Microbio Exam 3 😬

Infectious Disease

illness caused by a pathogen

Opportunistic pathogens

only caused disease when the host is weakened

True pathogen

does not require a host to cause disease

Epidemiology

the monitoring and controlling disease occurrence to promote public health

Exposure

potential or confirmed contact between a host and pathogen

Infection

pathogen enters the body and begin to multiply; only in a proportion of exposed hosts

Disease

cells in the body are damaged as a result of infection and symptoms of illness appear

Infectivity

describes how good an infectious agent is at establishing an infection

Pathogenicity

the general ability of an infectious agent to cause disease

virulence

severity of disease following infection

What are the 5 steps of disease progression?

1. Incubation Period

2. Prodromal Phase

3. Acute Phase

4. Period of Decline

5. Convalescent Phase

Incubation Period

time between infection and development of earliest symptoms

Prodromal Phase

Early symptoms develop

Acute Phase

the peak of the disease

Period of Decline

replication of the infectious agent is brought under control, symptoms start to resolve

Convalescent phase

patient recovers; in some cases pathogen is kept latant in the patient

Exogenous sources and Endogenous sources

Exogenous sources come from outside the body, while endogenous sources are produced within the body itself (like hormones or metabolic byproducts).

Reservoir

the habitat in which an infectious agent normally lives, grows and mutliplies

direct and indirect transmission

direct is physical contact between reservoir and host, indirect doesn’t require physical contact

Sporadic cases

occasional isolated infecitons in a particular population

Endemic infections

routinely detected in a population or region (cold viruses)

Epidemic

widespread disease outbreak during a specific time frame

Pandemic

occurs if an epidemic spreads to numerous countries

Symptomatic

having signs and symptoms of disease

Signs vs symptoms

Signs are objective indicators that can be measured or verified (fever, rash, blood in stool)

Symptoms are more objective, often being sensed by patient (not measured precisely. Eg. pain, fatigue, nausea)

Latent infection

Usually asymptomatic, remains in the body

Acute vs chronic diseases

acute have rapid onset and progressive while chronic have much slower onset and progression

Emerging vs reemerging pathogens

Emerging are newly identified agents and have only caused sporadic cases (COVID) or exhibit expanded geographical distribution (Ziki virus).

Reemerging pathogen were under control but now are resurfacing. Common culprits are antibiotic resistant bacteria and measles

Zoomatic, communicable, and contagious diseases

zoomatic is animals to humans (most are noncommunicable meaning they cannot spread human to human). Communicable diseases transport from human to human. Contagious disease are easily transmitted from one host to the next.

Rate, Ratio, and proportion

rate is a measure of an occurence of an event over time. Ratio is an occurence of an event compared to another group. Proportion is a percentage of a whole

Measures of frequency (3 measurements)

gives information about the occurrence of a disease in a population over a period of time

• Population: any defined group of people

• Morbidity: existence of disease in a population

• Prevalence: morbidity in a given population during a specified time.

Prevalence rate

describes the number of cases in a population over a particular period of time

What are the two main factors that impact prevalence rate?

Incidence rate: number of new cases in a defined population durign a defined time

Duration: how long the infection lasts

Measures of association

tell us what factors may be linked with cases of the disease and subsequently who might be at risk

Risk factor

a variable associated with an increased risk of infection or disease

Descriptive epidemiology vs Analytical epidemiology

Descriptive epidemiology examines the who, where, and when of health events, while analytical epidemiology investigates the why and how by testing causes and risk factors.

Case reports, Correlation studies, and cross-secitonal studies

Case reports describe detailed observations of a single patient or event, correlation (ecological) studies examine relationships between variables at the population level, and cross-sectional studies assess both exposure and outcome at a single point in time.

Observational vs Experimental studies

Observational studies involve watching and analyzing exposures and outcomes without intervention, while experimental studies actively assign treatments or exposures to test cause-and-effect relationships.

HAIs and most commons sources

healthcare-acquired infections. Most common sources are contaminated medical devices and healthcare workers’ hands

To establish an infection, what five tasks must a pathogen complete?

1. Enter

2. Adhere

3. Invade

4. Replicate

5. Transmit

Portal of entry (what is the most common entry?)

any site where the pathogen enters the host; mucous membranes are the most common membranes

Adhesion (two phases and what are used)

initial adhesion often being nonspecific. many target and exact surface molecule match on the host cell, influencing tropism (turning). Adhesins are used, and may involve joining a biofilm

Adhesins

virulence factors used to stick to host cells in a specific or nonspecific manner.

What are options for invasion to get nutrients?

Remain on surface, pass through cells to invade deeper tissue, enter cell to reside as an intracellular pathogen

Invasins

molecules that facilitate pathogen invasions. secrete enzymes break down host tissues, form blood clots, or induce the host to uptake the pathogen

Motility

invasion strategy that helps a pathogen spread

Cytopathic effects (virus and bacteria)

Bacteria: invade host cells, release toxins, and exploit host nutrients

Virus: disrupt normal host cell function, release from the host cell, or transform normal cells into cancer cells

Talk to me about the immune system hurting itself as a byproduct of fighting infections

Worthwhile, but can be dangerous, like the influenza pandemic. Ex: Tissue damage that develops in tuberculosis is due to immune system attacking cells infected with bacteria. MOST viral infections result in the immune system killing virus-infected cells

What does replication imply?

Both nutrient acquisition and immune escape

What are some microbial strategies for nutrient acquisition?

Extracellular enzymes for biomolecule acquisition.

• Break down nutrients in the environment for the pathogen

  • Ex: lipases and porteases

Siderophores for iron acquisition

• Transferrin binds to iron and shuttles it to tissues. Many bacteria produce siderophores that snatch iron from transferrin

What are some immune modulation mechanisms? (help microbes evade or undermining pathogen-finding tools of the immune system)

• Grow fast

• Replicate intracellularly

• Go latent, protecting the pathogen from immune system

What is the first immune modulation strategy? What happens in this phase?

Hide (immunoevasion)

• Antigenic masking: conceals itself with antigenic features, such as host molecules

• Antigenic mimicry: mimic host molecules. Capsules can resemble host carbohydrates

• Antigenic variation: periodically altering the surface molecules, preventing rapid immune response. Causes include mutations in the genome and change in protein expression

What is the second modulation strategy?

Interfere/inhibit

• Interfering with phagocytosis

• Inhibiting signaling required for cell recruitment/systemic immune activation

How do pathogens avoid phagocytosis?

1. Making a capsule

2. Bursting free of the phagosome

3. Blocking fusion of the phagosome with the lysosome

4. Neutralizing enzymes of the phagocytes

5. Damaging phagocytic cells using toxins

6. Pathogen may have evolved to thrive inside the harsh environment of the phagolysosome

How can pathogen suppress immune function?

• Directly targeting immune system cells

• Making proteases that break down host antibodies

• Interfering with the transcription of interleukins

• Interfering with the molecular signaling that activate parts of the immune response

Portal of exit

transmission to new host, portal of entry is often the same as the portal of exit

Virulence factors

cellular structures, molecules, and regulatory systems that enable microbial pathogens to achieve colonization in the host, entry/exit out of cells, immunoevasion/immunosuppression, and nutrient acquisiton from the host

What are virulence factors properties of?

Pathogens, not hosts.

Give an example of a virulence factor that facilitates Adhesion

Adhesins due to their surface proteins

Give an example of a virulence factor that facilitates Invasion

Invasins: Proteins that force host cells to ingest the pathogen via endocytosis.

Flagella: Provide motility to navigate through mucus or host fluids.

Give an example of a virulence factor that facilitates Nutrient Acquisition

Extracellular enzymes for biomolecule acquisition

• Lipases: break down lipids

• Proteases: break down proteins

Siderophores for iron acquisition

What role do toxins play in immune evasion and nutrient acquistion?

Have a toxin effect on targeted host cells

Toxigenic: microbes that make toxins

Toxemia: toxins in the bloodstream

Classified into 2 categories

• Endotoxin

• Exotoxins

Endotoxin

Derived from lipopolysaccharide (LPS) in Gram-negative outer membrane, stimulating a strong inflammatory (immune) response

What is the problem with Endotoxins?

High levels can be damaging and hard to neutralize. Mainly released when Gram-negative bacteria die. Too much causes septic shock, killing the host as the organs fail

Exotoxins

Soluble proteins that affect a wide range of cells. Generated by both Gram-positive and Gram-negative bacteria. Named based on the organims that it effects

What are three classes of exotoxins

Type 1: Toxin binds at plasma membrane and generates a signal that generates effects; does not enter cell

Type 2: Toxin disrupts host cell membrane by forming pores or breaking down membrane lipids

Type 3: Binding protein of toxin binds to plasma membrane, txoin enters cell by endocytosis, active protein enters the host cell and causes effect

Compare and contrast major characteristics of endotoxins vs exotoxins (Made of, Made by, Released from, Vaccines, Fever, Able to Be Neutralized in Patient, Toxicity level

Made of: Endo are lipid, Exo are protein

Made by: Endo are Gram-Negative, Exo are both

Released from: Endo are when Gram-negative cell wall when bacteira divide or die, Exo are activiely growing bacteira,

Vaccines: Endo: No, Exo: Yes

Toxicity: Endo: lower, Exo: Higher

Lethal dose-50

Amount of toxin lethal to 50% of affected hosts that are not treated

Identify at least three host factors that influence virulence of microbial infections

Immune Status: Impairment (e.g., HIV, chemotherapy) prevents effective pathogen neutralization.

Age: Very young or very old individuals have underdeveloped or waning immune defenses.

Nutritional Health: Deficiencies weaken physical barriers and decrease immune cell production.

Infectious dose-50

Number of cells or virions needed to establish active infection in 50% of hosts exposed to that dose

Basic Reproduction Number

R0; measure of a pathogen’s transmissibility

ID50 and LD50

• ID50 (Infectious Dose 50%): The number of pathogen cells or virions required to cause infection in 50% of a sampled population.

• LD50 (Lethal Dose 50%): The number of pathogen cells or virions required to kill 50% of a sampled population.

What are the implications of these measurements?

Both values are inverse measures of virulence. A lower ID50 or LD50 indicates a more virulent pathogen because it takes fewer organisms to cause harm.

What is the pathogen strategy of this?

Pathogens with low ID50 (e.g., Norovirus) are highly transmissible and excel at colonizing the host at low concentrations.Pathogens with low LD50 (e.g., Botulinum toxin) are highly lethal and target critical host systems quickly.

Attenuated

pathogen is still infectious, but is weakend

What are two useful applications of attenuated pathogens?

Research studies and as vaccine candidates

BSL-1 agents

well characterized, rarely causing disease in healthy people

BSL-2 agents

infectious agents that can cause modestly virulence disease in humans, often being preventable. NO airborne transmission. Human bodily fluid are treated as BSL-2

BSL-2+ agents

Dangerous and incurable, not vaccine preventable

BSL-3 agents

Serious or lethal human diseases, may have airborne transmission. Treatable, but high severity. It required PPE

BSL-4 agents

Highly dangerous pathogens, no cure

Antigens

a molecule on an organism that is recognized as “foreign,” causing an immune response

Epitope

the small specific region where the antibody or T cell binds

T cell vs B cell location

T cell mature in thymus, B cell in bone marrow

T cell vs B cell function

B cells produce antibodies while T cells coordinate immune response

T cell vs B cell longevity

Memory B cells are long lived while T cells aren’t

Outline the adaptive immune response in 4 stages.