Mature feline tapeworms measure about 15 to 60 cm in length. If several parasites are present, they are usually smaller. The head is armed with a large double circlet of 26 to 52 hooks and clearly visible suckers. The very large hooks are 315-485 µ long and therefore clearly differentiate Taenia taeniaeformis from all other Taeniae species. This tapeworm has a very short, invisible neck. The first proglottids are very short, the next ones have a characteristic clock shape and the last ones are 8 to 10 mm long and 5 to 6 mm broad, and have numerous (16-18) lateral branches.

Predator cats can harbor feline tapeworms for most of the year. Prevalence studies have established that it is the most common tapeworm species in domestic cats living outdoors and in stray cats. The reservoir consists of numerous intermediate hosts with bladder worms. In dead wild cats up to 30 parasites have been found in a single animal.
In civilized pedigree cats that do not catch prey the feline tapeworm does not occur since infection is transmitted only by carnivorism.

An infected cat eliminates about four mature proglottids daily. The proglottids contain one to two thousand eggs on average, with a minimum of 0 and maximum of 12000 eggs. Over 60% of the segments contain less than 500 eggs. Feline tapeworms are clearly less fertile than other Taeniae species. The proglottids disintegrate and the released eggs are infective immediately. The eggs are spread by rainwater, various insects and vermin. They remain viable for months, which increases the chance of their being ingested by an intermediate host.

Cycle
After 42 days, the hexacanth embryo released from the egg that was ingested by a suitable host penetrates the intestinal wall. It reaches the liver or body cavity through the blood circulation and develops into a strobilocercus bladder worm. This is a single bladder that produced segments already in the intermediate host.
The strobilocercus of the feline tapeworm is called Cysticercus fasciolaris. It develops in the liver or body cavity of the intermediate host. C. fasciolaris has a specific and characteristic shape. This bladder worm is elongated and consists of a series of segments, already resembling those of the adult tapeworm, without the genital organs. The front of the bladder worm is 4 to 5 mm wide and has a pocket in which the scolex is invaginated. The tip ends in a blister the size of a pea. The full length of the bladder worm varies between 3 and 20 cm. In the liver of rats or mice this bladder worm is coiled up neatly in a cyst and is called strobilocercus.
In a number of intermediate hosts, hepatic function may be blocked by excessive development of the cysticerci and the animal dies. In South Bohemia this parasite is the main cause of death in muskrats. The presence of strobilocerci in the liver is also associated with sarcomas, which are important in laboratory animals in particular.
In rats the presence of strobilocerci has a very negative effect on fertility in both males and females.

When a cat ingests an infected intermediate host, the strobila is digested, but not the scolex of this intermediate form. The scolex attaches itself to the intestine and produces new proglottids. After a prepatent period of 34-80 days, the tapeworm develops into a mature form, which can live for 6 months to 3 years. Cats develop little immunity against feline tapeworms and therefore remain susceptible to re-infection.

Harmful effects
Feline tapeworms that are attached with their large hooks in the mucous membrane of the small intestine cause local damage and inflammatory reactions.
In the case of one or a few tapeworms the lesions are usually limited and symptoms are hardly noticeable.
In the event of a massive infection the cat loses its appetite and even refuses food. A brief episode of diarrhea is followed by constipation and the animal develops a tight, retracted abdomen. The cat remains seated and does not seem to hear or see anything. If the cat is able to vomit it looks better for a while, but becomes listless again afterwards. Small hemorrhages and hypertrophic villi occur in the inflamed intestine.

Diagnosis
Cats that catch a lot of mice or rats are often infected with T. taeniaeformis. Occasionally, a suspected infection can be confirmed by the detection of proglottids. They can occur in feces or be seen around the anus or even stuck in the cat's coat. Microscopic examination of the feces can reveal (see ) the typical Taenia eggs.
Autopsy can disclose the adult worms or pieces of them in the small intestine. Through post-mortem migration they can even occur in the stomach.

Treatment and prevention
Treatment with a potent cestocide, such as praziquantel (5 mg/kg orally), is adequate, but obviously will not prevent re-infection; i.e. new adult tapeworms may be present after 6 to 7 weeks. Repeated administration of benzimidazoles, such as mebendazole, fenbendazole and flubendazole, can also be effective against feline tapeworms.
In order to avoid infection, cats should be prevented from catching mice or rats. The only alternative is to keep the animals indoors all the time.