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What are Worm Infestations?

While there are many kinds of worm infections in dogs, the most common ones include roundworms, hookworms, whipworms, tapeworms, and the most life-threatening, heartworms. Adult dogs with mild infestations can live seemingly healthy lives. Weak and malnourished pets are more at risk for severe blood loss and even fatalities.

Puppies are also at a higher risk of serious complications, as well as a reduction in growth. Giving puppies with worms treatment for the condition is essential to their continued health. Regularly using preventative methods can protect your furry buddy from a worm infestation, and can be as easy as a spot-on treatment or a chewable tablet.

Dogs can become infected after the ingestion of the eggs or larvae of various worm species. Worms are parasitic and need to live off of our dogs to survive. They can proliferate in the intestines, the heart, or other vital organs, causing digestive and respiratory distress, or a reduction in heart function.

Signs are often absent in the early stages of an infestation. Chronic diarrhea and the presence of worms in the feces are usually the first indications that your dog is infested with worms. For example, you may see white worms in your dog's poop before you even realize that your pal has contracted them.

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Symptoms of Worm Infestations in Dogs

Often, you may not see any signs that your dog has a worm infection. Changes in elimination and the presence of worms in the stool are often the alert that something has invaded your dog. Symptoms of a worm infestation in your dog can include:

  • Diarrhea, often chronic
  • Watery or bloody stool
  • Mucus in the stool
  • Gas 
  • Worms in the poop, which can appear as white to tan spaghetti, rice grains, sesame seeds 
  • Worms in vomited material
  • Worms stuck to anal area
  • Changes in appetite
  • Poor hair coat
  • Weight loss 
  • Abdominal or rectal pain or discomfort
  • Abdominal swelling
  • Scooting rear end along ground
  • Irritation around anus
  • Excessively licking or biting anal area
  • Soft, dry cough
  • Shortness of breath
  • Weakness
  • Pale gums
  • Listlessness
  • Irritability 
  • Restlessness 
  • Loss of stamina
  • Anemia
  • Skin irritation or itching, such as in paws
  • Retarded growth in puppies


There are many types of parasitic worms that live in dogs. The most common include:


Heartworms are spread through mosquito bites, which allows infective larvae to mature inside a dog. Heartworms live in the heart and blood vessels where they can interfere with heart function and clog the blood vessels, thereby reducing blood flow to other vital organs. Once infected, it may take several years for symptoms to appear in your dog, and once they do, the infection is quite advanced. Signs are often most noticeable after exercise, and can include a soft, dry cough, weakness, and shortness of breath. This infestation can be fatal.


These parasites have long necks and short bodies, which give them a whip and handle appearance. They live in the cecum and large intestines of dogs, where they bury their heads into the intestinal walls to feed. A whipworm infection results in bloody diarrhea that can be chronic, and a general debilitation. The microscopic eggs they shed with the stool can live up to 5 years in the environment, and can infect or re-infect healthy dogs.


Also inhabitants of the intestines, these long, flat, ribbon-like parasites do not have mouths, but rather, they feed by absorbing their food through their skin. They attach to your dog’s intestinal wall through suckers and hooks on their heads. Tapeworms can live in your dog without causing too much harm, but they can hinder the growth in puppies. They are composed of segments which often break off as the tapeworm matures, and can be seen as rice grains in your dog’s feces. You might also see your dog vomit up an entire tapeworm, or just become generally dull or restless. A heavy infestation can cause a more serious illness, involving diarrhea, pain, and weight loss.


This term refers to various types of nematode worms. The type most commonly seen in dogs is the Toxocara canis. These round-shaped parasites live in the intestines where they feed off of the partially digested food. Roundworms can be seen in poop and in your dog's vomit. What do roundworms look like? They look similar to a spaghetti noodle and can be light brown or white. These harmful parasites can also inhabit other organs, including the lungs, in the larval stage. Adult dogs may not show signs of a roundworm infestation, or they may exhibit respiratory or digestive problems, such as diarrhea, vomiting, or coughing. Puppies are at the most risk, as a roundworm infection can cause a reduction in growth. 


These intestinal dwellers live off of blood, and attach their sharp teeth onto your dog’s intestinal wall. Despite the fact that they are very small and difficult to see with the naked eye, they can consume so much blood that it can result in anemia in your dog. They also release an anti-coagulant into their attachment sites, causing continued bleeding even after they have become detached. Dogs can become infected by eating the eggs, or the larvae can burrow into a dog’s skin from the ground. Symptoms of heavy blood loss, bloody diarrhea, and weight loss are due to heavy infestations in the intestines, while irritated and itchy paws can be a result of larval entry into your dog.

Causes of Worm Infestations in Dogs

While most worm species can infect your dog through ingestion of the eggs, there are various other ways that your dog can become infected. Each type of worm has its own unique life cycle. Ways worms can be transmitted to your dog include:


  • Mosquito bite transmits infective larvae


  • Consuming infected soil, stool, or water


  • Consuming an infected intermediate host, such as flea, rabbit, mouse, or fish


  • Consuming infected soil, stool, or vomit
  • Consuming infected intermediate host, such as rodents, earthworms, birds, or roaches
  • Invasion through the skin and paws
  • Passed from mother to fetus during pregnancy
  • Passed from mother to puppy through milk


  • Consuming infected soil or stool
  • Absorption through the skin
  • Passed from mother to fetus during pregnancy
  • Passed from mother to puppy through milk
  • Invasion through the skin and paws

Diagnosis of Worm Infestations in Dogs

If you have seen worms in your dog’s stool or around their anus, or they are having chronic diarrhea or other digestive issues, your veterinarian can determine what has infected your dog through examination of a stool sample. Bring in a fresh sample that is no more than 24 hours old to be tested if you can. By fecal floats and microscopic analysis, your vet can diagnose which worm is infesting your dog. A definitive diagnosis may need multiple samples as deceased worms may not be in the stool at any given time.

Your veterinarian may also take a blood sample to test for heartworms. If heartworm-related proteins are found, then your vet will use a stethoscope to listen to your dog’s heart. Heartworms are life-threatening, so before your dog undergoes treatment, your vet will need to run more tests to evaluate the extent of the infection, and to be sure that your dog can physically handle therapy. Such tests include further blood testing, X-rays of the chest area to determine if there is swelling in the heart and pulmonary artery, an electrocardiogram to look for abnormal heart rhythms, and echocardiography to evaluate heart health and to visualize the heartworms.

Treatment of Worm Infestations in Dogs

Treatment of most types of worms comes in the form of a deworming medication, either given orally or injected. Some dewormers will dissolve the worms so that you will not see them passed in the stool, such as those for tapeworms. In many cases, multiple treatments will be needed. The anti-parasitics available as treatment for roundworms and hookworms in dogs usually only kill the adult worms, so your veterinarian will outline a treatment plan to ensure that the infestation is eliminated.

During this period of deworming, you will need to ensure that re-infection cannot take place. This will entail disposing of feces right away, cleaning any areas your dog inhabits indoors to remove any leftover eggs, and administering routine deworming medications to protect him in the future. Be sure to wear gloves, as not only can you unknowingly transport eggs to another location, but some hookworms can cause skin irritation if allowed contact. 

Heartworm is much more difficult to treat. Once signs of a heartworm infection appear in your dog, the infection has become severe, and may have caused substantial damage to the heart and blood vessels, as well as to the lungs, liver, and kidneys. New medications have seen fewer side effects with a 95% success rate in infected dogs. However, dogs who are very severely infected may not be able to withstand heartworm treatments and may be prescribed therapies to address the organ damage. Treatments can include injectable heartworm medications, antibiotics, anti-inflammatories, diuretics, and specialized heart medications. Your dog will need complete rest between treatments, and may need continued treatments for the remainder of their life.

Recovery of Worm Infestations in Dogs

Recovery is good for many types of worms. With proper deworming treatments and preventative measures to prevent re-infection, your dog can become worm-free and live a healthy life. If your dog has contracted heartworm, most often by the time it is diagnosed, the prognosis is fair to poor, depending on the severity of the infection. Your veterinarian will discuss your dog’s recovery based on their particular case.

Prevent a worm infestation in your dog by using routine preventative medications, such as chews for heartworm and spot treatments to keep away fleas and ticks. Be sure your dog does not consume possible host animals, and if he does, get him tested and dewormed. Using a dewormer on a regular basis can protect your puppy or dog from becoming infected from most species of worms.

Worm Infestations Questions and Advice from Veterinary Professionals

9 Months
Moderate condition
0 found helpful
Moderate condition

Has Symptoms

Anal Discharge
Anal Itching

Hi I was walking my dog today and he had diarrhea. I thought it was a normal case but then he went again and I saw what I thought was a piece of string in his stool but then it broke apart and started moving and I realized they were long white worms. We treated him last time with Drontal for Hookworms would that work again this time?

Dr. Michele King, DVM
Dr. Michele King, DVM
1611 Recommendations
There are many different types of intestinal parasites that dogs can get, and many need specific therapy. It would be best to take a fecal sample to your veterinarian to have it analyzed and get appropriate therapy for him.

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Japanese Spitz
2 Years
Moderate condition
0 found helpful
Moderate condition

Has Symptoms


Our dog had sore eyes and has been tearing alot 6 days ago to a point where he can ni longer open his eyes. We cleaned his eyes every few hours and so and his condition got better in 2 days time, no more tearing but still slightly red eyes. We gave him water with sugar and a dose of antibiotics. Now 4 days down the line, for a total of 6 days since his first symptom of sore eyes, he has been lethargic and has been lying down our couch most of the day. He has been losing so much weight but he eats and walks around to urinate and poo whenever he needs to.

I asked my friend who is expert at dogs for advice, she said she shspects it's most likely worm infection. shr told me to give our dog ivermectin, which i did 12 hours ago. We mixed it together with his food. 2 hours ago he has already defacated, but we failed to see if there were worms since it was 5 am and we were sleeping. Now he's lying beside me sleeping, with obvious weight loss. What should we do?

Dr. Callum Turner, DVM
Dr. Callum Turner, DVM
3320 Recommendations
Ivermectin isn’t approved for use in dogs due to some dogs having a gene which makes them susceptible to toxicity; however Spike should be wormed regularly regardless with an effective (approved) anthelmintic as well as getting a topical spot on flea & tick medication. There are many different causes for the a loss of appetite and lethargy (lethargy is usually due to a lack of food intake) which may include infections, parasites, foreign objects, other obstructions, tumours, dental disorders among many other causes. You should visit your Veterinarian for an examination to determine what specifically the underlying cause is instead of giving medications randomly. Regards Dr Callum Turner DVM

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