Exam 3: Infection and Epidemiology Part 1 Flashcards
Define Synergism and give an example.
Relationship between two or more FREE-living organisms. Beneficial to both members but not necessary for survival.
Example; Aerobic bacteria using up O2 and producing waste. Anaerobic bacteria benefit from the reduced oxygen concentration and consume the waste. Intestinal bacteria in the human colon. Bacteria receive food and hospitable habitat. Humans receive nutrients released by bacteria. Both benefit but each could survive without the other.
Antagonism
Association between FREE-living species arising from competition. One organism secretes a substance that inhibits or kills another.
Example; Vaginal flora. Lactobacillus (lactic acid bacterium) in the vagina produces lactic acid which inhibits the growth of the yeast Candida albicans.
What is mutualism? Give at least two specific examples of mutualism.
Symbiotic relationship in which both organisms benefit.
Example; relationship between eukaryotic cells and their mitochondria. Mitochondria gets food and a hospitable environment while eukaryotic hosts get ATP released by mitochondria. Microbes in the termite gut. Microbes (protozoa and bacteria) get a hospitable environment and free food (wood pulp). Termites receive nutrients following the enzymatic hydrolysis of the wood pup.
What is parasitism? Give at least two specific examples of parasitism.
Symbiotic relationship when one benefits (parasite) and one is harmed (host). Parasite causing disease is termed a pathogen.
Example; Treponema pallidum causes syphilis in humans and fleas that feed on blood of hosts and carry disease.
What is commensalism? Give at least one specific example of commensalism.
Symbiotic relationship where one benefits and the other is not significantly affected.
Example; satellite colonies. Central bacterial colony is resistant to ampicillin. Satellite colonies grow in a localized environment devoid of ampicillin due to degradation by the central colony. Satellite colonies benefit and the central colonies are not affected.
Are all hosts equally affected by a given pathogen? Will all hosts exhibit identical reproductive success? Explain.
No, some hosts are less affected by a given pathogen than others. Those that are less affected are more likely to survive and thus have an increased reproductive success.
Are all individuals in a pathogen population equally pathogenic? Will variations in pathogenicity within a population affect the reproductive success of individual pathogens? Will the population evolve in predictable ways? Explain.
No, some are more pathogenic. Parasites that allow their hosts to survive are more likely to spread. As a result over time parasite populations become less pathogenic.
Are all individuals in a host population equally sensitive to a given pathogen? Will variations in this sensitivity affect their reproductive success? Will the population change in a predictable way over time? Explain.
No, some hosts are better able to fight off pathogens than others. The hosts who are less sensitive to pathogens are more likely to survive and pass their genetics on to the next generation. Over time the population will change to have decreased sensitivity to the given pathogen.
Describe the phenomenon of balanced pathogenicity, and the mechanism by which it occurs.
Parasites that allow their hosts to survive are more likely to spread resulting in parasites becoming less pathogenic. Hosts are able to tolerate a parasite and are more likely to reproduce thus host populations become more resistant.
Overall the result is a movement towards commensalism or mutualism.
Ancestors of mitochondria were almost certainly parasitic. Is this the case today? How and why did this change?
No, now the relationship between mitochondria and eukaryotic cells where they reside is symbiotic. Over time the parasite becomes less pathogenic and the host becomes more resistant until a symbiotic relationship occurs.
How prevalent are microorganisms in and on the human body? Are they equally distributed throughout the human body? Explain.
Trillions of microorganisms present on and within the human body. Not equally distributed throughout the body some parts are free of microbes while others are plentiful.
Axenic
Portions of the body that are free of microbes.
What are normal flora? What are other terms for normal flora?
Microorganisms colonizing the human body surfaces without normally causing disease. Also called microbiome, normal microbiota, and indigenous flora.
Resident microbiota
Type of normal flora that constitutes the body microbiome early in life and remains part of the body throughout life. Most are commensal, feeding on dead cells and waste w/o causing harm.
Transient microbiota
Remain in the body for short periods of time before disappearing. Hours, days, or months. Found in the same locations as resident microbiota.
Why do transient microbiota fail to persist?
Competition with other microbes, elimination by body defenses, and dislodged by chemical and physical changes in the body.
How and when do resident microbiota initially colonize and become established in an individual?
Early in life during birth starting with the rupture of the amniotic sac and passage to the vaginal canal. First breath, first mean, and skin contact all transfer these microbes to the infant’s body.
In what ways are normal microbiota beneficial to humans? Explain.
Protection against pathogens: covering binding sites usable by pathogens, consuming available nutrients, producing compounds toxic to other microbes.
Stimulate the adaptive immune system: antibodies produced against normal biota often also bind to pathogen services. Oral tolerance by the immune system: Reduced response to microorganisms and food in the digestive system. Microbes in food are killed off by stomach acid but some make it further down the digestive tract. Down the line there are beneficial microbes so constant encounters with these normal microbes will help build a tolerance so we don't attack the good microbes we want.
Explain how normal microbiota protect humans against pathogens.
Covering binding sites usable by pathogens (so bad ones cannot attach), consuming available nutrients (no nutrients left for other pathogens), producing compounds toxic to other microbes (e.g weak organic acids).
Under what conditions might a member of one’s normal microbiota become an opportunistic pathogen?
Introduction of normal microbiota into an unusual site: E.coli is a mutualistic intestinal bacterium, but can produce disease (UTI’s) when introduced into the urethra or in the eye (pink eye).
Immune suppression: can be suppressed by disease, malnutrition, stress, age, cancer therapy, immunosuppressive drugs. Immune system normally keeps normal microbiota in check so they don't get out of hand, but if it's preoccupied normal things can grow excessively. AIDs patients often die from opportunistic pathogens. Changes in normal microbiota: Some formal microbiota naturally keep other microbes in check. Antibiotics use can kill vaginal bacteria flora, leading to reduced competition and increased Candida albicans growth, causing yeast infections.
What are the three reservoirs of infection?
Animal Reservoirs
Human Carriers
Nonliving Reservoirs
Reservoir of infection
Any person, animal, plant, soil or substance in which an infectious agent normally lives and multiplies. The reservoir typically harbors the infectious agent without injury to itself and serves as a source from which other individuals can be infected
Animal Reservoirs
Many pathogens of non-humans can also infect humans. The greater the physiological similarities the greater the likelihood the pathogens can affect human health.
Humans can be infected via many routes, direct contact, eating animals and their waste, blood-sucking arthropods. Difficult to eradicate because extensive animal reservoirs are often involved.
Why are humans generally dead-end zoonotic pathogens?
Movement from other animals to humans is favored. Movement from humans to other animals is not favored. Those transmitted via bloodsucking arthropods are the most likely to be transmitted back to non-human animal hosts.
Human Reservoirs
Humans with active disease both symptomatic and asymptomatic carriers can be infective. “Typhoid Mary” is a great example. Often infective prior to or following symptoms. Some infected people remain asymptomatic and infectious for years. Kids with chickenpox are infectious prior to symptoms. People with HIV can be asymptomatic but infectious for years.
