Parasitic Stomach Worm Infection in Cats

Adult stomach worms attach to the inner lining of the stomach where they feed, reproduce, and lay eggs. The eggs pass through the animal’s digestive tract and are shed through the feces of an infected vertebrate. The contaminated feces is left in the open for coprophagous (feces-eating) insects, which become infested with the stomach worm eggs while feeding. A beetle, cockroach or cricket could serve as an intermediate host. The infected insect is then eaten by natural born insect predators, such as a frog or mouse, where the egg hatches into larvae. That transport host is then eaten by its natural predator (your cat) and the larvae reside in the stomach, maturing into adult parasites. 

The presence of an adult roundworm, known to the veterinary world as a Physaloptera spp, causes irritation to your cat’s stomach lining, leading to the initial symptom of chronic vomiting. As the parasite infection worsens, your cat may lose weight, develop dark diarrhea, which suggests digested blood from stomach ulcerations, and the cat will soon become malnourished.

If your cat is experiencing a case of chronic vomiting and you have not changed her diet, she could be infested with a parasitic stomach worm. A parasitic stomach worm is classified as a nematode, or species of roundworm, that uses felines and other vertebrates as its final host. 

The stomach worm goes through three life stages and three separate hosts during its life cycle. At the egg stage, the parasite requires an intermediate host, as larvae, it needs a transport or paratenic host, and as an adult, the worm uses its final host. 

The presence of one or more parasitic stomach worms in a cat’s stomach can cause irritation to the stomach walls, or gastritis. A feline becomes nauseous due to the parasite-induced gastritis and begins vomiting on a routine basis, known as chronic vomiting. If the feline has a severe number of nematodes inhabiting the stomach organ, the gastric mucosa (the mucus lining that covers the entire inner body of the stomach to prevent stomach acids from corroding the soft tissues) thickens, accumulates fluids (edematous), and causes folding of the inner stomach walls.

Although a parasitic stomach worm infection does not always affect each cat in the same way or clinically affect the feline at all, additional symptoms a cat may present include: 

• Weight loss
• Chronic vomiting 
• Dark diarrhea 
• Anemia 
• Bleeding 
• Chronic gastritis
• Ulcerations on the stomach wall from nematode attachment
• Vomiting up worms 

Types

Several species of parasitic stomach worms can be found through the world, however, each species of nematode remains in one geographical area. 

• Physaloptera felidis is found in North America.
• Physaloptera rara is found in North America.
• Physaloptera pacitae is found in Central America.
• Physaloptera praeputialis is found throughout several world regions.

A cat can be infected with a parasitic stomach worm upon ingestion of an infected intermediate or transport host. Physaloptera worm infections are common in outdoor cats that scavenge or hunt for prey animals. Parasitic stomach worm infections are not zoonotic, meaning that they cannot be transmitted to humans, but the eggs can be shed in the feline’s environment and infect another potential host. 

Your veterinarian will want to rule out other possibilities for your cat’s primary symptom of chronic vomiting. It will be helpful for you to discuss any diet changes you have made, any possible prey animals your cat has caught lately, and if any nematodes are present in your pet’s vomit. A review of your cat’s medical history and a physical examination will also take place at this time to begin the veterinary diagnostic plan. 

Your veterinarian may request a sample of your cat’s feces to complete a fecal flotation test. A fecal flotation test involves a dilution of feces, allowing eggs to rise to the surface and stick to a microscope slide. However, a fecal floatation test often presents a negative result as nematode eggs do not readily float. Your veterinarian may decide to perform a fecal sedimentation (fecal smear) test instead. 

The most effective diagnostic test for a parasitic stomach worm infection in cats is a gastroscopy exam. A gastroscope is a flexible tube with a camera attached that is passed through the esophagus and into the stomach to visualize the problem.

Parasitic stomach worms can often be removed during the diagnostic exam using the gastroscope. The veterinarian can see exactly where the worms are in your cat’s stomach and pull them out, but worms often hide in the stomach mucus, making additional treatments necessary. Anthelmintic active agents, or deworming medications, such as pyrantel pamoate, ivermectin and Fenbendazole have proven effective against parasitic roundworms in cats. However, these anthelmintic agents are used off-label in felines, meaning your veterinarian is the only one who can approve an appropriate drug regimen.

Felines respond very well to anthelmintic active agents, removing the parasitic stomach worm infection completely. Initially after treatment, your cat may still have stomach ulcerations from the detachment of worms and may remain nauseous for a couple of days. Talk to your veterinarian about treating feline nausea at home and how to prevent another parasitic stomach worm infection in your cat.