How do dogs get worms?

Worms are internal parasites that can cause serious illness and even death in dogs if left untreated. Some can also be transferred to humans. The good news: they're treatable and preventable. Here's what you need to know.

Types of Worms and How to Identify Them

Heartworms

Transmitted by infected mosquitoes, heartworms (Dirofilaria immitis) travel to the dog's heart and lungs, where they can grow large enough to restrict blood flow — potentially fatal. Symptoms often don't appear until 6–8 months after infection and may include coughing, fatigue, decreased appetite, weight loss, abdominal fluid, or heart failure. Contact your vet immediately if you notice these signs.

Roundworms

Contracted by eating infected soil, stool, or rodents, roundworms hatch in the intestines and reproduce continuously. They can be transmitted to humans. Signs include weight loss, diarrhea, mucous or blood-flecked stool, vomiting, abdominal fluid, and poor coat quality. Roundworms may be visible in stool — off-white or tan, spaghetti-like in appearance. Always examine your dog's stool when picking it up.

Tapeworms

Usually contracted from infected fleas or rodents, tapeworms live in the intestines and shed egg-containing segments through stool. Look for white segments (quarter- to half-inch long) in stool or around the anal area. Dry segments resemble sesame seeds or grains of rice.

Hookworms

Hookworms can enter dogs through ingestion of contaminated matter or through the skin. They consume blood and can cause diarrhea, weight loss, poor coat quality, dehydration, and pale mucous membranes. Too small to see with the naked eye — diagnosis requires a microscopic stool exam. Humans can contract hookworms through skin contact, so notify your physician if your dog is infected.

Whipworms

Contracted through contaminated soil or stool, whipworms live in the large intestine. Also microscopic — identified via stool exam. Signs include diarrhea, weight loss, and blood-tinged or mucous-covered stools.

How to Treat and Prevent Worms

See Your Vet

If you suspect worms, schedule a vet appointment immediately. Your vet will perform a stool exam and prescribe the appropriate treatment based on the worm type. Over-the-counter dewormers are often ineffective — prescription treatment is usually necessary. Roundworms require two dewormings 10–21 days apart; hookworms may require hospitalization if blood loss is significant.

Treat Your Yard

Fleas, ticks, and mosquitoes — all potential parasite carriers — are most active in warmer months. Treating your yard reduces exposure risk. See our guide on protecting your dog from ticks in the yard for tips.

Use Preventive Medication

Routine flea, tick, and heartworm preventives are essential. Ask your vet for the right products for your dog's age and weight. Routine dewormers can also help — available in injectable, liquid, or pill form depending on your dog's needs.

Schedule Regular Vet Visits

Most dogs should have two annual exams with stool analyses. Dogs with a history of parasites may need more frequent checkups. Early detection makes treatment far simpler and more effective.

For more on keeping your dog safe from outdoor hazards, see our guides on tick prevention and protecting your dog in winter.