Disease and Society

Normativists

Defines disease by the undesirability of disease and the harm and imitations they bring (E.g., illness and sickness)

Naturalists

Require just the presence of biological dysfunction (E.g., disorders)

Dutch Elm Disease

Via a vector disease, a fungal pathogen from bark beatles

Taxonomy

A classification scheme for diseases (E.g., why Tuberculous spondylitis, vertebral caries, Pott’s disease are same name for ONE disease)

World Health Organization

Classifies diseases as ICD-10 via codes

Morality statistics

Keeps track of how much people are dying

Public health/morbidity data (CDC):

How many people, how many diseases, how it spreads, how to prevent

Billing Purposes

Electronic medical records

Classifying a disease: Parts of the body

Muscular, Digestive, Nervous, Urinary, etc.

Classifying a disease: Etiology

By cause so infectious, genetics/DNA, and enviornmental

Classifying a disease: Morality

Deaths, so looking at excess deaths (more deaths that are what are historically expected), case fataility rate so proportion of people who die out of those who test positive

(E.g., “how many people in a given population die from a disease”

Classifying a disease: Morbidity

About illness, how many people in a population are suffering from a disease, so prevalence (all casts) or incidence so new cases of a disease in a population

Classifying a disease: Burden

Measured by DALYS, so how much people die or how their lives are impacted by a disease (Issue is that it concerns with diseases and oversimplifies. Like on disease in one country could be more dire or more or a burden that another country)

Test-based classification: Confirmed 

A positive result from a highly specific diagnostic test

Test-based classification: Probable 

Antigen test that a person can purchase themself

Test-based classification: Suspect

Antibody test in blood and see if there is a detection in a hospital

Nutritional deficiency diseases

Lack of essential nutrients in diet

Underlying risk factor meaning

Increasing the chance of developing a disease

Etymology

The study of the origin of words, not the meaning. (E.g., malaria was named for “bad air” in swamps even tho that is not true and is a parasite)

Infectious diseases types

Through etiology, it's bacterial, fungi (including yeasts), viruses, protists, helminths (parasitic worms), and prions (has no replication)

Infectious diseases definition

Invasion by and multiplication of pathogenic microorganisms in a bodily part or tissue

Infection classification: scale

Local – infection confined to a small region of the body

Systemic – widespread infection in many systems of the body; often travels in the blood or lymph

Focal – infection that serves as a source of pathogens for infections at other sites in the body

Infection classification: time

Primary – initial infection within a given patient

Secondary – infections that follow a primary infection, often by opportunistic pathogens

Infection classification: how quickly

Acute – disease in which symptoms develop rapidly and that runs its course quickly (e.g., a cold)

Chronic – Disease with symptoms that develop slowly and last a long time (e.g., syphilis)

Latent – disease that appears a long time after infection (e.g., leprosy, aids, hiv)

Infection classification: how it spreads

Communicable – disease transmitted from one host to another (e.g., strep throat)

Contagious – communicable disease that is easily spread (e.g., also strep throat)

Non-communicable – disease arising from outside hosts or from opportunistic pathogens (e.g., tetanus is a wound infection in soil bacterium,, legionnaire's disease fine water particles in air)

Communicable spreads: human to human:

hand to hand contact, indirect contact (doors, handles which is FOMITE), airborne, bodily fluids (can get HIV,) oral fecal (food prep, not washing hands)

Communicable spreads: animal to animal

Zoonotic – zoonotic are infectious diseases caused by germs that spread from animals to people or vice versa

Toxoplasmosis – infected people never develop signs but infant born can be affected

Cats are the primary host

Undercooked meat

T. gondii – capable of infecting virtually all warm-blooded animals, but members of the cat family are the only known definitive hosts

Infected rodents are more active, less fearful of cats and their smells

Ebola – virus can be transmitted from typically bats (or other animals) to other animals

SARS-CoV 2: Bats may have led to disease outbreaks in animals and humans

‘Spillover zoonoses’

Communicable spreads: via vector

From insects like mosquitos (E.g., malaria, lyme disease), there are attmepts with vector control and DDT was affective but a carciogen

S-I-R MODEL:

Susceptible

Infected

Recovered

What is R₀?

R naught): Basic Reproduction Number. It’s the average number of new infections that one infectious person generates, in an entirely susceptible population, during the time that person is infectious

If R₀ <1, the infection will not spread

If R₀ > 1, an epidemic will occur

R₀ depends on:

Duration of infectious period

Probability of infecting susceptible individual during contact

Number of susceptible individuals contacted per unit of time

Number of susceptible individuals contacted per unit of time

Herd Immunity

Herd of recovered people

If most have antibodies, the virus is contained

Small pop, disease has a 0% recovery

Dies off quickly because fatality is too high (E.g., measles epidemic)

Big pop, disease has a 0% recovery

The fatality rate kills all when the population is way larger

Has a 30% recovery, and an 80% chance to recover

Host and virus co-exist, an epidemic disease

Epidemic disease

Neither humans nor the disease go extinct

Maintained without outside input

Depends on new births ‘naïve newborns”