chapter 14

Pathology

is the study of disease; how they start, develop, and affect your body

Etiology

The cause of a disease 

Pathogenesis

• The manner in which a disease develops or progresses

• Process of disease

  • How its transmitted, developed, entrance

Bodily changes

• The physical (structural ) and functional changes that result from the disease

Infection VS Disease

• When a microbe gets inside your body and starts to grow

• You can be infected without feeling sick

Infection VS Disease

• When that growth actually causes an abnormal state of health or noticeable illness

• You can be infected but not have a disease yet

Pathogenicity  VS Virulence

• The ability of a microbe to cause disease at all

• "Can it make you sick?"

Pathogenicity  VS Virulence

• How bad the microbe is - how severe the disease is

• "how badly?"

Infectious Disease Cycle

• To cause disease, a microbe must follow these steps:

 

1. A microbial pathogen is stored in a reservoir (a source)

2. The pathogen uses transmission to reach a suspectable host

3. The pathogen must enter the host and overcome host barriers

4. The pathogen must use its virulence factors (tools it uses to harm you) to invade the host and damage the host

5. This damage results in pathology (the disease state)

Transmission of disease

• Via contact, vehicles & vectors

 

• Contact: direct

  • Physical contact between source + host

 

• Contact : indirect

  • Transmission via inanimate object -> fomite

 

• Contact : droplet

  • Short distance

  • Sneezing, coughing

  • Travels < 1 meter

  

• Vehicle

• Congenital transmission

• Vector

Vehicle

• Transmit disease via water, food, or air; also blood, drugs

 

• Waterborne

  • Contaminated (fecal) water treatment system compromised

  • Fecal-oral transmission

 

• Airborne

  • Dust particles

  • Pet dander

 

• Foodborne

  • Contaminated food storage @ improper temp

  • Undercooked food

  • Unsanitary handling of food

Congenital transmission

• Mother -> child

Vector

• Insects typically

• Mechanical transmission:

  • Passive via body parts

• Biological transmission

  • Involves parasite life cycle

Human Microbial Flora

• Normal microbiota (or flora)

  • Millions of microbes (mostly bacteria) that live naturally and permanently on your body without causing disease

    • Skin

    • Mouth

    • Nose

    • Gut

    • Lungs

• They colonize based on

 

• Physical factors

  • Temp

  • Moisture

 

• Chemical factors

  • pH

  • Oxygen levels

Normal vs transient microbiota

Microbes that are only present for a short period (days or week) before they disappear

Sterile areas

If microbes are found in areas that should normally be microbe-free (like blood or internal organs), it signals true infection

Host-Microbiota Relationship (Symbiosis)

• Symbiosis is the relationship between the host and the microbes

 

Microbiota exhibit Microbial antagonism (competitive exclusion)

• Prevents colonization of pathogenic microbes

 

• The normal, healthy bacteria precent pathogenic bacteria from settling down. They do this by competing for nutrients and space, or by producing substances that kill or inhibit the pathogens

 

• Normal biota protect you by:

  • Competing with pathogens

  • Taking up space

  • Using nutrients

  • Making toxins to kill bad microbes

 

• If the balance is upset -> disease

 

 

Types of symbiosis

• Commensalism (+/0)

  • Microbes benefit; host unaffected

  • Normal skin bacteria

 

• Mutualism (+/+)

  • Both benefit

  • Gut bacteria making vitamins

 

• Parasitism (+/-)

  • Microbes benefits/ host is harmed

  • Pathogens

 

• Opportunistic pathogens

  • Normal microbiota that turn harmful when

    • Immune system weak

    • Balance disrupted

    • Microbes enter wrong location

Koch's Postulates

• 4 steps used to prove a specific microbes is the cause (etiology) of a specific infectious disease

 

1. Same pathogen must be found in every single case of the disease 

 

2. The pathogen must be isolated from the diseased host and grown in a pure culture (container w/ only one type of microbe)

 

3. The isolated microbe from the pure culture must cause the same disease when injected into a healthy suspectable animal host

 

4. The pathogen must be re-isolated from the second host and confirmed to be identical to the original pathogen

Koch’s Postulates Exceptions:

• There are healthy carriers - people who carry the pathogen but don’t show any symptoms

 

• Some microbes cant be grown in labs (pure culture)

  • Treponema pallidum

  • Viruses

 

• One diseases can be caused by many microbes

  • Pneumonia

 

• One microbe can cause multiple diseases

  • Streptococcus pyogenesis

    • Strep throat, scarlet fever, flesh eating disease

 

• Viruses need host cells - cannot grow in pure culture normally

Classifying infectious disease

1. By spread (transmission)

2. By occurrence (frequency)

3. By severity or duration

4. By extent of infection

By spread (transmission)

• Communicable disease

  • Disease that can spread direclty or indirectly from one host to another

    • Contagious disease

      • A communicable disease that is very easily and rapidlt spread

      • Cold, pink eye

 

• Non communicable disease

  • A disease that cannot be spread from host to host

    • Tetanus; caused by bacteria in the soil

By occurrence (frequency)

• Incidence

  • Number of new people who get a disease in a given time period

  • Shows the spread of the disease

 

• Prevalence

  • The total number of people who have a disease in a given time period

  • It shows the spread of the disease

By occurrence (frequency): TYPES

Frequency Type	Definition	Example
Sporadic	Disease occurs infrequently (randomly and rarely)41.	Isolated cases of typhoid fever. tetanus
Endemic	Disease is always present in a population at a certain level42.	Common cold, cholera.
Epidemic	Disease develops rapidly and affects many people in a specific area43.	A large regional flu outbreak.
Pandemic	An epidemic that is worldwide44.	The global spread of COVID-19.

By severity or duration

• Acute disease

  • Symptoms develop rapidly but last only a short time

    • The flu

 

• Chronic disease

  • Disease develops slowly and last a long time

    • Tuberculosis

 

• Subacute disease

  • Symptoms fall somewhere in between acute and chronic

 

• Latent disease

  • A disease with a period where the pathogen is inactive and there are no symptoms

  • It can reactivate later

    • Shingles, cold sores

By extent of infection

• Local infection

  • The pathogen is limited to a small, specific are

 

• Systemic infection

  • The pathogen spreads throughout the entire body, usually via the blood or lymph systems

 

• Focal infection

  • Starts as a local infection but then spreads to specific areas of the body

    • Infection spreading from a tooth/tonsil

 

• Primary infection

  • The illness that causes the first infection

  • The initial sickness

 

• Secondary infection

  • An infection caused by an opportunistic pathogen after the body has been weekended by the primary infection

 

• Sepsis

  • A dangerous inflammatory condition caused by toxins or bacteria spreading in the blood from a focus of infection

  • Ex: Septicemia (bacteria multiplying in the blood)

 

• Subclinical (inapparent) infection

  • Infection that occurs without any noticeable signs or symptoms of illness

Herd immunity

• Immune individuals (vaccinated or recovered from the disease) act as a barrier to the spread of infection

  • This protects non-immune individuals

    • Like infants or Immunocompromised

 

• Threshold

  • The specific percentage of population that must be immune to stop the disease from spreading

 

• R0 (reproduction number)

  • The average number of people who will catch a contagious disease from one person who is sick

    • Diseases with higher R0 (like measles R0=18) require a higher vaccination threshold (up to 94%) to achieve herd immunity

Patterns of Development of Disease: Predisposing factors

• Predisposing factors

  • Factors more susceptible to disease

 

• - Age

 

• - Fatigue

 

• - Lifestyle

  • Diet, exercise, stress

 

• - Climate and weather

 

• - Inherited traits

  • Sickle cell gene

 

• - Gender

 

• - Chemotherapy

  • Or other immunosuppressive treatment

 

Patterns of Development of Disease: Development of disease stages

• The disease follows strict sequential pattern over time

 

1. Incubation period

   • The time from initial infection until the first signs or symptoms appear

 

2. Prodromal period

• A short time when mild signs or symptoms begin

 

3. Period of illness

• The disease is at its peak intensity; the most severe signs and symptoms are present

 

4. Period of decline

• The signs and symptoms subside

 

5. Period of convalescence

• The body returns to its normal state

Epidemiological studies

• Form basis for disease control and prevention through tracking

  • Prevalence of disease

  • Identifying determinants/causes of disease

  • Defines risk factors

 

• Only 1 in 10 reported

  • 150/100,000 more realistic

REVIEW P1

How Infection spreads

• The infection cycle is the route an organism takes to get from one person/source to another

 

• The starting point is:

• A. Reservoir of infection

How Infection spreads: Reservoir of infection

• The place where the disease causing microbe normally lives

• 3 types

 

1. Human reservoir

 

2. Animal reservoir

 

3. Non living reservoirs

1. Human reservoir

• People who carry the microbe

• 2 types

  • People with symptoms

  • Carriers

    • Carry disease but show no symptoms

      • Inapparent infections (hidden infections)

      • Or latent diseases (inactive)

2. Animal reservoir

• Diseases that animals give to humans called zoonoses

  • Rabies

  • Lyme

  • Ebola

3. Non living reservoirs

• Are soil, water, or other environmental sources

  • Tetanus (soil)

  • Cryptosporidiosis (water)

  • Cholera (water)

  • Legionella (water systems)

How Infection spreads: Modes of Transmision

• How diseases move between people

• Three main ways: contact, vehicles, and vectors

1. Contact Transmission

2. Vehicle transmission

3. Vector transmission

4. Other ?

Contact Transmission

• Requieres contact between source and the host

 

• Direct contact:

  • Physical contact between source and host

 

• Indirect contact

  • Transmission via inanimate object called fomite

    • Fomite = contaminated object

 

• Droplet contact

  • Transmission via droplets (sneezing/coughing) that travel a short distance <1 meter

 

• Not same as airborne because it travels farther

Vehicle transmission

• Transmission via inanimate reservoir like water, food, or air

• Microbes spread through a medium

 

• Airborne

  • Transmission via dust particles or pet dander

 

• Foodborne

  • Transmission through contaminated, undercooked, or improperly stored food

 

• Other vehicles

  • Disease can also be transmitted via blood or drugs

 

• Congenital (vertical) transmission

  • Mother to child

Vector transmission

• Animals, typically insects

 

• Mechanical transmission

  • No biting required

  • The insect passively carries the microbe on its body

 

• Biological transmission

  • The insect is an active part of the disease cycle, as the parasite/microbes must go through part f its life cycle inside the vector before it can be transmitted

  • Usually bites you and injects pathogen

Other ?

• Fecal-oral transmission

  • Infection from swallowing contaminated feces traces

 

Healthcare-Associated Infections (HAI)

• Infections you get while receiving medical care

  • Not illness you came in for

  • Affect 4-5% of hospital patients

 

Healthcare-Assocated Infections (HAI): WHY ?

1. Microbes in hospitals

   • Hospital environment is a reservoir

 

• Lots od opportunistic pathogens

 

• Lots of drug resistant microbes (MRSA , etc.)

 

 

2. Compromised host

• Someone whose defenses are weakened sue to underlying disease, burns, or therapy

 

• This can be due to a suppressed immune system or having broken skin/mucous membrane (from surgery or IV lines)

 

 

3. Chain of transmission

• The ways infection spreads inside hospitals

 

• Direct contact

  • Staff to patient or patient to patient

 

• Indirect contact

  • Fomites

    • Equipment, bedding, clothing

 

• Airborne

 

• The use of devices (like catheters or reparatory devices) to assist patients is a major source of infection

Control of HAI's

• Universal

General rules to prevent spread

• Standard precautions

 

• Transmission based precautions

 

Standard precautions

• Applies to all patients

 

• Basic, minimum precautions applied to all levels of patient care

  • Includes, frequent handwashing, aseptic techniques, proper handling of contaminated materials, and educating staff

  • Use of isolation and wards

  • Use of ppe

• Transmission based precautions

• Used to supplement standard precautions when dealing wth individuals who have a known or suspected infection that is highly transmissible

 

• Contact precautions

 

• Droplet precautions

  • Short distance

 

• Airborne precautions

  • Long distance

 Emerging infectious diseases (EID)

• Disease that is

  • New

  • Changing

  • Increasing in numbers

  • Likely to increase soon

 

• Caused by bacteria, viruses, fungi, protozoa, or worms

 

• 75% are zoonotic, mainly of viral origin , and often vector borne

 

Criteria to identify an EID

- -Disease might be considered emerging if:

• Distinctive disease symptoms

  • Symptoms are new or unusual

 

• Improved diagnostic techniques that allow identification of a new pathogen

 

• A rare disease becoming common

 

• A local disease becoming widespread

 

• A mild disease becoming more severe

Factors contributing to EIDs

• Genetic recombination/evolutions

  • Microbes changing

• Misuse of antibiotics/pesticides

  • Resistance

 

• Climate change

  • New habitats for vectors

 

• Increased human transportation

 

• Ecological changes

  • Affecting animal/human contact

 

• Public health failures

  • Poor vaccination rates

  • Poor sanitation

Epidemiology: 

• Where and when diseases occur

• How they are transmitted

• How to control them

Epidemiology: Study of

• Where and when diseases occur

• How they are transmitted

• How to control them

Epidemiology: Helps determine

• Cause of diseases

• Patterns of spread

• Risk factors

  • Age, race, income, lifestyle

• How well prevention methods work

Epidemiology: Important for

• Determining the etiology (cause) of disease

 

• Identifying other important factors concerning the spread of disease

  • Demographic data, socioeconomic status, etc

 

• Developing methods for controlling disease

  • (control of reservoirs, food inspection, vaccination)

 

• Assembling data and graphs to outline the incidence of disease

  • Determine disease frequency

  • Test effectiveness of disease control (vaccination)

Case reporting

• Healthcare workers are required to report specific diseases (like aids, meningitis, or tetanus) to local, state, and national offices

  • Establishes the chain of transmission

Nationally notifiable Infectious diseases

• Diseases that physicians are legally required to report when they occur

CDC

National organization that collects and analyzes epidemiological information in the us and publishes the morbidity and mortality weekly report

Morbidity vs Mortality 

• Morbidity

  • The incidence (new cases) of specific notifiable disease

 

• Morbidity rate

  • Rate at which diseases occurs

 

• Mortality 

  •  the deaths form notifiable diseases

  • Mortality rate

    • The rate at which death occurs