MORBIDITY: +

MORTALITY: +

ETIOLOGY: PARASITIC

Adult tapeworms are found in the intestinal tracts of their definitive, or final, hosts. Each adult tapeworm consists of a head (scolex), which attaches the tapeworm to the intestinal wall, neck, and various numbers of segments, developing from the neck region. As new segments are formed at the neck, older segments are pushed back. Tapeworms are hermaphroditic; each segment has two sets of male and female reproductive organs, which will fill the segment with fertile eggs as the segment is pushed back from the neck. When the segment is full of eggs, it detaches itself from the adult tapeworm and is passed in the feces (Figure 40).

FIGURE 40 Tapeworm morphology.

Each genus and species of tapeworm has at least one intermediate host, which ingests the tapeworm eggs. After the eggs hatch, the immature tapeworms migrate out of the intestine of the intermediate host and travel to various tissues in the body, depending on the genus of tapeworm. The immature tapeworm enters tissue in the intermediate host and is enclosed in a cyst, in which young tapeworms develop to an infective stage. Definitive hosts are infected by eating the cystic tissues of intermediate hosts infected with immature tapeworms.

There are three tapeworms of zoonotic importance in North America: Dipylidium caninum, Diphyllobothrium latum, and Echinococcus spp.

DIPYLIDIUM CANINUM

Dipylidium caninum is also known as common dog tapeworm, flea tapeworm, cucumber seed tapeworm, and creeping seeds.

HOSTS

The definitive hosts for D. caninum are dogs, cats, foxes, and sometimes humans. The intermediate host is a flea or a louse.

TRANSMISSION

Adult tapeworm segments are passed in the host’s feces (Figure 41). These segments look like cucumber seeds or grains of rice and are sometimes seen around the anus of the host or in the feces. After the segments are passed, they can move around. They eventually dry up and release egg packets. The egg packets are then eaten by flea or louse larvae, and hatch in the larvae’s small intestines. The larval form of the tapeworm then penetrates the intestinal wall of its tiny host and forms cysts in the body cavity. As the flea or louse matures, the tapeworm larva matures, to an infective, cystic stage. The final host is infected by eating a flea or louse infected with immature tapeworms (Figure 42).

FIGURE 41 Tapeworm segments in dog feces

(From Hendrix CM, Robinson E: Diagnostic parasitology for veterinary technicians, ed 3, St Louis, 2006, Mosby.)

FIGURE 42 Dipylidium infection.

DISEASE IN ANIMALS

Dogs, cats, and foxes are usually not much affected by the presence of tapeworms. Dogs may “scoot” or drag their hindquarters to relieve irritation when there are segments stuck to the anal region.

DISEASE IN HUMANS

D. caninum infection is seen most often in children. The only way a person can become infected with D. caninum is to eat a flea or louse larva. Most people with D. caninum infection do not exhibit any clinical signs. Some may develop diarrhea, abdominal pain, and perianal itching from the presence of segments.

DIAGNOSIS

Diagnosis of D. caninum infection is based on finding tapeworm segments that look like cucumber seeds or grains of rice under an animal’s tail, around the anus, or on feces passed by the animal. Because the eggs are released in packets, they might not be found on a routine microscopic fecal examination unless the egg packet has broken.

Children infected with D. caninum will pass segments in their stool or have segments, which are irritating and cause itching, stuck to the skin around the anus.

TREATMENT

Drugs are available to kill adult tapeworms in both animals and humans. After tapeworms have been killed, they are usually digested by the host, so there may be no adult tapeworms passed in the feces.

PREVENTION

The best prevention is parasite control. Without fleas and lice, there can be no D. caninum. If tapeworms are detected in pets, have them treated. Clean up after pets, especially if they defecate in public areas such as parks or near sidewalks. Do not let children play around areas soiled with dog or cat feces. Make sure children wash their hands after playing with dogs and cats or when they come in from playing outdoors.

It is important to note that sometimes the presence of D. caninum is the first indication that fleas are present in a household.