The Infectious Disease Challenge

eradication - worldwide, cases of disease drop to 0

measles makes you very vulnerable because it resets your immune system

  • airborne so easy to spread

Eradication of Smallpox

  • USSR started process of eradication/vaccination

    • very large country

Motivations of 1st and 2nd World Countries

  • elimination does not = eradication

  • productivity of natural resources

  • healthy countries are great markets for stuff we make

  • expanding influence among the LMICs

Silent Pandemic

  • antimicrobial resistance (AMR)

Infectious Disease

  • agent - cause/risk factors

  • host - susceptible

  • environment - where agent & host meet

  • vector - typically insects (sometimes arachnids - mites), helps get disease to host

    • mechanical

    • biological

the great white plague - tuberculosis

  • spread by aerosols

  • in cities, limited fresh air

  • belief in miasmas - foul smells associated with cities; if you breathe it in you get sick

  • women got TB more, reportedly - effeminacy (men who got it were too feminine - treatment = going hunting, fishing, writing, etc)

humoral theory - 2x bile, blood, phlegm

  • treatments - bloodletting, induce vomiting

germ theory

  • pasteur

  • contagions

tort - obligation to help/save people

  • can’t withhold treatment to see the natural health of disease

natural history of disease

  • refers to the progression of a disease process in an individual over time, in the absence of treatment

  • case report - 1 patient

  • many diseases have a characteristic natural history

  • process beings with exposure of a susceptible host to sufficient numbers of the pathogen or amounts of pathogenic agent

  • stage of susceptibility → exposure → stage of subclinical disease (pathologic changes) → onset of symptoms → stage of clinical disease (usual time of diagnosis) → stage of recovery, disability or death

  • incubation period (no sign or symptoms) → prodromal period (vague general symptoms) → illness (most severe signs and symptoms) → decline (declining signs and symptoms) → convalescence (no signs or symptoms)

infection cycles

  • direct horizontal

  • indirect horizontal

    • fomites - objects someone has had contact with that you then have contact with

    • food

    • water

    • air

  • vertical (mother/father to fetus)

  • vector (animals, arthropods, insects)

non-communicable infection disease

  • anthrax, botulism, tetanus

Ro “naught”

  • basic reproduction number

  • may change during course of an epidemic

  • between 0 and 1 → self-limiting

  • greater than or equal to 1 → likely to spread

Rt

Herd Immunity

  • what proportion of the population needs to be vaccinated for the disease to not spread

  • does not protect against certain vaccine-preventable diseases

    • non-communicable infectious diseases e.g., anthrax, tetanus, botulism

Free Riders

  • in a population, there are those who cannot receive the vaccine for medical reasons:

    • those with allergies to vaccine ingredients

    • those with compromised immune systems

    • those who are too young or too old

    • those who are being treated for cancer

    • those with autoimmune conditions

  • benefit from herd immunity without receiving the vaccine

Contact Tracing

  • identifying those who are sick → who have they been in contact with during the asymptomatic/incubation period in which they are contagious

Community Tracing

Why do some diseases spread faster than others?

  • generation time - time between when someone is infected and when they pass the infection onto another person

    • hard to measure

    • estimated by looking at interval between infections in primary & secondary cases

  • serial interval - time between successive cases in a chain of transmission

    • estimated from interval between clinical onsets if observable

    • proxy for generation time

  • force of infection - rate at which susceptible individuals acquire an infectious disease

    • can be used to compare the rate of transmission between different groups of the population for the same infectious disease, or even between different infectious diseases

    • number of new infections / number of susceptible persons exposed x average duration of exposure