Flashcards in Cholera, Malaria and Measles (Chapter 10) Deck (37)
What is the pathogen that causes cholera?
Vibrio cholerae (bacterium)
What is the site of action of vibrio cholerae?
The wall of the small intestine
What are the symptoms of cholera?
Severe diarrhoea, loss of water and salts, dehydration, weakness
How is cholera diagnosed?
Analysis of faeces
Where does cholera occur?
As the disease is water-borne, cholera occurs where people do not have access to proper sanitation, a clean water supply or uncontaminated food
How is cholera transmitted?
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
What is an obstacle for vibrio cholerae?
- 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
What happens when vibrio cholerae reaches the small intestine?
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
How can cholera be controlled/treated?
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
How can cholera be prevented?
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)
Why is cholera still present in certain developing countries?
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
What was the new strain of vibrio cholerae originating in 1992?
V. cholerae 0139 (there are many different strains)
What is the pathogen that causes malaria?
Plasmodium falciparum (protoctist) - one of four species
What is the insect vector (method of transmission) of malaria?
The female Anopheles mosquito
What are the sites of action of malaria?
Liver, RBCs and brain
What are the symptoms of malaria?
Fever, anaemia, nausea, muscle pain
Why do female anopheles mosquitoes feed on human blood?
To obtain the protein they need to develop their eggs
How is malaria transmitted?
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
What other three ways can malaria be transmitted?
1) during blood transfusion
2) when unsterile needles are re-used
3) across the placenta from mother to foetus
How does plasmodium improve its chances of infection?
It multiples in both hosts and at each stage there is huge increase in the number of parasites
How can people become immune to malaria?
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
How are anti-malarial drugs used?
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
What are examples of anti-malarial drugs?
Quinine, chloroquine (now resistance), doxycycline
What are the three main ways to control malaria?
1) reduce the number of mosquitoes
2) avoid being bitten by mosquitoes
3) use drugs to prevent the parasite infecting people
How can the number of mosquitoes be reduced?
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
How can mosquito bites be avoided?
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
Why has a worldwide eradication of malaria not succeeded?
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
Why is there worldwide concern over malaria?
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
What are improvements being made to control malaria?
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