Topic 26- Infectious Diseases

What is virulence?

The ability of a pathogen to cause disease.

What is a pathogen?

An organism that causes disease.

What are intrinsic vs extrinsic factors in disease?

Intrinsic = host-based; Extrinsic = pathogen-caused.

Define epidemic and pandemic.

Epidemic = widespread outbreak; Pandemic = global outbreak.

Name 4 historical pandemics.

COVID-19, HIV/AIDS, Bubonic Plague, Cholera.

Name 3 types of pathogens.

Bacteria, Parasites, Viruses.

What are viruses made of?

Protein shell (capsid) and genetic material (DNA/RNA).

Can viruses replicate on their own?

No, they require host cells.

Do viruses perform metabolism?

No.

What type of virus is influenza?

An RNA virus with 8 genome segments.

What are H and N proteins on influenza?

Surface proteins that define strain type (e.g., H1N1).

List common symptoms of influenza.

Fever, chills, aches, congestion.

What happened during the Spanish flu (1918)?

⅓ of world infected; >20 million died; 12,000 deaths in Philadelphia in 5 weeks.

How is Lyme disease transmitted?

Through the bite of infected ticks (deer → tick → human).

Are humans part of the tick's life cycle?

No, humans are dead-end hosts.

How is Lyme disease treated?

With antibiotics.

What is the most common tick-borne disease in the US?

Lyme disease.

What is a parasite?

Organism that lives on/in a host and harms it.

How many malaria cases occur annually?

~200 million.

How many malaria deaths in 2019?

409,000 (⅔ were children under 5).

What transmits malaria?

Anopheles mosquitoes.

What are the two hosts for Plasmodium?

Human and mosquito.

What happens in the human liver during malaria infection?

Sporozoites enter and multiply, forming merozoites.

What do merozoites do?

Burst from liver and infect red blood cells.

What happens in the mosquito?

Gametocytes form a zygote → meiosis → oocyst → sporozoites.

What are early malaria eradication strategies?

Barriers, behavior changes, vector control.

What are two malaria vaccines?

RTS,S/AS01 (Mosquirix), R21 (Oxford).

What type of virus is SARS-CoV-2?

Enveloped RNA virus.

How many human coronaviruses exist?

7 total (4 = cold, 3 = SARS, MERS, COVID-19).

What is a zoonotic virus?

A virus that jumps from animals to humans (e.g., SARS-CoV-2, HIV).

How does COVID-19 spread?

Person-to-person via droplets/aerosols.

How quickly did COVID-19 spread globally?

~2 months.

What is CFR?

Case Fatality Rate – % of infected people who die.

Compare CFRs: SARS, MERS, COVID-19, Flu.

SARS ~10%, MERS ~35%, COVID-19 ~0.5–5%, Flu ~0.1%.

What is the goal of public health measures?

Decrease R (reproduction number) to <1.

Effective control strategies?

Social distancing, lockdowns, testing, contact tracing, isolation.

Early COVID-19 treatment?

Treated as ARDS; overuse of ventilators.

Current COVID-19 treatment?

Treat hypoxia, manage blood clots, supportive care.

Examples of antiviral use?

Tamiflu (flu), various antivirals in use for COVID-19.

What types of COVID-19 vaccines exist?

mRNA (Pfizer/Moderna), viral vector (J&J).

Compare and Contrast: Intrinsic, Extrinsic, and Zoonotic Sources of Disease [Definition, Example]

Source	Definition	Example
Intrinsic	Host-based factors (genetic, immune, etc.)	Autoimmune disease, cancer
Extrinsic	External, pathogen-based causes	Viruses, bacteria, parasites
Zoonotic	Disease transmitted from animals to humans	COVID-19, HIV, Ebola

Compare and Contrast: mRNA, Viral vector, Subunit/proteins, Live-attenuated, Inactivated Types of Vaccines [Mechanisms, Examples]

Type of Vaccine	Mechanism	Examples
mRNA	Teaches cells to make viral proteins → immune response	Pfizer, Moderna (COVID-19)
Viral Vector	Uses modified virus to deliver genetic material	J&J (COVID-19), Ebola
Subunit/Protein	Contains pieces of the virus (antigens)	Novavax
Live-attenuated	Weakened version of the pathogen	MMR, varicella
Inactivated	Killed virus or bacteria	Polio (Salk), flu shot

Sequence: Herd Immunity

• Vaccinate or infect a portion of the population

• Build immunity within those individuals

• Transmission decreases as immune individuals act as buffers

• Pathogen spread slows even among unvaccinated people

• Threshold reached where R < 1 → disease fades

Compare and Contrast: Viruses, Bacteria, and Parasites [Size, Living?, Metabolism, Replication, Treatment, Examples]

Feature	Viruses	Bacteria	Parasites
Size	Smallest	Small (but larger than viruses)	Large, multicellular (some unicellular)
Living?	No	Yes	Yes
Metabolism	No	Yes	Yes
Replication	Needs host	Self-replicating	Complex life cycles
Treatment	Antivirals/vaccines	Antibiotics	Antiparasitic drugs
Examples	Influenza, SARS-CoV-2	TB, strep throat	Malaria (Plasmodium), tapeworms

Sequence: Influenza Infection

• Virus enters body (inhaled droplets)

• Virus binds to cells using H proteins

• Virus enters host cell → uncoats

• RNA genome released → replicated

• New virions assembled with H & N proteins

• Virus buds off → infects more cells

• Symptoms appear: fever, chills, aches

Sequence: Antibiotic Resistance

• Antibiotics used to kill bacteria

• Most bacteria die; resistant ones survive

• Resistant bacteria reproduce

• Resistance genes spread via plasmids

• Antibiotic becomes less effective

• Multidrug resistance may evolve

Hypothesize & Diagnose: Impact of Variability on Antibiotic Resistance

Cause of Variability	Impact on Resistance
Overuse of antibiotics	Increases selective pressure → resistance develops faster
Incomplete antibiotic courses	Allows partially resistant bacteria to survive and evolve
Misuse in livestock/agriculture	Spreads resistance genes to human pathogens
Genetic variation in bacteria	Some mutations → drug resistance (random, but selected for)

Sequence: Parasite Transmission (Plasmodium Example)

1. Mosquito bite injects sporozoites

2. Sporozoites → liver, infect cells and divide

3. Liver cells burst, releasing merozoites

4. Merozoites infect red blood cells → replicate

5. Some develop into gametocytes

6. Another mosquito bites, taking in gametocytes

7. In mosquito gut: gametes fuse → zygote → sporozoites

8. Cycle restarts with next bite