Parasitology: Helminths

nematodes

round worms

• Enterobius vermicularis (pinworm)

• Trichuris trichiura (whipworm)

• Ascaris lumbricoides

• Strongyloides stercoralis (threadworm)

• Trichinella spiralis

• Wuchereria bancrofti

cestodes

tapeworms

• Diphyllobothrium latum

• Taenia sp.

• Hymenolepsis nana

• Hymenolepsis dimunita

• Dipylidium caninum

trematodes

flukes (intestinal, lung, and blood)

• Fasciolopsis buski

• Fasciola hepatica

• Clonorchis sinensis

• Paragonimus westermani

• Schistosoma spp.

Flukes: structure, infection, and reproduction

• structure

  • flattened, oral sucker at the anterior end and a ventral midline sucker (picture: liver fluke)

• infection

  • ingestion of raw or undercooked aquatic animals or vegetation

• reproduction

  • intestinal and organ flukes are hermaphroditic

  • blood flukes reproduce sexually

Fasciolopsis buski

• giant intestinal fluke

• hermaphroditic

• finding adult flukes or eggs is diagnostic

Fasciola hepatica

• common liver fluke

• human infections are rare (diarrhea, upper right quandrant pain, hepatomegaly, cirrhosis, and liver obstruction)

Paragonimus westermani

• lung fluke

• excysts in the small intestine and burrows through the duodenal wall into the peritoneal cavity, then migrates to the lungs

• diagnosed with sputum specimens

Shistosoma spp.

• blood flukes

• male and female forms

• cylindrical shaped

• humans are infected by direct penetration of the skin

• S. mansoni - lives in the venules of the large intestine

• S. japonicum - lives in the venules of the small intestine

• S. haematobium - lives in the veins around the bladder

characteristics of tapeworms (cestodes)

• requires immediate hosts

• hermaphroditic

• growth includes the addition of proglottids

• scolex has suckers as a means of attaching to intestinal mucosa

• diagnosis made by finding eggs in feces

What is the common name of the tapeworm Diphyllobothrium latum, and what symptoms does it cause in human hosts?

• fish tapeworm

• vitamin B12 deficiency and megaloblastic anemia, intestinal obstruction, and abdominal pain

T. saginata is the ___ tapeworm and T. solium is the ___ tapeworm

beef, pork

Hymenolepsis nana common name

dwarf tapeworm

Hymenolepsis diminuta common name

rat tapeworm

Dipylidium canium common name

dog tapeworm

roundworm (nematode) characteristics

• largest group of helminths

• bilateral symmetry

• unsegmented

• separate sexes

Enterobius vermicularis

• pinworm

• female migrates out of the anus at night to lay eggs

• stool specimens not good for diagnosis

Trichuris trichiura

• whipworm

• often seen alongside Ascaris infections

Ascaris lumbricoides

• large intestinal roundworm

• seen alongside Trichuris trichiura

• heavy infection may cause lactose intolerance

Necantor americanus is known as the ___ ___ hookworm and Ancylostoma duodenale is known as the ___ ___ hookworm

new world, old world

What is the difference between the hookworms Necantor americanus and Ancylostoma duodenale?

• N. americanus has cutting plates and A. duodenale has teeth

How do adult hookworms infect humans?

by attaching to the small intestine and ingesting blood for nutrition

• they secrete platelet inhibitors, anticoagulants, and also inhibit nutrient absorption

Strongyloides stercoralis

• threadworm (type of roundworm)

• has a direct and indirect life cycle

• can cause severe, chronic infections due to the ability to cause “hyperinfection syndrome”

Trichinella spiralis

• infection of muscle tissue with larvae

• how it migrates to muscle tissue:

  • human eats undercooked meat

  • adult lives in the intestine and gives birth to larvae

  • larvae penetrate the intestinal wall and enter circulation

  • larvae are deposited in striated muscle where they coil and become encapsulated

Wuchereria bancrofti

• causative agent of elephantitis (lymphatic filariasis)

• adult worm lives in the lymphatics and lymph nodes of the lower extremities

• sexual reproduction produces microfilariae (motile larva of filarial worms), which enters the bloodstream

• edema and hyperplasia

Define the following: operculum and unembryonated

• operculum

  • a cap-like structure

  • found in flukes and tapeworm eggs

• unembryonated

  • eggs that are not in the infective larval stage yet

What is this?

Fasciolopsis buski egg

• unembyonated

• yellow-brown

What is this?

Clonorchis sinensis egg

• flask-shaped

• ‘shoulders’ on one end (right in pic) and a knob on the other (left in pic)

What is this?

Paragonimus westermani egg

• oval-shaped with an operculum

What is this?

Schistosoma mansoni egg

• prominent lateral spine

• elongated

What is this?

Schistosoma japonicum egg

• round

• has a lateral knob

What is this?

Schistosoma haematobium egg

• elongated

• terminal spine

What is this?

Diphyllobothrium latum egg

• operculated (small in pic)

• unembryonated

• yellow-brown

• small knob like protuberance on one end

What is this?

Diphyllobothrium latum adult tapeworm

• proglottids have a rosette-shaped uterus

• scolex has two sucking groves

What is this?

Taenia egg

• embryonated (infective)

• round

• thick wall with radial striations

What is this?

T. saginata adult tapeworm

• 15-20 uterine branches (more branches than T. solium)

• 4 suckers with NO hooks

What is this?

T. solium adult tapeworm

• 7-13 uterine branches (less than T. saginata)

• 4 suckers with hooks

• rostellum with two rows of hooks

What is this?

Hymenolepsis nana egg

• spherical or oval

• inner membrane has a hexcanth embryo with 6 hooklets

• (H. diminuta eggs are slightly larger)

What is this?

Dipylidium caninum eggs

• appears in packs of 15-25 eggs

What adult tapeworm is this?

Dipylidium caninum (dog tapeworm)

• retractible scolex

• proglottids are pumpkin seed shaped and have a genital pore on each side

Which roundworm egg is this?

Enterobius vermicularis

• oval

• colorless

• slightly flat on one side

What adult roundworm is this?

Enterobius vermicularis

• males have a curved posterior end

• females have a long pointed tail

What roundworm egg is this?

Trichuris trichiura

• brown and barrel-shaped

• unembryonated

• thick walls

• bipolar plugs

What adult roundworm is this?

Trichuris trichirua

• males have a thin anterior and a thick coiled posterior (pic)

• females have a thin anterior and a thick straight posterior

Which roundworm egg is this?

Ascaris lumbricoides

• elongated and granulated

• fertile eggs are oval, have thick walls, and a brown outer layer

• picture is an unfertilized egg

What egg is this?

Ascaris lumbicoides, fertilized

What do the eggs of Necator americanus and Ancylostoma duodenale look like?

• oval

• colorless

• thin-shelled

• usually contains an embryo

What adult roundworm is this?

Strongyloides stercoralis

• blue: esophageal bulb

• red: genital primordium

What adult roundworm is this?

Wuchereria bancrofti microfilariae