Cholera, Malaria and Measles (Chapter 10)

Question 1

What is the pathogen that causes cholera?

Answer 1

Vibrio cholerae (bacterium)

Question 2

What is the site of action of vibrio cholerae?

Answer 2

The wall of the small intestine

Question 3

What are the symptoms of cholera?

Answer 3

Severe diarrhoea, loss of water and salts, dehydration, weakness

Question 4

How is cholera diagnosed?

Answer 4

Analysis of faeces

Question 5

Where does cholera occur?

Answer 5

As the disease is water-borne, cholera occurs where people do not have access to proper sanitation, a clean water supply or uncontaminated food

Question 6

How is cholera transmitted?

Answer 6

1) infected people pass out large numbers of bacteria in their faeces
2) if the faeces 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

What is an obstacle for vibrio cholerae?

Answer 7

• To reach this site of action in the small intestine the bacteria have to pass through the stomach
• If the contents of the stomach are sufficiently acidic (less than pH 4.5), the bacteria are unlikely to survive

Question 8

What happens when vibrio cholerae reaches the small intestine?

Answer 8

1) it multiplies and secrete choleragen (a toxin) which disrupts the functions of the epithelium lining the intestine, so that salts and water leave the blood
2) this causes severe diarrhoea and the loss of fluid can be fatal if not treated within 24 hours

Question 9

How can cholera be controlled/treated?

Answer 9

1) oral rehydration therapy (if they can drink)
2) a solution of salt and glucose given intravenously to rehydrate the body - glucose is absorbed and takes ions with it
3) maintain osmotic balance of the blood and tissue fluids - make sure patient’s fluid intake equals fluid losses in urine and faeces

Question 10

How can cholera be prevented?

Answer 10

1) large cities having sewage treatment and clean water, which is chlorinated to kill bacteria, breaking the transmission cycle
2) vaccine (but only provides short-term protection and only for travellers)

Question 11

Why is cholera still present in certain developing countries?

Answer 11

1) countries with huge debts do not have the financial resources to tackle large municipal projects such as providing drainage and a clear water supply to large areas of substandard housing
2) the use of raw human sewage to irrigate vegetables
3) inadequate cooking and washing in contaminated water
4) large cities with no sewage treatment

Question 12

What was the new strain of vibrio cholerae originating in 1992?

Answer 12

V. cholerae 0139 (there are many different strains)

Question 13

What is the pathogen that causes malaria?

Answer 13

Plasmodium falciparum (protoctist) - one of four species

Question 14

What is the insect vector (method of transmission) of malaria?

Answer 14

The female Anopheles mosquito

Question 15

What are the sites of action of malaria?

Answer 15

Liver, RBCs and brain

Question 16

What are the symptoms of malaria?

Answer 16

Fever, anaemia, nausea, muscle pain

Question 17

Why do female anopheles mosquitoes feed on human blood?

Answer 17

To obtain the protein they need to develop their eggs

Question 18

How is malaria transmitted?

Answer 18

1) if the female anopheles mosquito bites a person infected with plasmodium, they will take up some of the pathogen’s gametes with the blood meal
2) male and female gametes fuse in the mosquito’s gut and develop to form infective stages which move to the mosquito’s salivary glands
3) when the mosquito feeds again, she injects an anticoagulant from her salivary gland that prevents the blood meal from clotting
4) ∴ the infective stages of plasmodium pass from the mosquito’s salivary glands into the uninfected human’s blood together with the anticoagulant in the saliva
5) the parasites enter the RBCs, where they multiply

Question 19

What other three ways can malaria be transmitted?

Answer 19

1) during blood transfusion
2) when unsterile needles are re-used
3) across the placenta from mother to foetus

Question 20

How does plasmodium improve its chances of infection?

Answer 20

It multiples in both hosts and at each stage there is huge increase in the number of parasites

Question 21

How can people become immune to malaria?

Answer 21

1) if people are continually re-infected by different strains of malaria and survive the first 5 years of life (when mortality is very high), they become immune
2) immunity only lasts as long as people are in contact with the disease

Question 22

How are anti-malarial drugs used?

Answer 22

1) to treat infected people
2) to stop an infection occurring if a person is bitten by an infected mosquito (as a prophylactic/preventative) - needs to be taken before, during and after visiting malaria-endemic countries

Question 23

What are examples of anti-malarial drugs?

Answer 23

Quinine, chloroquine (now resistance), doxycycline

Question 24

What are the three main ways to control malaria?

Answer 24

1) reduce the number of mosquitoes
2) avoid being bitten by mosquitoes
3) use drugs to prevent the parasite infecting people

Question 25

How can the number of mosquitoes be reduced?

Answer 25

1) spread oil over the surface of water to make it impossible for mosquito larvae, which hatch underwater, to breathe
2) drain marshes and clear vegetation
3) stocking ponds, irrigation and drainage ditches, and other permanent bodies of water with fish that feed on mosquito larvae
4) spraying a preparation containing the bacterium Bacillus thuringiensis which kills mosquito larvae

Question 26

How can mosquito bites be avoided?

Answer 26

1) sleep beneath mosquito nets
2) use insect repellents
3) soaking mosquito nets in insecticide every 6 months
4) not exposing skin when mosquitoes are active at dusk

Question 27

Why has a worldwide eradication of malaria not succeeded?

Answer 27

1) plasmodium became resistant to the drugs used to control it
2) mosquitoes became resistant to DDT and other insecticides
3) hugely expensive and unpopular as tackled insensitively
4) needed to involve local people

Question 28

Why is there worldwide concern over malaria?

Answer 28

1) increase in drug-resistant forms of plasmodium
2) increase in the percentage of cases cause by P. falciparum which causes severe and often fatal malaria
3) difficulties in developing malaria vaccine
4) increase in the number of epidemics because of climate and environmental changes that favour spread of mosquitoes
5) migration of people from malaria-endemic areas

Question 29

What are improvements being made to control malaria?

Answer 29

1) improve diagnosis by using simple and quick dipstick tests
2) improve supply of effective drugs and using them in combination to reduce chances of drug resistance
3) promote appropriate methods to prevent transmission
4) whole genome of plasmodium has been sequenced - could lead to development of effective vaccines
5) development of vaccines targeted against different stages of plasmodium’s life cycle
6) renewed international will to remove burdens of disease from poorest parts of world and donations

Question 30

What is measles caused by?

Answer 30

A virus (Morbillivirus)

Question 31

What does the measles virus do?

Answer 31

Enters the body and multiplies inside cells in the upper respiratory tract

Question 32

What are the symptoms of measles?

Answer 32

• No symptoms for 8-14 days then rash, fever, runny nose, cough, red and watery eyes, small white spots inside cheeks
• Complications: pneumonia, ear and sinus infections, brain damage, convulsions (can be fatal)

Question 33

How is measles transmitted?

Answer 33

1) when infected people cough or sneeze, they release droplets containing many millions of virus particles (aerosol infection)
2) if these are inhaled by uninfected people with no immunity, they will become infected and develop symptoms
3) also spread by touching an infected surface and putting fingers in mouth

Question 34

What is the treatment for measles?

Answer 34

• Bed rest and taking medicines to lower fever
• No specific medicines for measles
• After roughly 10 days, disease clears up and there are rarely any complications

Question 35

Who is most affected by measles?

Answer 35

• People living in overcrowded, insanitary conditions in cities of developing countries with a high birth rate
• Malnourished children with vitamin A deficiency living in overcrowded conditions - among these children, measles is a serious disease and a major cause of death and child blindness

Question 36

Why do infants (less than 8 months) not have to be vaccinated?

Answer 36

They have passive immunity from antibodies that have crossed the placenta from the mother

Question 37

Why has the death rate from measles largely fallen?

Answer 37

Mainly as a results of a mass vaccination programme (MMR)