In the adult stage of its life, Trichinella spiralis lives in the intestinal mucosa of the infected animal. It is at this point that it will reproduce. Mating often takes place approximately one week after infected meat has been consumed. The adult worms will continue to produce larvae for up to 16 weeks. The larvae then exit the animal with the feces. There are five recognized species of Trichinella spiralis. Some of these parasites can be found in North America, however, cases of infection are becoming rare. While many cats may be infected with these hair-like worms, most will not produce adverse side effects from the infestation.

The nematode, or worm, known as Trichinella spiralis chooses mammals and select birds as its host. An infestation of this parasite is known as trichinellosis or trichinosis. The parasite is generally ingested and, once inside the body, larvae follow the bloodstream to muscle tissue where they encapsulate into a type of cyst. The larvae can live in the animal for years, waiting for another host to complete their development. Once a second animal ingests the host animal, the capsules break down in the new animal's stomach, releasing the larvae. 

This parasite often goes undiagnosed in cats. Sometimes a cat that is infected will not show any symptoms. In rare instances, severe symptoms may develop. Signs to watch for include:

For a cat to become infected with the parasite, it must come into direct contact with organic matter that contains the worms. Often if an environment is infected with Trichinella spiralis, any outdoor cats in that environment are also infected. Possible causes are listed below.

It should be noted that the chance of infection increases the more cysts that are consumed. Eating one cyst does not always lead to parasitic infestation.

If your cat does begin to manifest symptoms, bring it in to your veterinarian. Be sure to provide the vet with your cat's full medical history so that other possible causes of the symptoms can be differentiated. The cat will undergo a complete physical examination during which the vet may take note of any signs of muscular pain from palpation.

Full blood work will need to be run including a complete blood count to see if eosinophils (white blood cells that contain granules) are elevated. A creatine phosphokinase test (CPK) may reveal increased muscle enzymes due to inflammation caused by the cysts. The only way to confirm the diagnosis is to take a biopsy of affected muscle tissue and have it histopathologically examined for the spiral shaped Trichinella spiralis worms.

Treatment is generally only administered if the infection is causing severe symptoms to occur in the cat. Secondary health problems may arise because of the infestation and may also need treatment.

A prescription for deworming medication, such as albendazole, may be used to treat trichinellosis. These medications can reduce the number of larvae that are present in the cat. It may take a longer period of treatment to fully eradicate the worms from the cat.

If a secondary infection of the lungs has caused pneumonia to set in, a course of antibiotics may also be needed. These prescriptions usually last between one and four weeks. 

Some symptomatic cases of trichinellosis resolve on their own over time. Severe cases have the potential to affect major organs in the cat, such as the heart, lungs and brain. These infections may be more difficult to treat. Be sure to administer all prescriptions as the veterinarian has instructed. To confirm that treatment has worked, a second biopsy will need to be collected and sent for evaluation. If no worms are present, the infestation may be eradicated.

A cat who has been diagnosed with trichinellosis may pass worms in its feces. It is best to clean the litter box daily and to disinfect it on a regular basis with scalding water or bleach. Wild game often contains Trichinella spiralis and should not be fed raw to your cat. Raw pork should be avoided unless it has been frozen for at least three weeks. Keeping your cat indoors can greatly reduce the chance of it hunting and eating small infected animals.