Parasitology Flashcards
What does DALY stand for?
Disability Affected Life Years
Name some of the factors that contribute to a parasite being successful.
- Morphological adaptations
- Biochemical changes
- Specialized mechanisms for entry
- complex life cycles and transmission opportunities
- Mechanisms for immune evasion (ex. antigenic variation )
- Impact on host vs. impact of host
What are the two main parasitic groups? How do you distinguish between the two? Give examples.
Microparasites (protists) and Macroparasites (Helminths, Arthropods). Microparasites are small unicellular parasites that use the host as the unit of study (ex. kinetoplastea, Ciliophora, Apicomplexa). Macroparasites are larger and visible to the naked eye. The number of parasites present is considered the unit of study because a larger number of parasites translates to greater symptoms and increased morbidity (ex. Platyhelminthes, Nematoda, Arthopoda).
Which parasitic group often causes acute disease? Chronic?
Microparasites often provoke more acute disease whereas macroparasites cause more chronic disease.
How many micro and macroparsites fall under the category of Neglected Tropical Diseases (NTDs)?
There are 17 NTDs. There are 9 microparasites and 8 Macroparasites.
What is the total DALY for NTDs?
56.6 Million DALYs with 534, 000 deaths
According to Cecilia, what are the top 5 parasitic infections in the US?
Chagas Disease, Cysticercosis, Toxocariasis, Toxoplasmosis, and Trichomoniasis
Which parasite is also known as the Guinea worm and how is infection being prevented?
Dracunculus medinensis. Infection is being prevented by using a pipe to drink water to prevent ingestion of parasites.
What causes Toxoplasmosis?
Toxoplasma gondii
Which phylum does toxoplasma gondii fall in?
Apicomplexa (aka. Apicomplexia)
What is the major factor that makes toxoplasma gondii successful? Explain.
It has multiple routes of transmission
- Ingestion of oocyst (via food, H20, sand or dirt contaminated with cat feces)
- Ingestion of tissue cysts in undercooked contaminated meat
- Vertical transmission (Mother with acute tachyzoite infection to fetus)
- Blood transfusion or organ transplant (rare)
- Lambing
Explain the life cycle of Toxoplasma gondii. Include key cell stages.
T. gondii primarily exists in three forms: oocysts, tachyzoites, and bradyzoites. Oocysts (encapsulated zygote) are only produced in the definitive host, members of the family Felidae (felines), after they ingest intermediate hosts infected with bradyzoites (slow dividing stage in host tissue to make tissue cysts). Unsporulated oocysts are produced in the definitive host via merogony (asexual reproduction of apicomplexan) followed by gametogony (sexual reproduction) and are then passed in the cat feces. The oocysts then sporulate in the soil forming sporozoites (a spore-like stage in the life cycle that invade intestinal epithelium). When passed in feces and then ingested (via food, H2O, soil etc.), the oocysts can infect humans and other intermediate hosts (pigs, goats, birds, rodents etc). They develop into tachyzoites, which are the rapidly multiplying trophozoite (a growing stage in the life cycle of some sporozoan parasites, when they are absorbing nutrients from the host) form of T. gondii. They divide rapidly in cells, causing tissue destruction and spreading the infection. Tachyzoites can live in macrophages. Tachyzoites in pregnant women are capable of infecting the fetus. Eventually tachyzoites localize to muscle tissues and the CNS where they convert to tissue cysts, or bradyzoites. This is thought to be a response to the host immune reaction. Ingestion of cysts in contaminated meat is also a source of infection, as bradyzoites transform back into tachyzoites upon entering a new host.
What is a definitive host?
The host where sexual reproduction of the parasite occurs.
What is a tachyzoite? Provide example of parasite
The cell stage that is ~rapidly dividing~ in any cell of the intermediate host and in non-intestinal epithelial cells of the definitive host. This is the ~spreading stage~. Example of parasite - T. gondii.
What is a Bradyzoite? Give example of parasite.
The cell stage that is ~slowly dividing~ enclosed in the tissue of an intermediate host forming a tissue cyst. Tissue cysts can contain 2 to 100s of bradyzoites in the intermediate host. They can lie dormant in body and contaminated items for many years and be reactivated if the host becomes immunocompromised. Example of parasite - T. gondii.
What is an oocyst?
A hardy, thick-walled stage of the life cycle of coccidian parasites (ex. T. gondii). The thick wall encapsulates a zygote. This is the stage that is shed in the feces.
What happens in rodents infected with toxoplasmosis?
They behave differently. They no longer fear cats thus becoming more susceptible to predation.
