(4) Chapter 14: Principles of Disease and Epidemiology

What are the three major methods of disease transmission?

Contact transmission, vehicle transmission, and vector transmission.

What is contact transmission?

The spread of disease through direct contact, indirect contact, or droplet transmission.

What is direct contact transmission?

The spread of pathogens through physical contact between an infected host and a susceptible host.

What are examples of direct contact transmission?

Kissing, hugging, shaking hands, and sexual intercourse.

What is congenital transmission?

The transmission of pathogens from an infected mother to her fetus through the placenta or to the newborn during birth.

What diseases did your professor use as examples of congenital transmission through the placenta?

Zika virus, syphilis, and Trypanosoma infections.

What diseases did your professor use as examples of transmission during birth?

Neonatal herpes simplex infection and gonorrheal eye infections (ophthalmia neonatorum).

What is indirect contact transmission?

The spread of disease through contaminated nonliving objects called fomites.

What is a fomite?

Any contaminated nonliving object capable of transmitting pathogens.

What are examples of fomites?

Tissues, drinking cups, diapers, contaminated syringes, needles, toys, coins, and doorknobs.

Why are contaminated needles considered dangerous fomites?

They can transmit bloodborne pathogens directly into another person's bloodstream.

What is droplet transmission?

The spread of pathogens through respiratory droplets produced by coughing, sneezing, talking, or laughing.

Approximately how many droplets can be produced by one sneeze according to your professor?

About 20,000 droplets.

How far do droplets travel in droplet transmission?

Less than 1 meter (about 3 feet).

What diseases did your professor use as examples of droplet transmission?

The common cold and influenza.

What is vehicle transmission?

The spread of pathogens through contaminated substances such as food, water, air, blood, or other materials.

What is foodborne transmission?

The spread of pathogens through contaminated food.

How can food become contaminated?

By being undercooked, improperly refrigerated, contaminated during handling, or through cross-contamination.

What is an example of cross-contamination?

Using the same knife to cut raw meat and then cutting lettuce without washing the knife.

What types of foods did your professor mention as sources of foodborne disease?

Raw or undercooked poultry, beef, pork, and contaminated foods.

What is waterborne transmission?

The spread of pathogens through contaminated water.

What diseases did your professor list as examples of waterborne transmission?

Cholera, shigellosis, salmonellosis, and cryptosporidiosis.

What is airborne transmission?

The spread of pathogens through dust particles or tiny respiratory droplets that remain suspended in the air and travel more than 1 meter.

How is airborne transmission different from droplet transmission?

Airborne pathogens remain viable over distances greater than 1 meter, while droplet transmission occurs over distances less than 1 meter.

What diseases did your professor use as examples of airborne transmission?

COVID-19, chickenpox, tuberculosis, and fungal diseases spread by spores.

Why did people practice social distancing during the COVID-19 pandemic?

Because respiratory droplets and aerosols carrying the virus could travel more than 1 meter and still infect others.

What is vector transmission?

The spread of pathogens by living organisms that carry pathogens from one host to another.

What is a vector?

A living organism, usually an arthropod, that transmits pathogens between hosts.

What are the two types of vectors?

Mechanical vectors and biological vectors.

What is a mechanical vector?

A vector that passively carries pathogens on its body without becoming infected.

What is an example of a mechanical vector?

A housefly carrying bacteria from feces to food.

What is a biological vector?

A vector in which the pathogen reproduces or completes part of its life cycle before being transmitted to another host.

What are examples of biological vectors?

Mosquitoes, ticks, and fleas.

Which mosquito transmits malaria?

Anopheles mosquitoes.

Which mosquito transmits Zika virus and West Nile virus?

Aedes aegypti mosquitoes.

Which vector transmits Lyme disease?

Deer ticks (Ixodes ticks).

Why are biological vectors generally more dangerous than mechanical vectors?

The pathogen multiplies or develops inside the biological vector before transmission to the next host.