Cellular Basis for the Spread of Infectious Diseases

Question 1

What are the five stages of infections diseases?

Answer 1

1. Incubation period (no signs or symptoms)
2. Prodromal period (vague, general symptoms)
3. Illness (most severe signs and symptoms) - usually the most infectious stage
4. Decline (declining signs and symptoms)
5. Convalescence (no signs or symptoms)

Question 2

What are the means of entry and exit for infection?

Answer 2

Means of entry:
- Face: eyes, nose, ears, mouth
- Skin: broken skin, insect bite
- Genital: anus, placenta, vagina/penis, urethra

Means of exit:
- Face: eyes, nose, mouth, ears
- Skin: broken skin, skin (flakes)
- Genital: anus, urethra
- Females: mammary glands, vagina
- Males: seminal vesicles

Question 3

How does infection spread? (chain of infection)

Answer 3

1. Causative agent: pathogenic organism
   - Virus/bacteria/parasite
2. Reservoir/source
   - Human/animal/fomite (inanimate objects with the pathogenic organism on them)/food/water
3. Means of exit: way out of the body
   - Excretions/secretions/droplets
4. Mode of transmission: method of spread
   - Contact/airborne/vector
5. Portal of entry: way into the body
   - Respiratory/GI/GU/mucous/skin
6. Person at risk
   - Young/elderly/immunocomprimised

These six components must be present for an infection to spread from one person to another.

Epidemiology is the study of disease transmission.

Question 4

Describe ways to break the chain of infection

Answer 4

1. Causative agent: pathogenic organism
   - Rapid detection and treatment
2. Reservoir/source
   - Good hygiene / sterilisation / disinfection
3. Means of exit: way out of the body
   - Waste removal / disinfection
4. Mode of transmission: method of spread
   - Airflow control / bed spacing
5. Portal of entry: way into the body
   - Aseptic technique catheter / wound care
6. Person at risk
   - Identifying at risk and targeting them for special care, vaccination and education.

Question 5

Mortality vs. Morbidity

Answer 5

Mortality: is the incidence of death in a population.

Morbidity: of a disease refers to the incidence of disease, including fatal AND nonfatal diseases.

Question 6

Incidence vs. Prevalence

Answer 6

Incidence: The incidence of a disease is the number of new cases of the disease in a given period of time

Prevalence: The prevalence of a disease is the total number of new AND existing cases in a population in a given time.

Question 7

Describe HIV infection in the USA

Answer 7

In the late 1980’s the number of incidence increased rapidly, and then started to go down as people realised the mode of transmission and started practicing safe sex.
However, the rate of prevalence kept increasing even though the rate of incidence had gone down. This was due to:
- Antivirals that had started to be produced, keeping people with HIV alive for longer
- And some people were still getting HIV (incidence was still a thing)
So the total number (prevalence) still increased.

Question 8

Define the classifications of disease

Answer 8

• Endemic: the amount of a particular disease that is usually present in a community os referred to as the baseline or endemic level of the disease (of a particular geographic area)
• Sporadic: a disease that occurs infrequently and irregularly
• Epidemic: an increase, often sudden, in the number of cases of a disease above what is normally expected in that population in that area
• Pandemic: an epidemic that has spread over several countries or continents, usually affecting a large number of people.