10. Infectious Diseases

Question 1

What are infectious diseases?

Answer 1

Diseases that are caused by pathogens

Question 2

What is the pathogen that causes cholera?

Answer 2

Vibrio cholerae
(Bacterium)

Question 3

What is the pathogen that causes malaria?

Answer 3

(Protoctist)
Four species of Plasmodium:
Plasmodium falciparum
Plasmodium malariae
Plasmodium ovale
Plasmodium vivax

Question 4

What is the pathogen that causes HIV/AIDS?

Answer 4

Human immunodeficiency virus
(Virus)

Question 5

What is the pathogen that causes TB?

Answer 5

Mycobacterium tuberculosis
Mycobacterium bovis
(Bacterium)

Question 6

How do infected cholera patients spread their bacterium?

Answer 6

They carry out large numbers of bacteria in their faeces so if these contaminate the water supply or if infected people handle food or cooking utensils without washing their hands then bacteria are transmitted to uninfected people

Question 7

Define the word disease

Answer 7

An illness or disorder of the body or mind that leads to poor health.

Question 8

What is the treatment for cholera?

Answer 8

People are given oral rehydration therapy by a solution of salts and glucose.
People who can’t drink are given this solution intravenously

Question 9

How effective is the treatment for cholera?

Answer 9

Glucose is effective because it is absorbed into the blood and this is linked to the uptake of sodium and potassium ions

Question 10

What is a disease vector?

Answer 10

An organism which carries a pathogen from one person to another or from an animal to a human.

Question 11

How does Malaria spread?

Answer 11

May be transmitted during blood transfusion
When unsterile needles are re-used
The plasmodium can also pass across the placenta from mother to fetus

Question 12

Why does female Anopheles mosquito feed instead of the male?

Answer 12

Female Anopheles mosquitoes feed on human blood to obtain the protein they need to develop their eggs.

Question 13

What are the two drugs used to treat malaria?

Answer 13

Quinine and chloroquine- prophylactic drugs taken before and after visiting a place where malaria is prevalent.

Question 14

What is chloroquine and how does it work?

Answer 14

It can be used as a prophylactic drug, stopping an infection occurring if a person is bitten by an infected mosquito. Chloroquine inhibits protein synthesis and prevents the parasite spreading within the body.

Question 15

As a result of drug resistance strains, what is the best treatment for malaria currently?

Answer 15

Artemisinin based combination therapy (ACT)

Question 16

What are the three main ways to control malaria?

Answer 16

1. Reduce the number of mosquitoes
2. Avoid being bitten by mosquitoes
3. Use prophylactic drugs to prevent Plasmodium infecting people.

Question 17

What is the most effective method to control malaria?

Answer 17

To kill the insect vector and break the transmission cycle. Mosquitoes lay their eggs in water and the larvae hatch and develop in water but breath by coming up to the surface so oil can be spread over the surfaces of water to make it impossible for mosquito larvae and pupae to breathe.

Question 18

Name the 2 biological control measures that can be used for malaria

Answer 18

1. Stocking ponds, irrigation and drainage ditches with fish which feed on mosquito larvae
2. Spraying a preparation containing the bacterium Bacillus thuringiensis which kills mosquito larvae but is not toxic to other forms of life.

Question 19

The best protection against malaria is to avoid being bitten, how can people do this?

Answer 19

People are advised to sleep beneath mosquito nets and use insect repellents.
Insecticides must also be sprayed inside the house

Question 20

What three factors may lead to improvements in the control of malaria?

Answer 20

1. The use of modern techniques in gene sequencing and drug design
2. Development of vaccines targeted against different stages of the parasites life cycle
3. A renewed will to remove burden if malaria from the poorest parts of the world allied to the generous donations from wealthy individuals and foundations

Question 21

How does the HIV virus affect the human body?

Answer 21

It infects and destroys the body’s immune system so that their numbers gradually decrease. When T helper lymphocytes are low the body is unable to defend itself against infection, so allowing a range of pathogens to cause variety of opportunistic diseases.

Question 22

What is an opportunistic infection?

Answer 22

An infection caused by pathogens that take advantage of a host with a weakened immune system, as may happen with an HIV infection

Question 23

How is HIV spread?

Answer 23

Spread by intimate human contact
Transmission is only possible by direct exchange of body fluids

Question 24

Name 4 ways HIV can be spread?

Answer 24

1. Sexual intercourse
2. Blood donation
3. Sharing of needles by intravenous drug users
4. From mother to child across the placenta.

Question 25

What has been successful over the years in terms of treating HIV?

Answer 25

Drug therapy can slow down the onset of AIDS so that an HIV+ person can have a normal life expectancy. The drugs are similar to DNA nucleotides. Stops the replication of the viral genetic material and leads to an increase in some of the body’s lymphocytes

Question 26

What makes HIV hard to control?

Answer 26

The virus’s long latent stage means that it can be transmitted by people who are HIV+ but who show no symptoms and do not know they are infected.

Question 27

Why is the body not able to recognize the virus?

Answer 27

The virus changes its surface proteins which makes it hard for the body’s immune system to recognize it, this also makes developing a vaccine very difficult

Question 28

Name ways to prevent the spread of HIV?

Answer 28

-People can be educated about the spread of the infection and encouraged to change their behavior so as to protect themselves and others. -Condoms, femidoms and dental dams are effective protection during intercourse as they form a barrier between body fluids.

Question 29

What is contact tracing and why is it important?

Answer 29

It is an important part of controlling the spread of HIV. If a person who is diagnosed as HIV+ is willing and able to identify the people he or she has put at risk of infection by sexual intercourse or sharing needles then these people will be offered an HIV test.

Question 30

What is the first opportunistic infection to strike HIV+ people?

Answer 30

TB. The HIV infection may reactivate dormant infections of M. Tuberculosis which may have been present from childhood of if you’re uninfected making them susceptible to infection.

Question 31

How does TB spread?

Answer 31

It is spread when infected people with the active form of the illness cough or sneeze and the bacteria are carried in the air in tiny droplets of liquid. The transmission cycle ends when uninfected people inhale the droplets.

Question 32

Who is typically most vulnerable to TB?

Answer 32

It spreads most rapidly among people living in overcrowded conditions. People who sleep close together in large numbers The homeless People who live in poor substandard housing Those with low immunity because of malnutrition or being HIV+

Question 33

What happens if TB is not treated or if the patient stops treatment before the bacteria are completely eliminated?

Answer 33

The bacteria spread throughout the body, increasing the likelihood that mutations will arise as the bacteria survive for a long time and multiply.

Question 34

How can the spread of M. Bovis from Cattle be controlled?

Answer 34

TB bacteria are killed when milk is pasteurized Cattle are routinely tested for TB and any found to be infected are destroyed.

Question 35

What is an antibiotic?

Answer 35

A drug that kills or stops the growth of bacteria without harming the cells of the infected organism

Question 36

How do antibiotics work?

Answer 36

They interfere with some aspect of growth or metabolism of the target bacterium: 1. Synthesis of bacterial cell walls 2. Activity of proteins in the cell surface membrane 3. Enzyme action 4. DNA synthesis 5. Protein synthesis

Question 37

How does Penicillin work?

Answer 37

Bacterial cell have walls made of peptidoglycan which is held together by cross links that form between them. So penicillin prevents the synthesis of the cross links between the peptidoglycan polymers in the cell walls of bacteria by inhibiting the enzymes that build these cross-links

Question 38

Explain how the enzymes secreted in the bacterial cells progressively damages itself.

Answer 38

A growing bacterial cell secretes enzymes called autolysons which make little holes in its cell wall and these holes allow the wall to stretch so that new peptidoglycan chains can link together. However, penicillin prevents the peptidoglycan chains from linking but the autolysons keep making new holes. The cell wall therefore becomes progressively weaker. The bacterial also live in watery environments and take up water by osmosis. When they are weakened the cell walls cannot withstand the target pressure exerted on them and the cell bursts

Question 39

Why does penicillin have no effect on M. Tuberculosis?

Answer 39

Because the cell wall of this bacterium is not very permeable and because the bacterium has a gene that codes for an enzyme that catalyzes the breakdown of penicillin

Question 40

How can we reduce the number of circumstances in which bacteria develop resistance to antibiotics?

Answer 40

1. Using antibiotics only when appropriate and necessary 2. Reducing the number of countries in which antibiotics are sold without a doctor’s prescription 3. Making sure that patients complete their course of medication 4. Making sure patients do not keep unused antibiotics for self medication in the future 5. Avoiding using antibiotics in farming to prevent rather than cure infections

Question 41

How can we reduce the number of circumstances in which bacteria develop resistance to antibiotics?

Answer 41

1. Using antibiotics only when appropriate and necessary 2. Reducing the number of countries in which antibiotics are sold without a doctor’s prescription 3. Making sure that patients complete their course of medication 4. Making sure patients do not keep unused antibiotics for self medication in the future 5. Avoiding using antibiotics in farming to prevent rather than cure infections 6. Reducing the use of wide spectrum antibiotics and using antibiotics specific to the infection.

Question 42

Why is malaria very difficult to control?

Answer 42

1. No vaccine as plasmodium is eukaryotic and antigens differ in the different life stages. 2. Drug resistance in Plasmodium 3. Insecticide resistance in Plasmodium 4. Infected individuals not identified

Question 43

What factors led to the successful eradication of smallpox

Answer 43

1. It did not mutate 2. Same vaccine was used for whole program 3. Vaccine gave strong immune response