11 - Parasitology: Nematodes

Question 1

Describe some characteristics of the phylum Nematoda? Is their body segmented? What is the structure of their body cavity? What is it’s digestive system like?

Answer 1

Free-living parasites: ingestive and invasive.

Mostly dioecius round worms with unsegmented body.

Cavity filled with pressurized fluid; epidermis covered with tough elastic cuticle; development requires molting. Hydroskeleton for locomotion.

Complete digestive system.

Question 2

What are the important round worm parasites in humans?

Answer 2

1. Enterobius vermicularis
2. Trichuris trichiura
3. Ascaris lumbricoides
4. Necator americanus
5. Strongyloides stercoralis
6. Trichinella spiralis
7. Toxocara canis

Question 3

What is the life cycle of enterobius vermicularis (pinworm)?

Answer 3

Eggs on perianal folds with larvae inside the eggs mature in 4-6 hrs.

Embryonated eggs ingested by humans and larva hatch in small intestines.

Adults in lumen of cecum and migrate to perianal region at night to lay eggs.

Question 4

What is the appearance of enterobius vermicularis adult worms and eggs?

Answer 4

Adult worms can be 2-13 mm.

Up to 20000 eggs/females in perianal folds.

Question 5

How is enterobius vermicularis transmitted? What is the epidemiology?

Answer 5

Ingestion of eggs, inhalation of egg-laden dust (eggs can survive indoors 2-3 weeks); autoinfection.

Occurs world-wide, common in temperate redions. Spread in crowded conditions such as daycares and schools.

Question 6

What is the pathology associated with enterobius vermicularis?

Answer 6

Enterobiasis: intense perianal itching, secondary infections due to scratching.

Rare urogenital problems in females due to worm migration into vagina.

Psychological trauma.

Question 7

How do you treat and prevent Enterobiasis from enterocius vermicularis?

Answer 7

Albendazole, mebendazole, pyrental pamoate.

Whole family repeated treatment to stop reinfection. Good personal hygiene, thorough house cleaning.

Question 8

What is the life cycle of Trichuris trichiura (whipworm)?

Answer 8

Unembryonated eggs in feces.

Obligatory 2-cell stagef in soil.

Advanced cleavage. Embryonated eggs ingested and larva hatch in sm. intestine.

Adults in cecum.
(humans are only host).

Question 9

What is the size and shape of the adult worms and eggs of trichuris trichiura?

Answer 9

Adult worm: 3-5 cm with skinny anterior portion.

3000,10000 eggs/day per female. Bile-stained eggs that are oval in shape with a blob on each end; ~50 microM.

Question 10

What is the transmission and epidemiology of trichuris trichiura?

Answer 10

Ingestion of embryonated egggs; no direct person to person (soil stage!).

Worldwide: common in tropical regions (third most common worm infection). Use of human waste as fertilizer.

Question 11

What is the pathology caused by Trichuris Trichiura?

Answer 11

Trichuriasis (depends on worm burden).

Low to moderate: usually none. Some bleeding and secondary bacterial infection. Anterior end of worm penetrates deep into intestinal mucosa.

High: disrupted mucosa; bloody stool, abd. pain, apandicitis. Anemia in kids. Impaired growth and cog development.

Question 12

What is the immunity associated with Trichuriasis from Trichuris Trichiura? What is the treatment?

Answer 12

Some evidence for acquired immunity in natural infections.

3 days of albendazole, mebendazole, ivermecton; iron supplementation.

Question 13

What is the life cycle of Ascaris lumbricoides (round worm)?

Answer 13

Fertilized egg from feces goes through obligatory soil stage.

Ingested by humans (only host) and migrates to the lungs to be coughed up and then swallowed and then grows in small intestine.

Question 14

What is the structure and size of adult worms and eggs of Ascaris lumbricoides?

Answer 14

Fertilized egg is 45-75 microM and round. Unfertilized is oval.

Adult worm is long and round and boring.

Question 15

What is the transmission and epidemiology of Ascaris Lumbricoides?

Answer 15

Ingestion of embryonated eggs; no person to person contact (soil stage)

Worldwide; tropical and subtropical regions. (most common worm infection)

Considered a US neglected disease of poverty.

Question 16

What is the pathology of Ascaris lumbricoides (low and high)?

Answer 16

Called Ascariasis

Low: usually non; worms do NOT attach to intesine mucosa but adult may migrate into bile duct and liver.

High: abd. tenderness, obstruction, growth impairment in children. Stressed worms may migrate to nose or peritoneum through body wall.

Question 17

What is the immunity and diagnosis of ascaris lumbricoides? What about the treatment?

Answer 17

Immunity: inflammation from larva migration in lung, pneumonitis and eosinophilia.

Diagnosis: Bile-stained fertilized and unfertilized eggs in stool. (in pulm phase there’s eosinophilia in sputum).

Treatment: 1-3 days of albendazole, mebendazole, ivermectin.

Question 18

What is the life cycle of Necator Americanus and Ancyclostoma duodenale (hookworms)?

Answer 18

Eggs in feces and Rhabditiform larva hatches.

Obligatory soil stage occurs and forms a filariform larva which can penetrate the skin (ie the foot).

Migrates to small intestine.

Question 19

What are the life stages of the hookworm?

Answer 19

Filariform larva is the infective form.

Anterior end of adult has chewing abilities (teeth) that chew into the wall of the intestine and suck blood out of the patient.

Question 20

What is the epidemiology of hookworms? What is the pathology?

Answer 20

Worldwide; tropical conditions. Poor public sanitation; children and farmers without shoes.

Rash and itching near penetration. Microcytic anemia due to significant blood loss. Eosinophilic enteritis with abd. pain.

Severe: mental and physical retardation.

Question 21

What is the drug only used on flatworms? (not nematodes)

Answer 21

Praziquantal.

Inhibits their purine synthesis.

Question 22

How are hookworms diagnosed and treated? What are some ways to prevent them?

Answer 22

Eggs in (concentrated) stool, larva for species differentiation; anemia.

1-3 days albendazole, mebendazole, pyrantal pamoate; iron supplements/blood transfusion.

Public hygeine; wearing shoes, avoiding skin contact with contaminated soil.

Question 23

What are the three developmental options for Rhabditiform larvae or Strongyloides stercoralis?

Answer 23

1. Direct: hookwork-like except larvae in feces; no amplification
2. Indirect: sexual repro in soil, environmental amplification
3. Autoinfection: matrucation in host, penetration of colonic mucosa or perianal skin. Host amplification.

Question 24

What is the transmission and epidemiology of Strongyloides stercoralis?

Answer 24

Penetration of the skin by filaform larvae; autoinfection possible.

Globally in tropical regions and warm temperate zones. Caused by poor public sanitation, often associated with agriculture. Domestic pets are reservoir hosts.

Question 25

What is the pathology of Strongyloides stercoralis? Where does a rash generally occur with autoinfection?
What can autoinfection lead to?

Answer 25

Strongyloidiasis

Pulm symptoms as in ascariasis and hookworm infections. Heavy worm load leads to dysentary, malabsorption, epigastric pain.

Rash on buttocks, legs, lower back due to autoinfection.

Autoinfection and immunosupression leads to hyperinfection and can eventually grow in all organs. (mortality ~85%).

Question 26

What is the immunity of Strongyloides stercoralis? How would you diagnose?

Answer 26

Inflammation from larval migration in lung causing pneumonitis.

Larvae in concentrated stool or sputum. Larval culture of fecal samples.

Question 27

What is the life cycle of Trichinella spiralis?

Answer 27

Ingestion of undercooked meats.

Adult worms and encysted larvae develop in a single vertebrate host.

Infected animals serve as definitive and potential int. host (can be pigs or bears).

Second host is needed to complete life cycle. Humans are dead end hosts.

Question 28

What is the structure of Trichinella spiralis? What do the females release?

Answer 28

Scale of mms.

Female releases about 1500 live larvae (no eggs) in about 4 weeks of life in the intestine.

Curly-looking larvae.

Question 29

What is the transmission and epidemiology of Trichinella spiralis? What is an example of a hosts?

Answer 29

Eating raw and undercooked meat (pork, wild game) containing cysts.

Strong association with pork consumption. Wide range of hosts: rodents.

Question 30

What is the pathology of Trichinella spiralis?

Answer 30

Trichinellosis, Trichinosis.

Mild infection is asymptomatic, flu-like.

More extensive: persistent fever, GI distress, muscle pain and weakness, periorbital edema, splinter hemorrhage beneath nails.

Heavy: muscle destruction (diaphragm), myocarditis, pneumonitis, death.

Question 31

What immunity is associated with Trichinella spiralis? How would it be diagnosed?

Answer 31

Humoral immune response, eosinophilia.

Myositis, fever, periorbital edema, eosinophilia. Muscle biopsy.

Question 32

What is the life cycle of toxocara canis (cati)?

Answer 32

Eggs passed in feces from dogs. Dogs take it up again to close the life cycle.

Other animals can take up embryonated eggs, which humans can get from meat with cysts.

Humans can also get cysts from bunnies.

Migrates all over the body - commonly in the eye and in the brain.

Question 33

How is toxocaris canis transmitted and what’s the epidemiology?

Answer 33

Ingestion of embryonate eggs; no person to person (soil stage).

Worldwide: 30%-100% of puppies infected. Common in warm climates because eggs develop in soil.

Commonly transmitted to puppies and children.

Question 34

What is the pathology of

toxocaris canis?

Answer 34

Toxocariasis.

Light infections often asymptomatic. Heavier ones lead to lead to severe damage in any location due to neural larva migrans.

Fever, enlarged liver, pulmonary symptoms, ocular disease, seizure, death.

Question 35

What is the immunity of toxocaris canis? How it is diagnosed?

Answer 35

Immune hypersensitivity common, eosinophilic granulomas.

Signs of ocular toxocariasis: eosiniphilia

Serology for larval antigens.

Habit of eating dirt, exposure to dogs Exposure to dogs.

Question 36

How is toxocaris canis treated?

Answer 36

albendazole, mebendazole; symptoms with steroids.