Chapter 10: Infectious disease

Question 1

Define the term “infectious disease”

Answer 1

A disease caused by a pathogen which

can be transmitted.

Question 2

Define the term “non-infectious disease”. Give two

examples.

Answer 2

A disease that cannot be transmitted by
direct contact between individuals, e.g.
sickle cell anaemia or lung cancer.

Question 3

State the binomial name and pathogen type for

cholera.

Answer 3

● Vibrio cholerae

● Bacterium

Question 4

State the binomial names and pathogen type for

malaria.

Answer 4

●  Plasmodium ovale
●  Plasmodium falciparum
●  Plasmodium malariae
●  Plasmodium vivax
●  Protoctist

Question 5

State the binomial names and pathogen type for

tuberculosis.

Answer 5

● Mycobacterium tuberculosis
● Mycobacterium bovis
● Bacterium

Question 6

State the pathogen type for HIV/AIDS

Answer 6

Virus

Question 7

What does HIV stand for?

Answer 7

Human immunodeficiency virus

Question 8

What does AIDS stand for?

Answer 8

Acquired immunodeficiency syndrome

Question 9

What causes HIV/AIDS?

Answer 9

1. HIV virus is transmitted by direct contact with blood, semen, rectal
   fluids, vaginal fluids and breast milk
2. Attachment proteins bind to complementary CD4 receptor on TH cells
3. HIV particles replicate inside TH cells, killing or damaging them
4. AIDS develops when there are too few TH cells for the immune system
   to function

Question 10

How is HIV/AIDS treated?

Answer 10

Taking a combination of antiretroviral drugs
prevents HIV replication. Post exposure
prophylaxis (PEP) can prevent infection after
exposure.

Question 11

What causes tuberculosis (TB)?

Answer 11

1. Transmitted by droplet infection (inhalation)
2. Trigger inflammatory response by infecting phagocytes in lungs
3. Infected phagocytes are sealed in waxy-coated tubercles so
   bacteria remain dormant. Primary TB has no symptoms
4. If another factor weakens immune system, bacteria become
   active. Secondary TB destroys lung tissue

Question 12

Outline the symptoms and primary treatment of TB.

Answer 12

Patients take a combination of antibiotics

for several months.

Question 13

How is cholera transmitted?

Answer 13

● Fecal/oral transmission.

● Ingesting contaminated food or water

Question 14

How is cholera treated?

Answer 14

● Rehydration (fluid and electrolytes)

● Antibiotics

Question 15

Why may the incidence and prevalence of

communicable diseases change over time?

Answer 15

● Development of vaccines
● Development of treatments, e.g. antibiotics
● Random mutations cause antigen variability in
pathogens. Memory cells no longer complementary
● Random mutations result in treatment-resistant strains

Question 16

How can the spread of HIV be prevented?

Answer 16

● Take PEP
● Multi-drug treatment (HIV difficult to control due to high antigen variability)
● Use clean needles
● Screen blood donations to ensure they are not HIV positive (ethically
important not to outsource cheap blood e.g. from prison donations)
● Education

● Use of condoms

Question 17

How can the spread of TB be prevented?

Answer 17

● Combination of drugs and vaccinations (expensive)
● Cover mouth & nose when coughing/ sneezing
● Quarantine (socially isolating)
● Improved sanitation

Question 18

How can the transmission of cholera be prevented?

Answer 18

● Education on water sanitation i.e. don’t drink
untreated water

● Education on contamination of water supply
e.g. sewage

Question 19

Outline the mode of transmission and infection of the

Plasmodium spp. parasite.

Answer 19

● Female mosquito acts as vector when it transfers
saliva to another organism during feeding

● Parasite reproduces asexually in red blood cells
in liver, causing lysis

Question 20

How is endemic malaria controlled?

Answer 20

● Preventing mosquito bites - mosquito nets, insect repellent

● Controlling mosquito numbers - pesticides, chemical
treatment of standing water and sewage, introduction of
predators for mosquitoes

● Drug treatment

Question 21

Consider the biological, social and economic factors

of preventing infectious disease.

Answer 21

● Diseases generally spread faster in densely populated and poorly sanitized areas

● Countries with healthcare systems and good education often have less disease. People educated
on how to prevent the spread of disease and can access treatments and vaccines

● Social stigma - some countries may see diseases (e.g. HIV) as socially stigmatising. People may
avoid seeking treatment for risk of social fallout

● Patronage of developed countries - vaccination programmes from developed nations considered
suspicious. Programmes used in the past to sample DNA without the consent of indigenous people

Question 22

Describe and explain the global patterns of malaria,

TB and HIV/AIDS.

Answer 22

● Malaria - generally in tropical countries (warm temperatures required for survival of
plasmodium). Such countries tend to lack education and healthcare. Malaria is uncontrolled
and there is a lack of or no education regarding prevention methods.

● TB - common in developing countries where people live in cramped, poorly sanitised
conditions (proximity essential for TB transmission). Treatment and education in prevention
are rare.

● HIV/AIDS - common in developing nations. Lack of access to education in prevention. Lack of
access to healthcare means many people go undiagnosed and untreated.

Question 23

How does penicillin act as an antibiotic? Name its

type and mode of action.

Answer 23

Penicillin inhibits the synthesis of the peptidoglycan wall in
bacteria, preventing new cell walls forming. The cell bursts.

This class of antibiotic is bactericidal. They work by 
preventing cell wall synthesis or disrupting protein synthesis

Question 24

Why do antibiotics have no effect on viruses?

Answer 24

Antibiotics work by targeting machinery
found in bacteria (prokaryotic cells). Viruses
do not have this machinery ∴ antibiotics
have no effect on viruses.

Question 25

Why is it important antibiotics do not affect

eukaryotes?

Answer 25

Humans (host) are eukaryotic. If
antibiotics affected eukaryotic cells they
could potentially kill the recipient.

Question 26

How does antibiotic resistance occur?

Answer 26

● Spontaneous mutation of bacterial plasmids can occur which may lead to
improved tolerance to an antibiotic. These cells are able to survive long
enough to divide, increasing the prevalence of the mutation and making the
population more resistant to a particular antibiotic.

● Resistance can be spread ‘horizontally’ – the movement of genetic material
between unicellular and/or multicellular organisms (conjugation) other than
by the ‘vertical’ transmission of DNA from parent to offspring via reproduction.

Question 27

How can we mitigate bacterial resistance?

Answer 27

● Complete the course of antibiotics to ensure the bacterial infection is eliminated
● Do not overuse antibiotics
● Do not use antibiotics in animal feed
● Reduce contamination in hospitals
● Aseptic techniques in hospitals
● Isolation of infected patients
● Emphasis on hygiene
● Reduce use of antibacterial hand gel – removes non-pathogenic bacteria, allowing
pathogenic bacteria to survive.