Dog Tapeworm, Echinococcus granulosus
The dog tapeworm (Echinococcus granulosus), also known as the hyper tapeworm or the hydatid worm, is classified within the Platyhelminthes phylum. This species can reach an average length between .07 and .2 inches and its body is comprised of three segments, called proglottids, if it has not been damaged. These segments are known as gravid proglottids, mature proglottid, and immature proglottids. As is common to most tapeworm species, the adult dog tapeworm has four suckers on its head, or scolex, and hooks which can be found along the nose area. Although its definitive, or main host, is always a species of canid, this worm must have an intermediate host to mature properly. These hosts are typically livestock or humans that often contract hydatid disease because of the worm.
Adult dog tapeworms reside in the small intestine of their canine hosts, reproducing eggs that are released in the host’s feces. Intermediate hosts such as mice, deer, sheep, wallabies, kangaroos, and humans consume these eggs when accidently eating some of the infected feces. Once inside these secondary hosts, the eggs develop into oncosphere larvae that move through the blood stream. The larvae continue to mature in the blood, developing into hydatid cysts that rest in the internal tissues. The cysts can grow to be as large as a basketball, and often hold “balloon” cysts that are smaller. When the cysts break, particles travel to other areas of the host’s body to form new cysts. The “balloon” cysts contain young tapeworms, and if the dog eats prey that is infected by the worm, the resulting infection can be severe. Because the cysts appear in the lungs, liver, or brain of the intermediate host, it is thought that these hosts are weaker, allowing canid species to hunt the infected animals more efficiently.
The symptoms of a dog tapeworm infection include hooks within the sputum, an enlarged liver, and occasionally anaphylactic shock, a reaction caused by the immune system to a ruptured cyst. Common diagnosis tools for humans include immunoelectrophoresis, an MRI, or an ultrasound. In dogs, diagnosis can be more difficult, because the eggs of the Taenia and Echinococcus are similar in appearance. The best method of detecting this species within dogs is to perform an ELISA test, but a PCR test, which locates the DNA of the worm separately from the dog’s DNA, can also be used.
Hydatid disease is typically treated by a careful surgery that takes caution in protecting the cyst from damage in order to prevent the infection from spreading. Along with surgery, a medicine like mebendazole is used in low doses. Prevention of a dog tapeworm infection in canid species is usually successful if the dog is not allowed to eat the internal organs or entrails of other animals. These products are also known as offal. In humans, prevention of an infection is successful if proper hygiene is used around food or when encountering dog feces.
Image Caption: Scolex of Echinococcus granulosus from hydatid cyst. Parasite. Credit: CDC/Dr. L.L.A. Moore, Jr/Wikipedia