chapter 14 - micro

Pathology

Study of disease

Etiology

Cause of disease

Etiological agent

The pathogen that causes the disease

Infection

Invasion/colonization of host by microbe that causes harm

Human Microbiome

Microbial community within the host

Normal Flora

Approximately 4 × 10²³ bacteria in/on the body

Bacteria to human cell ratio

10 bacteria : 1 human cell

Colonization

Begins at birth

Vaginal flora

Lactobacillus that enter newborn intestine

Transient Flora

Present for short time (minutes-weeks)

Commensalism

One benefits, other unaffected

Mutualism

Both benefit (normal microbiome)

Microbial antagonism

Normal microbiota protect host

Parasitism

One benefits, other harmed

Hygiene Hypothesis

Insufficient early exposure interferes with normal immune system development. too clean is not good

Communicable disease

Can spread host → host

Non-communicable disease

Cannot spread person → person

Contagious diseases

Easily spread

Examples of communicable diseases

Measles, coronavirus, HIV, tuberculosis

Examples of non-communicable diseases

Tetanus, UTI caused by E.

Reproductive Number (R₀ / R-naught)

Indicates number of people infected by one infected person.

R₀ Value Under 1

Disease will die out.

R₀ Value = 1

Stable rate; no outbreaks.

R₀ Value Over 1

Higher rate; epidemics possible.

Higher R₀

Higher % population must be immune for protection.

Infectious Dose

Number of microorganisms needed to infect a new host and cause disease.

Infectious Dose Example - Smallpox

10-100.

Infectious Dose Example - Gonorrhea

1,000.

Infectious Dose Example - Cholera

100,000,000.

Symptom

Subjective; examples include pain, malaise, fatigue.

Signs

Objective, measurable.

Acute Disease

Develops rapidly, short duration; example: Influenza.

Chronic Disease

Develops slowly, long-lasting; example: Tuberculosis.

Subacute Disease

Between acute & chronic; example: Sclerosing panencephalitis.

Latent Disease

Inactive, can reactivate; examples: Herpes, shingles.

Subclinical / Asymptomatic Disease

No noticeable symptoms; example: Hepatitis A, sometimes poliovirus.

Incidence

Number infected in a given period of time.

Incidence Rate

X per population (ex: X/1000 per year).

Prevalence

Total number infected in population.

Mortality Rate

Deaths compared to infected or total population.

Morbidity Rate / Hospitalization Rate

# sick compared to population.

Sporadic Disease

Occurs occasionally; examples: tetanus, rabies.

Endemic Disease

Constantly present in population; examples: common cold (US), coccidioidomycosis.

Epidemic Disease

Large number infected in area in short time.

Contact Transmission

Transmission through direct contact, congenital transfer, or indirect contact via fomites.

what is Direct contact?

Transmission from person to person, such as touching, kissing, or sexual contact.

Congenital

Transmission from mother to fetus or newborn through blood or vaginal secretions.

Indirect contact

Transmission from a source to a host via a fomite, which is a nonliving object.

Droplet Transmission

Transmission via mucous droplets from coughing, sneezing, laughing, or talking, usually traveling 1 meter or less.

how many droplets are in Sneezes?

Contain approximately 20,000 droplets.

Droplet size

Droplets range from 1 to 360 μm.

Airborne Transmission

Transmission that travels greater than 1 meter.

Waterborne Transmission

Transmission through contaminated water.

Foodborne Transmission

Transmission through food contamination, improper storage, or cross-contamination.

when does Cross contamination occur?

Occurs when feces or raw meat are touched and then food is touched.

Vector Transmission

Transmission by agents that carry infection from host to host, primarily arthropods.

Mechanical Vector

Passive transfer of pathogens, such as houseflies with fecal pathogens.

Biological Vector

active process, Pathogen reproduces in the vector, such as mosquitoes with malaria.

Incubation period

Time between infection and the first symptoms.

Prodromal period

Period with mild early symptoms, not present in all diseases.

Period of illness

Time when the most severe signs and symptoms occur.

Period of decline

Time when signs and symptoms decrease, and the individual regains strength.

Period of convalescence

The stage where the individual returns to a pre-disease state.

R₀ (Basic reproduction number)

The average number of secondary infections produced by one infected individual.

Influenza (1918 pandemic)

R₀ of 1.4-2.8.

Influenza H1N1 (2009)

R₀ of 1.4-1.6.

Ebola

R₀ of approximately 2.

SARS-CoV-2

R₀ of 2.2-2.7, with approximately 82% needed immune for protection.

Measles

R₀ greater than 18, with over 90% immune needed.