Epidemiology Basics Quiz

Microbial Infections and Infectious Diseases

• Summary of Injuries and Diseases:

  • Types of Injury and Responses:
    • Injurious stimulus types: altered physiological stimuli (e.g., increased demand, decreased stimulation), chronic irritation (physical/chemical), reduced oxygen supply, chemical injury, microbial infection.
    • Cellular responses to injurious stimuli: Cellular adaptations (e.g., hyperplasia, hypertrophy, atrophy, metaplasia), cell injury (acute & transient, progressive & severe, including DNA damage), cumulative sublethal injury over long life span, metabolic alterations, genetic/acquired chronic injury, intracellular accumulations, calcification, cellular aging, and cell death (necrosis or apoptosis).
  • Causes of Diseases:
    • Vascular, inflammatory, neoplastic, degenerative, infectious, congenital, auto-immune, traumatic/toxic, environmental/endocrine.

Introduction to Communicable Diseases

• Microbiology:
  • The study of organisms (often small in size and simple in structure, excluding plants and animals except parasites and algae).
• Communicable Diseases:
  • Spread directly or indirectly between people or from other species to humans
  • Caused by pathogenic microorganisms (bacteria, viruses, fungi, parasites, or prions).
• Definition of an "infectious agent" using Koch's postulates (1876):
  • Occurrence of the parasite in every case of the disease, absence in other cases
  • Isolation from the body and pure culture of the parasite.
  • Ability of the parasite to cause the disease when introduced to a susceptible host
  • Re-isolation of the parasite from the experimental host that developed the disease.

Classification of Infectious Agents (Microbes)

• Size, cell type, presence of nuclei, and tools for visualization are used to classify microbes.

  -Helminths: Size from 1mm to 10 meters; eukaryotes with nuclei; visible with naked eye, magnifying glass, or light microscope. -Protozoa: Size from 2 µm to >100µm; eukaryotes with nuclei; typically viewed with a light microscope. -Fungi: Size from 3-10 µm (yeasts) to multicellular; eukaryotes with nuclei; often visualized with a light microscope. -Bacteria: Size from 0.5 µm to 5µm; prokaryotes (no nuclei); typically viewed using a light microscope. -Viruses: Size from 0.02 µm to 0.2 µm prokaryotes (no nuclei); often visualized using electron microscopy. -Prions: Size less than 1 nanometer, consist of proteins only; use molecular techniques for their visualization.

Disease Outbreaks and Epidemics

• Outbreak/Epidemic: Cases of an illness/event exceeding normal expectancy in a community or region.
• Pandemic: An epidemic extending through wide geographical boundaries, affecting a large number of people worldwide.
• Endemic: Constant presence of a disease/agent within a specific geographic area/population.
• Zoonosis: Diseases of animals that can be transmitted to humans.
• Epidemic: An increase in cases of disease above the usual or expected frequency within a certain population.
• Epidemic Curve: A graph showing the progression of disease cases over time, which can identify sources of outbreaks.

Anatomy of an Epidemic

• Identification of the progression, magnitude, size, time trend and spread patterns of an outbreak over time is essential. A graph plotting the number of cases by the date of illness onset.

Public Health Surveillance

• Public health surveillance: The ongoing, systematic process of collecting, interpreting, disseminating information about a health-related event for public health action to reduce morbidity and mortality.
• The purpose is to measure and monitor disease burden, investigate outbreaks, evaluate interventions or practices.

Host-Microbe Relationship

• Incubation Period: Time between exposure to a pathogen and the onset of symptoms.
• Prodromal Period: The onset of nonspecific, general symptoms following the incubation period.
• Illness Period: The period of prominent/specific symptoms and signs of an infectious disease.
• Decline Period: When symptoms start to resolve and decrease in severity.
• Convalescence: The recuperation phase after the symptoms decline.

Types of Infection

• Acute viral infection followed by viral clearance
• Acute viral infection followed by latent infection and periodic reactivation
• Acute viral infection followed by chronic infection
• Acute viral infection followed by a chronic infectious disease

Other Types of Infectious Agents

• Defective viruses: Viruses that lack all the proteins needed to replicate, meaning they rely on another virus type to replicate.
• Prions: Infectious proteins that cause other proteins to fold incorrectly.

Medically Important Gram-Positive Bacteria

• Gram-positive bacteria: Includes aerobic & anaerobic spore-forming species, and non-spore-forming species.

Medically Important Gram-Positive Cocci

• Gram-positive cocci, some species are highly pathogenic, some are not.

Pathogenic Neisseriae

• Gram-negative diplococci; oxidase-positive bacteria that cause disease and have specific virulence factors

Medically Important Gram-Positive Bacilli

• Gram-positive bacilli: Bacteria are rod-shaped, some are spores; various infections result from this group

Introduction to Fungi

• Fungi (Mycetology): Eukaryotes, contain β-1,6-Glucans, β-1,3-Glucan & Chitin in their cell walls, ergosterol in cell membrane, and have a distinct cellular structure.

Fungal Infections and Disease

• Superficial infections: Candidiasis (oral or vaginal thrush), dermatophytosis (Ringworm) → infections on surface of the body.
• Systemic Infections: Fungal infections that have spread throughout the body, affecting multiple organs (common in immunocompromised patients).
• Other (less common): Mycetoma → fungal disease, occurring locally or regionally.

Treatment of Fungal Infections

• Antifungal agents – various methods for targeting different cellular and metabolic processes in fungi: -Polyenes: interfere with plasma membrane -Azoles: inhibit ergosterol synthesis -Nucleoside analogues: inhibit some fungal components (e.g., 5-fluorocytosine) -Echinocandins: impede cell wall synthesis.

Introduction to Parasites

• Parasites are organisms that live on or in a host organism, deriving benefit from it, and often causing harm
• Protozoa: Unicellular parasitic microorganisms with diverse life cycles and clinical importance.
• Helminths: Multicellular parasitic worms (Nematodes, Trematodes, Cestodes) often involve intermediate hosts for transmission.
• Arthropods: Insects and arachnids which can act as vectors for other pathogens or cause direct harm.

Malaria

• Plasmodium spp.: Five parasite species that cause malaria in humans (vivax, falciparum, malariae, ovale, knowlesi).
• Transmission: Vector (female Anopheles mosquitoes) transmitted via saliva.

Important Medical Viruses

• Coronaviruses: Large group of viruses that cause various infections, including but not limited to some types of the common cold and significant diseases like SARS, MERS, COVID-19.
• Herpesviruses: Enveloped ds DNA viruses. HSV-1 & HSV-2, VZV/Varicella-Zoster (cold sores/shingles), CMV, EBV.
• Enteroviruses: Diverse group of small, non-enveloped, ssRNA viruses. Common cold-like symptoms in respiratory tract, but also affects various other body systems.
• Japanese Encephalitis (JE): Enveloped, + ssRNA. Severe encephalitis, but most infections are asymptomatic.

Other Infectious Agents

• Not all viruses are capable of replication independently; some rely on other viruses to complete their infectious cycles, while others rely on eukaryotic hosts. Prions are misfolded proteins that act as infectious agents.