Infectious Diseases

Question 1

What does the term disease mean?

Answer 1

A disease is an illness or disorder of the body or mind that leads to poor health; each disease is associated with a set of signs and symptoms

Question 2

What are infectious diseases? What is an example?

Answer 2

• An infectious disease is a disease caused by pathogens
• They are sometimes called communicable doses as they are passed from infected to unaffected people
• Some also affect animals are passed from animals to humans

Question 3

What are non-infectious diseases? What is an example?

Answer 3

• They are not caused by pathogens and can be long-term degenerative diseases, e.g. lung cancer and COPD
• Inherited or genetic diseases, such as cystic fibrosis and sickle cell anaemia are another group of non-infectious diseases
• There are other categories of non-infectious disease including deficiency diseases that are caused by malnutrition and mental diseases

Question 4

What is the name and type of causative organism (pathogen) for cholera?

Answer 4

• Vibrio cholera

- Bacterium

Question 5

What is the name and type of causative organism (pathogen) for malaria?

Answer 5

• Four species of plasmodium: Plasmodium falciparum, P. vivax, P. vale, P. malariae
• Protoctist

Question 6

What is the name and type of causative organism (pathogen) for tuberculosis (TB)?

Answer 6

• Mycobacterium tuberculosis and M.Bovis

- Bacterium

Question 7

What is the name and type of causative organism (pathogen) for HIV/AIDS?

Answer 7

• Human Immunodeficiency Virus (HIV)

- Virus

Question 8

What is the name and type of causative organism (pathogen) for small pox?

Answer 8

• Variola virus

- Virus

Question 9

What is the name and type of causative organism (pathogen) for measles?

Answer 9

• A species of morbillivirus

- Virus

Question 10

How is cholera transmitted?

Answer 10

• Water borne disease
  1. No access to proper sanitation (clean water supply) and uncontaminated food
  2. Infected people faeces in water supply, or infected people handle food or cooking utensils without washing they hands then bacteria are transmitted to uninfected people
  3. To reach their site of action in the small intestine, the bacteria have to pass through the stomach and if the contents are sufficiently acidic (pH less than 4.5), the bacteria are unlikely to survive
  4. However if the bacteria do reach the small intestine, they multiply and secrete a toxin, choleragen, which disrupted the function of the epithelium lining the intensive so that salts and water leave the blood
  5. This causes severe diarrhoea and the loss of fluid can be fatal if not treated within 24 hours

Question 11

How is measles transmitted?

Answer 11

1. Infected people sneeze or cough they release droplets containing many millions of virus particles
2. These are inhaled by uninfected people who have no immunity to the disease
3. Easily transmitted in conditions such as
   - overcrowding
   - unsanitary conditions and
   - high birth rate and it infects making malnourished infants suffering from Vitamin A deficiency (infants under 8 months have passive immunity from antibodies passed in placenta)

Question 12

How is malaria transmitted?

Answer 12

1. Female Anopheles mosquitos feed on human blood to obtain the protein they need to develop their eggs
2. If the person they bite is infected with plasmodium, they will take up some of the pathogen’s gametes with the blood meal
3. Male and female gametes fuse in the mosquitos gut and develop to from infective stages, which move to the mosquitos salivary glands
4. When the mosquito feeds again, she injects an anticoagulant from her salivary glands that prevents the blood meal from clotting, so that it flows out of the host into the mosquito
5. The infective stages pass from the mosquitos salivary glands into the human’s blood together with the anticoagulant in the salvia
6. The parasites enter the red blood cells, where they multiply

Question 13

What is a vector?

Answer 13

• A vector is an organism which carries a disease for one perms to another or from an animal to human, do not confuse it with he causative agent, which in this case is plasmodium
• The female anopheles mosquito is therefore a vector of malaria and she transmits the disease when she passes the infective stages into an uninfected persons

Question 14

How else can malaria be transmitted?

Answer 14

1. Malaria can also be transmitted during blood transfusions and when unsterile needles are re-used
2. Plasmodium can also pass across the placenta from mother to fetus

Question 15

Why is malaria so bad?

Answer 15

1. Plasmodium multiples in both hosts, the human and the mosquito; and at each stage there is a huge increase in the number of parasites, and this improves the chances of infecting another mosquito or human host
2. If people are continually re-infected by different strains of malaria, they become immune
   - However this only happens if they survive the first five years of life, when mortality from malaria is very high
3. The immunity only lasts as long as people as in contact with the disease
   - This explains why epidemics in places where malaria is not endemic can be very serious, and why malaria is more dangerous to those in areas where it only occurs during and after the rainy season
4. This often coincides with the time of maximum agricultural activity, so the disease has a disastrous effect on the economy: people cannot cultivate the land when they are sick

Question 16

How is TB transmitted?

Answer 16

1. TB 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
2. Transmission occurs when people who are uninfected inhale the droplets
3. TB spreads most rapidly among people living in overcrowded conditions and people who sleep close together in large numbers are particularly at risk
   - The disease primarily attacks the homeless and people who live in poor, substandard housing; those with low immunity, because of malnutrition or being HIV positive are also particularly vulnerable

Question 17

How is TB with M.bovis transmitted?

Answer 17

1. The form of TB caused by M.bovis also occurs in cattle and is spread to humans in meat and milk
2. The incidence of TB in the UK decreased steeply well before the introduction of a vaccine in the 1950s, because of improvements in housing conditions and diet

Question 18

Why could there be just as high levels of TB in areas of London as that in LEDCs?

Answer 18

1. Some strains of TB bacteria and resistant to drugs
2. The HIV/AIDS pandemic
3. Poor housing in inner cities and homelessness
4. The breakdown of TB control programmes, partial treatment for TB increase the chance of drug resistance in Mycobacterium

Question 19

Explain how HIV/AIDS is transmitted?

Answer 19

• HIV is a virus that is spread by intimate human contact; there is no vector (unlike in malaria) and the virus is unable to survive outside of the human body (like cholera or malaria pathogens)
• Transmission is only possible by direct exchange of body fluids and so this means that in HIV is spread easily: 1. Sexual intercourse
  2. Blood donation
  3. The sharing of needles used by intravenous drug users
  4. HIV is also transmitted from mother to child across the placenta and, more often, through the mixing of blood during birth

Question 20

How do you treat cholera?

Answer 20

1. Almost all people with cholera who are treated make a quick recovery and a death from cholera is an avoidable death
2. The disease can be controlled quite cheaply by a -solution of salts and glucose given intravenously to rehydrate the body
3. If people can drink, they are given oral rehydration therapy
4. Glucose if effective because it is absorbed into the blood and takes ions (for example sodium and potassium ions) with it
5. It is important to make sure that a patient’s fluid intake equals fluid losses in urine and faeces, and to maintain the osmotic balance of the blood and tissue fluids

Question 21

In what sort of conditions is cholera found?

Answer 21

1. In developing countries, large cities that have grown considerably in recent years, but as yet have no sewage treatment or clean water, create perfect conditions for the spread of disease
2. Increasing quantities of untreated faeces from a growing population favour cholera’s survival

Question 22

Which sort of countries have cholera?

Answer 22

1. Countries that have huge debts do not have the financial resources to tackle large municipal projects such as providing drainage and a clean water supply to large areas of substandard housing
2. In many countries, the sue of raw human sewage to irrigate vegetables is a common cause of the debases, as are inadequate cooking, or washing in contaminated water
3. Areas of the work where cholera is endemic are West and East Africa and Afghanistan

Question 23

Why is cholera almost unknown in the developed world?

Answer 23

1. Cholera is almost unknown in the developed world, as a result of
   - sewage treatment
   - provision of clean piped water, which is chlorinated to kill bacteria
2. The transmission of the cycle has been broken

Question 24

What circumstances may lead to a cholera outbreak?

Answer 24

1. Health authorities always fear outbreaks of cholera and other diarrhoeal diseases following natural disasters
2. In Haiti in 2010, a cholera epidemic broke out several months after the earthquake that destroyed large parts of the country
3. Travellers from areas free of cholera to those where cholera is endemic used to be advised to be vaccinated, although the vaccine only provided short-term protection and this recommendation has now been dropped

Question 25

What are the different strains of cholera?

Answer 25

• There are many different strains of V.cholerae
• Until the 1990s, only the strain know as O1 caused cholera.
• Between 1817 and 1923, there were six pandemics of cholera. Each originated in what is now Bangladesh and was caused by the ‘classical’ strain of cholera, O1, named ‘El Tor’, originated in Indonesia. El Tor soon spread to India, then to Italy in 1973, reaching South America in January 1991, where it caused an epidemic in Peru. The discharge of the ship’s sewage into the sea may have been responsible
• Within days of the start of the epidemic the disease had spread 2000km along the coast, and within four week had moved inland. In February and March 1991, an average of 2550 cases a day we being reported. People in neighbouring countries were soon infected. In Peru, many sewers discharge straight into shellfish beds. Organisms eaten as seafood, especially filter-feeders such as oysters and mussels, become contaminated because they concentrate cholera bacteria when sewage is pumped into the sea
• Fish and shellfish are often eaten raw. Because the epidemic developed so rapidly in Peru, it is thoughts that the disease probably through contaminated seafood
• A new strain, known as V.cholera O139, originated in Chennai (the called Madras) in October 1992 and has spread to other parts of India and Bangladesh. This strain threatens to be responsible for an eighth pandemic. It took El Tor two years to displace the ‘classical’ strain in India; O139 replaces El Tor in less than two months, suggesting that it may be more virulent. Many adult cases have been reported, suggesting that previous exposure to El Tor has not given immunity to O139

Question 26

How is malaria treated?

Answer 26

1. Anti-malarial drugs such as quinine and chloroquine are used to treat infected people
2. They are also used as prophylactic (preventative) drugs, stopping an infection occurring if a person is bitten by an infected mosquito
3. Prophylactic drugs are taken before during and after visiting an area where malaria is endemic
4. Chloroquine inhibits protein synthesis and prevents the parasite spreading within the body
5. Another prophylactic, progunail, has the added advantage of inhibiting the sexual reproduction of plasmodium inside the biting mosquito

Question 27

What happens in places that anti-malarial drugs have been used widely?

Answer 27

1. Where anti-malarial drugs have been used widely, there are strains of drug-resistant plasmodium, the drug is no longer effective against the pathogen
2. Chloroquine resistance is widespread in parts of South America, Africa and New Guinea
3. Newer drugs such as mefloquine are used in these areas
4. However, mefloquine is experience and sometimes causes unpleasant side-effects such as restlessness, dizziness vomiting and disturbed sleep
5. Resistance to mefloquine has developed in some areas, notably the border regions of Thailand

Question 28

What is another drug used against malaria?

Answer 28

1. The antibiotic doxycycline is also sued as a prophylactic drug
2. The drug artesunate, derived from the plant compound artemisia, is used in combination with mefloquine to tear infections of P. falciparum

Question 29

What advice is given to travellers going to places with malaria?

Answer 29

1. People from non-malarial countries visiting many parts of the tropics are at great risk of contracting malaria
2. Doctors in developed counties, who see very few cases of malaria, often misdiagnose it as influenza, since the initial symptoms are similar
3. Many of these cases are among settled immigrants who have been visits relatives in Africa or India
4. This people do not take prophylactic drugs because they do not realise that they have lost their immunity

Question 30

What are the three main ways to control malaria?

Answer 30

1. Reduce the number of mosquitos
2. Avoid being bitten by mosquitos
3. Use drugs to prevent the parasite infecting people

Question 31

How is it possible to breaks the transmission cycle of malaria?

Answer 31

1. It is possible to kill the insect vector and break the transmission cycle
2. Mosquitos lat their eggs in water
3. Larvae hatch and develop in water but breathe air by coming to the surface
4. Oil can be spread over the surface of water to make it impossible for mosquito larvae and pupae to breathe
5. Marshes can be drained and vegetation cleared

Question 32

What are two biological control measure that can be used to prevent malaria?

Answer 32

1. Stocking ponds, irrigation and drainage ditches and other permanent bodies of water 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 33

What is the downside to the biological controls against malaria?

Answer 33

1. However mosquitos will lay their eggs in any small puddle or pool, which makes it impossible to completely eradicate breeding sites, especially in the rainy season
2. The best protection against malaria is to avoid being bitten
3. People are advised to sleep beneath mosquitos nets and use insect repellents
4. Soaking mosquito nets in insecticide very six months has shown to reduce mortality from malaria
5. People should not expose their skin when mosquitos are active at dusk

Question 34

What happened with malaria in the 1950s?

Answer 34

• In the 1950s the WHO coordinated a worldwide eradication programme. Although malaria was cleared form some countries, the programme was not generally successful and there were two main reasons for this:
  1. Plasmodium became resistance to the drugs used to control it
  2. Mosquitos became resistance to DDT and the other insecticides that were used at the time, such as dieldrin

Question 35

What was wrong with the WHO programme for malaria?

Answer 35

1. The programme was also hugely expensive and often unpopular
2. People living in areas where malaria was temporarily eradicated by the programme lost their immunity and suffered considerably, even dying, when the disease returned
3. Some villagers in South-East Asia lost the roofs to their houses because dieldrin killed a parasitic wasp that controlled the number of thatch-eating caterpillars
4. Some spay dreams were set upon and killed by angry villagers in New Guinea
5. The programme could have been more successful if it has been tackled more sensitively, with more involvement of the local people
6. In the 1970s, war and civil unrest destroyed much of the infrastructure throughout Africa and South-East Asia, making it impossible for mosquito control teams to work effectively

Question 36

What are some of the reasons for the worldwide concern over the spread of malaria?

Answer 36

1. An increase in drug-resisatnct forms of Plasmodium
2. An increase in the rpportaimn of cases caused by P.falciparum, the from that causes severe and often fatal malaria
3. Difficulties in developing vaccines against malaria
4. An increase in the number of epidemics, because of climatic and environmental changes that favour the spread of mosquitos
5. The migration of people from areas where malaria is endemic, for economic and political reasons

Question 37

Why is malaria still a threat?

Answer 37

1. Malaria is still one of the world’s biggest threats to health
   - 40% of the world’s population lives in areas where there is a risk of malaria
   - Between 2000 and 2011, control measures have achieved a decrease in mortality rates of about 25% across the world, and 33% in the WHO’s African region

Question 38

What do control measures for Malaria now include?

Answer 38

1. Control methods now concentrate on working within the health systems to improve diagnosis, improve the supply of effective drugs and promote appropriate methods to prevent transmission
2. Several recent advances give hope that malaria may one day be controlled, the introduction of the dip stick tests for diagnosing malaria means that diagnosis can be done quickly without the need for labortories
3. The whole genome of plasmodium has been sequence, and this may lead to the development of effective vaccines
4. Several vaccines are being trialled, but it is not likely that a successful vaccine will be available for some time
5. Drugs are used in combination to reduce the change of drug resistance arising

Question 39

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

Answer 39

1. Use of modern techniques in gene sequencing and drug design
2. Development of vaccine targeted against different stage of the parasite’s life cycle
3. A renewed international will to remove the burden of disease form the poorest parts of the world, allied to generous donations from wealthy individuals and foundations

Question 40

What is an antibiotic?

Answer 40

An antibiotic is a drug that pulls or stop the growth of bacteria, without harming the cells of the infected organism

Question 41

Where are antibiotics derived from?

Answer 41

• Antibiotics are derived from living organisms, although they are often made more effective by various chemical processes
• There are a wide range of antibiotics to treat bacterial infections and other antimicrobial drugs such as isoniazid, used for the treatment of TB, are synthetic (made in laboratories)

Question 42

How do antibiotics work?

Answer 42

• Antibiotics interfere with some aspect of growth or metabolism of the target bacteria which include:
  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 43

How does penicillin work?

Answer 43

1. Bacterial cells have walls made of peptidoglycans and these are long molecules continuing peptides and sugars
2. In the bacterial cell wall, peptidoglycans are held together by cross-links that from between them
3. Penicillin prevents the synthesis of the cross-links between the peptidoglycan polymers in the cells walls of bacteria by inhibiting the enzymes that build these cross-links
4. This means that penicillin is only active against bacteria while they are growing
   - Some bacteria are not sensitive to particularly antibiotics e.g. penicillin against M. tuberculosis and even among the types of bacteria that were killed by penicillin there were certain strains that were not affected and these strains had become resistant to antibiotics

Question 44

What happens when newly formed bacterial cell is growing?

Answer 44

1. When a newly formed bacterial cell is growing, it secretes enzymes called autolysis, which make little holes in its cell wall
2. These little holes allow the wall to stretch so that new peptidoglycan chains can link together
3. Penicillin prevents the peptidoglycan chains from linking up, but the autolysins keep making new holes
4. The cell wall therefore becomes progressively weaker and bacteria live in water environments and take up water by osmosis
5. When they are weakened, the cell walls cannot withstand the pressure potential exerted on them by the cell contents and the cells burst
   - This explains why penicillin does not affect human cells as our cells do not have walls

Question 45

Why do antibiotics not affect viruses?

Answer 45

1. Viruses do not have cells, let alone cell walls
2. Viruses do not have the targets and for example when a virus replicates, it uses the host’s cells mechanisms for transcription and translation and antibiotics do not bind to the proteins that host cells use in these processes
3. Eukaryotic cells have proteins that are different from those in bacteria so they are unaffected by such antibiotics
4. Other drugs, called antivirals, are used to control viral infections and there are fewer antivirals that there are antibiotics

Question 46

Why does penicillin have no effect on M. Tuberculosis?

Answer 46

• The thick cell wall of this bacterium is not very permeable and because the bacterium has the gene that codes for an enzyme that catalysis the breakdown of penicillin
• Proteins in the membrane fo other species of bacteria can inactivation antibiotics so they have no effect; bacterial membranes also have proteins that pump out antibiotics if they enter the cytoplasm and in some cases, the antibiotics simply cannot bind to the intended site of action

Question 47

What is it called when bacteria are sensitive to an antibiotic?

Answer 47

• Bacteria sensitive to an antibiotic are described as being susceptible to that antibiotic
• They may become resistant if they gain a gene coding for a protein that protects them from the antibiotic

Question 48

How is soil bacteria resistant?

Answer 48

1. Soil bacteria have many resistance mechanisms as they grow in an environment where there are many molecules that interfere with their metabolism and these resistance mechanisms are very similar to those found in pathogenic bacteria
2. Before the introduction of antibiotics, enzymes known as beta-lactamases were not common among pathogenic bacteria
3. The genes for these enzymes have spread into many different forms of bacteria and it is believed that they have cone from soil bacteria

Question 49

How does penicillin affect soil bacteria?

Answer 49

1. Penicillin has a structure that can be broken down by Beta-lacatamse (penicillinase) enzymes
2. Pathogenic bacteria that have become resistant to penicillin have often done so excuse they have acquired the genes that code for these enzymes

Question 50

How can antibiotic resistance arise through mutation?

Answer 50

1. Antibiotic resistance can arise when an existing gene within the bacterial genome changes spontaneously to give rise to a nucleotide sequence that codes for a slightly different protein that is not affected by the antibiotic
2. This change in DNA is a mutation
3. When someone takes penicillin to treat a bacterial infection, bacteria that are susceptible to penicillin will die and in most cases, if the dose is followed correctly, this will be the entire population of the disease-causing bacteria
4. However if the dose is not followed, perhaps because people stop taking the penicillin when they feel better as the symptoms disappear, then some susceptible bacteria sire and if any mutations occur these might confer resistance
5. The next time there is an infection with this strain of bacteria, penicillin may not be effective

Question 51

Why is a mutant gene important for bacteria?

Answer 51

1. Bacteria only have one copy of each gene, sine they only have a single loop of double stranded DNA
2. This means that a mutant gene will have an immediate effect on any bacterium possessing it
3. These individuals will have a tremendous advantage as bacteria without this mutant gene will be killed, while those bacteria resistant to penicillin with survive and reproduce

Question 52

How do bacteria reproduce?

Answer 52

1. Bacteria reproduce asexually by binary fission
2. The DNA in the bacterial chromosome is replicated and the cell divides into two with each daughter cell receiving a copy of the chromosome
3. This happens very rapidly in ideal conditions, it might produce ten thousand million descendants within 24 hours
4. A large population of a penicillin resistant satin of bacteria, would result
5. This method of spreading antibiotic resistance in a population of bacteria is called vertical transmission

Question 53

What is horizontal transmission?

Answer 53

1. Genes for antibiotic resistance often occur on plasmids which are small loops of double-stranded DNA
2. Plasmids are quite frequently transferred from one bacteria to another, bene between different species
3. This happens during conjugation when a tube forms between two bacteria to allow the movement of DNA
4. During conjugation, plasmids are transferred from a donor bacterium to a recipient
5. Transfer of part of the DNA form the bacterial chromosome also occurs in the same way, this method of transmission is horizontal transmission
6. Thus it is possible for resistance to a particular antibiotic to arise in one species of bacterium and be passed on to another

Question 54

What happens when we misuse antibiotics?

Answer 54

1. The more we misuse antibiotics, the greater the selection pressure we exert on bacteria to evolve resistance to them
2. Antibiotic-reisstanct strains of bacteria and continually appearing
3. Antibiotic-reisatnt infection increase the risk of death and are often associated with long stays in hospital and sometimes serious complications
   - There us a constant race to find new antibiotics as resistant strains keep arising

Question 55

In what circumstances does antibiotic resistance arise?

Answer 55

1. Where there is widespread use in antibiotics, such as in hospitals or on farms, resistance quickly spreads among different species of bacteria
2. Resistance may first appear in a non-pathogenic bacterium, but then be passed to a pathogenic species
3. Bacteria living where there is widespread use of antibiotics may have plasmids carrying resistance genes for several different antibiotics, giving multiple resistance
4. This presents major problems for doctors
   - For example, methicillin-resistant Staphylococcus aureus (MRSA) has become a problem in hospitals around ht work and in prisons in the USA and it is now also infects people in the general population
   - MRSA caused dangerous infections after surfer, which were mostly controlled by vancomycin, an antibiotic often used as a last resort for treating infections when everything else has failed, so as to lessen the chance of the development of more such resistant organisms
   - Then another bacterium common in hospitals, Enterococcus faecalis, developed resistance to vancomycin and this resistant passed to S. aureus

Question 56

How do you chose which antibiotic to use?

Answer 56

1. Antibiotics should be chosen carefully, testing antibiotics against the strain of bacterium isolated from people ensure the the most effective antibiotic can be used in treatment
2. As fast as we develop new antibiotics, bacteria seem to develop resistance to them. It follows from this that there is a constant search for new antibiotics, especially ones that work in a completely different way from this currently in use
3. Fortunately, a bacterium resistant to a particular antibiotic may not be resistant to that a antibiotic with a slightly altered chemical structure
4. Chemists can make such semi-synthetic antibiotics to extend the range available, however many experts believe that we will not be able to keep ups and that soon there will be no antibiotics left to treat disease and this is fast becoming the case with gonorrhoea, a STI

Question 57

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

Answer 57

1. Using antibiotics only when appropriate and necessary; not prescribing them for viral infections
2. Reducing the number of countries in which antibiotics are sold without a doctor’s prescription
3. Avoiding the use of so-called wide-spectrum antibiotics and using instead an antibiotic specific to the infection (known as narrow spectrum)
4. Making sure that patients complete their course of medication
5. Making sure that patients do not keep unused antibiotics for self-medication in the future
6. Changing the type of antibiotics prescribed for certain diseases so that the same antibiotic is not always preceded for the same disease
7. Avoiding using antibiotics in farming to prevent, rather than cure, infections

Question 58

What is the fact file for Cholera?

Answer 58

1. Pathogen: Vibrio Cholerae
2. Methods of Transmission: food-borne, water-borne
3. Global Distribution: Asia, Africa, Latin America
4. Incubation Period: two hours to five days
5. Site of action of pathogen: wall of small intestine
6. Clinical features: severe diarrhoea (‘rice water’), loss of water and salts, dehydration, weakness

Question 59

How is measles transmitted?

Answer 59

Infected person sneezes and uninflected person inhales

Question 60

What is the danger of measles?

Answer 60

1. Measles is a major disease in developing countries
2. Mass vaccination programme
3. Few cases in developed countries (usually if so from in someone entering country infected with disease that they caught elsewhere) and in outbreaks can spread rapidly so children should be vaccinated and adults who were not vaccinated and did not have empales as a child are at risks of severe complication in epidemics

Question 61

Describe HIV

Answer 61

• Retrovirus (RNA not DNA) and the viral DNA converted back into DNA once in host to be incorporated into human chomtomses
• Virus infects and destroys body’s immune system cells such as helper T cells
• As body canopy defect allow a range of pathogen to cause a variety of opportunistic infections
• AIDS is not a diseases it is a collection of these opportunistic diseases associated with the immunodeficiency caused by HIV
• Since HIV is an infective agent, AID is called acquired immunodeficiency to distinguish it from other type e.g. an inherited form
• Slow virus and after infection may not be any symptoms until years later
• Flu like symptoms may be HIV positive but not have AIDS
• Infections (oral thrush and form of pneuonomia) can opportunistically develop to create AIDS
• In developing countries usually dies within 12 hours of contracting this form of pnuenomia but now can be managed much better and drugs prescribed to prevent disease developing
• Immune system less effective at finding and destroying cancers

Question 62

Why is HIV an issue for developing countries?

Answer 62

1. Makes people more vulnerable to existing diseases such as malnutrition TB and malaria
2. Most economically productive age gap also sexually active is drained
3. Expensive for government to purchase drugs

Question 63

How is HIV treated?

Answer 63

1. No cure for AIDS and no vaccine for HIV
2. Drug therapy can slow down onset of AIDS
   - But drugs expensive and side effects
3. With combination of drugs prevent replication of virus inside host cells and so can prolong life
4. Course of Combination therapy must be followed strictly or can become susceptible to strains of HIV that have developed resistance to the drugs

Question 64

How do the drugs for HIV work?

Answer 64

• Similar to DNA nucleotides
• E.G binds to viral enzyme reverse transcriptase and blocks its action and stops replication of the viral generic material and leads to increase in persons lympotcytes

Question 65

How is cholera transmitted from an infected person to an uninfected person?

Answer 65

1. Infected person with infected feaces in water

2. Uninfected person drinking contaminated water

Question 66

How can control spread of cholera?

Answer 66

1. Purified water supply
2. Sewage treatment
3. Break transmission cycle

Question 67

Why is lung cancer sometimes referred to as a lifestyle disease?

Answer 67

• Mainly linked to habits of life

- Result of choices made by person e.g smoking

Question 68

Why could there be a rise in measles cases?

Answer 68

1. Infected people retuning from countries where measles occurs
2. Unvaccinated people retiring from travel abroad
3. Reduction in vaccination rates
4. Percentage cover too low
5. Change in reporting pattern
6. Existing vaccine no longer effective