(Section D: Other Infectious Agents) Lecture 28 Flashcards
Parasitic Metazoa
* Size
* Endoparasite or Ectoparasite
- Macroparasite
- Endoparasite or Ectoparasite
How long are parasitic metazoa?
Millimeters to Meters
Classifications of Helminths
- Nematodes
- Cestodes
- Trematodes
What are cestodes commonly known as?
Tapeworms
Describe:
Nematodes
Non-segmented roundworm
Describe:
Cestodes
Segmented flatworms
Describes:
Trematodes
Non-segmented flatworms
What are mechanisms of entry for helminths?
- Fecal-Oral
- Transdermal
- Vector-borne
- Predator-Prey
What are some mechanisms of survival for helminths?
(6)
- Imitating host (incorporation of host serum proteins on surface)
- Inhibiton of complement system
- Secretion of anti-inflammatory molecules
- Avoiding direct contact with host tissue
- Pausing life cycle when host develops resistance
- Others
Ascaris lumbricoides
* Condition that it causes
* Type of helminth
* Location in humans
- Ascariasis
- Large nematode
- Small intestine
How many people approximately are infected worldwide by A. lumbricoides?
807 million - 1.2 billion
How does infection occur for Ascariasis?
Ingestion of eggs via fecal contamination of:
* Soil
* Foodstuffs
* Water supplies
Symptoms of Ascariasis
Rarely show symptoms
* Usually show as mild abdominal discomfort
* Problems occur more in children
* Common in areas with malaria
Lifecycle of Ascaris lumbricoides
- Ingestion of eggs
- Hatch in small intestine
- Enter bloodstream
- Goes to liver
- Migrates to heart
- Goes to alveoli
- Moves through lung tissue and up trachea
- Swallowed down into GI tract
- Matures into worms
- Eggs released into environment
Lifecycle of Ascaris lumbricoides
* Where do eggs embryonate?
In the soil
Lifecycle of Ascaris lumbricoides
* Why do the larva go to the liver?
As a food source
Lifecycle of Ascaris lumbricoides
* Where do the worms mature?
In the gastrointestinal tract when swallowed
Lifecycle of Ascaris lumbricoides
* What type of reproduction worms undergo in the gastrointestinal tract?
Sexual reproduction
Lifecycle of Ascaris lumbricoides
* Are eggs mature when they are released into the environment?
No, they mature (embryonate) in the soil after they are released
Antihelmintic treatment
Substances or drugs that are used to treat infections caused by helminths
How do antihelmintic treatments work?
- Kill parasites
- Host expels them from the body
What are the two anthelmintic treatments used for Ascariasis?
- Albendazole
- Ivermectin
Albendazole
* Mechanism of action
- Binds to beta-tubulin and disrupts microtubules
- Depletes energy
Ivermectin
* Mechanism of action
- Binds with high affinity to glutamate-gated chloride channels found in nerve and muscle cells of invertebrates, including nematodes and arthropods
- Paralyzes worms
Taenia saginata
* Disease
* Type of worm
* Host(s)
- Taeniasis
- Very large cestodes
- Cows and Humans
Where do T. saginata parasitize?
Small intestine
How do cows become infected with T. saginata?
Feeding in areas that are contaminated with Taenia eggs from human feces
How do humans become infected with T. saginata?
When they eat raw or undercooked beef
Lifecycle of Taenia saginata
(5)
- Cysticerci in muscle tissue of cows are ingested with raw/undercooked beef
- Enter stomach
- Live and mature in small intestine
- Eggs are released with feces
- Enters cows and restarts cycle
Lifecycle of Taenia saginata
* What in the meat of cows infects humans?
Cysticerci
* Only happens with raw or under cooked beef
Lifecycle of Taenia saginata
* Characteristics of the worms in the small intestine
- Scolex: Contains 4 suckers
- Can move around in intestine
- 10 meters in length
- Only 1 worm can be supported per host
Lifecycle of Taenia saginata
* How does sexual reproduction work?
- 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
Lifecycle of Taenia saginata
* Lifecycle in cows
- Ingested by cows
- Eggs hatch
- Oncospheres migrate to muscle tissues
- Develops into cysticerci
Taenia saginata
* Type of parasite
* Host types
- Diheteroxenous
- Definite (human), intermediate (cow)
Symptoms of Taeniasis
- Mild symptoms to no symptoms
What is used to treat Taeniasis?
Anthelmintic medication
* Praziquantel
Praziquantel
* Mechanism of action
Hypothesized to disrupt calcium homeostasis resulting in uncontrolled calcium ion influx
* Causes paralysis of the worm (death, excreted by humans)
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