-Infectious proteins without genetic material.
-Come into contact with normal proteins and transform them to infectious prions.
-Affects the cells of the brain.
-Creutzfeldt-Jakob disease (mad cow).
Prions derive their name from
Proteinaceous infectious particle.
All known prion diseases affect the cells of the brain. The current collective terminology for these diseases is
transmissible spongiform encephalopathies. The term spongiform comes from the cytopathic effect on brain tissue. Infection produces microscopic holes in the brain which resemble holes in a sponge.
Fill in the blank (f/b):
Characteristic Viruses Prions
Nucleic acid (genome) f/b f/b
Viewed by f/b f/b
Host f/b f/b
1st Row: V- Yes (RNA or DNA) P- None
2nd Row: V- Electron microscopy P-Cell damage in host
3rd Row: V- Animals, bacteria & plants P- Mammals
Prions have the following characteristics:
-They are generally resistant to inactivation by heating to 90 degrees, a temperature that will inactivate almost all viruses.
-Prion infection is resistant to radiation treatments which inactivate organisms with genomes.
-They are not susceptible to enzymes that inactivate RNA and DNA.
-Prions are susceptible to protein denaturing agents.
Current research suggests that prions are normal proteins found on the plasma membranes of cells, that arrange themselves differently by an abnormal folding. These abnormally folded proteins
stick together, forming small fibers that eventually kill the cell.
The most infamous of diseases caused by prions is
bovine spongiform encephalopathy (BSE), also called "mad cow disease", which causes a slow loss of neural function and eventual death.
Humans are believed to acquire the disease by ingesting infected animal by-products. The human disease is a variation of ________-_______ _______, which is a slow, neural degenerative disease, resulting in eventual death. Other prion diseases include _________, and _____ ______ _______ in deer and elk. There is __ _____ treatment for any of the prion diseases.
Creutzfeldt-Jakob disease; scrapie (in sheep); chronic wasting disease; no effective
-important for the decomposition and recycling of organic material.
- -divided into two groups, yeasts and molds.
- Examples: Candida albicans (yeast infection) and Tinea Corporis (ringworm, mold)
Most fungi, such as molds and mushrooms, are ________, Only yeasts are_______.
In the environment, fungi are
important decomposers of organic matter.
The growth of the mold begins as one or more _______ deposited from the environment grows into filamentous, thread-like masses called a _________. Spores are eventually produced by _______. Spore arrangement and appearance depend on the _______ _______.
spores; mycelium; molds; fungal species
Some molds cause _________ ________ in humans, especially among individuals with compromised ______ ______. Many of these opportunistic infections affect the _____ system due to ______ of the _______ _______ from the _________.
opportunistic infections; immune systems; respiratory; inhalation; fungal spores; environment.
Pathogenicity of the molds varies, but most are usually limited to infections of the _____, ______ and ______. Molds cause such infections as _______ ______, ______ ______, and _________.
hair; nails; skin; athlete's foot; jock itch; ringworm.
YEASTS: These unicellular fungi are also ______ in nature. They are very important in ____, ____ and _______ production, and other commercial applications.
diverse; bread; beer; alcohol.
Most common yeast infections are caused by a species called
Candida albicans which causes an infection of the mouth and pharynx called thrush. This yeast is also a common cause of vaginitis.
Individuals with ________ and compromised _____ _______ are particularly susceptible, and systemic infections do occur. Several species of yeast exist as ______ _____, especially on _____ _________ and the __ tract.
diabetes; immune systems; normal flora; mucus membranes; GI
Parasitic Organisms: Protozoa and Helminths
Live at the expense of the host.
- Transmitted to humans by vectors:
- -Biological (mosquito transmitting malaria)
(transmission of parasite eggs to food by flies and other insects.
Parasites in contaminated food and water, exposure to a carrier vectors, and other factors account for up to
20 million deaths per year either from the parasitic disease itself, or from complications that arise from the disease.
Parasites can be broadly classified into two large groups:
the single-celled protozoa and the multi-cellular helminths, or worms
All parasitic organisms are in the
kingdom protista, one of the 5 major kingdoms of living organisms.
-Motile trophozoite stage (infective stage)
-Cyst stage (dormant state)
Examples of Common Protozoans Pathogenic for Humans
ingesting cysts from animal contaminated water.
intense gastrointestinal (GI) distress and diarrhea.
self-limiting GI symptoms.
if infected can become a carrier.
recently associated with recreational water use.
There are severa species, but all are transmitted by the _________ mosquito which serves as the definitive host.
350-500 million cases/year worldwide; over 1 million deaths, primarily in African children.
Humans are intermediary hosts.
Organism invades RBC's
The helminths come in four groups:
flukes, tapeworms, roundworms, and the tissue parasites.
Helminths: Parasitic Worms
- Hosts are definitive or intermediate
- Definitive: harbor parasite when it reproduces.
Intermediate: harbor parasite during a developmental stage in the parasite's life cycle.
: not part of the normal life cycle.
segmented worms that contain a head (scolex) and many segments (proglottids).
Hermaphrodites. (containing both ovaries & testes)
infective stage is larvae found in cattle and swine.
Most prevalent: Beef and Pork (Taenia); Fish (Dibothrocephalus)
Several cm to meters in length.
Live in lumen of intestinal tract.
Infection occurs by ingestion of egg or by penetration of the skin by the larvae.
Pinworms (Enterobius); Ascarids; Hookworms.