Parasitology SOLO 3

Cestodes, trematodes, arthropods

Tapeowrm bodies

• flattened, segmented and ribbon-like with three sections

• scolex

  • anterior end of worm (head)

  • modified for attachment to intestinal wall of host

  • very short

  • four cup-shaped suckers, sometimes hooks (used in attachment to host)

  • has a rostellum (fleshy anterior protuberances of the scolex, may bear circular row(s) of hooks and may be retractable)

• neck

  • very short

  • just posterior to scolex

  • from which the rest of the worm grows

• strobila

  • main body of worm

  • consists of a chain of segments known as proglottids

  • newest proglottids are near the neck and become older and more mature toward the end of the tail

Overview of tapeworms

• hermaphroditic

  • each proglottid near the tail contains fully developed sex organs (gravid proglottids- uterus filled with fertilized eggs)

• nutrients are absorbed through the outer surface of the body

• onchosphere (hexacanth larvae)

  • motile, first stage of certain cestodes

  • scolex has six hooklets

• cysticercus larvae

  • thin-walled, fluid filled, bladder-like structure enclosing a scolex

Taenia saginata

• AKA beef tapeworm

• disease

  • usually asymptomatic but sometimes see GI disease w/ abdominal pain/diarrhea

• human location

  • small intestine

• infective stage is cysticercus larvae in beef

• diagnosis

  • identification of eggs, gravid proglottids, or sometimes scolices in stool

• lifecycle

  • onchosphere larvae devlops into cysticercus larvae in tissue of itnermediate host

  • cysticercus larvae ingested by humans in raw or undercooked beef

  • larvae attaches to small intestine

  • matures to adult gravid proglottids

  • free eggs and scolices passed in stool

  • eggs eaten by intermediate host

• morphology

  • gravid proglottids has 15-30 lateral branches

  • scolex has 4 cup-shaped suckers and no hooks

  • egg contains onchosphere embry with 3 pairs of hooklets

Taenia saginata onchosphere

Taenia saginata scolex

Taenia saginata gravid proglottid

Taenia solium

• AKA pork tapeworm

• disease

  • mostly the same as saginata

  • cysticercosis (when egg accidentally ingested, cyst in muscle, brain, other tissues)

• human location

  • adult in small intestine

  • occasionally cysticercus larvae in tissues

• intermediate host is pig

• diagnosis same as saginata

  • occasionally diagnosed by cysticercus larvae in stained biopsy tissue

• morphology

  • eggs is same as T. saginata

  • gravid proglottis has 7-12 uterine branches

  • scolex contains 4 suckers and a circular crown of hooks

Taenia solium scolex

Taenia solium gravid proglottid

Diphyllobothrium latum

• AKA broad fish tapeworm

• disease

  • GI disease symptoms, macrocytic anemia and neurological disturbances due to B12 deficiency

  • sparganosis (procercoid larvae invades various tissues, symptoms ass, with inflammatory reaction)

• human location

  • small intestine

• diagnosis made by identification of eggs in stool

• lifecycle

  • procercoid larvae develops into plaurocercoid larvae in fish muscle after crystacean is ingested by fish

  • plaurocercoid larvae ingested by human in raw or undercooked freshwater fish

  • plaurocercoid attaches to intestinal mucosa and matures to adult

• morphology

  • eggs is double walled and oval shaped

    • contains an operculum and a terminal knob

  • scolex has no hooks or suckers; has two long grooves called bothria which serve in attahcment to host

  • width of proglottid is greater than length; has rosette-shaped central uterus

Diphyllobothrium latum egg

Diphyllobothrium latum scolex

Diphyllobothrium latum gravid proglottid

Hymenolepsis nana

• AKA dwarf tapeworm

• disease

  • light, asymptomatic infection

  • heavy infection including GI disease with abdominal pain and diarrhea

• infective stage

  • egg

• human location

  • small intestine

• diagnosis

  • identification of eggs in feces

• lifecycle

  • eggs are ingested in contaminated food or water

  • eggs hatch in small intestine

  • onchosphere larvae invade intestinal villi

  • cysticeroid larvae matures and emerges from larvae

  • scolex everts and attaches to mucosa

  • larvae matures to adult and eggs are release in disintegrating gravid proglottids

  • eggs passed in feces

• can cause autoinfection

Hymenolepsis diminuta

• disease

  • similar to H. nana

• human location

  • small intestine

• diagnosis

  • identification of eggs in stool

• vector is rats

• only occasionally infects humans

Dipylidium caninum

• causes mild GI disease

• vector is flea

  • rarely infects humans

  • main host is dogs or cats

• flea infected with cysticercoid larvae is ingested

  • cysticercoid attaches to intestine and mature to adults

  • eggs released

• uterus contains numerous egg packets

  • 8 to 15 colorless eggs

  • contain onchosphere larvae with six hooklets

Echinococcus granulosis (dog tapeworm)

• AKA hydatid cyst or hydatid disease

  • symptoms vary according to location and size of cyst

  • liver and lung are most common locations

  • usually no symptoms until cyst is very large

  • rupture of cysts lead to anaphylactic shock and death

• sheep and other herbivores main intermediate host

• diagnosis

  • serology, ultrasound, Xray

  • ID of scolices, hooks, etc in cyst fluid (not recommended due to anaphylactic shock)

• lifecycle

  • eggs are ingested

  • larvae hatches and penetrates intestinal mucosa

  • larvae migrate to liver or lungs

  • hydatid cyst forms

  • viscera of infected herbivore eaater by dog

  • eggs passed in feces of canine

  • treatment includes removal of cyst without rupture

trematodes overview

• AKA flukes or flatworms

  • flattened, nonsegmented, leaf-shpaed worms

• adults have two suckers (acetabula); oral and ventral

• tegument (body surface)

  • metabolically active, absorbs nutrients and releasess waste

• digestive system

  • oral cavity is in center of oral sucker

  • intestinal tract ends blindly in one or two sacks

  • solid waste products regurgitated

• two types of parasitic flukes in humans

  • organ flukes- found in intestine or other tissues; hermaphroditic

  • blood flukes- found in blood vessels; unisexual

larval stages of flukes

• metacercaria

  • thickwalled, nonmotile, encysted

• miricidium

  • ciliated, first-stage, free-swimming

• sporocyst

  • encysted zygote in invertebrate host (snail)

• rediae

  • small, sac-like larval form

• cerecaria

  • adult form, free-swimming, has a tail

organ flukes infective stage

• metacercaria is the infective stage

• metacercaria ingested from water plant or aquatic creature

• rediae develop into cercariae

blood fluke infective stage

• cercaria is the infective stage

• cercaria penetrate skin

• sporocyst develops into cercariae

Fasciola hepatica

• AKA sheep liver fluke

• disease

  • fever, headache, chills, enlarged spleen, eosinophilia

  • severe infections cause biliary instruction, jaundice, and anemia

• human location

  • bile duct

• sheep is main host, but can be ingested by humans eating water plants

• diagnosis

  • identification of eggs in stool

Fasciolopsis buski

• AKA large intestine fluke

• causes GI disease with nausea, diarrhea, and mucosal ulcers

  • heavy infections can be fatal due to intestinal obstruction

• human location

  • small intestine

• humans infected by ingesting encysted metacercariae on water plants

• diagnosis

  • identification of eggs in stool

Clonorchis sinensis

• AKA Chinese/oriental river fluke

• disease

  • abdominal pain, diarrhea, enlarged liver, and jaundice

• human location

  • bile duct

• infective stage

  • metacercariae in tissue of undercooked fish

• diagnosis

  • identification of eggs in stool

• egg morphology

  • anterior end includes a thickened rime aorund the operculum

  • small knob at posterior end

Opisthorchis felineus

biliary tract fluke very similar to Clonorchis sinensis

Paragonimus westermani

• AKA oriental lung fluke

• disease

  • chest pain, cough, bloody sputum, and fever

• human location

  • fibrous cysts in lung

• infective stage

  • metacercariae in tissue of undercooked freshwater crabs or crayfish

• diagnosis

  • identification of eggs in sputum or feces

  • xray (resemble TB) serology

• egg morphology

  • includes an opercular rim on the anterior side and a terminal shell thickening at posterior end

Schistosoma species overview

• AKA blood flukes

• Schistocomiasis ranks second behind malaria as a cause of serious worldwide morbidity and mortality due to parasitic infection

• all species cause dermatitis, then fever, chills and body aches

  • more specific disease caused by different species

  • can also cause “swimmer’s itch”

Schistosoma mansoni

• causes cirrhossi of liver, bowel obstruction, bloody diarrhea, enlarged liver/spleen, and toxic reactions due to granulomas around eggs in tissues

• eggs moves through blood vessels and become trapped in liver where they mature

  • adults found in liver sinuses and veins around intestinal tract

• diagnosis is identification of eggs in stool

• found in Africa, South and Central America and West Indes

• eggs i more elongated with a lateral spine

Schistosoma japonicum

• life cycle similar to S. mansoni

• found in far east

• eggs is more spherical with lateral knob

Schistosoma haematobium

• causes urinary tract disease with leasions in bladder and bloody urine

  • also causes toxic reactions due to granulomas around eggs

• adults are found in veins of urinary bladder

  • eggs can move through blood vessels and become trapped in other tissues

• diagnosis is identification of eggs in concentrated urine

• found in Africa, and Middle East

• eggs are more elongated and has a terminal spine

body louse/crab

scabies

bed bug

flea

tick