At the Animal Clinic of Billings and Animal Surgery Clinic, our veterinarians and support staff love helping to educate our clients about parasite detection and prevention methods in dogs. We take great pride in providing our canine patients in and around the Billings area with the best treatment protocols and highest standard of veterinary care to keep our patients as happy, healthy, and parasite free as they possibly can be.

How worms are contracted in dogs

Almost every dog is at risk of contracting worms at various points throughout their lives due to their high level of outdoor exposure, social behaviors, and natural curiosity to investigate everything they come across.

Common ways a dog can contract parasites or worms include:

  • Ingestion of the mother’s milk when nursing as a puppy
  • Via mosquito, flea, and tick bites
  • Ingestion of infected rodents, birds, reptiles and insects, or remnants of dead ones
  • Contact with contaminated feces or vomit
  • Contact with another dog or infected animal
  • Contact with a contaminated environment (including most outdoor areas)

Very severe medical problems can result from a dog contracting worms if the parasites are left untreated. Because of this, we recommend discussing worm prevention with one of our veterinarians and implementing a deworming protocol for your dog. During your de-worming consultation, one of our veterinarians will discuss what symptoms to watch for that may indicate a worm infection in your dog.

What types of worms and parasites affect dogs?

Intestinal parasites are among the most common types of worms contracted by dogs. The most common types of intestinal parasites in dogs in the US include:


Roundworms are the most commonly encountered intestinal worm in dogs. Roundworms can grow up to 3-5” long, and resemble a strand of cooked spaghetti. Roundworms burrow themselves into the intestinal tract of a dog and their eggs are shed in the dog’s stool. 

Roundworms can be transmitted to dogs while nursing from an infected mother, or if a dog comes into contact with another infected animal’s fecal matter in the environment. Eggs are able to survive and remain infective for extended periods of time in the environment. 

If your dog has roundworms that have had enough time to grow into adulthood, dead worms may be visible in your dog’s feces. If you notice worms of any kind in your dog’s feces, schedule an appointment with your veterinarian as soon as possible.

Because it is possible for a dog to be infected with roundworms even if no adult worms are visible in their stool, a veterinarian will typically perform a microscopic fecal exam to check for the presence of eggs, a more definitive way to diagnose an infection with this parasite. 

If diagnostic testing reveals the presence of roundworms in your dog, your veterinarian will prescribe one of several effective medications to eliminate the infection.  

It is important for all pet owners to be aware that roundworms can be transmitted to humans, in whom they can cause potentially life-threatening damage as they migrate through internal organs. Most human infections occur in babies and children who inadvertently ingest eggs from a contaminated environment.


Tapeworms can grow to lengths of eight inches and have a long and flat ⅛” segmented body. Dogs commonly contract tapeworms by ingesting a host carrying tapeworm eggs, like a flea or other insect. Tapeworms attach themselves to the inside wall of a dog’s small intestine with a sharp, hook-like mouth. Outdoor dogs have a greater risk of contracting tapeworms than inside dogs as contact with infected bugs or insect larvae such as fleas is the means of transmission.

Typically tapeworms are contracted via ingestion of eggs deposited on the skin by a flea as a dog engages in grooming behavior, or through direct ingestion of a flea while grooming.  

Tapeworms rob dogs of critical vitamins, minerals, and nutrients by feeding on the partially digested foods that are being broken down in the dog’s intestines. This is why it is extremely important to initiate an appropriate tapeworm treatment protocol immediately if you notice the presence of tapeworm segments, resembling small grains of rice, either in your dog’s stool or on the skin and fur around the anus.

If you notice any of these indicators, please contact your veterinarian immediately. We have extremely effective tapeworm treatments for dogs, but as with every medical condition, early detection and intervention go hand-in-hand with a better prognosis for a full recovery.


Hookworms, measuring less than 1 inch in length, are primarily found in the small intestines of infected canines, where they feed on the host’s blood. A dog can become infected through ingestion of microscopic larvae from a contaminated environment or from their mother’s milk. 

These larvae are also able to burrow directly through the skin and migrate to the intestine. Hookworms can cause life-threatening anemia in dogs of all ages, but are especially dangerous in puppies and dogs with chronic health conditions. 

Hookworm eggs are passed in the host dog’s feces, where they can spread to infect other animals and people as well. Hookworms are diagnosed by detecting eggs on a microscopic fecal exam. Several medications are effective in eliminating a hookworm infection.

It is important for all pet owners to be aware that hookworms can be transmitted to humans, in whom they can cause a very itchy and uncomfortable skin infection. While generally not life-threatening in humans, hookworms can cause significant distress and discomfort. 


Whipworms are transmitted via ingestion of eggs from a contaminated environment. Adult whipworms reside in a dog’s colon, where they cause inflammation which may result in bloody diarrhea, anemia, and weight loss. 

Because adults can’t grow much longer than a fourth of an inch, this parasite is usually not visible in an infected dog’s stool, so it must be diagnosed with a microscopic fecal exam by your vet. Whipworms have the potential to cause serious blood loss, especially in puppies and dogs with chronic health conditions. Several medications are effective in eliminating whipworm infections.


Heartworms live in the heart and large pulmonary arteries of infected dogs. A mosquito carrying heartworm larvae (picked up from feeding on an infected dog) transmits them to a dog through its bite. The transmitted heartworm larvae then take 6 full months to migrate throughout the dog’s body before finally anchoring themselves in the heart. 

Adult heartworms cause a partial obstruction of the flow of blood through the heart, which over time results in severely compromised heart and lung function. Heartworms are treatable if detected before they are able to cause irreversible damage to the heart and lungs. However, there is no treatment for dogs with advanced stages of heartworm, and the condition is fatal. 

Heartworms are easily preventable by giving a dog a chewable heartworm medication once a month for each month mosquitoes are present in their area. Heartworm testing and medication is a routine component of preventive veterinary care, and your veterinarian will inform you of when to test for heartworms and which heartworm preventatives are best for your dog.


Ringworm is a common skin disease found in dogs, humans, and many other animals. It’s caused by the growth of a fungus on the outer layer of the host’s skin that results in circular lesions and sores that form a ring shape. Ringworm infection doesn’t involve a worm at all, but rather it’s a fungal infection of the skin. Properly treating ringworm takes time, but the condition is curable.

How can I tell if my dog has worms?

Staying on top of preventive health care protocols and regular bi-annual wellness examinations with your veterinarian are integral to keeping your dog healthy and parasite free. Generally, by the time your dog is displaying symptoms of a worm infestation, the parasitic problem has been present and growing for quite some time already.

happy dog at veterinary clinicSome of the most common symptoms your dog might display if worms are present include:

  • Vomiting
  • Weight loss
  • Increase or decrease in appetite
  • Pot-belly or protruding abdomen
  • Chronic coughing
  • Lethargy
  • Diarrhea
  • Hair loss, dry dull haircoat
  • Itchy skin
  • Anal rubbing or dragging across the floor

The symptoms listed above, however, can also indicate other illnesses in dogs so please call your veterinarian to schedule an appointment ASAP if your dog is showing any of these symptoms or behaviors.

How are worms treated in dogs?

Generally, treating worms in dogs has an excellent prognosis, as long as dogs receive treatment before the worms are allowed to progress into the advanced stages of infestation. If your dog is found to have a parasite, your veterinarian will prescribe an appropriate deworming medication, depending on the type of parasite, the extent of the infestation, and other medical considerations specific to your dog’s individual needs.

Please Note: It is extremely important that you do not try to address any worm-related problems in your dog with over-the-counter medications without consulting your veterinarian first. The type and severity of the infestation and medical management strategy can only be determined by a veterinarian. If your dog has worms or shows other concerning signs of illness, please call the Animal Clinic of Billings and Animal Surgery Clinic today to schedule a consultation with one of our veterinarians.


Are worms in dogs a danger to myself or my family?

Yes. Some worms can certainly pose a threat to humans if contracted from the family dog. Roundworms, for example, are extremely dangerous to people, especially children who play in outside areas that are likely frequented by potential host animals such as dogs, cats, and raccoons.

In the U.S., 10,000 children are infected with worms each year, and the most severe cases can result in blindness. This is one reason why implementing an effective worm prevention protocol with your veterinarian is so important.

Parasite Prevention and De-worming for dogs and puppies


Puppies will need their first deworming at three weeks of age and then as directed by your veterinarian. Monthly heartworm preventive medications are recommended which also helps prevent some types of intestinal parasites. This should serve as the starting point for your dog’s annual deworming protocol.

Adult Dogs

After puppies have been properly dewormed, adult dogs should receive monthly preventives year round. Additionally, we recommend performing fecal tests between 2-4 times per year.

Newly Acquired Dogs

If you have newly acquired or adopted a new dog, they should be dewormed by your veterinarian immediately. No matter what your new dog’s age or documented history, an initial microscopic fecal exam and deworming should be performed, followed by monthly preventive deworming medication.

What to do if you think your dog has worms

If you suspect your dog might have contracted worms or another parasite, please call us to schedule an appointment with one of our veterinarians right away. Our dedicated veterinary team is here to provide treatment options and help answer any dog parasite questions you might have.


Our dedicated veterinary team is here to provide treatment options and help answer any dog worms questions you might have.

If you suspect your dog has worms, please call to schedule a veterinary appointment for your canine friend with us today.






providing our region’s companion animals and their families what they need and deserve since 1981

1414 10th St. West, Billings MT 59102