Parasitology Exam 2

helminths

nematodes: roundworms

cestodes: tapeworms

trematodes: flukes

What are nematodes commonly known as?

Roundworms

What is the largest group of worms that infect humans?

Nematodes

How is the severity of disease caused by nematodes related to worm burden?

Disease is proportional to worm burden

Are nematodes directly fatal?

Rarely

What types of nematodes can cause infection?

Gut, filarial (microfilariae), and zoonotic

gut nematodes

•Enterobius vermicularis (pinworm)

•Trichuris trichiura (whipworm)

•Ascaris lumbricoides

•Hookworms

•Strongyloides stercoralis

Are the eggs of gut nematodes usually seen?

Yes, but not always!

What is the common name for Enterobius vermicularis?

Pinworms

What is the most common symptom of Enterobius vermicularis infection?

Nocturnal pruritus ani (nighttime anal itching)

What is the life cycle of Enterobius vermicularis?

Eggs are ingested, mature in the small intestine, and females travel to the perianal folds to lay eggs.

How long does it take for Enterobius vermicularis eggs to mature?

4-6 hours

What is the morphology of adult female Enterobius vermicularis?

Pointed tail about 1 cm long

What is the morphology of Enterobius vermicularis eggs?

Medium size, oval but flattened on one end, resembling a 'D'

Do Enterobius vermicularis eggs require soil to develop into the infective stage?

No, they can develop without needing soil.

What method can be used to look for Enterobius vermicularis eggs?

Scotch tape method

Swube Tube

Why are adult Enterobius vermicularis worms rarely seen in stool?

They do not attach and may travel to other areas.

Who is most commonly affected by Enterobius vermicularis infections?

Children

What causes the itching associated with Enterobius vermicularis infection?

Glue-covered eggs

What is the common name for Trichuris?

Human whipworm

What is a key feature of the life cycle of Trichuris trichiura?

It requires soil incubation for eggs to mature.

How do Trichuris trichiura eggs develop into an infective stage?

They need soil for maturation, often from 'night soil' used as fertilizer.

Where do Trichuris trichiura eggs hatch in the human body?

In the small intestine.

What is the primary location of adult Trichuris trichiura in the human body?

Cecum of the intestine.

What is a significant symptom of severe Trichuris trichiura infection?

Trichuris dysentery syndrome, which can cause blood diarrhea.

What is a common complication associated with Trichuris trichiura infection?

Rectal prolapse

Describe the egg morphology of Trichuris trichiura.

They have mucoid bipolar plugs and are very oval in shape, like lemons

What is the adult morphology of Trichuris trichiura?

The head is thin, allowing it to insert into the intestine. The tail forms a spiral "whip", and is thicker.

What disease is caused by Ascaris lumbricoides?

Ascariasis

What are the clinical features of Ascaris lumbricoides infection in the lungs?

Loeffler's syndrome (dry cough, asthma, fever)

What are the clinical features of Ascaris lumbricoides infection in the intestine?

Vague abdominal discomfort, acute colicky pain, restless sleep, diarrhea, malabsorption

What is a major complication of Ascaris lumbricoides infection?

Intestinal obstruction

What is the life cycle of Ascaris lumbricoides?

Eggs develop in soil, larvae migrate to lungs, are coughed up and swallowed, then mature in the intestine.

What is the morphology of fertile Ascaris lumbricoides eggs?

Rounder

45-75 microns

Mammallations

Smoother

What is the morphology of infertile Ascaris eggs?

Oblong

90 microns long

Mammallations

What can happen to Ascaris lumbricoides eggs that lose their mammillations?

They can become decorticated

What is the adult worm morphology of Ascaris lumbricoides?

Largest gut nematode

How do Ascaris lumbricoides worms prevent being passed in the intestine?

They swim upstream instead of attaching.

How long can adult trematodes live for?

decades

What does an operculated egg indicate?

The egg goes into water

What are ectopic infections caused by Ascaris lumbricoides?

Infections in the appendix, pancreas, or bile ducts.

What is the common name Ancylostoma/Necator?

Hookworm

What are the clinical features of hookworm infection?

Ground itch (foot), Loeffler's syndrome, anemia due to blood loss

What is the life cycle of hookworm?

Eggs in feces mature into larvae, penetrate skin (usually in lower limb), migrate to lungs, are coughed up and swallowed, and then grow in the small intestine.

What is the egg morphology of hookworm?

Bumpy inside and smooth outside/cell wall

Inside is noticed first - cell wall is less easily visible

What is the adult worm morphology of Necator americanus?

Two cutting blades

What is the adult worm morphology of Ancylostoma duodenale?

Vampire teef

Ground itch

a skin condition caused by skin penetration of hookworm larvae, usually in lower limbs

Loeffler's syndrome

Symptoms associated with the lung migration stage of intestinal nematodes

How do hookworms cause anemia?

They bite into the intestinal mucosa and feed on blood (lil vampies)

What is the common name for Strongy?

Threadworm

What is the process by which Strongyloides stercoralis larvae enter the body?

Skin penetration

What kind of infection can Strongy cause?

Ongoing autoinfection

What skin condition can result from Strongyloides stercoralis infection?

Ground itch

What syndrome can occur in the lungs due to Strongyloides stercoralis infection?

Loeffler's syndrome

What intestinal symptoms can Strongyloides stercoralis cause?

Bloody diarrhea and chronic colitis

How long can a Strongyloides stercoralis infection persist?

10-20 years

Why is Strongyloides infection particularly dangerous for immunocompromised individuals?

Hyperinfection can occur and be deadly

When might serology be used to diagnose Strongyloides?

To determine a previous exposure - often before an individual is immunosuppressed

What is the adult worm morphology of Strongyloides?

Are Strongy eggs seen?

No, and even larvae are difficult to see

What organism can be identified the agar culture method?

Strongy

Agar culture method

Stool is plated on agar and the migration of the larvae will drag bacteria with it in characteristic directional patterns

What type of food is commonly associated with anisakiasis?

Undercooked fish, particularly cod.

What happens to anisakis larvae in humans?

They cannot mature and instead burrow into the small intestine tissue, causing pain.

What are the symptoms of anisakiasis?

Violent abdominal pain.

What can happen to anisakis larvae after they burrow into human tissue?

They may die or curl up and wait to be eaten by another host.

What kind of nematode is Trichinella:

zoonotic

What type of meat is commonly associated with Trichinella spiralis infection?

Undercooked pork and bear.

What happens to the larvae of Trichinella spiralis after ingestion?

They are released into the intestine, mature, and go into circulation.

Is Trichinella symptomatic?

may be asymptomatic if the infection is light

Where do the larvae of Trichinella spiralis migrate after entering the bloodstream?

muscle tissue

What are some potential complications of Trichinella spiralis infection?

CNS involvement and myocarditis.

What symptoms can muscle encystment from Trichinella spiralis cause?

Myalgia and weakness.

What type of tissue do we examine to diagnose Trichinella spiralis infection?

Muscle tissue

Another name for the muscle cells containing encysted Trichinella

nurse cells

Practice associated with fecal-oral transmission of the nematodes

Use of night soil

scotch tape/swube method for E. vermicularis

Sticky side of clear tape is pressed to perianal folds in the morning to collect eggs

Which nematodes have a soil maturation phase?

Trichuris

Ascaris

Necator/Ancylostoma

Strongy

Which nematodes have a larval migration phase through the lungs?

Ascaris

Necator/Ancylostoma

Strongy

Which nematode is diagnosed by finding rhabditiform larvae in the stool?

Strongyloides

Which nematode is acquired through ingestion of contaminated meat?

Anisakis (fish)

Trichinella (pork, bear)

Which nematode has an auto-infective stage?

Strongyloides

Which nematodes infect humans via skin penetration?

Necator/Ancylostoma

Strongyloides

Cestodes

Tapeworms, flatworms

Types of cestodes

· Taenia solium

· Taenia saginata

· Diphyllobothrium latum

· Dipylidium caninum

· Hymenolepsis nana

· Echinococcus spp.

Where do most adult Cestodes/Tapeworms reside?

In the intestine

What can stool samples show in relation to Cestodes/Tapeworms?

Eggs and/or proglottids

What diseases are caused by larval tapeworms when humans are the intermediate host?

Cysticercosis and Echinococcosis

What methods are used to diagnose Cysticercosis and Echinococcosis?

Serology and examining larvae in tissue

What does the presence of hooklets in an egg indicate?

It is some kind of tapeworm

What is the general morphology of cestodes?

Long, flattened ribbonlike worms

Do cestodes have a gut or body cavity?

No, they absorb nutrients through their skin.

What are the main parts of an adult cestode?

Scolex (head), neck, and body (made of proglottids).

What are proglottids?

Self-contained hermaphroditic reproductive units.

How are proglottids connected to the rest of the cestode body?

By a common cuticle, nerve trunks, and excretory canals.

What is unique about the reproductive capability of each proglottid?

Each proglottid produces its own eggs.

What is the definitive host for Taenia species?

Humans

What type of reproduction occurs in the definitive host of Taenia?

Sexual reproduction

Where do adult Taenia worms reside in humans?

In the gut