BIOL123

What type of infections do viruses, bacteria, and fungi typically cause versus parasites?

Viruses, bacteria, and fungi: Typically cause acute infections.

Parasites: Typically cause chronic infections.

In biological terms, what is symbiosis?

An interaction between two different organisms living in close physical association.

Define Parasitism.

A symbiotic relationship between two species in which one species benefits and the other species is harmed.

Differentiate between Mutualism and Commensalism.

Mutualism: Both organisms benefit (e.g., bacteria in the human colon).

Commensalism: One organism benefits, while the other neither benefits nor is harmed (e.g., Staphylococcus on the skin).

What is the Incubation period?

The time between the initial infection and the first occurrence of symptoms or signs of the disease.

What is the Prodromal period, and does it occur in all diseases?

• A short timeframe characterized by generalized, mild symptoms (like fatigue).

• No, it does not occur in all infectious diseases.

Define the Illness stage of an infectious disease.

The most severe stage of the disease where symptoms are most evident and the host's immune system has not yet fully responded.

What is Convalescence?

The stage where the body gradually returns to normal. Its duration varies depending on the pathogen and the amount of damage caused.

What are the 4 main stages in the Progression of Disease?

1. Invasion

2. Multiplication

3. Spread

4. Pathogenesis

Define Invasion in the context of disease progression.

Entry of the pathogen into the host and its transmission from one host to another.

How does multiplication differ between Protists and Helminths inside the host body?

Protists: Can multiply inside the body; disease can occur from just a few initial stages, and severity depends on how fast they multiply.

Helminths: Most cannot multiply within the body; severity depends heavily on the number of infectious stages acquired over time.

Define Spread in disease progression.

The ability of an organism to move from the initial site of infection to other areas or systems of the body (e.g., circulatory, nervous, or digestive systems).

What is Pathogenesis, and what three main factors influence it?

The causation and development of clinical disease. It is influenced by:

1. The number of pathogenic organisms present.

2. The virulence of the organism (e.g., killing cells, toxins, or causing immunopathology).

3. The host's reaction/immune resistance.

Differentiate between Incidence and Prevalence.

Incidence: The number of new cases of infection occurring in a population during a defined period of time.

Prevalence: The total number of infected individuals (both new and old cases) in a population at a specific point in time.

Define Mortality.

The total number of deaths caused by a disease in a population over a defined period of time.

What is a DALY and what is its formula?

Disability Adjusted Life Year—a metric measuring overall disease burden by combining life years lost to premature death and healthy years lost to disability.

Formula: DALY = YLL (Years of Life Lost) + YLD (Years Lived with Disability)

What are the limitations of using DALYs alone to measure disease impact?

DALYs only measure direct health loss. They fail to account for:

• Economic impacts (e.g., on agriculture/productivity).

• Direct costs of treatment, prevention, and surveillance.

• Social stigma or general healthcare system overload.

What is the Biological Response Gradient?

• The concept that pathogens rarely cause the exact same severity of disease in all hosts.

• The clinical outcome depends on variables like dose, age, biological sex, genetics, nutrition, and co-infections.

What is the "Iceberg" concept of infectious disease?

• The idea that the visible portion of a disease (severe/apparent clinical cases) represents only a small fraction of the total infections

• While a large, hidden base of individuals are asymptomatic or experience less severe disease.

Contrast the primary causes of death between High-income and Low-income countries.

High-income countries: Predominantly die of chronic, non-communicable conditions (cardiovascular disease, cancer, dementia) later in life.

Low-income countries: Heavily impacted by communicable/infectious diseases (lower respiratory infections, diarrheal diseases, malaria, TB), with child mortality (under 15) accounting for roughly 40% of deaths.