IB 114 - Midterm 1

What is the definition of disease in humans?

Any condition that reduces an individual's well-being.

What is the definition of disease in organisms?

A condition that negatively affects the organism's fitness.

What causes non-infectious diseases?

Internal or external conditions unrelated to infectious agents.

What causes infectious diseases?

Infectious agents like pathogens or parasites, resulting from interactions between the host and the pathogen/parasite.

What is the etiology of a disease?

The cause of the disease.

What are infectious agents called when they harm their host?

Parasites or pathogens.

How are parasites classified?

By size (micro vs. macro), taxonomic diversity, and transmission strategy.

What is taxonomic diversity?

Number, abundance, and distribution of species.

What is transmission strategy?

Vertical versus horizontal transmission, vector-borne pathogens, STDs, trophically-transmitted parasites.

What are microparasites, and how do they behave in a host?

Microparasites (e.g., protozoa, viruses, bacteria, fungi) are small, multiply rapidly in the host, have short generation times, and cause transient infections.

How are microparasite infections measured?

By counting the number of infected individuals.

What are macroparasites, and how do they behave in a host?

Macroparasites (e.g., nematodes, tapeworms, fleas) are larger, have longer generation times, can persist outside the host, and typically cause persistent infections without lasting immunity.

How are macroparasite infections measured?

By counting both the number of infected individuals and the number of parasites within them (parasite load).

What is parasite load?

The number of parasites in an infected individual, important in macroparasite infections.

What is vertical transmission?

The transmission of disease from parent to offspring.

Why is vertical transmission not the most efficient way for pathogens to spread?

It can only infect offspring, so pathogens must also rely on horizontal transmission to spread widely.

What is the most common type of vertical transmission?

Female-to-offspring transmission.

Give examples of vertical transmission pathways.

Cytoplasmic (West Nile virus), trans-placental (HIV, rubella), perinatal (HIV, gonorrhea), and postnatal (HIV).

What is horizontal transmission?

Disease transmission between unrelated individuals within the same generation.

Name two types of direct contact horizontal transmission.

Sexual transmission (e.g., syphilis) and non-sexual transmission (e.g., common cold).

How does aerial transmission spread diseases?

Through aerosols or airborne spores.

What is waterborne transmission?

Transmission of disease through contaminated water, typically via the fecal-oral route (e.g., cholera).

What is vector transmission?

The spread of disease through a vector, which can be biological (e.g., mosquitoes for malaria) or passive.

Define trophic transmission.

Transmission of disease through feeding, such as cannibalism or consuming infected intermediate hosts.

What are fomites?

Inanimate objects that can harbor infectious agents and facilitate disease transmission.

What is iatrogenic transmission?

Transmission of disease caused by medical procedures, such as through contaminated instruments.

What are nosocomial infections?

Infections that occur in hospitals, often due to medical interventions.

What is zoonotic transmission?

Diseases that primarily affect animals but can be transmitted to humans (e.g., rabies).

What is frequency-dependent transmission?

Transmission that depends on the proportion of infected individuals in the population, often seen in sexually transmitted diseases.

What is prevalence?

The percentage of hosts infected or expressing disease in a population at a given time.

What is incidence?

The rate of new disease cases in a population over a period of time.

What is intensity?

The average number of parasites within infected hosts, especially important for macroparasites.

How is abundance calculated?

By multiplying prevalence by intensity.

What is an endemic disease?

A disease that is consistently present in a population.

What is an epidemic?

A sudden increase in disease prevalence or intensity, often leading to periodic outbreaks.

Define morbidity.

The weakness or illness caused by a disease, not necessarily resulting in death.

What is virulence?

The impact of a parasite or pathogen on the host's fitness, often increasing the death rate.

What is herd immunity?

When a high proportion of individuals in a population are immune, reducing the likelihood of disease outbreaks.

What are reservoir hosts?

Species that carry a pathogen without showing symptoms but can still infect others.

In the S-I model, what does "S" represent?

The number or density of susceptible individuals, or those who are not yet infected but are at risk of infection.

In the S-I model, what does "I" represent?

The number or density of infected and infectious individuals, meaning those who can transmit the disease.

In the S-I model, what does "N" represent?

N is the total population size and is the sum of susceptible and infected individuals: N = S + I.

What does the transmission coefficient (β) in the S-I model represent?

β is the disease transmission coefficient, which represents the likelihood that contact between a susceptible and an infected individual will result in infection.

How is the rate of infection calculated in the S-I model?

Rate of infection = β × S × I, where S is the number of susceptible individuals, I is the number of infected individuals, and β is the transmission coefficient.

In the SIR model, what does "R" represent?

R represents the number or density of recovered individuals, who are now immune or resistant (or have died from the disease).

What does the parameter b represent in the SIR model equations?

b is the birth rate of the host population, adding new susceptible individuals into the population.

What does d represent in the SIR model?

d is the natural mortality rate, which reflects the rate at which individuals die from natural causes unrelated to the disease.

What does α represent in the SIR model?

α is the disease-induced mortality rate, or the rate at which infected individuals die due to the disease.

What does γ represent in the SIR model?

γ is the recovery rate, which indicates how quickly infected individuals recover and move into the "recovered" category (R), becoming immune.

What is the equation for the change in susceptible individuals over time in the SIR model?

dS/dt=b(S+I+R)−dS−βSI

This equation accounts for the birth rate adding new susceptibles, the natural death rate removing susceptibles, and the rate at which susceptible individuals become infected.

What is the equation for the change in infected individuals over time in the SIR model?

dI/dt=βSI−dI−αI−γI

This equation describes the rate at which susceptible individuals become infected (βSI), balanced by the natural death rate (dI), disease-induced mortality (αI), and the rate of recovery (γI).

What is the equation for the change in recovered individuals over time in the SIR model?

dR/dt=γI−dR

This equation reflects how recovered individuals increase as infected individuals recover (γI), balanced by the natural death rate (dR) of recovered individuals.

What is the basic reproduction number (R₀)?

R₀ is the average number of new infections generated by one infected individual in a completely susceptible population.

How is R₀ calculated?

R₀=(βS)/(α+d+γ)

This formula balances the transmission rate (βS) with the rates of disease-induced death (α), natural death (d), and recovery (γ). R₀ must be greater than 1 for a disease to spread.

What happens when R₀ is less than 1?

If R₀ < 1, the disease will not spread and will eventually die out in the population.

What is density-dependent transmission?

Density-dependent transmission means the rate of new infections increases as population density increases, typical of many directly transmitted diseases.

What is frequency-dependent transmission?

Frequency-dependent transmission occurs when the rate of disease transmission depends on individual contact behavior, typical of diseases like sexually transmitted infections.

How does seasonality affect disease transmission?

Seasonal changes, such as temperature or vector activity, can cause disease transmission rates to fluctuate, leading to higher transmission during certain times of the year (e.g., malaria peaks in warmer months).

What is the dilution effect in vector-borne diseases?

The dilution effect occurs when, in very dense populations, vectors (like mosquitoes) become "satiated" and can't bite more individuals, leading to a plateau in the number of new infections.

What are prions?

Infectious proteins that cause disease by inducing the misfolding of normal proteins in the brain.

How do prions differ from typical pathogens like bacteria or viruses?

Prions contain no DNA or RNA; they are purely misfolded proteins that cause normal proteins to misfold, leading to disease.

What happens to brain tissue when infected with prions?

The brain tissue develops sponge-like lesions as nerve cells are destroyed, leading to neurodegeneration.

Why does the immune system not respond to prions?

Prions are just misfolded proteins, so the immune system does not recognize them as foreign invaders.

What is Creutzfeldt-Jakob Disease (CJD)?

A rare, fatal neurodegenerative disease caused by prions, leading to memory loss, personality changes, and death, with sponge-like lesions in the brain.

How is Chronic Wasting Disease (CWD) transmitted?

It is thought to spread through direct contact between infected animals (deer, elk, moose) or via contaminated feed and water.

What are the two origins of abnormal prion proteins?

- Endogenous origin: Mutation in the gene coding for the prion protein.

- Exogenous origin: Ingesting or coming into contact with external abnormal prion proteins.

What is the endogenous origin of prion diseases?

Prions arise from genetic mutations in the gene coding for normal prion proteins, leading to abnormal folding.

What is the exogenous origin of prion diseases?

Prions are acquired by ingesting or coming into contact with abnormal prion proteins from an external source.

What is the role of normal prion proteins (PrP)?

Normal prion proteins help maintain the myelin sheaths of nerve cells, ensuring efficient nerve signal transmission.

How do prions cause other proteins to misfold?

Abnormal prions interact with normal prion proteins, inducing them to misfold and creating a chain reaction that spreads the misfolding.

What is Bovine Spongiform Encephalopathy (BSE), also known as mad cow disease?

A prion disease in cattle that can be transmitted to humans through contaminated beef, leading to variant CJD.

What are viruses made of?

Viruses consist of genetic material (DNA or RNA) surrounded by a protein coat (capsid).

Can viruses replicate on their own?

No, viruses require a host cell to replicate, as they use the host's machinery to produce new viral particles

What are the main steps in viral replication?

Adsorption, entry, uncoating, transcription, synthesis of viral components, assembly, and release of new virions.

What is the difference between positive-strand (+) and negative-strand (-) RNA viruses?

Positive-strand RNA acts like mRNA and can be directly translated into proteins. Negative-strand RNA must first be converted into a positive strand before it can be translated.

How do viruses generate new variants?

Through mutations, recombination, and reassortment.

What is antigenic drift?

Antigenic drift is the accumulation of small mutations in viral surface proteins, allowing the virus to evade the immune system over time.

What is antigenic shift?

Antigenic shift is a major genetic change in a virus, often due to the reassortment of viral genome segments, which can lead to the emergence of new viral strains.

What are the key features of the influenza virus?

Influenza is a segmented ss(-) RNA virus that undergoes both antigenic drift and shift, making it highly variable.

How is HIV transmitted, and what does it target?

HIV is transmitted through sexual contact and infected blood. It targets T-helper cells of the immune system, leading to immune destruction.

What is a retrovirus, and how does HIV replicate?

A retrovirus like HIV uses reverse transcriptase to convert its RNA into DNA, which is then integrated into the host's genome with integrase, allowing the virus to replicate alongside the host's DNA.

What challenges make it difficult to create vaccines or drugs for HIV?

HIV has high genetic variability due to frequent mutations and recombination during replication, making it hard to target with vaccines or drugs.

What are the two replication cycles of bacteriophage Lambda?

- Lytic cycle: The virus replicates, bursts the bacterial cell, and releases new virions.

- Lysogenic cycle: The virus integrates into the host genome and replicates without destroying the cell.

What is lytic viral release?

Lytic release occurs when new virions burst the host cell, killing it and releasing the virus.

What is non-lytic viral release?

Non-lytic release occurs when viruses bud off from the host cell without killing it, such as in HIV.

How does influenza undergo antigenic shift?

Antigenic shift occurs when two different strains of influenza infect the same host and their genome segments reassort, leading to a new viral strain.

What are bacteria?

Bacteria are prokaryotic organisms with no nucleus and a single circular chromosome, often with smaller plasmids.

What are plasmids?

Plasmids are small, circular DNA molecules in bacteria that exist independently of the main chromosome and can carry genes for antibiotic resistance or virulence.

What are the three main mechanisms of genetic recombination in bacteria?

- Transformation: Uptake of external DNA.

- Transduction: Transfer of bacterial DNA via bacteriophages.

- Conjugation: Transfer of DNA through a pilus via a conjugative plasmid.

How do mutations contribute to bacterial variation?

Mutations are changes in the DNA that occur during replication and can lead to new traits like antibiotic resistance.

What are transposons?

Transposons, or "jumping genes," are DNA sequences that can move around within a genome, causing mutations when they insert into new locations.

How do bacteriophages influence bacterial behavior?

Bacteriophages can integrate into the bacterial genome as prophages, transferring genes that may enhance bacterial pathogenicity or behavior.

What is cholera, and how is it transmitted?

Cholera is caused by the bacterium Vibrio cholerae and is transmitted through contaminated water. It leads to severe diarrhea due to a toxin that stimulates water and salt secretion in the intestines.

What causes syphilis, and what are its long-term effects?

Syphilis is caused by Treponema pallidum and is sexually transmitted. If untreated, it can lead to severe complications, including dementia and neurological damage in its late stages.

How does antibiotic resistance arise in bacteria?

Bacteria acquire antibiotic resistance through mutations or by gaining resistance genes via plasmids, enabling them to survive in the presence of antibiotics.

How do bacteria acquire external DNA during transformation?

Bacteria take up DNA from their environment, often from dead bacterial cells, and incorporate it into their own genome.

What is the role of conjugation in bacterial genetic variation?

Conjugation allows bacteria to transfer plasmids to one another via a pilus, spreading genes like those for antibiotic resistance.

What are the major mechanisms for bacterial evolution?

Bacteria evolve through mutation, recombination (transformation, transduction, conjugation), and plasmid transfer.

KQ: T/F Vertical transmission is within one generation between unrelated individuals

False

KQ: Which of the following are examples of horizontal transmission routes?

A. Direct Contact Transmission

B. Aerial Transmission

C. Soil-borne transmission

D. All of the above

D. All of the above