MCB 100- Lecture 22 Transmission and Epidemiology

Infection

when another organism evades external and some internal defenses, multiplies, and becomes established

Epidemiology

the study of disease transmission within populations, often includes application of these studies to control of public health problems

Points of Emphasis in Transmission and Epidemiology, 7

1) sources of human pathogens (animal, human, and non living pathogens)

2) routes of entry (skin, mucous membranes, placenta, parenteral)

3) virulence factors (attachment, colonization, host defense evasion)

4) pathogen clearance

5) modes of transmission (contact, vehicle, vector)

6) epidemiology (epidemic, pandemic, sporadic, and endemic)

7) analyzing epidemiology data

Human Reservoirs

infected individuals often easily spread disease through close or direct contact, asymptomatic infected individuals can be infective to others (Typhoid fever)

Healthy Human Carriers

may have defensive systems that protect them (HIV elite controllers infected by HIV but their immune system holds the virus in check)

Nonliving Reservoirs

soil, water, and food can be reservoirs, presence of microorganisms is often due to contamination by feces or urine, common during storms/ natural disasters

Examples of Non-Living Things as Reservoirs

1) Staphylococcus infection

2) cryptosporidium parasite

3) E.coli, Listeria, Salmonella

Animal Reservoirs

zoonotic diseases, spread between animal and human hosts, humans are often dead end hosts for zoonotic pathogens

4 Different Ways to Acquire Zoonoses

1) direct contact with animal or its waste

2) eating animals

3) blood sucking arthropod bites

4) mosquitos transmitting Plasmodia (malaria), ticks and Borrelia (Lyme disease)

Difficulty with Eradicating Zoonotic Disease

1) money, logistics

2) hard to remove or contain all animals carrying a pathogen

Epizootic diseases Spread

spread among animal populations

Transmission

how a pathogen gets from a reservoir or infected host’s portal of exit to another host’s poral of entry

2 Different Modes of Infectious Disease Transmission

1) direct transmission

2) indirect transmission

Direct transmission

transfer immediately from person to person or from an animal/soil to person, requires close or physical proximity

3 Modes of Direct Transmission

1) direct contact- body contact between hosts or within a host

2) vertical transmission- directly from other to child across placenta, birth, by breast milk

3) aerosol droplet spread- direct contact with air borne droplets of mucus/bodily fluids through close proximity (sexual contact)

Indirect Transmission

transfer from reservoir to host by intermediate vehicle, surface, particle, or living carrier

3 Different Methods of Vehicle Borne Transmission

1) food, water, or blood borne spread- usually by fecal contamination of inanimate media

2) indirect fomite contact, spread by contaminated fomites (surfaces)

3) mechanical vectors, passive transfer between hosts by vector’s body (not by injection or bite) such as a fly landing on contaminated surface and then landing on another surface and transferring the pathogen

Vector Borne Transmission Method

Biological vectors- living organisms serve as host for part of the pathogen’s life cycle, most commonly biting or injecting insects (mosquitos, ticks, fleas etc)

How do pathogens gain access to the body?

portals of entry, openings into the body to provide portals of entry

Portals of Entry 3 Major Pathways

1) skin

2) mucous membranes

3) placenta

Parenteral Route Entry

injection, wound, circumvents usual portals

Pathogens often gain access to body by….?

the mucosa

Mucous Membrane (mucosa)

of resp and intestinal tracts are major sites where your body interacts with the outside world

5 Functions of Mucosa

1) mucosa line the body cavities open to the environment

2) mucosa provides moist, warm environment hospitable to pathogens

3) resp tract is the most common site of entry

4) entry is through the nose, mouth, or eyes

5) GI tract is a route of entry, but the pathogen must first survive the acidic pH of the stomach

Key Function of Virulence Factors

survival in the host: adhesion factors, biofilms, extracellular enzymes, toxins, antiphagocytic factors

Portals of Exit

openings into the body provide portals of exit, sites through which pathogens exit the body, many portals of exit are the same as portals of entry

3 Major Portals of Exit

1) skin, erupting or oozing from wounds

2) mucus, secreted or excreted fluids

3) clearance (elimination) by the immune system

Epidemiology

study of the transmission of diseases within populations, often includes the application of these studies to the control of public health problems

Epidemiologic Studies, Collection of Data

careful tabulation of data concerning a diseases, record location and time of the cases of disease, collect patient information, try to identify the index of disease

3 Ways to Present Epidemiologic Data

1) Geographic Heat Map, disease density by location, cases per population size for certain areas

2) Histogram Incidence Over Time, disease density over time, disease/deaths incidence over time

3) Histogram over population distribution/demographic- cases/deaths among certain population groups (Age)

EPIDEMIOLOGIC STUDIES

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