PARASITES

parasite (geo, exposure, diagnostic?, morphology)

• ascaris lumbricoides — ROUNDWORM

• GEO: global, burden highest in tropical/subtropical regions & rural SE USA

• most common helminthic infection

• EXP: ingestion of fertilized ova

• Diagnostic & Infectious

• Ova:

  • Fertilized

    • 45 - 60 um, cleavage of internal yolk

    • yellow/brown (bile)

    • oval/spherical 

    • Thick hyaline shell

  • Unfertilized

    • 80-90 um x 40 width

    • Difficult to recognize in stool – vegetable cell

• Adult Worm: 

  • 15 - 35 cm

  • Male worms smaller, curved tail

  • smooth without striations

parasite (geo, exposure, diagnostic?, morphology)

• Clonorchis sinensis, Chinese Liver Fluke OVA

• •Trematode – Liver Fluke

  •Geographic Distribution:

  §Endemic to East Asia and Eastern Russia

  •Exposure:

  §Ingestion of freshwater fish

  §Intermediate Host: Freshwater fish

  •Diagnostic: Eggs in stool or duodenal aspirate

  •Morphology:

  §Size: 30 um x 15 um

  §Convex operculum at shoulders of egg

  §Knob/hook protrusion at abopercular end

  §Indistinguishable from Heterophyes heterophyes and Metagonimus yokogawai ova

parasite (geo, exposure, diagnostic?, morphology)

• Diphyllobrium latum (giant fish tapeworm) ova

• cestode

• GEO: freshwater in northern hemisphere & SA

• Exposure: consuming undercooked fish

• Diagnostic ova

• OVA:

  • 55-75 um x 40-55 um

  • Smooth shell, non-shoulder operculum (only operculate cestode)

    • Lack of shoulder differentiates paragonimus westermanii

  • Knob-like thickening at abopercular end

• WORM:

  • Single proglottids rare in stool, distinct to organism

  • Diagnosis based on proglottid & ova morphology

  • Segments wider than longer

  • Uterus located in center of gravid proglottid

  • Contains coiled uterus in form of compact 

parasite (geo, exposure, diagnostic?, morphology)

Enterobius vermicularis (pinworm) - roundworm nematode

Pinworm

• worldwide

• consuming ova & eggs can be aerosolized

• infectious & diagnostic

• Ova: collect early morning – tape prep

  • 30 um x 50 um

  • Thin, smooth, transparent shell

  • Oval & asymmetrical with flattened side

  • Contains developed larvae

  • Infectious & diagnostic (eggs can be aerosolized)

  • fecal-oral

• Adult Worm: 

  • Female – 13 mm x 0.5 mm

  • Male – 2 - 5 mm

  • Thin flexible outer covering 

  • Fin-like expansion at anterior end 

  • Long pointed tail

parasite (geo, exposure, diagnostic?, morphology)

hymenolepis nana (dwarf tapeworm)

• Cestode - tapeworm

• GEO: worldwide, most common cestode infection

• EXP: fecal-oral, only cestode with NO immediate host 

• Diagnostic

• Ova: Eggs immediately infectious when passed in fecal material

  • 30 - 50 um, oval

  • Thin outer shell with hexacanth (6 hooklets) & pair of polar filaments

• Adult Worm: 

  • 15-44 mm in length, may be confused with pinworm

  • Associated with mucous threads, not common in stool

  • Small scolex with protruding rostellum with 20-30 hooklets

parasite (geo, exposure, diagnostic?, morphology)

hymenolepis diminute (rat tapeworm)

• Cestode - tapeworm

• GEO: worldwide, zoonotic

• EXP: zoonotic

• Diagnostic

• Ova: not infectious person to person

  • 70 - 80 um, round to oval

  • Striated outer membrane with space between 2 membranes is smooth

  • Oncosphere – hexacanth (6 hooklets)

• Adult: 

  • 20 - 60 cm length, short & wide proglottids with 3 oval testes

parasite (geo, exposure, diagnostic?, morphology)

Ancylostoma duodenale & necator americanus (hookworms)

• Ancylostoma duodenale (Old World) & necator americanus (hookworms) (New World)

• Eggs are indistinguishable

• Differentiate by mouth:

  • Ancylostoma = 2 pairs cutting teeth

  • Necator = cutting plate

• Distinguished from strongyloides by pointed tip of tail

• Cause anemia

• Larvae passed in stool & penetrate skin, carried through bloodstream into lungs & swallowed

• Adults attach to intestine causing blood loss & IDA

• In stool 

• Ova:

  • 2500-5000 eggs/day

  • 60 um x 40 um

  • Oval, thin-shelled, smooth

  • Non-pigmented & transparent

• Adult Worm: 

  • Up to 1.5cm length

  • Upper intestine attached to mucosa by biting “hooks”

  • Differentiate by mouth:

    • Ancylostoma = 2 pairs cutting teeth

    • Necator = cutting plate

parasite (geo, exposure, diagnostic?, morphology)

Morphology of Taenia saginata (Beef Tapeworm) & Taenia solium (Pork Tapeworm) ova

• GEO: endemic to SA, Africa, China

• EXP: undercooked beef (saginata)/pork (solium)

• Consumption of T. solium ova can cause cystericosis

• Cannot differentiate ova

• Ova:

  • 30 - 35 um

  • Radial striated edge

  • Internal oncosphere contains 6 refractile hooks

  • Lab contaminant

• Adult Worm: scolex & proglottid needed for ID

  • Gravid proglottids longer than wide

  • T. saginata: 

    • 4-10m

    • 1000-2000 proglottids

    • 12-40 lateral branches

    • Unarmed scolex

  • T. solium:

    • 2-4m

    • 800-1000 proglottids

    • 7-13 lateral branches

    • Armed scolex

parasite (geo, exposure, diagnostic?, morphology)

Trichuris Trichuria, Whipworm – Adult Worm

§Size: 

•Males: 30-45 mm x 1 mm, coiled posterior

•Females: 35-50 mm x 1 mm, straight posterior

§Long whip-like anterior

§Reside in large intestine, cecum, & appendix

parasite (geo, exposure, diagnostic?, morphology)

Trichuris Trichuria

• Ova: 

  • 50-55 um x 20-25 um

  • Barrel - shaped, thick shell, polar plugs at each end

  • Unembryonated when passed in stool 

• Adult Worm:

  • Males = 30-45 with coiled posterior

  • Females = 35-50 mm with straight posterior

  • Whip-like anterior

  • In large intestine, ceum, appendix

parasite (geo, exposure, diagnostic?, morphology)

Schistosoma mansoni (Blood Fluke)

• Fluke, trematode

• GEO: sub-saharan Africa & some SA countries

• EXP: laravel penetration through skin & freshwater

• Diagnostic

• Ova: 

  • Large, 114-180 um x 45-70 um

  • Prominent lateral spine near posterior

  • Anterior is tapered & slightly curved

  • excrete d in stool

  • Contain mature miracidium

parasite (geo, exposure, diagnostic?, morphology)

Schistosoma japonicum (Human Blood Fluke)

• Tematode – fluke

• GEO: china, philippines, sulawesi

• EXP: snail intermediate host, larvael penetration

• Diagnostic

• Ova:

  • Large & rounded

  • 70-100 um x 55-64 um

  • Spine is smaller & less conspicuous than other species

  • Shed in stool

parasite (geo, exposure, diagnostic?, morphology)

Schistosoma japonicum, Blood Fluke – Male

§Size:

•Males: 1.2 cm x 0.5 mm

§Spines on oral & ventral suckers

§Flatworm with hooks

parasite (geo, exposure, diagnostic?, morphology)

Schistosoma japonicum, Blood Fluke – Female

Size:

•Females: 2 cm x 0.4 mm

§Spines on oral & ventral suckers

§Female integument is rigid with fewer spines than in oral/ventral sucker

§Flatworm with hooks

parasite (geo, exposure, diagnostic?, morphology)

Schistosoma japonicum, Blood Fluke – Male & Female in Copulum

Size:

•Males: 1.2 cm x 0.5 mm

•Females: 2 cm x 0.4 mm

§Spines on oral & ventral suckers

§Female integument is rigid with fewer spines than in oral/ventral sucker

§Flatworm with hooks

parasite (geo, exposure, diagnostic?, morphology)

Schistosoma haematobium (Urinary Blood Fluke)

• GEO: Africa & ME

• EXP: larvael penetration through skin

• Diagnostic

• Ova:

  • Large, 110-170 um x 40-70 um

  • Terminal spine

  • Eggs with mature miracidium

  • Shed in URINE

parasite (geo, exposure, diagnostic?, morphology)

Trichinella spiralis, Pork Worm – Encysted Larvae

•Geographic Distribution: Worldwide

•Exposure:

§Undercooked meat

•Infectious & Diagnostic

•Morphology:

§Size: 152 um x 117.5 um

§Coiled larvae (C shaped)

parasite (geo, exposure, diagnostic?, morphology)

Trichinella spiralis, Pork Worm – Adult Worm

•Geographic Distribution: Worldwide

•Exposure:

§Undercooked meat

§Neither? Infectious or Diagnostic

§Morphology:

§Size:

•Males: 1.2 mm - 1.6 mm length

•Females: 2.2 mm – 3.5 mm length

§Small, slender

§Tapers at anterior

§Collagenous cuticle with ridges & creases

parasite (geo, exposure, diagnostic?, morphology)

vegetable spiral fiber

parasite (geo, exposure, diagnostic?, morphology)

Schistosoma intercalatum 

\Restricted to east-central Africa

• Eggs similar to s. Haematobium in shape with terminal spine

• Longer, 140-240 um

• Equatorial bulge & shed in stool