POD parasitology 2

what species are under class cestoda (tapeworms)?

• taenia spp

• echinococcus spp

• dipylidium caninum

• anoplocephala perfoliata

• moniezia spp

• diphyllobothrium latum

cestode general adult morphology:

• 3 body regions

• no mouth or digestive tract (absorb nutrients)

• hermaphroditic

what are the 3 cestode body regions:

• scolex (holdfast)

• neck (germinal region)

• strobila (chain of developing segments)

cestode general egg morphology:

• hexacanth embryo fully developed within embryophore

• eggs shed in feces or, more commonly, shed into environment within degenerating segments

cestode general life cycle:

• indirect

• eggs in feces

• hexacanth embryo infects intermediate host→migrates to final site of development and transforms into infective form→transmission occurs when intermediate host is eaten→scolex of juvenile tapeworm attaches to gut and matures (produces eggs)

what are the major taenia spp?

• taenia pisiformis

• taenia taeniaeformis

• taenia crassiceps

• taenia saginata

what kind of larva are taenia pisiformis (rabbit tapeworm) larvae?

where do adult taenia pisiformis (rabbit tapeworm) infect?

small intestine of dogs

what animal do larval taenia pisiformis (rabbit tapeworm) infect?

rabbits

taenia pisiformis (rabbit tapeworm) adult morphology:

• shiny white strobila, up to 2 m long

• scolex with 4 suckers and 2 rows of hooks on the rostellum

• single genital pore on each rectangular segment

taenia pisiformis (rabbit tapeworm) egg morphology:

• 40 micrometers

• thick radially striated embryophore (shell)

• found as single eggs

taenia pisiformis (rabbit tapeworm) larva morphology:

• cysticerus

• fluid filled bladder containing invaginated scolex (bladder worm surrounded by host cyst)

taenia pisiformis (rabbit tapeworm) life cycle:

predator-prey life cycle

• eggs released from segments ingested by IH

• hexacanth larvae hatch and migrate to peritoneal cavity or liver to mature to cysticerus

• when dog eats rabbit, scolex in cysticerus evaginates, attaches to gut and begins to form strobila

taenia pisiformis (rabbit tapeworm) PPP:

6-8 weeks

taenia pisiformis (rabbit tapeworm) signs:

presence of motile gravid segments in feces or perianal regions

taenia pisiformis (rabbit tapeworm) treatment:

cestodicides

taenia pisiformis (rabbit tapeworm) prevention:

prevent hunting to block transmission

taenia taeniaeformis (rat tapeworm) intermediate host is…

rodents (found in liver)

taenia taeniaeformis (rat tapeworm) definitive host is…

cats (found in small intestine)

taenia taeniaeformis (rat tapeworm) adult morphology:

• scolex with 4 suckers and 2 rows of hooks on rostellum

• strobila up to 60cm long

what kind of larva are taenia taeniaeformis larvae?

strobilocerus (partially developed cysticerus with scolex evaginated and a small, 1 cm strobila connected to fluid filled bladder)

taenia taeniaeformis (rat tapeworm) egg morphology:

• 40 micrometers

• thick radially striated embryophore (shell)

• found as single eggs

taenia taeniaeformis (rat tapeworm) life cycle:

predator-prey life cycle

• eggs released from segments ingested by IH

• hexacanth larvae hatch and migrate to peritoneal cavity or liver to mature to cysticerus

• when cat eats rodent, scolex in cysticerus evaginates, attaches to gut and begins to form strobila

taenia taeniaeformis (rat tapeworm) treatment:

cestodicides

taenia taeniaeformis (rat tapeworm) prevention:

prevent hunting to block transmission

what kind of larva are taenia crassiceps larvae and why is it important?

budding cysticerus amplifies infections

taenia crassiceps is a zoonotic threat to humans if what animal becomes infected?

dogs

taenia saginata IH is…

cattle (found in muscle)

taenia saginata DH is…

humans (found in small intestine)

what kind of larva are taenia saginata larvae?

taenia saginata adult morphology:

• white, up to 8m long

• unarmed rostellum with 4 suckers

• segments with one lateral genital pore irregularly alternating from side to side

taenia saginata life cycle:

• cattle ingest eggs, hatches and hexacanth larvae penetrate small intestine to appear in muscle

• larva develop into cysticercus

• humans eat undercooked meat containing cysticercus, which evaginates and attaches to small intestine and matures

what are the major echinococcus spp?

• echinococcus granulosus

• echinococcus multilocularis

echinococcus granulosus has a sylvatic life cycle with…

wolves (DH) and moose (IH)

echinococcus granulosus adult morphology:

• smallest tapeworm of dogs (less than 1 cm long)

• scolex has 4 suckers and 2 rows of prominent hooks

• strobila only 3-4 segments long

what kind of larva are echinococcus granulosus larvae?

allows for massive asexual replication (up to 50cm in diameter)

echinococcus granulosus egg morphology:

• 40 micrometers

• thick radially striated embryophore (shell)

• found as single eggs

echinococcus granulosus pathogenesis in humans:

• humans act as IH

• hydatid cysts in liver, lungs, or other organs cause space occupying lesion with pressure necrosis as they grow

• rupture of cysts can cause anaphylactic shock and death

echinococcus granulosus diagnosis in humans:

radiology

echinococcus granulosus diagnosis in dogs:

eggs in feces

echinococcus granulosus treatment in dogs:

praziquantel

echinococcus granulosus treatment in humans:

surgery and antihelmintics

echinococcus mulitlocularis has a sylvatic life cycle with…

fox (DH) and rodents (IH)

echinococcus mulitlocularis adult morphology:

• smallest tapeworm of dogs (less than 1 cm long)

• scolex has 4 suckers and 2 rows of prominent hooks

• strobila only 3-4 segments long

echinococcus mulitlocularis larva morphology:

• alveolar hydatid cyst (hydatid cyst not confined by capsule)

• exogenous budding of cyst acts like neoplasm to invade surrounding tissue

echinococcus mulitlocularis egg morphology:

• 40 micrometers

• thick radially striated embryophore (shell)

• found as single eggs

echinococcus multilocularis pathogenesis in humans:

• humans act as IH

• alveolar hydatid cysts in liver with metastasis to other organs makes it difficult to control

echinococcus multilocularis diagnosis in dogs:

eggs in feces

echinococcus multilocularis treament in dogs:

praziquantel

echinococcus multilocularis diagnosis in humans:

radiology

echinococcus multilocularis treatment in humans:

surgery (often unsuccessful due to metastasis)

dipylidium caninum (double-pored tapeworm) IH is…

fleas or biting lice

dipylidium caninum (double-pored tapeworm) DH is…

dogs, cats, humans (small intestine)

dipylidium caninum (double-pored tapeworm) adult morphology:

• scolex with 4 suckers and a rostellum with several rows of fine hooks

• strobila up to ½ meter long

• segments are somewhat barrel shaped with pores on each side

dipylidium caninum (double-pored tapeworm) larva morphology:

found in hemoceol (body cavity) of insect IH

dipylidium caninum (double-pored tapeworm) egg morphology:

• eggs in packets

• eggs are each 40 micrometers with a thick unstriated embryophore

dipylidium caninum (double-pored tapeworm) life cycle:

• eggs passed within motile segments

• liberated eggs ingested by flea larvae

• hexacanth embryo hatches from embryophore and penetrates body cavity of insect

• cysticeroid matures there

• when adult flea is ingested, scolex attaches to gut and strobila matures

dipylidium caninum (double-pored tapeworm) PPP:

2-3 weeks

dipylidium caninum (double-pored tapeworm) signs:

migrating gravid segment

dipylidium caninum (double-pored tapeworm) diagnosis:

• segments in feces

• squashes of segments (± rehydration) for egg masses

dipylidium caninum (double-pored tapeworm) treatment:

cestodicides

dipylidium caninum (double-pored tapeworm) prevention:

flea control

anoplocephala perfoliata DH is…

equine (ileocecal junction)

anoplocephala perfoliata IH is…

oribatid mites

anoplocephala perfoliata adult morphology:

• up to 8 cm long, flat, wedge shaped

• unarmed scolex with 4 suckers each with a lappet

anoplocephala perfoliata egg morphology:

irregular eggs with pyriform apparatus (pair of prong like processes)

moniezia spp DH are…

cattle, sheep, goats (small intestine)

moniezia spp IH are…

oribatid mites

moniezia spp treatment:

albendazole

diphyllobothrium latum first IH is…

copepod

diphyllobothrium latum second IH is…

fish

diphyllobothrium latum kind of larva in first IH is…

diphyllobothrium latum kind of larva in second IH is…

diphyllobothrium latum DH is…

fish eating mammals including humans

diphyllobothrium latum adult morphology:

• scolex has pair of bothria (grooves)

• large strobila (some many meters long)

diphyllobothrium latum egg morphology:

• operculate, light brown egg with ciliated hexacanth larva

• ciliated hexacanth embryo called coracidium

diphyllobothrium latum pathogenesis in humans:

may cause pernicious anemia (B12 deficiency) in genetically predisposed people

what are the orders of nematodes?

• rhabditida (rhabditids, threadworms)

• strongylida (strongylids, hookworms, lungworms)

• oxyurida (pinworms, oxyurids)

• ascaridida (ascarids)

• spirurida (spirurids, filarids, Dracunculus)

• enoplida (trichurids, dioctophyme, capillarids, trichinella)

nematode general features:

• elongate tubular bodies

• thick, resistant cuticle

• muscles under cuticle

• hydrostatic pressure maintains shape and rigidity

• simple alimentary tract

• separate sexes

male nematode anatomy:

• single convoluted tube consisting of testes, vas deferens, and ejaculatory duct

• sometimes supplemented with cuticular spines

• some have pronounced copulatory bursa

female nematode anatomy:

• pair of blind ended ovaries leading to uteri

• common vagina and vulva

• often store sperm for protracted periods

nematode general life cycle:

• egg→L1→L2→L3→L4→L5→adults (L3s are the infective form)

• life cycle can be divided among different hosts

nematode tracheal migration

extensive migration leading to alveoli from which larvae move up the airways to the trachea to the gut

nematode somatic migration

stay in bloodstream to be distributed around body

nematode mucosal migration

penetrate gastric pits or mucosa for a period of development prior to returning to lumen as adult

ascarids (roundworms) general features:

• adults are host specific

• various life strategies, most involving tracheal migration

• resistant eggs

• infect small intestine of DH (exception is heterakis gallinarum)

ascarid pathogenesis:

• poor growth

• obstruction in heavy infection

• lesions from migrating stages

• ocular or visceral larval migrans associated with tracheal migration

what are the major species of ascarids?

• toxocara canis

• toxocara cati

• toxocaris leonina

• parascaris equorum

• ascaris suum

• ascaridia galli

• heterakis gallinarum

• baylisascaris procyonis

toxocara canis adult morphology:

• large, heavy bodied, up to 18cm

toxocara canis egg morphology:

thick shelled, pitted egg containing single cell when passed in feces

toxocara canis DH is…

dogs (small intestine)

hypobiosis

pause in development by nematodes

toxocara canis life cycle:

• no intermediate hosts

• larvae develop to L3 in egg→infective eggs are ingested by dog

• fate of larvae depends on host

  • < 3 months: primarily tracheal migration with PPP of 4-5 weeks

  • 3-6 months: increasingly somatic migration

  • > 6 months: only somatic migration

  • pups in utero infected by transplacental migration of larvae from bitch to fetus

transplacental and transmammary transmission of toxocara canis:

• some hyobiotic larvae are mobilized by pregnancy

• enter liver and lung of fetus and wait for birth of pup

• tracheal migration to form adults (PPP: 3 weeks)

• some larvae may enter milk and infect pups by transmammary route

toxocara canis intestinal phase signs:

• heavy infections: cachexia, unthriftiness, vomit with worms, painful abdomen, death

toxocara canis migration phase signs:

• eosinophilia

• focal lesions

• eosinophilic gastroenteritis or lung problems

toxocara canis should be treated with anthelmintics that…

do not induce hyperactivity in roundworms or kill worms quickly

toxocara cati DH is…

cats (small intestine)

toxocara cati adult morphology:

• 10 cm worms with cervical alae that give arrowhead appearance to worm

toxocara cati egg morphology:

thick shelled, pitted egg containing single cell when passed in feces