Dog tapeworm
Echinococcus granulosus
ORDER
Cyclophyllidea
FAMILY
Taeniidae
TAXONOMY
Hydatigena granulosa Batsch, 1786, Germany.
OTHER COMMON NAMES
French: Ténia échinocoque; German: Hülsenwurm.
PHYSICAL CHARACTERISTICS
Adult 0.12–0.24 in (3–6 mm) long, consisting of scolex, short neck, and three to five proglottides. Scolex bearing 30–36 (rarely more) rostellar hooks. Gravid proglottis highly elongate.
DISTRIBUTION
Cosmopolitan.
HABITAT
Microhabitats are intestines of carnivore mammals, mostly of the family Canidae (dogs, wolves, jackals, etc). Larvae occur in internal organs (liver, lungs, musculature) of herbivorous mammals. Macrohabitats include natural ecosystems where parasites circulate along the food chain wild herbivores—wild carnivores or in habitats associated with humans (pastures, farms, villages) where major final hosts are dogs and intermediate hosts are domestic animals (sheep, cattle, camels, pigs, goats, horses, etc.).
FEEDING ECOLOGY AND DIET
Internal parasite absorbing nutrients through the tegument.
BEHAVIOR
The released gravid proglottis is able to crawl. Some data indicate that such proglottides may climb up grasses, where they are able to disperse their eggs more efficiently and contaminate a larger area of grassland. Some gravid proglottides may stay around the anus of the dog, contaminating its fur with eggs.
REPRODUCTIVE BIOLOGY
Oncospheres hatching from eggs in the intestine of the intermediate host migrate to the liver or the lungs, sometimes to the musculature or even to the eyes. They grow very slowly and transform into a cyst named "unilocullar hydatid." Its wall consists of two layers. The inner layer is able to produce numerous scoleces (i.e., asexual reproduction occurs during the larval development). The inner layer also is able to produce daughter cysts, situated within the mother cyst, which also can produce numerous scoleces. The development of the hydatid may continue for 20–30 years. When a carnivorous mammal eats a liver or another organ containing a hydatid, it becomes infected. In its intestine, each scolex produces an adult tapeworm.
CONSERVATION STATUS
Not listed by the IUCN.
SIGNIFICANCE TO HUMANS
Echinococcosis, or hydatid disease, is one of the most serious parasitic diseases of human in Asia, Africa, South America, and Europe. Humans are infected as intermediate hosts, i.e., hydatids develop in the internal organs. Some recent attempts for drug treatment are very promising. However, in 2000–2002, surgery remains the only routine method of treatment.
Echinococcus granulosus is also of primary veterinary importance because the hydatid disease is dangerous for many domestic herbivores (sheep, pigs, goats, cattle, camels, horses, etc.).
