112.2 Parasitology

How are pinworm infections acquired

How are pinworm infections acquired

Direct hand to mouth an autoinfections

Name the patient specimen that best detects pinworm infections

Mature eggs on a scotch tape prep from the perianal area first thing in the morning

Where do adult pinworms live in humans

Hand to mouth and migrate from the colon to the perianal area and lay eggs in the perianal region

Describe patient symptoms of heavy Enterobius infections

Perianal itch and local irritation and scratching

List the infective and diagnostic stages of pinworm infections

Infective: mature egg with larva
Gravid stage: migrates from colon to perianal area (12 midnight to 2am) and lays eggs in perianal region
Diagnostic: The mature eggs on scotch tape prep

Describe and picture mature pinworm eggs

Eggs are oval, flattened on one side, thin, colorless shell, egg embryonated with C-shape larva

Explain why pinworm infections do not require development in the soil to become infective

Because it's immediately infective

Define autoinfection

Reinfection produced by a parasite that is already in the patients body

Which intestinal roundworms are autoinfective

Enterobius and Strongyloides

Which patient specimen is most commonly used to ID roundworm infections

Stool

Distinguish between immature and mature helminth eggs

Immature: oval with or without a thick coat
Mature: round to oval, thick, bumpy corticoid coat with a thick shell beneath it (some may or may not have a coat)

Name 2 roundworms whose infections are acquired by "eating dirt"

Ascaris lumbricoides and Trichuis trichiura

Where do Ascaris and Trichuis adult worms live

Colon and small intestines

Describe symptoms of heavy burdens of Ascaris

Transient pneumonia (they migrate through the lungs), diarrhea, obstruction of bile duct/intestines/ or aappendix

Describe and picture Corticated fertile Ascaris eggs

Round to oval, thick mammilated coat

Describe and picture Decorticated fertile Ascaris eggs

Round to oval but no thick coat

Describe and picture Infertile Ascaris eggs

Oval with or without a thick coat

Describe the symptoms of heavy burdens of Trichuris (whipworm)

Mimics ulcerative colitis in children and IBS in adults, diarrhea (bloody or mucoid), rectal prolapse (especially in children

Describe and picture eggs of Trichuris seen in patient stools

Barrel shaped egg, undeveloped unicellular embryo, smooth shell surface with thick yellow-brown shell color due to bile staining, hyaline plug at each pole

List the infective and diagnostic stages of Trichuris infections

Infective: eggs embyonate in soil by 1 month
Diagnostic stage: undeveloped eggs in feces

Which roundworm may cause a transient pneumonia in its host because it migrates through the lungs

Ascaris lumbricoides

How are primary infections of hookworm and Strongyloides infections acquired

Filariform larvae hatch in soil and penetrate skin, especially through the feet

Between hookworm and Strongyloides, which one causes autoinfection

Strongyloides stercoralis

List the two genera/species of hookworms

Necator americanus and Ancylostoma duodenale

Where do adult hookworms live in the body

Small intestine

How do hookworms feed in humans

They are bloodsuckers

Describe "ground itch" and explain what causes it

Dermatitis from repeat infections

Describe the blood disorder caused by heavy burdens of adult hookworms

Microcytic hypochromic anemia

Explain how adult hookworms cause microcytic hypochromic anemia

They cause chronic blood loss

Describe and picture hookworms seen in patients stool

Eggs broadly oval, thin, colorless shell, 4-8 cell stage embryo when passed in stool (rhabditiform larvae rarely seen in stool)

Which other roundworm egg may be confused with a hookworm egg

Ascaris eggs, dercorticated

List the infective and diagnostic stage of hookworm infection

Infective: filariform larva, eggs shed in stool and mature in soil; two larval staged develop in soil: rhabditiform and filariform; rhabditiform may been seen only if stools left at room temp for several days
Diagnostic: eggs in feces; embryo develops rapidly to rhabditiform larva and hatches in warm, moist soil (24-48 hours) and rapidly molts

Distinguish between the rhabditiform and filariform larvae of hookworm

Rhabditiform larva have a long buccal cavity and a small genital primordium. Filariform larva have a pointed tail and a esophageal intestinal ratio of 1:4

Why is the hookworm rhabditiform larvae not normally seen in a patients stool

Because they need time to hatch

Under what conditions may hookworm rhabditiform larva be seen in stool

If the stool is left at room temp for several days

List two ways Strongyloides infections may be acquired

Penetrate the skin and enter the lymphatic system or blood; autoinfection when larva develops to infective stage in intestine

Where do adult Strongyloides live in humans

Mucosa of the small intestine. Parthenogenic parasite is female only

Distinguish between the Strongyloides rhabditiform and filariform larvae

Rhabditiform is the first stage seen in stools. Short buccal cavity, large genital primordium. Filariform is the second stage. Infective form, notched tail and esophageal/intestinal ratio is 1:2

Which of the two larvae of Strongyloides is most commonly the diagnostic stage

Rhabditiform

Under what conditions may a Strongyloides filariform larvae be seen in stool

If the patient has a heavy burden

Distinguish between rhabditform larvae of Strongyliodes and hookworm

-Strongyloides is short buccal cavity with large genital primordium
-Hookworm is long buccal cavity with small genital primordium

Describe patients symptoms of heavy burdens of Stongyloides infections

Larval dermatitis from repeat infections, transient pneumonia when migrating through the lungs, diarrhea, vomiting, moderate eosinophilia

What population are most susceptible to heavy Strongyloides infections

Immunocompromised hosts

Which roundworms are infective by ingesting mature eggs

Ascaris lumbricoides and Trichuris trichiura

Which roundworms are infective by filariform larvae penetrating the skin

Stronglyloides and Necator americanus

Which roundworm infection is not dependent on the soil for development of its infective stage because its egg is immediately infective

Enterobius vermicularis

Which two roundworms may cause a transient pneumonitis because its larvae migrates through the lungs

Ascaris and Strongyloides

Name the roundworm infections most commonly diagnosed by finding eggs in stool

Ascaris

Name the roundworm infections most commonly diagnosed by rhabditiform larvae in stool

Strongyloides

Name the roundworm infections most commonly diagnosed by eggs on scotch tape preps

Enterobius

Which roundworm egg would not be recovered by concentrating the stool by the Zinc sulfate flotation procedure

Ascaris eggs

Which of the intestinal roundworm infections are best controlled by good sanitary waste disposal methods

Necator americanus

Which of the intestinal roundworm infections are best controlled by good personal hygiene

Enterobius

Where do adult Trichinella live in humans

The intestines

Where do larval Trichinella forms live in humans

Encysted in striated (skeletal) muscle. "Nurse cells"

List the definitive and intermediate hosts of Trichinella spiralis

Definitive: Humans
Intermediate: Pigs, bear, deer, walrus, etc

How do humans acquire Trichinella spiralis infections

Eating undercooked pork or bear

Describe the symptoms of heavy Trichinella infections

Eye edema, blurred vision, eosinophilia, fever, headache, local muscle inflammation, epilepsy if in brain tissue, nausea, vomiting, abdominal pain, diarrhea, and headache

Describe the diagnostic stage an best specimen for diagnosing Trichinella

Larva encysted in striated muscle; gastrocenemuis, deltoid. Muscle biopsy is where diagnostic larva is; adults and larvae are not seen in stool

How do humans acquire Drancuculus infections

Infected copepod ingested in drinking water

How is the diagnosis made for Drancuculus

Visually observe skin blisters or emerging worms

How is the adult worm of Drancuculus removed

Slow withdraw from blister by wrapping it around a revolving small stick over several days (process can be completed in a few days but usually requires weeks or even months; surgical removal of adults

How are Filariae infections acquired

Enter skin from arthropods feeding site, adults live in the lymphatic system or subcutaneous tissues, microfilariae are ingested by arthropods from blood or subcutaneous nodules, where they develop into the infective larval form

Describe and picture Wuchereia bancrofti

No nuclei in tail tip with a sheath present
Causes: granulomatous lesions, fever, chills, eosinophilia, and elephantiasis

Describe and picture Brugia malayi

Nuclei in tail tip, no continuous nuclei with a sheath present
Causes: granulomatous lesions, fever, chills, eosinophilia and elephantiasis

Describe and picture Loa loa

Nuclei in tail tip in a posterior continuous row with a sheath
Causes: Calabar swellings (eye edema), proteinuria and endomycardial fibrosis

Describe and picture Onchocerca volvulus

No nuclei in the tip with no sheath present
Causes: fibrotic skin nodules, blindness

How do humans acquire zoonotic nematode infections

Accidentally acquired from contact with contaminated animal feces, contaminated soil, or encountering the larvae eggs

How are Zoonotic infections most commonly diagnosed

Based on patient's symptoms

How does the phrase "strangers in a strange land" describe Zoonotic infections

Migrating larvae that are unable to develop into adults in their foreign host (larvae eventually die off and symptoms subside

Describe viceral larval migrans

An infection by zoonotic helminth larvae that migrate aimlessly throughout the boy because they are in an aberrant host

Describe how humans acquire VLM

By ingesting things that have been contaminated by the eggs

How to humans acquire Dirofilaria infections

Mosquito bites

Where do adult Dirofilaria live in dogs

Heart

Describe cutaneous larval migrans

Red, itchy tracts under the skin on the legs as larvae migrates

How do humans acquire CLM

When people walk or sit on the beach sand or soil where infected dogs or cats have defecated

barrel-shaped, thick shell, bipolar plugs

Trichuris

round to oval, thick shell, mammalated

Fertile Ascaris

oval, flattened on one side, thin shell

Enterobius

large, oval, with thick coat or no coat

Infertile Ascaris

oval, thin shell, 4-8 cell embryo

Hookworm

What is Ascaris infective form

Egg

What is Strongyliodes infective form

Filariform larva

What is Hookworm infective form

Filariform larva

What is Enterobius infective form

Egg

What is Trichuris infective form

egg