NRSG 205 Chapter 14 Part 1 - Disease and Epidemiology (THREE)

Pathogen

disease-causing microorganism

Infection

the invasion and colonization of the pathogen causes disease in the body (physical presence of a pathogen)

Intoxication

the pathogen produces a toxin, which causes the disease

Disease

Abnormal state in which part or all of the body is not properly adjusted or is incapable of performing normal functions (change in health state)

What determines if a host falls into a disease state?

The ability of the pathogen to overcome your body’s defenses

Host

organism that shelters and supports the growth of the pathogen

Pathology

study of disease

3 focuses of pathology

1. Etiology: cause of disease

2. Pathogenesis: development of disease over time

3. Effects of the disease

2 types of microbiota found in the body

1. Normal microbiota

2. Transient microbiota

Normal microbiota

microorganisms that establish permanent colonies inside the body without producing disease (resident microbes)

When does colonization of resident microbiota occur?

Placental microbiome - established during vaginal delivery

How does the colonization of resident microbiota occur for babies born by C-section?

In C-section, this occurs over time through breastfeeding, interaction with the environment, etc.

Transient microbiota

microbes that are present for various periods and then disappear

2 types of relationships between the normal microbiota and host

1. Microbial antagonism

2. Symbiosis

Microbial antagonism

microbiota prevent pathogens from causing infection through the process of competitive exclusion - there are limited resources, which are used by the microbiota

Symbiosis

we live in harmony with the microbiota

3 types of symbiotic relationships (one isn’t really symbiotic)

1. Commensalism

2. Mutualism

3. Parasitism

Commensalism

one organism benefits and the other is unaffected

Example of commensalism

Bacteria that lives in the ear and eats earwax

Mutualism

both organisms benefit from the relationship

What is a parasitic relationship associated with?

associated with disease state

Parasitism

one organism benefits, but the other is harmed

Example of a parasitic relationship

COVID-19

Opportunistic microorganims

microorganisms that do not cause disease under normal conditions, but can cause disease under special conditions

3 examples of opportunistic microorganisms

1. E. Coli

2. Yeast and fungal infections in the genital tract and mouth

3. Skin bacteria in the presence of a wound can infect the dermal layer

E. Coli mechanism (opportunistic infection)

non-pathogenic E. Coli in the GI tract is normal, but if the E. Coli makes its way to the urinary tract, it can cause a UTI

What is cooperation associated with?

Disease state

Cooperation

one microorganism to cause disease or produce severe symptom

Koch’s Postulates

criteria that established that specific microbes cause specific disease (determines etiology)

4 requirements of Koch’s postulates

1. The same pathogen must be present in every case of the disease

2. The pathogen must be isolated in pure culture

3. The pathogen that was isolated must cause disease in a healthy, susceptible lab animal

4. The pathogen must be re-isolated from the inoculated lab animal

5 exceptions to Koch’s postulates

1. Viruses and some bacteria cannot be grown on artificial media → must use tissue culture or “trust” the system

2. Some diseases have unequivocal signs and symptoms

3. Some diseases may be caused by a variety of microbes

4. Some pathogens cause several different diseases

5. Some pathogens cause disease in humans only

Example of a bacterium that cannot be grown on artificial media

Mycobacterium leprae

Example of a disease that has unequivocal signs and symptoms

Tetanus

3 examples of diseases that may be caused by a variety of microbes

1. Pneumonia

2. Nephritis

3. Meningitis

Example of. apathogen that can cause several different diseases (and 2 diseases it can cause)

S. pyogenes → causative agent of strep throat, heart issues

Example of a pathogen that can cause disease in humans only

HIV

Signs vs. symptoms

• Signs: measurable changes

• Symptoms: subjective changes in the body function

Diagnosis

identification of the disease and/or pathogen

Syndrome

a specific group of symptoms and/or signs that always accompanies a specific disease

2 types of diseases (classified by transmissibility)

1. Communicable

2. Non-communicable

Communicable disease

transmitted directly or indirectly from one host to another

Non-communicable disease

disease is caused by a microbe that normally grows outside of the human body - not able to be transmitted from one host to another

Contagious disease

communicable diseases that spread easily and rapidly from one person to another

How is occurrence reported?

 by incidence (number of people contracting the disease) and prevalence (# of people with the disease) in a defined population and in a specified time

4 types of frequencies of occurrence

1. Sporadic

2. Endemic

3. Epidemic

4. Pandemic

Sporadic occurrence

pops up sporadically in a defined population

Is incidence high or low in sporadic occurrence? How about prevalence?

• High incidence

• Low prevalence

Is prevalence high or low in endemic diseases?

• High prevalence

Epidemic

number of incidences is high for a specific population

Pandemic

epidemic that spreads to multiple geographical locations across the globe

4 ways to describe the scope of a disease

1. Acute

2. Chronic

3. Subacute

4. Latent

Acute disease

high severity, short duration with a beginning and end

Chronic disease

severity may be lower, but it is spread out over a longer period of time

Subacute disease

between acute and chronic

Latent disease

 present but dormant, but can recur

Herd immunity

associated with the presence of immunity to a disease in most of the population

How is herd immunity typically accomplished?

Immunization

What is herd immunity dependent on?

Immune response to the pathogen

Epidemic curve

visual display of the onset of illness among cases associated with an outbreak

What do the x-axis and y-axis of the epidemic curve show?

• X-axis: date or time of illness onset among cases

• Y-axis: number of cases

Magnitude of epidemic curve

number of cases in an outbreak

Time trend of epidemic curve

distribution of cases over time

Outliers of epidemic curve

cases that stand apart from other cases

Index case

source of the outbreak

Secondary spread

often indicated by cases that occur well after other cases

Mode of spread of epidemic curve

how the disease is transmitted

3 modes of spread

1. Point source

2. Continuous common source

3. Propagation (person-to-person spread)

Point source mode of spread

 persons are exposed over a brief time to the same source

2 characteristics of point source mode of spread

1. The number of cases rises rapidly to a peak and falls gradually

2. The majority of cases occur within one incubation period of the disease

Continuous common source mode of spread

persons are exposed to the same source by exposure is prolonged over a period of days, weeks, or longer

Characteristic of an epidemic curve of continuous common source spread

Epi curve rises gradually and might plateau

Propagation mode of spread

there is no common source because the outbreak spread from person-to-person

Epidemic curve of propagation mode of spread

Graph assumes the classic epi curve shape of progressively taller peaks, each being one incubation period apart

2 examples of mutualistic relationships

1. Lactobacillus in the human GI system

2. E. Coli in the human GI system

Example of a commensal relationship

Staphylococcus epidermidis on human skin

Examples of a parasitic relationship

Taenia solium (beef tapeworm)