Infection, Infectious Disease, and Epidemiology Flashcards
Chapter 14
What is the word for members of a symbiotic relationship?
Symbionts
What is symbiosis?
The relationship between organisms (or microorganisms)”living together”
What are the 4 symbiotic relationships?
Mutualism, Commensalism, Amensalism, & Parasitism
In what type of symbiotic relationship do both symbionts benefit from their interaction?
Mutualism
True or False: Symbionts in a mutualism interaction require each other to survive. Why or why not?
False. Despite the benefits, not every mutualistic relationship is necessary for either symbionts survival.
Explain Commensalism
One symbiont benefits from the relationship without significantly affecting the other symbiont
Why is it difficult to prove an absolute example of commensalism?
Because there may be unobserved benefits experienced by one of the symbionts
What is Amensalism?
One symbiont is harmed by the second symbiont, but the second symbiont is not harmed or helped by the first symbiont.
Explain Parasitism
Symbiotic relationship where a parasite benefits from its host while causing harm to said host. The harm sustained by the host can vary greatly.
What is a parasite that causes disease called?
A pathogen
Why might there be a coevolution towards commensalism/mutualism from an originally parasitic relationship?
Because there are parasites that allow their host to survive, making it more likely to spread. Similarly, some hosts better tolerate a parasite and are more likely to reproduce.
Define Bioterrorism
The deliberate release of viruses, bacteria, or other germs to cause illness or death.
What characterizes Axenic Environments in our body?
places free of any microbes
What is the human microbiome made of?
Microbes that colonized our body without causing disease (normally)
List 3 other ways to refer to the body’s microbiome
Normal Microbiota, Normal Flora, or Indigenous Microbiota
What 2 main types of organisms make up the microbiome?
Resident microbiota & transient microbiota
Where is resident microbiota found?
On the skin, on mucous membranes of digestive tract, upper respiratory tract, distal urethra, and vagina.
What does it mean that most resident microbiota are commensal?
It means that they feed on excreted cellular waste/dead cells without harming a person
What layers of the skin are Axenic?
dermis & hypodermis
Explain transient microbiota
Microbes that remain in the body for a few hours, days, before peacing out.
Why can’t transient microbes persist in the body even though they are found in many of the same locations as resident microbes? (3 reasons)
Because of competition from other microorganisms; from being eliminated by the body’s defenses; or chemical/physical changes in the body that dislodges them
Why don’t we develop a microbiome in the womb?
Because you are surrounded by an amniotic membrane/fluid that keeps microogranisms at bay. And the mother’s uterus also grants additional protection.
When do we begin to develop a microbiome?
When the amniotic membrane is ruptured during birth
When is most of our resident microbiota established?
During the first months of life
What are 4 ways normal microbiota can become opportunistic pathogens?
- From normal microbiota being introduced into an unusual site in the body that they do not typically inhabit
- From immune suppression
- From changes in the normal microbiome
- From stressful conditions
What is microbial antagonism/competition?
The situation in which normal microbiota function in such a way as to make it less likely for arriving pathogens to compete well enough to produce disease
What sort of stressful conditions can lead to opportunistic pathogens?
Hormonal changes, unresolved emotional stress, abrupt diet changes, or exposure to a very large number of pathogens
What do we call living or nonliving sources of infectious diseases?
Reservoirs of infection
What are the 3 reservoirs of infection?
- Animal (or zoonotic)
- Human
- Nonliving
What makes it more likely for a pathogen to affect human health that is originally zoonotic?
The more similar the animals physiology is to human physiology
What are zoonoses?
Diseases that spread naturally from animals hosts to humans
List an example of a zoonoses
Anthrax, bubonic plague, rabies, etc.
Why is it difficult to eradicate human infections with zoonoses?
Because of the extensive animal reservoirs involved
Why can it be challenging to control the spread of disease to humans from animals?
Sometimes the contact between humans and animals is extensive, making it more difficult and costly to control disease spread. Larger animal reservoirs also makes it difficult as more animals and animal types are infected.
What are sylvatic animals?
wild animals
True or false: it is no more difficult to control the spread of disease to humans from animals when both sylvatic and domesticated animals are reservoirs.
False. Both sylvatic and domesticated animals serving as a reservoir make it more difficult to control the spread of disease. Although sometimes you can take precautions like vaccinations to prevent domesticated pets from being infected by sylvatic animals.
Why are humans usually dead-end hosts for zoonotic pathogens?
Because humans are not the optimal reservoir to reinfect animal hosts; zoonoses transmission favour movement from animals to humans but not the other way around.
What makes human reservoirs difficult to identify as infectious at times?
The fact that some humans can act as carriers for an infection, without ever getting sick themselves.
What are examples of nonliving reservoirs?
Soil, water, food, etc.
Define contamination
the presence of microbes in/on the body
What are 3 potential outcomes of contamination?
- Microbes remain and become part of resident microbiota
- Microbes remain for a short amount of time as part of transient microbiota
- Microbes invade and multiple within the body, leading to infection
True or False: An infection results in disease
False. Infections may or may not adversely affect the body, so they do not always result in disease.
What are portals of entry?
sites where pathogens can enter the body
What are the 3 major portals of entry types?
- Skin
- Mucous membranes
- Placenta
Why is the parenteral route not considered a portal of entry for pathogens?
Because it is not a proper portal, but rather a way for pathogens to circumvent the other usual portals
List some portals of entry
the skin, placenta, conjunctiva, & mucous membranes of the respiratory, gastrointestinal, urinary, & reproductive tracts.
What is the parenteral route of infection?
A puncture through the skin
How can microbes get past the skin barrier if it still appears to be intact?
Via hair follicles or sweat gland ducts
What lines every body cavity that is open to the outside world?
Mucous membranes
What is the conjunctiva?
the thin membrane covering the surface of the eyeball & underside of each eyelid
Why do microbes typically find mucous membranes to be easier portals of entry than the skin?
Unlike skin, the mucous membrane is thin, moist, and warm in comparison.
What is the most frequently used portal of entry?
Respiratory tract
How do viruses enter the respiratory tract via the eyes?
Viruses can be introduced to the conjunctiva by contaminated fingers. The virus can then be washed into the nasal cavity with tears.
Microbes that can infect via the gastrointestinal mucous membrane are typically able to survive what?
The acidic pH of the stomach & the digestive juices of the intestinal tract
Why is the placenta typically effective in barring most pathogens from a fetus?
Because, despite the close contact of the wall of the mother’s uterus and the placenta, the two blood supplies do not contact each other.
What must symbionts do after they enter the body to successfully establish colonies?
Adhere to cells
What is adhesion (or attachment)?
The process by which microorganisms attach themselves to cells
How do pathogens accomplish adhesion? Explan.
Through adhesion factors; specialized structures or attachment molecules
Give an example of how adhesion via attachment molecules is possible, and what microbes do this
Viruses and some bacteria have ligands that enable them to bind to complementary receptors on host cells
What are ligands?
lipoproteins or glycoproteins on the surface of viruses/bacteria
Bacterial Ligands are called what?
Adhesins
Virus Ligands are called what?
Attachment proteins
What can be done to ligands to prevent infection?
Changing them or blocking them so that ligands on microbes cannot adhere to host cells
What interaction can determine the specificity of pathogens for particular hosts?
The interaction of adhesins on microbes and host cell receptors
How do some pathogens adapt to help them evade the immune system?
By having more than one type of adhesin or the ability to change their adhesins over time
Define avirulent in the context of microbes.
Microbes that are harmless because of mutations or physical/chemical agents (such as a vaccine) that have stopped that microbes ability to make ligands.
What is biofilm?
A community of microbes growing on a surface within a host, but that do not actually attach to host cells directly
What is dental plaque an example of?
Biofilm
Define Disease
An adverse internal condition that interferes with normal bodily functioning
What is morbidity?
any change from a state of health
Define syndrome
a group of symptoms and signs that collectively characterize a certain disease or abnormal condition
What is another word for asymptomatic infections?
Subclinical infections
What is etiology?
the study of the cause of a disease
List 2 microbiologists that helped propose the germ theory of disease?
Louis Pasteur & Robert Koch
What is the germ theory of disease?
Theory that disease is caused by infections of pathogenic microorganisms (referred to as germs at the time)
What must a scientist satisfy to prove that a given infectious agent causes a given disease?
They must satisfy Koch’s Postulates in order
List Koch’s Postulates
- Suspected agent must be present in every case of the disease
- agent must be isolated and grown in pure culture
- cultured agent must cause the disease when inoculated into a healthy, susceptible experimental host
- Same agent should be found in the diseased experimental host
What are some exceptions to Koch’s 2nd postulate?
Pathogens that have not been able to be cultured in a laboratory. I.e mycobacterium leprae which causes leprosy.
Why might it be difficult to attribute a singular pathogen to a disease?
Because some diseases are a result of a combination of pathogens and cofactors; so the pathogen alone my be unable to cause disease
What is an important ethical consideration of Koch’s postulates in regards to the 3rd postulate?
It is not ethical to inoculate a healthy susceptible host for diseases/pathogens that only occur in humans
Why is it not always possible to establish a single cause for some infectious diseases? Give an example
Because some diseases, such as pneumonia, meningitis, hepatitis, refer to conditions that can be caused by more than one pathogen (different pathogens causing the same disease)
How can we “know” the causative agent of a disease if we cannot apply Koch’s postulates?
Via epidemiological studies
Define pathogenicity
The ability of an agent to cause noticeable disease
Define virulence
What are virulence factors?
What are the 5 virulence factors discussed in the textbook?
- adhesion factors
- biofilm formation
- extracellular enzymes
- toxins
- antiphagocytic factors
In the context of pathogens, what are extracellular enzymes/what do they do?
Enzymes that are secreted by the pathogen to dissolve structural chemicals in the body to maintain infection, invade further, and avoid the bodies defenses
What does coagulase do? How does this impact bacteria?
Causes blood proteins to clot, providing a “hiding place” for bacteria within a clot
What are toxins?
chemicals that harm tissues or trigger host immune responses that cause damage
What are exotoxins?
toxins released by microorganisms that destroy host cells or interfere with metabolism
What are the 3 types of exotoxins?
- Cytotoxins
- Neurotoxins
- Enterotoxins
What exotoxin kills host cells in general or affects their function?
Cytotoxins
Explain neurotoxins
Exotoxins that specifically interfere with nerve cell function
Explain enterotoxins
Exotoxins that affect the cells lining the gastrointestinal tract
How does the body protect itself from exotoxins?
With protective molecules called antibodies that bind to specific toxins & neutralize them
Explain antitoxins
antibodies against toxins
How can health care workers stimulate the production of antitoxins?
By administering immunizations composed of toxoids, which are treated to be non-toxic but still capable of stimulating the production of antibodies
What do endotoxins come from? What is the specific structure that is poisonous?
They come from Gram-negative bacteria. Lipopolysaccharides (LPS) in the outer membrane are released upon cell death, exposing the poisonous lipid A of LPS.
Is Lipid A the same between bacterias?
No. It varies between gram-negative bacteria and among bacterial strains
Is lipid A a single molecular structure?
No. It is an array of similar lipid molecules.
How are endotoxins released?
When gram-negative bacteria divide, die naturally, or are digested by phagocytic cells (like macrophages)
What stimulates the body to release chemicals that cause fever, inflammation, hemorrhaging, shock, and blood coagulation when released by gram-negative bacteria?
The endotoxin lipid A
Are gram-negative pathogens life threatening?
They are often life threatening, yes, because the endotoxin released from dead cells can produce serious systemic effects in a host
For which toxin is toxoid formations for immunization feasible?
Exotoxins; not feasible for endotoxins
What bodily structures attempt to limit the extent and duration of infections? How?
Phagocytic cells like white blood cells (macrophages) engulf invading pathogens and remove them
How are the capsules of pathogenic bacteria effective virulence factors?
They are effective because they are composed of chemicals normally found in the body, so they do not stimulate an immune response
Besides presenting a familiar chemical structure, how else do bacterial capsules effectively evade phagocytes?
The bacterial capsules are often slippery, making it difficult for phagocytes pseudopods to grip the capsule and phagocytize them
How do some bacteria survive inside phagocytes?
By preventing the fusion of lysosomes with phagocytic vesicles
What are the 5 stages of the disease process?
- Incubation Period
- Prodromal Period
- Illness
- Decline
- Convalescence
True or false; all infectious diseases follow the 5 step disease process
False
What is the incubation period of an infectious disease?
The time between infection and the first occurence of symptoms or signs of disease
Is the incubation period of a disease always the same?
Not always. Some have typical incubation periods whereas others vary considerably due to a multitude of factors, such as the strength of the hosts immune system.
What is the prodromal period?
A short period of time characterized by mild symptoms that precede illness.
What is the most severe stage of an infectious disease?
illness
Will a person’s immune system have started responding to a pathogen during the illness stage?
Not fully
Describe the Decline stage of disease
Period in which the body gradually returns to normal as the immune response and/or medical treatment destroys pathogens
In what stage of the disease process does immune response and its products peak?
During the stage of Decline
What is the convalescence stage of disease?
The point in which a person recovers from illness; tissues are repaired & return to normal
What does the length of the convalescent period depend on?
The amount of damage, the nature of the pathogen, the site of infection, and the overall health of the person
At what stages of disease are people infectious?
At likely every stage
At what stages of disease are people often unaware that they may be infectious?
During incubation and convalescence; just because you are feeling better does not mean you are no longer infectious.
How do pathogens typically exit hosts?
in materials secreted or excreted by the body
What are the 3 arbitrary categories of transmission?
Contact, vehicle, and vector transmission
Explain direct transmission
the spread of pathogens from one host to another by direct or indirect contact, or respiratory droplets
Explain Direct contact transmission
person-to-person spread via bodily contact
Transfer of pathogens from an infected mother to a developing baby across the placenta is what kind of transmission?
Direct contact transmission
What sort of transmission involves any form of touching, intercourse, scratching, etc.?
Direct contact transmission
Explain indirect contact transmission
the spread of pathogens via fomites
Define fomites
inanimate objects that can carry and transmit a pathogen between hosts
Contaminated needles represent what kind of transmission?
Indirect contact transmission via fomites
Explain droplet transmission
A type of contact transmission in which pathogens are transmitted within droplet nuclei when exhaling, coughing, and sneezing
What are droplet nuclei?
droplets of mucus
What distinguishes droplet transmission from airborne transmission?
droplet transmission occurs when pathogens travel less than a meter via respiratory droplets; if they travel more than 1 meter, it is considered airborne transmission
What type of transmission is characterized by the spread of pathogens via air, drinking water, food, and bodily fluids handled outside the body?
Vehicle transmission
Explain airborne transmission
the spread of pathogens beyond 1 meter to a new host via an aerosol
Actions such as sweeping, changing clothes, flaming inoculating loops in a lab and air-conditioning systems can results in what sort of transmission?
Airborne transmission
What can transmit staphylococcus, streptococcus, and hantavirus?
Dust particles
How is the measles virus and tuberculosis bacilli transmitted?
airborne droplets
Explain foodborne transmission
pathogens in and on foods that are inadequately processed, undercooked, or poorly refrigerated leading to transmission of pathogens
Arthropods that transmit disease are called what?
Vectors
What are the two types of vector transmission?
Biological and Mechanical
What is the difference between biological and mechanical vectors?
Both transmit pathogens but biological vectors can also be hosts for the multiplication of a pathogen, whereas mechanical vectors are not needed to host pathogens
What are the 4 vehicle transmission types?
- Airborne
- Foodborne
- Waterborne
- Bodily fluid
Classification of disease in which disease develops rapidly but last a short time
Acute disease
Classification of disease in which disease develops more slowly and usually with less severe symptoms
Chronic disease
What is the classification of disease that has durations & severities somewhere between acute and chronic?
Subacute disease
Explain Latent Diseases
Diseases in which a pathogen remains inactive for a long time before becoming active
What are the classifications of disease according to longevity & severity?
- Acute
- Subacute
- Chronic
- Latent
What is a communicable disease?
An infectious disease that comes from another infected host, either directly or indirectly
How do we refer to a communicable disease that is easily transmitted between hosts?
Contagious disease
Explain noncommunicable diseases
Diseases that are not spread from one host to another but arise either from outside a host or the resident microbiome
What is a local infection?
an infection confined to a small region of a body
What do we call a widespread infection in many systems of the body that often travels in the blood or lymph?
Systemic infection
What is a focal infection?
an infection site that serves as a source of pathogens for infections at other sites in the body
What is a primary infection?
Initial infection within a person
What is a secondary infection?
Infections that follow a primary infection; often by opportunistic pathogens
What is epidemiology?
The study of the distribution and determinants of disease & death within human populations
What is incidence?
The number of new cases of a disease in a certain area/population during a given time period
What is prevalence?
The total number of cases (new and old) in a given area/population during a given period of time
What is an endemic?
a disease that occurs continually (at moderately regular intervals) at a stable incidence within a population or geographical area
When do we consider a disease to be sporadic?
When only a few scattered cases occur within an area/population
What is an epidemic?
When a disease occurs at a higher frequency than is usual for an area/population
What is a common misconception about what can be considered an epidemic?
That a disease must infect thousands or millions to be considered an epidemic
What do we call an epidemic that occurs simultaneously on more than one continent?
A pandemic
What are the 3 approaches to epidemiology?
- Descriptive
- Analytical
- Experimental
What is an index case?
The first case of a disease in a given area or population
Why might it be difficult or even impossible to identify an index case?
Because sometimes the index case has recovered already, moved, or even died.
The time course and chains of transmission of a disease are important to what type of epi?
Descriptive Epi
When was the earliest descriptive epi study, who conducted it and why?
In 1854 by John Snow who studied a cholera outbreak in London.
When it is not ethical to apply Koch’s postulates what else might we use?
Analytical Epi
Analytical epi is used to investigate a disease in detail to determine what? (3 things)
- The probable cause of a disease
- The mode of transmission
- Possible preventions of the disease
What does experimental epi do?
Test a hypothesis concerning the cause of a disease
What are healthcare-associated infections? (HAIs)
Infections acquired by patients/health care workers while they are in health care facilities
What is another word for healthcare-associated infections?
Nosocomial infections
What are exogenous HAIs?
infections caused by pathogens acquired from a health care environment
What are endogenous HAIs?
Infections that arise from normal microbiota within a patient which become pathogenic because of factors within the health care setting
Opportunistic pathogens caused by hospital related care such as medical treatments are referred to as what?
Endogenous HAIs
What are iatrogenic infections?
Subset of HAIs caused by modern medical procedures
What are some procedures that can lead to iatrogenic infections?
Surgery, catheters, invasive diagnostic procedures, etc.
What are superinfections and what causes them?
Superinfections result from antimicrobial drugs that inhibit some resident microbiota, allowing others to thrive due to lack of competition
C Diff (Clostridium Difficile) is an example of what?
A superinfection
What are 3 factors influencing HAIs?
- Microorganisms present in hospital environment
- Immunocompromised persons
3.Transmission of pathogens between staff and patients
What is the ssingle most effective way to reduce HAIs?
Effective hand washing by medical and support staff
What 2 processes are used to reduce the number of pathogens in water supplies?
Filtration and chlorination
What sort of diseases are particularly difficult for public health officials to control?
Diseases that are transmitted sexually and through the air
Give an example of mutualism
bacteria in the human colon
Give an example of amensalism
The fungus penicillium inhibits nearby bacteria but is not affected by the bacteria
Give an example of parasitism
Tuberculosis bacteria in the human lung
Give an example of commensalism
Hair follicle mites that live on human skin
