Treatment: Heart disease cannot be cured but can be controlled with medication. Common medications include diuretics, ACE inhibitors, positive inotropes (such as Pimobendan), and anti-arrhythmic drugs. Combined with a low-sodium diet and moderate exercise. Regular follow-up appointments to monitor the condition are essential.

Joint Disease

Dog joint disease is a common problem in middle-aged and senior dogs, including osteoarthritis, hip dysplasia, and patellar luxation. Large breeds and overweight dogs are more susceptible to joint problems. Joint disease significantly impacts a dog's mobility and quality of life.

Symptoms:

• Joint stiffness after activity
• Difficulty standing, especially after rest
• Symptoms improve with rest
• Decreased activity level, lagging behind on walks
• Joint swelling
• Obvious pain when joints are touched
• Constant licking of affected joints
• Limping
• Decreased appetite
• Behavior changes (reluctance to jump or climb stairs)

Prevention: Maintaining a healthy weight is key to preventing joint problems. Avoid over-exercising or excessive jumping in puppies. Provide a comfortable resting environment. Large breed dogs can begin joint supplements (such as glucosamine, chondroitin) from a young age. Choose quality dog food to ensure balanced nutrition.

Treatment: Treatment includes weight management, moderate exercise, non-steroidal anti-inflammatory drugs (NSAIDs), joint supplements, physical therapy, and acupuncture. Severe cases may require surgery (such as hip replacement). Providing non-slip mats and low beds helps reduce strain during daily activities.

When Should You Take Your Dog to the Vet?

The following are warning signs requi