Tapeworms: Cestoda

Physical characteristics: Adult dog tapeworms are 0.1 to 0.2 inch (3 to 6 millimeters) long. The body consists of the scolex, a short neck, and 3 to 5 proglottids. The scolex has 30 to 36 hooks. The gravid proglottids are very long.

Geographic range: Dog tapeworms live all over the world.

Habitat: Adult dog tapeworms live in the intestines of meat-eating mammals, mainly dogs, wolves, and jackals. The larvae live in the liver, lungs, and muscles of plant-eating mammals such as sheep, cattle, camels, pigs, goats, and horses. The habitat includes areas where humans live and work, such as pastures, farms, and villages.

Diet: Dog tapeworms absorb nutrients from their hosts.

Behavior and reproduction: The released gravid proglottids of dog tapeworms can crawl, and the larvae probably climb up grasses. Some gravid proglottids may stay around the anus of the dog, contaminating The disease caused by dog tapeworms is one of the most serious parasitic diseases for humans in Asia, Africa, South America, and Europe. This is a micrograph of the larval form, maginfied 80 times. (Science Photo Library/Photo Researchers, Inc.) its hair with eggs. Embryos hatching from eggs in the intestine of the intermediate host travel to the liver or the lungs, and sometimes to the muscles or even the eyes. The embryos grow very slowly and transform into a covered ball. Inside this ball numerous scolices and additional larvae balls develop in a process that can continue for 20 to 30 years. Meat-eating mammals, the final hosts, become infected when they eat a liver or another organ containing a larvae ball. In the final host's intestine, each scolex produces an adult tapeworm.

Dog tapeworms and people: The disease caused by dog tapeworms is one of the most serious parasitic diseases for humans in Asia, Africa, South America, and Europe. Humans are infected as intermediate hosts, meaning larvae balls develop in their internal organs. Scientists are researching drug treatments, but until these drugs are developed, surgery remains the only method of treatment. The disease caused by dog tapeworms also is dangerous for many plant-eating domestic animals, such as sheep, pigs, goats, cattle, camels, and horses.

Conservation status: Dog tapeworms are not considered threatened or endangered. ∎