Topic 10 Infectious Disease.

Question 1

What is an infectious disease?

Otherwise known as a communicable disease.

Answer 1

An infectious disease is a transmissible disease in which the pathogen can be passed from one host to another.

Question 2

What is a pathogen?

Answer 2

A pathogen is a disease causing organism.

Question 3

Define disease transmission.
What are the two ways in which a pathogen is transmitted?

Answer 3

Disease transmission is the transfer of a pathogen from an infected person to an uninfected person.

By direct contact, including through blood and other body fluids.
Indirectly, including from contaminated surfaces, animals and air.

Question 4

What is a disease carrier?

Question 5

What is cholera?

Answer 5

Cholera is a disease caused by a bacterium which is transmitted in contaminated water.

Question 6

Answer the following questions about cholera:
- What is the causative agent (pathogen)?
- What type of pathogen is it?
- What are the methods of transmission?
- How long is the incubation period?
- What is the site of action of the pathogen?
- Explain the global pattern of distribution?
- What are the clinical features of the disease?
- What are some of the methods of diagnosis?
- Give the figures of the annual incidence worldwide in 2017.
- Give the figures of the annual morality worldwide in 2017.

Answer 6

• What is the causative agent (pathogen)?
  Vibrio cholerae.
• What type of pathogen is it?
  Bacterium (prokaryote).
• What are the methods of transmission?
  Food-borne and water-borne such as via the faecal oral route (e.g. when raw human sewage of an infected person is used to irrigate vegetables).
• How long is the incubation period?
  Two hours to five days.
• What is the site of action of the pathogen?
  Wall of the small intestine.
• Explain the global pattern of distribution?
  Prevalent in large cities in developing countries that do not have adequate sewage systems or clean water supply.
  Asia, Africa and Latin America.
• What are the clinical features of the disease?
  Severe diarrhoea, loss of water and ions from the blood, dehydration and weakness.
• What are some of the methods of diagnosis?
  Dipstick test of rectal swabs and identification of V.cholerae in faecal samples using microscopy.
• Give the WHO figures of the annual incidence worldwide in 2017.
  1.3 million to 4.0 million.
• Give the WHO figures of the annual morality worldwide in 2017.
  Twenty one thousand (21 000) to one hundred and fourty three thousand (143 000)

Question 7

What does cholera bacterium produces and what is the effect of this?

Answer 7

Cholera bacterium produces a toxin that causes secretion of chloride ions into the small intestine causing osmotic movement of water into the gut, causing diarrhoea, dehyradration and loss of ions from the blood.

Question 8

Give examples of how cholera is transmitted.

Answer 8

• Infected people pass out the pathogen (Vibrio cholerae) in faeces which contaminates water supply and food whilst handling (due to lack of hygiene).
• The bacteria pass through the stomach acid to reach the small intestine.
• They multiply and secrete a toxin called choleragen.
• It distrupts the functions of the epithelium lining in the small intestine.
• Ions and water leave the blood causing severe diarrhoea which may be referred to as ‘rice water’.

Question 9

In what ways can the spread of cholera be prevented and controlled?

Give 4 examples.

Answer 9

• Drink bottled or chlorinated water.
• Wash utensils and vegetable properly.
• Improve sanitation services and sewage treatment.
• Raise awareness.

Question 10

How can cholera be treated?

Answer 10

Treatment is via rehydration therapy (a mixture of glucose and salts) which can be administered in two primary forms:

• Oral Rehydration Solution (ORS): ORS packets are widely available in pharmacies and during outbreaks, they are often distributed by health organizations.
• Intravenous Fluids: In cases where patients are severely dehydrated or unable to drink sufficient fluids. IV therapy allows for rapid rehydration and is typically administered in healthcare settings.

Question 12

Why is glucose effective when used in rehydration therapy as a way of treating cholera?

Answer 12

Glucose’s effectiveness in rehydration therapy for treating cholera stems from its ability to enhance sodium and potassium ion absorption through transport mechanisms. It creates an osmotic gradient that facilitates water retention, maintain electrolyte balance, ensure rapid absorption despite ongoing fluid losses, and provide a cost-effective solution for those affected by this disease.

Question 13

What is an antibiotic?

Answer 13

An antibiotic is a drug that kills or stops the growth of bacteria, without harming the cells of the infected organism.

Question 14

Antibiotics interfere with some aspect of growth or metabolism of the target bacterium.
Outline the ways in which antibiotics work.

Question 15

Outline how penicillin acts on bacteria.

Answer 15

Penicillin acts specifically on the enzymes involved in the synthesis of the bacterial cell wall:

1. Inhibition of bacterial cell wall synthesis:
   Penicillin binds to penicillin-binding proteins, which are essential for cross-linking peptidoglycan layers during cell wall synthesis.
   This binding prevents the formation of cross-links that provide strength to the cell wall.
2. Cell wall weakening:
   As a result of this, the integrity of the cell wall is compromised. Without proper cross-linking, the cell wall becomes weak and unable to withstand osmotic pressure.
3. Lysis (bursting) and death:
   The weakened cell wall leads to bursting when the bacterium attempts to divide or when it experiences changes in osmotic conditions.
   This ultimately results in bacterial cell death.

Question 16

Why do antibiotics not affect viruses?