Week 6 (Part 3): Fungi, Protozoa, Prions

Question 1

Define fungi:

Answer 1

Fungi are free-living eukaryotic saprophytes found in every habitat on earth.
- Fungi are free-living eukaryotic saprophytes found in every habitat on earth.

Question 2

T/F

Serious fungal infections are rare and usually initiated through puncture wounds or inhalation.

Answer 2

True

Question 3

T/F
Intact immune mechanisms and competition for nutrients provided but the bacterial flora normally keep colonizing fungi in check, alterations in either of these components by disease states or antibiotic therapy can upset the balance, permitting fungal overgrowth and setting the stage for opportunistic infections.

Answer 3

True

Question 4

T/F

Fungi can only be superficial infections

Answer 4

False

Fungi can be superficial infections or deeper subcutaneous infections

Question 5

What are the 2 groups fungi are divided into:

- What about their cell wall?

Answer 5

1. Yeasts: single-celled organisms and reproduce by a budding process (the buds separate from the parent cell and mature into identical daughter cells.
2. Molds: produce long, hollow, branching filaments called hyphae

Cell Wall:
Yeasts and molds produce a rigid cell wall layer that is chemically unrelated to the peptidoglycan or bacteria and is therefore not susceptible to effects of penicillin-like antibiotics

Question 6

What type of reproduction does fungi undergo?

Answer 6

Most fungi are capable of sexual or asexual reproduction

Question 7

T/F

Some fungi are capable of growing as yeast at one temperature and as molds at another

Answer 7

True

These organsims are called dimorphic fungi

Question 8

How do protozoan infections pass?

Answer 8

Protozoan infections can be passed directly from host to host in a number of ways including sexual contact, indirectly throughout contaminated water or food, or by way of an arthropod vector.

Question 9

How do protozoans reproduce?

Answer 9

They can reproduce sexually by the fusion of 2 cells, followed by the exchange of DNA and separation into 2 cells again; OR
Asexually by undergoing DNA replication followed by division into 2 cells.

Question 10

What is a helminth?

• Reproduction?
• Transmission?

Answer 10

Protozoan:

• Worm-like parasites that include the nematodes or roundworms,, cestodes or tape-worms, and trematodes or flukes.
• They tend to be macroscopic, and reproduce sexually within the definitive host.
• Transmission occurs primarily through the ingestion of fertilized eggs (ova) or the penetration of infectious larval stages through the skin (directly or with the aid of an arthropod vector)

Question 11

What is a parasitic arthropod?

- Explain

Answer 11

Protozoan:

• Parasitic arthropods of humans and animals include the vectors of infectious diseases (tick, mosquitoes, biting flies) and ectoparasites.
• Vectors of infectious disease carry the organisms and inject them into humans while they feed (ie mosquitoes and malaria)

Question 12

What is a ectoparasite?

- Transmission?

Answer 12

Protozoan:

• Infest external body surfaces and cause localized tissue damage or inflammation secondary to the bite or burrowing action of the arthropod. (ie mites, scabies, lice)
• Transmission occurs directly by contact with immature or mature forms of the arthropod or its eggs found on the infested host or the hosts clothing, bedding etc

Question 13

Fancy name for Prions is:

Answer 13

Transmissible Spongiform Encephalopathies
- because these diseases are transmissible and create spongiform pathological changes in the brain resulting in encephalopathy, causing brain damage.

Question 14

What are prions responsible for?

Answer 14

• These are fatal neurodegenerative disorders of humans and animals

Question 15

How many human prions have been identified?

Answer 15

There are 4 human prion diseases identified, the most common “mad cow disease” or Creutzfeldt-Jakob disease (CJD)

Question 16

Prion Diseases share the following characteristics (4):

Answer 16

• Long incubation time (months to years)
• Gradual increase in severity leading to death within months of onset
• No host immune response
• Non-inflammatory process in the brain

Question 17

Prions:

- Neuro-pathological findings may include…

Answer 17

• Macroscopic examination is often normal, microscopic spongiform changes including neuronal loss, and amyloid plaques with accumulation of the prion protein PrP.
• Prion diseases are unique in that that are both inherited and infectious
• The nature of the infectious agent is still under investigation and debate but the most widely accepted hypothesis is the protein-only hypothesis that the infectious agent consists only of prion proteins with little if any nuceic acid
• Transmission can be inoculation but also oral, and also clinical evidence transfusion associated vCJD

Question 18

Prion Diseases share many clinical features; all are characterized by neurological symptoms (5)

Answer 18

• Rapidly progressive dementia
• Psychiatric symptoms
• Cerebellar symptoms (ataxia)
• Involuntary movements (myoclonic jerks)
• Ultimately fatal