Introduction to Fungi and Parasites Flashcards
Are fungi Eukaryotic or Prokaryotic organisms?
What are the implications of this?
- Eukaryotic organisms
- Fungi and humans share many characteristics such as both having:
- Nuclei
- Similar mitochondria
- Similar ribosomes
- Similar folate pathways
- This means that many anti-biotics won’t work on fungal infections
What are some unique characteristics of fungal cells that differentiate them from human cells?
-
Ergosterol in the cell membrane
- This is the target of many anti-fungal drugs
- Chitin
Yeast
- Unicellular form of fungi (spherical/ellipsoid)
- Reproduce via budding or fission
- Mother cell pinches off to produce daughter cell
- Form pseudohyphae: elongation of yeast cell budding (relatively short with no separation of cytoplasm)
- Mother cell pinches off to produce daughter cell
- Slightly smaller than RBCs
- Indentified via microscopic morphology and biochemical tests
Mold
- Multicellular form of fungi
- Tubular structures known as hyphae (2 types):
- Septate hyphae: crosss-wall between cells
- Coenocytic hyphae: nonseparated/nonseptate cells
- Reproduction occurs by formation of spores (some yeast can also produce spores)
Dimorphic fungi
- Occurs in both yeast and myceilal/hyphal forms
- Is a yeast at 37 degrees C (human body temperature)
- Is a mold at 25 degrees C (room temperature)
Budding
Process of yeast replication
Pseudohyphae
Elongation of yeast cell buddding; relatively short with no separation of cytoplasm
Hyphae/Germ Tube
Growths of mold (growth from spore has no constriction)
Vegetative hyphae
- Mold
- Form seen in tissue
- Grow on or beneath culture medium surface
- Angels of hyphae are one of the few distinguishing features
Aerial hyphae
- Mold
- Usually only seen in culture
- Contain structures for production of spores
- Hyphae that project above the surface of the media
Septate hypha and Coenocytic hypha picture
What type of fungi can have capsules?
Yeast
Primary Pathogens
A pathogen that can infect healthy individuals
Opportunistic Pathogen
A pathogen that can only infect immunocompromised (innate or acquired) individuals
What type of immune response is activated in response to fungi?
(General)
Usually a TH17 response that involves are large influx of neutrophils
Parasite Reservoir
Source of parasites in the enviornment
Parasite’s Definitive Host
Host in which sexual reproduction of the parasite takes place
This is where you will find mature adult parasites
Parasite’s Intermediate Host
Host that harbors an asexual or larval stage of the parasite
Parasite Vector
- Agent capable of transmitting the pathogen from one host to another (ex. flies, ticks, mosquitos)
- Mechanical Vector: Moves parasite from one organism to another
- Biological Vector: Parasite develops in the vector
Forms of Parasite Transmission
- Injury
- Ingestion
- Inhalation
- Person to person
- Contact with contaminated water or soil
- Transmission from vectors (ex. mosquitos)
- Fomites (objects/materials that can carry infection)
Do parasites have a cell wall?
No; parasites lack cell walls, and this can make them difficult to target.
What are the two major types of parasites?
- Protozoans: single celled organisms
- Metazoans: multicellular organisms
- Large worms called helminths
- Platyhelminths (flatworms)
- Nematodes (roundworms)
- Large worms called helminths
Protozoans
- Microscopic parasites
- Single cell organisms: can be free living or intracellular
- Morphologically diverse but biochemically similar to humans
Protozoan Pathology
- Pathology of infection is due to:
- Malnutrition (The Protozoan absorb nutrients)
- Blockage of systems
- Release of toxic byproducts
- Two main classes of infection:
- Gastroenteritis (Ex. Giardia)
- Systemic disease (Ex. Malaria)
Protozoan Transmission
- Ingestion
- Inhalation
- Mechanical vector
- Athropod vector (Ex. Tse tse fly)
Immune Response to Protozoan Infection
- No single immunologic response is associated
- GI an GU protozoan infections are self-limiting (results in clearance of the pathogen or death of the host)
- Generally lack eosinophilia
Protozoan Treatment
- Often difficult to treat
- Target mechanism of many anti-protozoan drugs is not well described
- Some antibacterials work on certain protozoans
Protozoan Life Cycle (Main Point/General Concept)
Main point = it’s complicated and it makes it difficult to treat
- Protozoan life cycles can be complex
- Can involve various hosts and vectors
- Can involve sexual and asexual reproduction
Helminths
- Free living obligate parasites
- Macroscopic and multicellular
- Reproduce sexually
- Each Helminth has a specific tissue tropism it prevers (Example: Liver, Lung, GI Tract, etc.)
Helminths Pathologies
- Local tissue damage
- Blockage of necessary flow
- Immunologic response
- Malnutrtion d/t directly absorbing nutrients from host
- Exception: Hookworms which ingest RBCs
Types of Helminths (Picture/Diagram)
Helminth Transmission
- Ingestion
- Inhalation/ingestion
- Anthropod Vector
- Biologic Vector (Ex. Black Fly)
- Mechanical Vector (Ex. House Fly)
- Direct infection (Ex. Hookworms burrow directly into skin)
Helminth Diagnosis
- Blood antigen or antibody tests
- Direct observation of eggs or parasite in patient sample (Example: fecal sample)
- Laboratory test on feces = OVA and Parasite Screen
Helminth Life Cycle (General Concept)
Helminth life cycle can be very complex with various hosts/vectors
Treatment of Helminth Infections
Helminth biochemistry is similar to humans which makes treatment difficult. Some treatments include:
- Glutamate-gated chloride channel (Avermectins/Ivermectin)
- Colchicine-sensitive site of B-tubulin (Bendazoles)
Immune Response to Helminth Infection
- Immune response to helminths is universally a TH2 response causing Eosinophilia
- Eosinophils have been shown to kill helminths in vivo
