W7 Epidemiology of infectious disease

Question 1

What is an agent?
Examples?

Answer 1

“A substance, living or non-living, or a force, the excessive presence or relative lack of which may initiate a disease process.”
E.g.,
* Biological agent: Bacteria, virus, fungi, etc.
* Nutrient: carbohydrate, protein, fat, etc.
* Physical agent: cold, heat, radiation, etc.
* Chemical agent: uric acid, bilirubin, etc

Question 2

What is the definition of Epidemiology of infectious disease:

Answer 2

• Epidemiology is the study of how often diseases occur in different groups of people and why. Epidemiological information is used to plan and evaluate strategies to prevent illness and as a guide to the management of patients in whom disease has already developed.

Question 3

What is an infection?
What is a transmission of an infection?

Answer 3

Infection – “Entry and development or multiplication of an infectious agent in the body of human or animals

Transmission of infection – “Spread of an infectious agent through the environment to another person from the reservoir and source”

Question 4

What is a host?

Answer 4

“Person or animal, including birds and arthropods that affords lodgement to an infectious agent under natural conditions

Question 5

What are some protective methods of the Human Immune System- in response to a simple pathogen? (3)

Answer 5

Barrier immunity- prevents pathogens from getting into the body (Mucus, Skin, Acidity)

Innate immunity - immediate response to breach of a barrier (Swelling + Redness)

Adaptive immunity- Delayed response but specific for each pathogen (T cells, B cells, Antibodies)

Question 6

What does the mode of pathogen transmission depend on?

Answer 6

• The mode of transmission of a given pathogen largely depends on how resilient the pathogen is when it is outside of the host.
  -Some pathogens can only survive for short periods outside the host and so require direct contact or transmission via droplets (also via vectors). Other pathogens are relatively robust, they survive for long periods outside of the host (e.g. on surfaces) and are highly contagious

Question 7

What are the three major ways pathogens can be transmitted?

Answer 7

1. Transmission between humans (Direct, Indirect contact, Airborne, Droplets, Fecal-oral)
2. Via environmental factors (such as soil or water)
3. Between humans and animals (via vectors)

Question 8

Human to human transmission:
What is Aerosol transmission?
Airborne Vs Droplets?

Answer 8

Aerosol
- Transfer of these pathogens is via the respiratory system when one person breathes, coughs, or sneezes pathogens into the air which then enter the respiratory system of
another person.

• Robust pathogens will remain infective for long periods in the air and their transmission is termed airborne. More fragile pathogens will only survive for short periods when encased in respiratory secretions and their transmission is termed droplet

Question 9

Human-to-human transmission
What is Direct contact?
Examples of infections that can be spread by direct contact? (3)

Answer 9

Contact with skin, mucous membrane, blood or any other body fluids
Ringworm, chickenpox and cold sores.

Question 10

Human-to-human transmission
What is Indirect contact?

Answer 10

• The pathogen gains entry to the new host via some other surface (or the air).
• Objects that can facilitate the transmission of pathogens are termed fomites – e.g., used tissue, handrails, utensils, etc.

Question 11

Human-to-human transmission
What is Faecal-oral transmission?
What are examples of diseases that can be transmitted this way?

Answer 11

• When pathogens are excreted from the gut of an infected person and then enter the gut of a new host via their mouth (usually indirectly via contaminated food, water or other fomite).
• E.g., cholera, hepatitis A, rotavirus and most intestinal worms

Question 12

Human-to-human transmission
What is meant by..?
* Transmission of blood-borne pathogens
* Vertical transmission (mother to child)

Answer 12

1. E.g., via unsafe injections, contaminated transfusions of blood or blood products, or needle-stick injuries
2. Can occur across the placenta, during childbirth or via breast milk

Question 13

What is Environmental transmission?

Answer 13

• The natural reservoirs for pathogens that can cause human infection are various environmental sites such as soil and water.
• E.g., the bacterium Clostridium tetani normally lives in soil where it produces spores -
• Water - This occurs when bacteria, bacterial spores (that can germinate in the gut) or toxins, viruses and protozoa survive and replicate within water without a human host

Question 14

How to prevent environmental transmission via water?
Examples of water-borne infections? (2)

Can environmental transmission from water sources occur from inhalation?

Answer 14

• Adequate sanitation to ensure safe water supply is essential for preventing the spread of diarrhoeal infections
• Examples of water-borne infections – Cholera & Legionnaire’s disease.
• Environmental transmission= human-to-human transmission via the faecal-oral route

Yes e.g. Legionella in natural environment water, bacteria amplify in man-made water systems, legionella aerosolize and are inhaled (or aspirated) from man-made/natural water systems, Host infection in humans,
Outcome:
Healthy immune status =Pontiac fever/no disease
Immunosuppressed= Legionnaire’s disease

Question 15

What are Zoonoses?

Answer 15

Zoonoses are infectious diseases where
the pathogen is transmitted from an infected animal to a human (in these cases the animals are the reservoirs

-E.g., avian influenza (birds shed virus in saliva or faeces and humans ingest or inhale it and rabies (from the bite or scratch of infected animals

Question 16

What is Vector-borne transmission?
Example?

Answer 16

• Vector-borne transmission - where part of the life cycle of the pathogen takes place in the human host, however, part of the life cycle must take place in another species which is known as the vector.
• E.g., malaria
  -Common vectors for infectious diseases
  include mosquitoes, flies, ticks and lice

Malaria spreads when a mosquito becomes infected with the disease after biting an infected person, and the infected mosquito then bites a noninfected person.

Question 17

What is the Antimicrobials spectrum of activity?

Answer 17

• Measure of how many different types of organisms the antimicrobial targets.
• An antimicrobial that targets only a specific group of organisms - narrow-spectrum
• An antimicrobial that targets a wide range of organisms - broad spectrum.
• The above applies to both antibiotics and antifungals

Question 18

What are broad-spectrum antibiotics? (in general)
Examples?

Answer 18

Broad-spectrum antibiotics commonly refer to antibiotics that target both Gram-positive and Gram-negative bacteria.
Amoxicillin, Penicillins, Cephalosporins, Glycopeptides, Carbapenems,Fluoroquinolones

Question 19

Which of the following pathogens or infections is most commonly transmitted via an airborne human-to-human transmission?
A. Rotavirus
B. Tuberculosis
C. Legionniere’s disease
D. Malaria

Answer 19

=B

Question 20

Graham is a 50-year-old male that has been recently diagnosed with influenza. He is very annoyed because he has made sure to avoid people sneezing and has worn a mask throughout winter to avoid droplets of
infection. Graham works at a major bank and shares a desk with 2 other colleagues. By which mode of transmission was the influenza virus most likely transmitted to Graham?
A. Airborne transmission
B. Indirect contact
C. Vector transmission
D. Oral-faecal route

Answer 20

=B
as he shares a desk with colleagues