Dogs encounter parasites through more than one route. Some are swallowed from contaminated soil or stool, others arrive through fleas or mosquitoes, and some are passed from a mother to her puppies. Because the exposure route and biology differ, preventing one parasite does not automatically prevent every other one.
How dogs pick up common parasites
Roundworms and hookworms: eggs or larvae in contaminated environments can infect dogs, and some puppies acquire parasites from their mothers. Whipworms: dogs may ingest infective eggs from contaminated ground. Tapeworms: some species spread when a dog swallows an infected flea; others have different life cycles. Giardia: may be acquired from contaminated water or environments. Heartworms: are transmitted by infected mosquitoes, rather than by touching another dog.
Fleas, ticks and mites are external parasites. Ticks can also transmit infectious agents, and some mites spread through close contact. Each group has different diagnostic and treatment needs.
Can a dog have worms without symptoms?
Yes. A normal appearance and absence of visible worms do not rule out infection. Some dogs develop diarrhea, weight loss, poor growth or a dull coat, while others have few signs. Hookworm infections can cause anemia, particularly in young dogs. A stool test helps the veterinarian identify relevant intestinal parasites, though a repeat or different test may sometimes be needed.
Which symptoms need prompt care?
Arrange a veterinary examination for persistent diarrhea, weight loss, visible worms, excessive scratching or suspected exposure. Bloody stool with weakness, pale gums, repeated vomiting, collapse or breathing difficulty deserves urgent or emergency care. Puppies can be more seriously affected by dehydration and anemia.
Prevention that matches the risk
The Companion Animal Parasite Council’s April 2025 guidance emphasizes year-round broad-spectrum parasite control and routine testing based on age and exposure. Its recommendations include at least four fecal examinations during the first year of life and at least twice-yearly fecal testing in healthy adults, with adjustments for individual circumstances.
- Talk to your veterinarian about heartworm, flea, tick and intestinal parasite coverage in each prescribed product.
- Remove stool from yards and public spaces promptly and wash hands after handling waste.
- Limit scavenging and consumption of prey or feces.
- Review protection before travel, boarding or exposure to different environments.
Why home remedies are not a substitute
Garlic, pumpkin seeds and herbs are not proven universal dewormers. Some can cause adverse effects. Parasite medicines vary in their targets, and the right product depends on a diagnosis or preventive plan. See our guide to risks of home parasite remedies for details.
What to ask at a routine veterinary visit
Ask which organisms are common in your area, which tests the dog needs, whether the current prevention covers ticks and heartworms as well as intestinal parasites, and when treatment or testing should be repeated. Keep a record of medication product names instead of assuming “dewormed” means fully protected.
References: CAPC: General Guidelines for Dogs and Cats; CAPC: parasite-specific guidance.
Educational information only. Veterinary advice is needed to diagnose parasite infections and select treatment.
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.