Lecture 6: Infectious Disease

Question 1

What are Sporadic diseases?

Answer 1

Occasional cases occurring at irregular intervals

Question 2

What is an Endemic disease?

Answer 2

Continuous occurrence at an expected frequency over a certain period of time and in a certain geographical location

Question 3

What is an Epidemic or outbreak?

Answer 3

Occurrence in a community or region of cases of an illness with a frequency clearly in excess of normal expectancy

Question 4

What is a Pandemic?

Answer 4

Epidemic involves several countries or continents, affecting a large population

Question 5

What are Special Features of an infectious disease epidemiology?

Answer 5

A case of disease may also be a risk factor (even if not recognised as a case)

Immunity can occur

Speed of intervention can be critical

Question 6

Define Infectious agent/ pathogen?

Answer 6

A viral, bacterial, protozoan or fungal substance that causes disease.

Question 7

Define Infection?

Answer 7

The entry and development or multiplication of an infectious agent in the body – the result may or may not be apparent.

Question 8

Define Infectious Disease= Communicable Disease

Answer 8

An illness due to a specific infectious agent or its toxic products that arises through transmission of the agent/ products to a susceptible host.

Question 9

What is the meaning of contagious?

Answer 9

Transmitted by contact

Question 10

What Happens Following a Disease Notification?

Answer 10

Tracing contacts of the index case infected person to:

a) identify source of the infection
b) prevent further dissemination, e.g. tuberculosis

Interviewing affected people to identify the source of infection, e.g. in foodborne poisoning case

Confirming the diagnosis by further testing the infected person, e.g. measles

Question 11

What Criteria Would You Use to decide Whether a Disease Should Be Notifiable?

Answer 11

Effectiveness
Prevalence and severity of disease Possibility of source and contact tracing Derived risks for vaccination policy International consequences
Feasibility
Workload
Possibility of diagnosis
Necessity
Subsidiarity Privacy

Question 12

What are the direct transmission routes?

Answer 12

Mucous to mucous membrane 
Across placenta 
Transplants, blood
Skin to skin
Sneezes, cough

Question 13

What are the indirect transmission routes?

Answer 13

Waterborne 
Airborne
Food borne
Vector borne
Object/Fomites

Question 14

What is a vector?

Answer 14

An insect or living carrier that transports an infectious agent from an infected individual or its wastes to a susceptible individual or its food or its immediate surroundings.

Question 15

What is Biological transmission?

Answer 15

Transmission of the infectious agent to susceptible host by bite of blood feeding vector, or by other inoculation.

Question 16

What is Mechanical transmission?

Answer 16

Transport of the infectious agent between hosts by arthropod vector with contaminated mouthparts, antennae, or limbs. There is no multiplication of the agent within the vector.

Question 17

What is the Extrinsic Incubation Period?

Answer 17

Time necessary after acquisition of infection by the vector for the infectious agent to multiply or develop sufficiently so that it can be transmitted by the vector to the vertebrate host.

Question 18

What is the Chain of Transmission?

Answer 18

The spread of infection from a source to a susceptible host is referred to as the chain of infection

Question 19

What are the stages of the Chain of Transmission?

Answer 19

Link #1: The Pathogen
This is the disease-causing organism. For many illnesses and diseases this is a virus or bacterium.
Link #2: The Reservoir
This is the natural environment that the pathogen requires for survival. Reservoirs can be a person, an animal, or an environmental component, such as soil or water. Link #3: The Portal of Exit
This link is needed for the pathogen to leave the reservoir. Link #4: The Means of Transmission
The pathogen can be transmitted either directly or indirectly. Link #5: The Portal of Entry
Entry of the pathogen can take place in one of three ways: penetration, inhalation, or ingestion.
Link #6: The New Host
Once in the new host, various factors influence the severity of infection, including the strength of the immune system

Question 20

What is the Epidemiological Triad?

Answer 20

The Epidemiological Triad describes the interaction between the agent, host and environment, which create the conditions for the transmission of infectious agents.