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Physaloptera (Stomach Worm) in Dogs and Cats
Published: November 16, 2020
Physaloptera worm vomited up by a cat. Photo courtesy of Dr. Brandi Bogner

Worms are parasites that live inside your pet’s body and steal nutrients away from them. They do so by either directly eating your pet’s tissue or feeding from their blood vessels. Different worms can inhabit different parts of your pet’s body from their lungs to their gastrointestinal system. Depending on the specific worm and your individual pet’s health, worms can cause little to no disease or serious sickness. Some worms cause anemia, others diarrhea, and in serious cases others can cause death if left untreated. It is also possible for your canine and feline companions to be infected with multiple types of worms at the same time, resulting in more severe sickness. Thus, it is important to work with your veterinarian to prevent your animals from getting infected in the first place and receiving treatment quickly if they do.

What are Physaloptera?

Physaloptera are a specific type of worm that affects cats and dogs. Also called stomach worms, they live mainly in the stomach and beginning of the small intestine of your furry companions. Adult stomach worms are stout, pink to tan in color and 3-6 cm in length. Once ingested by your cat or dog, stomach worms attach themselves to their stomach or small intestine where they feed off your pet’s tissue and blood. Stomach worms use their mouths, which are equipped with several sets of teeth, to bite into your pet’s tissue. Despite this damage, some cats and dogs do not show signs of disease when infected while others may have chronic intermittent vomiting, weight loss, and anorexia. Infection with Physaloptera are rare but most common in the Midwestern U.S., particularly in pets with access to the outdoors.

How are Physaloptera different from other worms?

There are many different types of worms that affect the gastrointestinal tract of cats and dogs. Among these, stomach worms are the only worms to predominately live in the stomach of their feline and canine hosts. Other worms, such as tapeworms and hookworms, mainly occupy the small intestines of dogs and cats. Moreover, unlike roundworms, stomach worms do not seem to have a predisposition for infecting certain age groups over others. In terms of feeding, stomach worms are similar to hookworms as both have teeth they use to bite into tissue, but stomach worms feed off both tissue and blood whereas hookworms only consume the latter. Finally, stomach worms are less likely than many other worms to cause sickness but when they do vomiting is common.

How does my pet get infected?

Physaloptera are maintained in wildlife carnivore species such as coyotes, wolves, foxes, bobcats and raccoons among others in North America. These wild carnivores pass stomach worm eggs in their feces. Other hosts ingest these eggs and become infected. These intermediate hosts include the German cockroach, field cricket, camel cricket, flour beetle, and ground beetles. Additionally, some small animals can eat these intermediate insect hosts and become infected; these include rodents, hedgehogs, lizards, frogs and snakes. Your pet can be infected by eating any of these infected insects or animals. Fortunately, your dog or cat cannot get infected by ingesting worm eggs in the environment or through interaction with affected wildlife carnivores.

Disease Caused

Once Physaloptera worms are ingested by your pet via an infected host, these worms attach themselves to the lining of your pet’s stomach or small intestine. From there, Physaloptera will feed on your pet’s tissue and ingest blood. As they move from one feeding site to another, they may cause bleeding wounds and inflammation. Despite this, some pets may not show any signs of disease. On the other hand, other pets may have chronic widespread inflammation of their stomach, which results in vomiting, anorexia and dark sticky feces with partially digested blood (melena). Vomiting, particularly chronic and intermittent, is the most common sign of infection and may contain one or more worms.


Diagnosis of Physaloptera can be difficult. One method is looking for stomach worm eggs using a fecal float. While a positive result means your pet is infected, a negative result does not rule them out because pets infected with stomach worms often have a low number of worms, sometimes as low as one. Thus, a fecal float may not accurately determine whether your pet has stomach worms or not.

Another method to diagnose stomach worms in your pets is to observe their vomit for any worms or eggs. It may be helpful to take pictures if you do see worms so your veterinarian can correctly identify them. Stomach worms in your pet’s vomit is diagnostic but lack of them does not rule out infection.

It is highly unlikely you will see stomach worms or their eggs in your pet’s feces. If you do notice something suspicious it would be a good idea to collect the poop in a bag and bring it in to your veterinarian to be examined more closely. When collecting feces, get a fresh sample no more than 24 hours old and as free as possible of grass, gravel, litter and other materials. In general, collecting feces that appear to have abnormal material or any eggs/worms is a good idea. Whether it turns out to be stomach worms or not, your pet may have some sort of parasite that needs to be addressed.

Finally, endoscopy can be used to diagnose stomach worms. While a much more expensive option than other methods, endoscopy allows your veterinarian to directly visualize and remove worms in your pet’s gastrointestinal tract. It is possible to miss worms, however, as they may be hidden by mucus, ingested food, and stomach folds. Thus, it is also possible to miss a diagnosis with this method as well.

Given the difficulty in diagnosing stomach worms, some veterinarians decide to treat your pet for them without confirming the diagnosis if there is high suspicion otherwise.

Treatment and Prognosis

Treatment involves either physical removal of worms by endoscopy followed by anthelmintic therapy or anthelmintic therapy alone (anthelmintics kill worms).

An endoscopy allows simultaneous diagnosis and treatment because worms can be visualized and removed at the same time. If all the worms are found and removed, then your pet’s symptoms may resolve sooner than with anthelmintic therapy alone. Endoscopy, however, is more expensive and is not always reliable. Stomach worms can be difficult to visualize, particularly immature larvae which are small and easily overlooked. Thus, endoscopy used in combination with anthelmintic therapy gives the added benefit of providing a definitive diagnosis when stomach worms are found.

Because the diagnosis of stomach worms is particularly challenging, it is often appropriate to treat your pet for stomach worms without performing endoscopy or finding eggs on a fecal float. This option is more economic and will eliminate any stomach worms if your pet has any. One drawback is that this option will likely not be effective if your pet does not have stomach worms and is instead sick for another reason. Drugs used to kill stomach worms in your cat or dog include ivermectin, pyrantel pamoate, and fenbendazole. Additional drugs that may be beneficial for your pet include anti-nausea medications to reduce their vomiting and gastroprotectants.

With appropriate therapy, prognosis is excellent. Success of therapy can be monitored by resolution of your pet’s symptoms, repeated fecal exams, or repeated gastric endoscopy examinations. Out of all these ways to track your pet’s response to therapy, monitoring whether their symptoms improve and eventually go away is the most economic and reliable. Stomach worms’ eggs are difficult to find on fecal floats and a negative result does not mean your pet is not infected. Similarly, while endoscopy is more reliable it is still not completely accurate and can miss worms. Thus, if your pet is not back to their regular, healthy self by the end of their medication course, it’s time to go back to your veterinarian. Your pet likely has some other problem that needs to be addressed.


The best way to reduce your dog or cat’s risk of being infected with stomach worms is to prevent them from eating the insects and animals that carry the worms, which includes preventing them from hunting and scavenging. You can do so by keeping your cat indoors and your dog on a leash or in a fenced yard to limit their contact with infected animals. With this in mind, small beetles and other insects can find their way into your home and thus there is always a possibility your pet can become infected.

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