4 Types of infectious agents

Question 1

What are the 5 types of infectious agents?

Answer 1

1. Parasites (protozoa, helminths, arthropods)
2. Bacteria
3. Viruses
4. Fungi
5. Prions

Question 2

How are bacteria classified?

Answer 2

🔸 O₂ req. (aerobic/anaerobic)
🔸 Gram stain (cell wall)
🔸 Shape (rod, cocci, spiral)
🔸 Surface: pili, flagella, capsule

Question 3

How are viruses classified?

Answer 3

🔹 Genome (DNA/RNA)
🔹 Capsid (icosahedral/helical)
🔹 Envelope ±
🔹 Replication mode
🔹 Cell tropism
🔹 Pathology

Question 4

What are protozoa and helminths?

Answer 4

🧫 Protozoa = unicellular euk. (1–50 µm), e.g. Plasmodium
🪱 Helminths = multi-cell worms (3–10+ mm), complex life cycle

Question 5

How do viruses differ from prions?

Answer 5

🦠 Viruses = DNA/RNA genome, capsid ± envelope, use host machinery
🧠 Prions = misfolded PrP proteins, no nucleic acid

Question 6

What are common features of fungi?

Answer 6

🍄 Euk., 2–200 µm
Yeast (round), hyphae (filament), or dimorphic
Superficial (e.g. tinea) or systemic (immunocompromised)