V4

Question 1

List the ways in which viruses can invade the human body and cause infection

Answer 1

• respiratory tract
• gastro-intestinal tract
• genital tract
• skin abrasions
• intravenous
• vertical transmission
• zoonosis
• vector-borne
• direct contact

Question 2

What are characteristics of a localised infection?

Answer 2

• Infection of epithelial surfaces
• Short incubation period (1 – 3 days).
• Replication restricted to local area, but effects may be more general

Question 3

What are the characteristics of a systemic infection?

Answer 3

• Virions enter through epithelial surface – limited replication.
• Migrate to regional lymph nodes and enter blood stream (primary viraemia)
• Prodromal symptoms – malaise and fever.
• Large reticulo-endothelial organs (liver, spleen, bone marrow) – multiplies again.
• Secondary viraemia – target organ (skin, lung, liver, CNS).

Question 4

List the most important target organs for viral infections giving examples of each

Answer 4

• skin: herpes simplex virus HSV
• lung: viral pneumonia
• liver: hepatitis A,B,C and E

Question 5

Explain the different disease patterns caused by viral infection

Answer 5

• Acute viral infection followed by viral clearance.
• Acute viral infection followed by latent infection and periodic reactivation.
• Acute viral infection followed by chronic infection.
• Slow chronic infection.

Question 6

Define epidemiology

Answer 6

The study of the distribution and determinants of
health related states or events in specified populations , and the application of this study to the control of health problems.

Question 7

Define prevalence

Answer 7

Total number of cases of a certain disease in a

defined population at a specified point in time.

Question 8

Define incidence

Answer 8

Number of new cases of a certain disease arising in a given period (e.g. 1 year) in a specified population.

Question 9

Define endemic

Answer 9

A certain disease is constantly present at a significant level in the community without the need for external input.

Question 10

Define epidemic

Answer 10

New cases of a certain disease in a community

substantially exceed what is expected based on recent experience.

Question 11

Define pandemic

Answer 11

An epidemic that spreads across a large region –

several continents.

Question 12

Define herd immunity

Answer 12

When vaccination of a portion of the population

provides protection to unvaccinated individuals.

Question 13

Define epidemic threshold

Answer 13

The critical number or density of susceptible hosts required for an epidemic to occur. The epidemic
threshold is used to confirm the emergence of an epidemic so as to step-up appropriate control measures.

Question 14

What are notifiable diseases?

Answer 14

Infections must be reported to the government