(Section D: Other Infectious Agents) Lecture 28

Question 1

Parasitic Metazoa
* Size
* Endoparasite or Ectoparasite

Answer 1

• Macroparasite
• Endoparasite or Ectoparasite

Question 2

How long are parasitic metazoa?

Answer 2

Millimeters to Meters

Question 3

Classifications of Helminths

Answer 3

1. Nematodes
2. Cestodes
3. Trematodes

Question 4

What are cestodes commonly known as?

Answer 4

Tapeworms

Question 5

Describe:

Nematodes

Answer 5

Non-segmented roundworm

Question 6

Describe:

Cestodes

Answer 6

Segmented flatworms

Question 7

Describes:

Trematodes

Answer 7

Non-segmented flatworms

Question 8

What are mechanisms of entry for helminths?

Answer 8

1. Fecal-Oral
2. Transdermal
3. Vector-borne
4. Predator-Prey

Question 9

What are some mechanisms of survival for helminths?

(6)

Answer 9

1. Imitating host (incorporation of host serum proteins on surface)
2. Inhibiton of complement system
3. Secretion of anti-inflammatory molecules
4. Avoiding direct contact with host tissue
5. Pausing life cycle when host develops resistance
6. Others

Question 10

Ascaris lumbricoides
* Condition that it causes
* Type of helminth
* Location in humans

Answer 10

• Ascariasis
• Large nematode
• Small intestine

Question 11

How many people approximately are infected worldwide by A. lumbricoides?

Answer 11

807 million - 1.2 billion

Question 12

How does infection occur for Ascariasis?

Answer 12

Ingestion of eggs via fecal contamination of:
* Soil
* Foodstuffs
* Water supplies

Question 13

Symptoms of Ascariasis

Answer 13

Rarely show symptoms
* Usually show as mild abdominal discomfort
* Problems occur more in children
* Common in areas with malaria

Question 14

Lifecycle of Ascaris lumbricoides

Answer 14

1. Ingestion of eggs
2. Hatch in small intestine
3. Enter bloodstream
4. Goes to liver
5. Migrates to heart
6. Goes to alveoli
7. Moves through lung tissue and up trachea
8. Swallowed down into GI tract
9. Matures into worms
10. Eggs released into environment

Question 15

Lifecycle of Ascaris lumbricoides
* Where do eggs embryonate?

Answer 15

In the soil

Question 16

Lifecycle of Ascaris lumbricoides
* Why do the larva go to the liver?

Answer 16

As a food source

Question 17

Lifecycle of Ascaris lumbricoides
* Where do the worms mature?

Answer 17

In the gastrointestinal tract when swallowed

Question 18

Lifecycle of Ascaris lumbricoides
* What type of reproduction worms undergo in the gastrointestinal tract?

Answer 18

Sexual reproduction

Question 19

Lifecycle of Ascaris lumbricoides
* Are eggs mature when they are released into the environment?

Answer 19

No, they mature (embryonate) in the soil after they are released

Question 20

Antihelmintic treatment

Answer 20

Substances or drugs that are used to treat infections caused by helminths

Question 21

How do antihelmintic treatments work?

Answer 21

1. Kill parasites
2. Host expels them from the body

Question 22

What are the two anthelmintic treatments used for Ascariasis?

Answer 22

1. Albendazole
2. Ivermectin

Question 23

Albendazole
* Mechanism of action

Answer 23

• Binds to beta-tubulin and disrupts microtubules
• Depletes energy

Question 24

Ivermectin
* Mechanism of action

Answer 24

• Binds with high affinity to glutamate-gated chloride channels found in nerve and muscle cells of invertebrates, including nematodes and arthropods
• Paralyzes worms

Question 25

Taenia saginata
* Disease
* Type of worm
* Host(s)

Answer 25

• Taeniasis
• Very large cestodes
• Cows and Humans

Question 26

Where do T. saginata parasitize?

Answer 26

Small intestine

Question 27

How do cows become infected with T. saginata?

Answer 27

Feeding in areas that are contaminated with Taenia eggs from human feces

Question 28

How do humans become infected with T. saginata?

Answer 28

When they eat raw or undercooked beef

Question 29

Lifecycle of Taenia saginata

(5)

Answer 29

1. Cysticerci in muscle tissue of cows are ingested with raw/undercooked beef
2. Enter stomach
3. Live and mature in small intestine
4. Eggs are released with feces
5. Enters cows and restarts cycle

Question 30

Lifecycle of Taenia saginata
* What in the meat of cows infects humans?

Answer 30

Cysticerci
* Only happens with raw or under cooked beef

Question 31

Lifecycle of Taenia saginata
* Characteristics of the worms in the small intestine

Answer 31

• Scolex: Contains 4 suckers
• Can move around in intestine
• 10 meters in length
• Only 1 worm can be supported per host

Question 32

Lifecycle of Taenia saginata
* How does sexual reproduction work?

Answer 32

• Forms proglottids (segments of the worm with male + female reproductive organs)
• Gravid proglottid: Filled with eggs
• Proglottids breaks off and goes into the environment via feces

Question 33

Lifecycle of Taenia saginata
* Lifecycle in cows

Answer 33

1. Ingested by cows
2. Eggs hatch
3. Oncospheres migrate to muscle tissues
4. Develops into cysticerci

Question 34

Taenia saginata
* Type of parasite
* Host types

Answer 34

• Diheteroxenous
• Definite (human), intermediate (cow)

Question 35

Symptoms of Taeniasis

Answer 35

• Mild symptoms to no symptoms

Question 36

What is used to treat Taeniasis?

Answer 36

Anthelmintic medication
* Praziquantel

Question 37

Praziquantel
* Mechanism of action

Answer 37

Hypothesized to disrupt calcium homeostasis resulting in uncontrolled calcium ion influx
* Causes paralysis of the worm (death, excreted by humans)

Question 38

REVIEW HEALTH EQUITY, ANTIPARASITIC MEASURES, WICKED PROBLEMS