Veterinary Parasitology CH6 - Tapeworms of Domestic Animals and Humans

Study material for Chapter 6 of Diagnostic Parasitology for Veterinary Technicians. For class BIO225 at MWCC.

Hymenolepis nana, Hymenolepis diminuta

“Dwarf tapeworm” (nana), “Rodent tapeworm” (diminuta)

• Hymenolepis nana: 1 mm by 25-40mm​

• Hymenolepis diminuta: 3 mm by 20-60 mm

• Affects: Mice, rats, gerbils, hamsters (definitive) dogs and humans (H. nana more common - incidental)​

• Adults: small intestine​

• Found: Worldwide​

• Cause of infection: Ingestion of infective fleas, beetle, cockroach (H. diminuta) which is intermediate host​; Ingestion of infective egg or autoinfection (H. nana) no intermediate host

Hymenolepis nana life cycle

1. Eggs pass in feces — direct life cycle – only tapeworm that does not need intermediate host​

2. Swallowed by host, hexacanth enters villus of small intestine​

3. Matures into nontailed cysticercoid​

4. Moves back to lumen, attaches to lining and matures to adult stage

Hymenolepis diminuta life cycle

1. Eggs pass in feces​

2. Ingested by arthropod intermediate host​

3. Hexacanth embryo matures into tailed cysticercoid​

4. Attaches to lining of small intestine and matures into adults

Hymenolepis sp. eggs

• Eggs are detectable in fecal floatation, but shed intermittently​

• Proglottids do not float​

Moniezia expansa

“Ruminant tapeworm”

• Affects: Cattle, sheep and goats (Moniezia benedini in cattle only)​

• Found in: Worldwide

• Adult in small intestine​

• Cause of infection: Ingestion of infected grain​

• Much larger than Hymenolepis (up 1.6 cm by 6m)

• Unarmed scolex​

• Short, wide proglottids​

• Unique eggs with square (M. benedini) or triangular (M. expansa) shells​

• Three-layered egg shell, inner-most is pyriform apparatus—pear shaped​

• Prepatent period: 40 days​

• Eggs seen on fecal flotation

Moniezia metacestode stage

• Proglottids and eggs in feces of infected ruminants​

• Cysticercoid found inside oribatid grain mites that have ingested hexacanth embryo​

• Ruminants infected by eating infected grain​

• Each cysticercoid forms one adult​

• Large numbers of adults can block intestines, especially in young animals​

• Pasture rotation as well as management of grain mites can help with reinfection rates

Thysanosoma actinoides

• Affects: Sheep, goats, cattle​

• Adults in lumen of bile duct, pancreatic duct, small intestine – can cause obstructions​

• Intermediate host: unknown, possibly psocids (“booklice” that feed off mold, lichen, grains and wallpaper and book- binding glue)​

• Derivation: “fringed body”– unique fringe on the posterior half of each proglottid​

• Unarmed scolex, form egg packets (6-12), no pyriform apparatus

Taenia saginata (adult), Cysticercus bovis (larval stage)

“Beef tapeworm”

• Adult: small intestine​

• Found: Worldwide​

• Definitive host: Human​

• Cause of infection: Ingestion of raw or undercooked intermediate host: beef cattle​

• Only member of Taenia with unarmed scolex, 14-32 branches of uterus in gravid

Taenia solium (adult), Cysticercus cellulosae (larval stage)

• “Pork tapeworm”

• Adult: small intestine​

• Found in: Mostly underdeveloped countries - Latin America, India, Africa, Far East​

• Definitive host: human​

• Cause of infection: Ingestion of undercooked intermediate host: pigs​

• Armed scolex, 7-16 branches of uterus in gravid​

• Can develop cysticercus in human muscle, brain, eye, spinal cord

Taenia hydatigena (adult), Cysticercus tenuicollis (larval form)

“Canine/dog bladder worm”

• Affects: Dogs, adults in small intestine

• Intermediate host: cattle, sheep, goats​

• Found in: Worldwide​

• Cause of infection: Ingestion of omentum of ruminants with golf-ball size cysticercus (not pathogenic to ruminants)​

• Armed scolex, proglottids have single lateral genital pore​

• Eggs can be seen in fecal flotation

Anoplocephala sp.

• A. perfoliata, A. magna, Paranoplocepha mamillana​

• Found in: Worldwide​

• Intermediate host: Grain mites​

• Unarmed scolex

• Cause of infection: Ingestion of mites​

• Unique morphology: unarmed oblong scolex, two round lappets behind each of the four suckers, only one pair of reproductive organs per glottid​

• Pyriform apparatus in egg with one or more flattened sides

Dipylidium caninum

“Double pore” or “cucumber seed tapeworm”

• Most common tapeworm of dogs and cats​

• Affects: Dogs and cats​

• Intermediate host: fleas​

• Cause of infection: Ingestion of fleas​

• 50 cm long​

• Long proboscis on armed scolex​

• Gravid proglottids can be motile when shed in feces, coat hair, bedding

• Each gravid proglottid contains thousands of egg packets​

• 20-30 eggs per packet, each with hexacanth embryo inside​

• Prepatent period: 14-21 days

Dipylidium caninum life cycle and prevention

• Metacestode stage is cysticercoid in intermediate host: flea​

• Larval fleas ingest hexacanth embryos​

• Dogs and cats ingest the infected fleas​

• Children are most likely humans to ingest fleas and get zoonotic infection​

• Must include good flea control in order to prevent reinfestation​

• Egg packets found in fecal flotation​

• Proglottids found in gross feces

Taenia sp.

• Affects: Dog​s

• Adults in small intestine​

• Intermediate hosts: Rabbits and hares (T. pisiformis), ruminants (T. hydatigena), sheep (T. ovis)​

• Cause of infection: Ingestion of intermediate host​

• 1-2 cm (T. ovis) to 200 cm (T. pisiformis) to 500 cm (T. hydatigena)​

• Armed scolex, motile gravid proglottids– if found in feces, hydrate​ in saline on slide to see eggs inside​

• Single lateral pore

• T. pisiformis has pea sized cysticercus, attached to greater omentum of rabbit​

• T. hydatigena has ping pong ball sized cysticercus, attached to greater omentum of ruminant​

• T. ovis has cysticercus found in muscle of sheep ​

• Preventing dogs and cats from eating viscera or musculature of intermediate hosts is best way to prevent Taenia infections

Taenia taeniaeformis (adult), Cysticercus fasciolaris (larval form)

• Affects: Cats​

• Intermediate host: Rats and mice​

• Found in: Worldwide​

• Cause of infection: Ingestion of rats and mice​

• 60 cm long​

• Armed scolex, bell shaped proglottids, taeniid egg

Taenia taeniaeformis life cycle

Unique in that larval stage is strobilocercus​

1. Rodents ingest hexacanth eggs from cat feces, develop into cysticercus inside liver for 42 days​

2. On day 42, cysticercus changes shape into strobilocercus with scolex and long neck attached to bladder (Cysticercus fasciolaris)​

3. Cat infected by eating rat or mouse liver​

4. Scolex attaches to cat intestine

Multiceps sp.

“Many headed worm”

• Affects: Dogs, not zoonotic​

• Adult in small intestine​

• Intermediate host: Sheep (M. multiceps) or rabbit (M. serialis)​

• 40 to 100cm long​

• Double row armed scolex, taeniid eggs

Multiceps sp. metacestode stage

• Forms coenurus that is found in sheep or rabbit intermediate host​

• Coenurus cerebralis (M. multiceps) or Coenurus serialis (M. serialis)​

• Single large bladder with several scolices attached to the wall​

• Unique in that many tapeworms mature from each coenurus, one for each scolex​

• In sheep, hexacanth embryos are ingested and larvae (5cm) migrate to nervous system (brain or spinal cord) and can produce neurological symptoms in infected sheep​

• Dogs infected by ingesting sheep parts​

• In rabbits, hexacanth embryos are ingested in dog feces, hatch and migrate into subcutaneous tissues which can interfere with movement, slow rabbits more likely to be caught and eaten by dogs

Echinococcus granulosus (dogs) and Echinococcus multilocularis (cats)

“Spiny berry”

• Intermediate host: Sheep, cattle, herbivores (E. granulosus), rats, mice and voles (E. multilocularis), ​

• Both are highly zoonotic ​

• Cause of infection: Ingestion of intermediate host​

• Form unilocular (E. granulosus) or multilocular (E. multilocularis) hydatid cysts​

• Adults are tiny: 1 to 7mm in length with only three proglottids: 1 immature, 1 mature, 1 gravid​

• Very difficult to diagnose as gravids are seen in feces, adults never get to numbers that cause obstruction

Diagnosis of Echinococcus

• Can find adults in intestinal tract at necropsy​

• Suspected infections can be diagnosed by purging animal of all feces using arecoline hydrobromide​

• All feces should be handled with caution using gloves and incinerated​

• Current ELISA tests for Echinococcus available​

• Cases in dogs, cats or intermediate hosts must be reported to state and federal public health officials​

• Taeniid eggs similar to Taenia and Multiceps sp.​

Echinococcus metacestode

• Larval stage is hydatid cyst​

• E. granulosus forms unilocular cysts within liver, lung, other organs of ruminant

(Thick cyst wall, thin germinal membrane​; “Brood capsules” contain protoscolices that bud from germinal membrane​; Each protoscolex forms one adult worm)

• E. multilocularis forms multilocular or alveolar cysts within liver, lungs of rodents

(No thick wall, grapelike cysts that are very invasive, replacing normal tissue almost like cancer​; Thin germinal membrane​; “Brood capsules” with protoscolices bud from membrane​; Praziquantel can treat adult Echinococcus but will not kill cyst stage)

Mesocestoides sp.

• Affects: Dogs, cats, other carnivores​

• 12cm to 2m in length​

• Oblong scolex, four acetabula, unarmed​

• Only true tapeworm with two intermediate hosts

Mesocestoides sp. metacestode stage

• If ingested by oribatid mite, develops into cysticercoid inside mite ​

• If cysticercoid ingested by mouse or reptile, develops into tetrathyridium which can multiply asexually to make large numbers that can infect dogs, cats​

• Tetrathyridia multiply heavily in intermediate host, mostly in serous cavities like peritoneum or liver causing large increase in girth​

• When ingested by definitive host, tetrathyridium develop into adults in small intestine

Pseudotapeworms Cotyloda

• Look similar to true tapeworms but have centrally located reproductive organs​

• Unembryonated operculated eggs (almost identical to trematodes)​

• Most release eggs directly from uterus passed in feces of definitive host​

• Sometimes short chains of proglottids are released​

• No acetabula or rostellum but two slitlike organs called bothria

Pseudotapeworms Cotyloda life cycles

• All use two intermediate hosts​

• Eggs that come into contact with water release ciliated hexacanth embryo called coracidium​

• Swims in water, ingested by microscopic crustacean and develops into procercoid​

• Then ingested by fish or amphibian, matures in muscle into metacestode larva called plerocercoid or sparganum​

• Definitive host eats intermediate host to become infected

Spirometra sp.

“Zipper tapeworm” (due to mature proglottids pulling apart or unzipping)

• Affects: Dogs and cats​

• Found in: North and South America, Far East, Australia, most prevalent in Florida and Gulf Coast​

• Adults in small intestine​

• Intermediate host: crustacean, then fish or frog​

• Rare to release gravid proglottids

Sparganosis

Spirometra sp. metacestode stage

• Sparganum larval stage, solid-body with slit-like mouthparts​

• Found in muscle of intermediate host

Diphyllobothrium latum

• “Double leaf” or “Broad fish tapeworm”

• Affects: Dogs, cats, humans​

• Adults in small intestine​

• Intermediate host: crustacean, then fish​

• Found in: Scandinavia, Ukraine, N. America​

• 2m to 12m long​

• Four acetabula and two bothria​

• Can cause pernicious anemia in host due to B12 absorption, gravids detach in small chains​

• Largest human tapeworm