Infectious Disease Life Cycle and Transmission Modes

This flashcard set covers the vocabulary and core concepts from Lecture 1 on infectious disease life cycles, transmission methods, the epidemiologic triangle, and bacterial toxins.

Aetiology

The study of the cause or origin of a disease.

Pathogenesis

The manner of development of a disease.

Microbemia

The presence of microorganisms in the blood.

Non-specific Host Defences

General protective mechanisms including skin, mucous membranes, white blood cells, inflammation, and defensive proteins.

Specific Host Defences

Immune responses involving white blood cells, B and T lymphocytes, humoral and cell-mediated immunity, and antibodies.

Infection Life Cycle Steps

The five steps for successful infection: Transmission, Adhesion, Penetration, Spread, and Survival in host.

Epidemiologic Triangle

A model used to explain the cause of disease, consisting of the Host, Agent, and Environment.

Endotoxins

Toxic lipopolysaccharide (LPS) components of the outer membrane of Gram negative bacteria, liberated when the bacteria die and the cell wall breaks apart.

Exotoxins

Toxic proteins produced inside pathogenic bacteria (mostly Gram-positive) and released into the surrounding medium following lysis or during growth.

Lipid A

The lipid portion of lipopolysaccharides (LPSs) that acts as the endotoxin in Gram-negative bacteria.

Neurotoxins

A category of exotoxins, such as the botulinum toxin from Clostridium botulinum.

Cytotoxins

A category of exotoxins that kills the host's cells, such as the diphtheria toxin from Corynebacterium diphtheriae.

Enterotoxins

A category of exotoxins, such as the shiga-like enterotoxin from E. coli.

Contact Transmission

Transmission directly from source to susceptible host or via airborne droplets spread less than $3\,\text{feet}$.

Common Vehicle Transmission

Transmission by a common inanimate vehicle like food or water, resulting in multiple cases.

Air Transmission

Transmission by droplet nuclei or dust spread more than $3\,\text{feet}$, such as in tuberculosis.

Vector Transmission

Transmission via arthropods, such as in malaria.

Pili

Attachment mechanisms used by bacteria like E. coli and Salmonella spp for adherence and colonization.

Capsules

Protective surface components that make bacteria resistant to phagocytosis and intracellular killing by host cells.

Upper Respiratory Tract Infection (URTI)

Infections where organisms enter via inhalation and invade the mucosa; examples include the common cold caused by Rhinovirus ($25\%$) or Coronaviruses ($10\%$).

Lower Respiratory Tract Infection (LRTI)

Infections where agents gain access to the distal airway by inhalation of aerosolized material, aspiration, or haematogenous seeding, such as Pneumonia.

Elementary Bodies

The infectious particles that represent the first stage of the Chlamydiae life cycle.

Reticulate Bodies

The intracytoplasmic, reproductive forms that represent the second stage of the Chlamydiae life cycle.

Conjunctivitis

Inflammation of the conjunctiva, often caused by opportunistic bacteria like Staphylococcus aureus or Chlamydia trachomatis.

Siderophores

One of the three main mechanisms by which bacteria cause tissue injury, alongside exotoxins and endotoxins.