Raw food diets – when will we learn that truly raw foods are the pathway for disaster? In addition to bacterial problems,
most tapeworm infections in dogs and cats are a result of eating raw food (prey) or ingesting untreated water. Pets should
be fed cooked or prepared food and provided with fresh, potable water.
All tapeworms of dogs and cats have an indirect life cycle. The definitive host is the one in which the tapeworm matures,
reproduces and generates eggs. The intermediate host is the host in which the metacestode (immature) form of the parasite
develops. The definitive host becomes infected by eating the intermediate host while the intermediate host becomes infected
by eating eggs in an environment contaminated by the definitive host. In general, dogs and cats serve as definitive hosts,
although metacestodes can sometimes develop within them.
There are over 60 species of Taenia worldwide, many of which use canid and felid definitive hosts. Within the US, more species tend to occur in domestic dogs
than domestic cats (Table 1).
Table 1. Some species of Taenia in domestic dogs and cats.
The life cycles are fairly straightforward. Gravid proglottids break free of the tapeworm and are shed in the feces. Eggs
are released from the segment either as it travels through the digestive tract or as it sits on the fecal. These eggs are
then ingested by the intermediate host, the embryo hatches and migrates to its developmental site, and the metacestode develops.
When the intermediate host is ingested by the definitive host, the metacestode is digested free, the scolex embeds itself
in the mucosa of the small intestine and the neck begins to grow, forming proglottids. The prepatent period is usually reported
as 5-12 weeks, depending on species. How long untreated tapeworms will survive is not known for sure but, T. taeniaeformis
has been reported to remain patent in cats for as long as 34 months.
Intestinal infections tend to not be pathogenic. Infections are generally diagnosed based on finding proglottids in the feces
although eggs can be found on fecal flotation if the proper specific gravity is used. Praziquantel, epsiprantel, and fenbendazole
are approved for the treatment of Taenia infections in dogs and cats.
Occasionally, dogs and cats develop cysticercosis as a result of infection with T. crassiceps. The metacestode of this species
of tapeworm is unique in that it is prolferative cysticercus that develops asexually through budding. Consequently, ingestion
of 1 or a few organisms can result in massive infections. Intraperitoneal, intrapleural, intracardiac, intracranial and subcutaneous
cystcercosis have been documented, most with fatal results. Why these animals develop cysticercosis is uncertain; however,
an impaired immune system is thought to play a key role. Route of infection is also speculative. Ingestion of eggs from
the environment, autoinfection via eggs from gravid tapeworms within the small intestine and ingestion of cysticerci in intermediate
hosts have all been proposed. Eggs, either ingested from the environment or autoinfection, are considered the most likely
Cysticercosis associated with T. crassiceps occurs in people as well. Although the source of infection (wild vs domestic
canid) is usually not known, at least one case was linked to the family dog.
Dogs can also develop cysticercosis as a result of infection with T. solium. Although uncommon any more in the United States,
this parasite is responsible for cerebral cysticercosis in humans in many areas of the world. In these same areas, dogs also
can be infected by ingesting eggs. If the cysticercus localizes to the brain, the dog can become aggressive. In developing
countries where rabies is endemic, aggressive behavior is often sufficient evidence for a diagnosis of rabies, resulting in
euthansia. While canine neurocysticercosis due to T. solium has not been weel recognized in the US, it does exist in Mexico
where many rescue groups travel to bring dogs back to the US.