Updated September 25, 2026. Fact-checked against veterinary sources; review by a licensed veterinarian is in progress. See our editorial policy.
Quick answer: Some parasites can seriously harm dogs and shorten their lives if untreated. Heartworm disease damages the heart and lungs and can be fatal. Intestinal worms can cause severe illness and even death in puppies. Tick-borne diseases can affect joints, blood, and kidneys. Fortunately, these risks are largely preventable with year-round veterinary preventives and regular testing.
Heartworm disease
- Spread by mosquitoes
- Worms live in the heart and lung vessels, causing lasting damage
- Signs include cough, tiring easily, weight loss, and a swollen belly
- Treatment is possible but lengthy and risky. Prevention is simple
Intestinal worms
- Heavy roundworm or hookworm infections can cause anemia, poor growth, and death in puppies
- In adults, they cause weight loss, diarrhea, and poor coat
Tick-borne diseases
- Lyme disease, ehrlichiosis, anaplasmosis, and others
- Can cause joint pain, fever, bleeding problems, and kidney damage
Fleas
- Cause allergies and skin infections
- Heavy infestations can cause anemia in small or young dogs
- Transmit tapeworms
Protecting your dog
- Year-round heartworm, flea, and tick prevention
- Yearly heartworm and fecal tests
- Deworming puppies on schedule
Sources
- Companion Animal Parasite Council (CAPC): General guidelines for dogs
- American Heartworm Society: Canine heartworm guidelines
- Merck Veterinary Manual: Gastrointestinal parasites of small animals
This article is for general education and is not a substitute for care from your own veterinarian. Learn about The Pet Vet and our editorial policy.