Module 2 - Infectious Diseases

Question 1

Impacts of Infectious Diseases in history:

Answer 1

✘ 14th century: Europe - plague kills 20-45% of the world’s population
✘ 1831: Cairo - 13% of population succumbs to cholera
✘ 1854-56: Crimean war – deaths due to dysentery were 10 times higher than deaths due to casualties
✘ 1899-1902: Boer War – deaths due to dysentery were 5 times higher than deaths due to casualties

Question 2

What is an Infectious (Communicable) Disease?

Answer 2

“An illness due to a specific infectious agent or its toxic products that arises through transmission of that agent or its products from an infected person, animal, or reservoir to a susceptible host, either directly or indirectly through an intermediate plant or animal host, vector, or the inanimate environment.”

Question 3

What is the Epidemiologic Triangle? What make it up?

Answer 3

One of the longstanding models used to describe the etiology of infectious diseases

Includes three major factors: agent, host, and environment

1. Agent: the cause of a disease
2. Host: an organism, usually an animal or human, that harbors disease
3. Environment: The domain in which disease-causing agents may exist, survive, or originate

Question 4

Examples of disease agents:

Answer 4

Toxin, Parasitic Disease, and Zoonosis

Question 5

Define toxin (agent) and give examples.

Answer 5

✘ Some infectious disease agents, instead of acting directly, produce a toxin that causes illness.
✘ A toxin usually refers to a toxic substance made by living organisms.
• Examples of illness: foodborne intoxications such as botulism

Question 6

What is Parasitic Disease (agent) and give examples?

Answer 6

✘ An infection caused by a parasite, which “…is an organism that lives on or in a host organism and gets its food from or at the expense of its host.”
✘ Example: amebiasis

Question 7

What is zoonosis (agent)?

Answer 7

“An infection or infectious agent transmissible under natural conditions from vertebrate animals to humans.”

Question 8

What are host characteristics?

Answer 8

Immunity is the host’s ability to resist infection by the agent (You’ll hear more about this in Unit 10).

Other factors related to host responses:
• Incubation period • Subclinical illness • Generation time • Carrier status

Question 9

How can infectious disease agents be transmitted?

Answer 9

✘ Direct transmission  
- (Person to person)
✘ Indirect transmission 
- Vehicle-borne infections 
- Airborne infections 
- Vector-borne infections

Question 10

What is the Portal of Exit)?

Answer 10

✘ For an infected person, a portal of exit is the site from which the agent leaves that person’s body.

✘ Examples: • Respiratory passages • Alimentary canal • Genitourinary system • Skin lesions

Question 11

What is the Portal of Entry?

Answer 11

Site where the agent enters the body, such as, a skin wound

Question 12

Define direct transmission:

Answer 12

“Direct and essentially immediate transfer of infectious agents to a receptive portal of entry through which human or animal infection may take place….”

Question 13

Define indirect transmission:

Answer 13

Involves intermediary sources of infection such as vehicles, droplet nuclei (particles), and vectors.

Question 14

Define vehicle-borne infections:

Answer 14

These infections result from contact with vehicles, which are contaminated, nonmoving objects.

Examples: • Fomites • Unsanitary food • Impure water

Question 15

What is a Fomite?

Answer 15

An inanimate object that carries infectious disease agents

Examples: • Classroom door-knob • Discarded tissues

Question 16

What are Airborne infections?

Answer 16

Involve the spread of droplet nuclei (particles) that are present in the air.

Example: infections caused by stirring up dust that carries fungi or microbes

Question 17

What are Vector-borne infections? Examples?

Answer 17

Transmission of an infectious disease agent may happen when the vector feeds on a susceptible host.

Examples include: • Bacterial diseases • Lyme disease (tick) • Arthropod-borne (arboviral) diseases • Eastern equine encephalitis (mosquito) • Parasitic diseases • Malaria (mosquito)

Question 18

Examples of Significant Infectious Diseases:

Answer 18

✘ Sexually transmitted diseases 
✘ Foodborne diseases
✘ Waterborne diseases
✘ Vector-borne diseases 
✘ Vaccine-preventable diseases 
✘ Zoonotic diseases 
✘ Emerging infections 
✘ Bioterrorism-related diseases

Question 19

What is a vector?

Answer 19

A vector is an animate, living insect or animal that is involved with the transmission of disease agents.

Question 20

What are zoonotic diseases? Examples?

Answer 20

✘ Diseases transmitted from vertebrate animals to human beings.
✘ Examples: • Rabies • Anthrax • Avian influenza • Hantavirus pulmonary syndrome • Toxoplasmosis • Tularemia (rabbit fever)

Question 21

What are Foodborne illnesses? Examples?

Answer 21

✘ Biologic agents of foodborne illness include bacteria, parasites, viruses, and prions (linked to mad cow disease).
✘ Examples of bacterial agents include: • Campylobacter • Clostridium botulinum • Salmonella

Question 22

What is infectivity?

Answer 22

The capacity of an agent to enter and multiply in a susceptible host and thus produce infection or disease.

Question 23

What is Virulence?

Answer 23

Refers to the severity of the disease produced, i.e., whether the disease has severe clinical manifestations or is fatal in a large number of cases.

Question 24

Why do infectious diseases still remain a threat?

Answer 24

• New types of diseases are constantly evolving and imperiling public health.
• Outbreaks caused by bioterrorism are a potential threat.
• Some infectious disease agents mutate into forms that resist conventional antibiotic treatment.