Chapter 10.1

Question 1

infectious diseases def and example

Answer 1

These are diseases caused by organisms known as pathogens. They are sometimes called communicable diseases as they are passed from the infected to uninfected people (they are transmissible.).

-Some also affect animals and are passed from animals to humans -Examples: Cholera, Malaria, HIV/AIDS, Tubercutosis (TB)

Question 2

Non-infectious diseases def and example

Answer 2

• these are long-term, degenerative diseases that are not caused by pathogens,
• Examples include diseases of the gas exchange and cardiovascular systems, inherited or genetic diseases caused by malnutrition and mental diseases examples: lung cancer, Chronic obstructive pulmonary disease, Sickle cell anemia and Cystic fibrosis

Question 3

Common Pathogens & Their Diseases

Answer 3

• A number of infectious diseases of worldwide importance are: cholera, malaria, tuberculosis (TB), HIV/AIDS, smallpox and measles
• Worldwide the number of people infected with these diseases remains very high and these diseases pose serious public health problems now and for the foreseeable future
• To control a disease, it is very important to know what causes it (known as the causative agent or pathogen)

Question 4

Cholera, malaria, TB & HIV/AIDS summary table

Answer 4

Question 5

Transmission of cholera

Answer 5

• Cholera is caused by the bacterium Vibrio cholerae
• The disease is water-borne (the bacterium lives in water) and food-borne
• This means the disease occurs where people do not have access to proper sanitation (clean water supply) and uncontaminated food
• Cholera can be transmitted when people; bath or wash in contaminated water, drink contaminated water or eat food exposed to contaminated water
• Infected people egest large numbers of the bacteria in their faeces

Question 6

Transmission of measles

Answer 6

• Measles is caused by a highly infectious virus Measles morbillivirus
• The virus is transmitted via the millions of tiny droplets discharged from the nose and mouth of an infected person when they cough or sneeze
• Measles is therefore caught when someone breathes in these droplets or touches a surface contaminated by them (the virus can survive several hours on a surface)
• Infected individuals are contagious from the onset of symptoms until about 4 days after the rash first appears

Question 7

Transmission of malaria

Answer 7

• Malaria is caused by one of four species of the protoctist Plasmodium
• These protoctists are transmitted to humans by an insect vector:
• Female Anopheles mosquitoes feed on human blood to obtain the protein they need to develop their eggs
• If the person they bite is infected with Plasmodium, the mosquito will take up some of the pathogen with the blood meal
• When feeding on the next human, Plasmodium pass from the mosquito to the new human’s blood
• Malaria may also be transmitted during blood transfusion and when unsterile needles are re-used
• Plasmodium can also pass from mother to child across the placenta

Question 8

Transmission of HIV/AIDS

Answer 8

• Human Immunodeficiency Virus is a retrovirus
• The HIV virus is not transmitted by a vector (unlike in malaria)
• The virus is unable to survive outside of the human body
• The virus is spread by intimate human contact and can only be transmitted by direct exchange of body fluids
• This means HIV can be transmitted in the following ways:
• sexual intercourse
• blood donation
• sharing of needles used by intravenous drug users
• from mother to child across the placenta
• mixing of blood between mother and child during birth
• from mother to child through breast milk

Question 9

Cholera occurs when people do not have access to

Answer 9

effective sanitation facilities and access to clean water

Question 10

Prevention of cholera can occur through:

Answer 10

• Providing adequate sewage treatment infrastructure
• The provision of clean, piped water that has been chlorinated to kill bacteria (as this occurs in developed countries cholera is very rare among them)
• Vaccination programmes in areas where cholera is endemic

Question 11

Cholera can be controlled by:

Answer 11

• Ready access to treatments such as oral rehydration therapy (a solution containing glucose, salts and water)
• Monitoring programmes by the World Health Organisation (WHO)
• Using antibiotics in severe cases (to reduce the risk of antibiotic resistance)

Question 12

It is difficult to prevent and control cholera because of:

Answer 12

• The fast-growing cities in developing countries not having the appropriate infrastructure.
• They have limited funds for large-scale projects such as the provision of drainage systems, sewage treatment facilities and clean water supplies
• Humanitarian crises (eg. displacement of people due to wars or natural disasters) which can cause the destruction of sanitation infrastructure and/or the provision of poor sanitation facilities in overcrowded temporary housing
• The use of raw human sewage to irrigate crops

Question 13

Prevention & control of measles

Answer 13

• Measles is highly contagious but can be effectively prevented by individuals being vaccinated with the measles, mumps and rubella (MMR) vaccine in early childhood
• Two doses of the vaccine are given – one at around 13 months of age and the second between the ages of 3 and 4
• The uptake of the MMR vaccine has fallen over the last two decades as a result of a now-discredited study that the MMR vaccine is linked to autism
• There is overwhelming evidence that there is no link between the vaccine and autism
• In most individuals, measles is a non-serious infection but it can cause complications in some (leading to pneumonia and brain encephalitis)

Question 14

The three main methods for reducing malaria are:

Answer 14

• Reducing the number of Anopheles mosquitoes in an area
• Reducing the chance of being bitten by these mosquitoes
• Using drugs to prevent Plasmodium infecting humans

Question 15

As Anopheles mosquitoes (specifically female mosquitoes) are the vectors that transmit Plasmodium between human hosts, the transmission cycle of malaria can be broken (or at least reduced) by reducing the number of these mosquitoes. This can be achieved by:

Answer 15

• Spraying living areas with insecticides, such as DDT
• Spreading oil over the surfaces of water bodies that the mosquitoes breed
• Draining marshes and other unnecessary bodies of water
• Ensuring ponds and irrigation or drainage ditches are stocked with fish that feed on mosquito larvae
• Spraying these water bodies with a preparation containing the bacterium Bacillus thuringiensis, which kills mosquito larvae but is not toxic to other organisms

Question 16

Unfortunately, mosquitoes lay eggs in even very small…..

Answer 16

puddles and pools of water and therefore it is practically impossible to control all breeding sites using the methods listed above

Question 17

Prophylactic (preventative) drugs

Answer 17

• (eg. chloroquine, mefloquine) are taken before, during and after a visit to a location where malaria is prevalent.
• However, the use of these drugs has resulted in drug-resistant strains of Plasmodium or the drugs are expensive and have disagreeable side-effects
• One of the best ways to prevent malaria is to avoid being bitten in the first place. People in malarial zones should sleep under bed nets (which can also be soaked periodically in insecticide to increase effectiveness) and should try to avoid exposing their skin at dusk when mosquitoes are most active

Question 18

In the 1950s, the World Health Organisation (WHO) coordinated a worldwide eradication programme. Whilst malaria was eradicated from some countries, the programme was mainly unsuccessful because:

Answer 18

• Plasmodium became resistant to the drugs being used to try and control it
• Anopheles mosquitoes became resistant to DDT and other insecticides being used against them

Question 19

To control malaria governments, WHO and institutions (eg. universities) are focusing on:

Answer 19

• Working within health systems to improve diagnosis
• Improving the supply of effective drugs
• Using drugs in combination to reduce drug resistance
• Promoting appropriate methods to prevent transmission (e.g. use of biological controls to target the larvae and insecticide-treated bednets)

Question 20

Recent scientific advances regarding the control of malaria are

Answer 20

• Simple dipstick tests for diagnosing malaria – this means a diagnosis can be made much faster and does not require a laboratory
• The entire Plasmodium genome has been sequenced, which will help in the development of vaccines

Question 21

The process of contact tracing

Answer 21

(and the subsequent testing of those contacts for the bacterium) is an important method of controlling the spread of TB

-Contacts are screened for symptoms of TB infection, although the diagnosis can take up to two weeks

Question 22

The form of TB that can be transmitted between cattle and humans (caused by Mycobacterium bovis) can be prevented by:

Answer 22

• Routinely testing cattle for TB and destroying those that test positive
• Pasteurising milk (kills any TB-causing bacteria present in the milk)
• Ensuring meat is cooked properly

Question 23

Prevention for TB occurs through the use of the BCG vaccine (the only vaccine for TB)

Answer 23

The vaccine protects up to 70-80% of those who receive it, although its effectiveness decreases with age unless the person is exposed to TB

Question 24

TB is spread quickly from person to person when

Answer 24

droplets released by the coughing or sneezing of an infected person with the active form of the illness are inhaled by an uninfected person (the droplets contain the TB-causing bacterium Mycobacterium tuberculosis)

Question 25

Preventing the spread of HIV is very difficult, as the virus has a

Answer 25

long latent stage, which results in it being transmitted by people who have the virus but show no symptoms and do not know they are infected

-This occurs because the virus can change its surface proteins, making it difficult for the human immune system to recognise it and for a vaccine to be developed

Question 26

To prevent the transmission of HIV the following measures can occur:

Answer 26

• Blood donations can be screened for HIV and heat-treated to kill any viruses
• HIV-positive mothers and their babies can be treated with drugs (as HIV can be transmitted across the placenta, during birth and through breast milk
• Condoms, femidoms and dental dams can be used to decrease the infection risk during sexual intercourse and oral sex by forming a physical barrier between body and fluids
• Education programmes about how the virus is transmitted can be released into the community to encourage people to change their behaviours in order to protect themselves and others
• Intravenous drug users encouraged not to share needles

Question 27

Controlling HIV can occur by

Answer 27

• Contact tracing (and the subsequent testing of those contacts for the virus)
• Screening blood donations
• Public health measures widespread HIV testing of the population and education programmes
• Needle-exchange schemes have been set up in some places to exchange used needles for new, sterile ones -Encouraging high-risk groups (eg. male homosexuals, prostitutes, injecting drug users) to be tested -Using anti-retroviral drugs

Question 28

Factors affecting the distribution of malaria

Answer 28

• Malaria is caused by one of four species of the protoctist Plasmodium but these protoctists are transmitted to humans by an insect vector (female Anopheles mosquitoes)
• The Anopheles mosquitoes favour habitats that have high rainfall, high temperatures and high humidity
• This means malaria can occur where these mosquitoes are present and, as a result, is found throughout the tropics and sub-tropics (about 80% of cases are in Africa)
• The Anopheles mosquitoes found in Africa also have longer lifespans and prefer biting humans than animals
• There is evidence that there are an increasing number of malaria epidemics due to climatic and environmental changes that favour the spread of the Anopheles mosquitoes

Question 29

In the 1950s, the World Health Organisation (WHO) coordinated a worldwide eradication programme. Whilst malaria was eradicated from some countries, the programme was mainly unsuccessful because:

Answer 29

Plasmodium became resistant to the drugs being used to try and control it

-Anopheles mosquitoes became resistant to DDT and other insecticides being used against them

Question 30

Factors affecting the distribution of tuberculosis (TB)

Answer 30

• TB has a worldwide global distribution
• TB is spread quickly from person to person when droplets released by the coughing or sneezing of an infected person with the active form of the illness are inhaled by an uninfected person (the droplets contain the TB-causing bacterium Mycobacterium tuberculosis)
• TB, therefore, spreads more quickly among people living in overcrowded conditions
• People who sleep close together in large numbers are at a higher risk
• TB primarily affects the homeless and people who live in poor, substandard housing
• Some people may be infected with TB but not show symptoms. Whilst the bacteria is inactive there is no spread of the disease however if the person becomes infected with HIV (TB can be the first opportunistic infection for HIV-positive people) or is malnourished they can become infectious thus contributing to the spread
• High rates of TB can also be found in cities with populations of migrants from countries where TB is more common (eg. parts of London have much higher TB rates than the rest of the UK)

Question 31

Factors affecting the distribution of HIV/AIDS

Answer 31

• HIV/AIDS has a worldwide global distribution but is especially prevalent in sub-Saharan Africa and South-East Asia, mainly due to a lack of education about how the virus is transmitted and a lack of access to items that offer protection from the virus during sexual intercourse such as condoms and femidoms
• 70% of the world’s deaths from AIDS occur in Africa
• AIDS is widespread throughout sub-Sahara Africa and is a serious public health problem because HIV infection makes people more vulnerable to existing diseases such as malnutrition, TB and malaria, which are all prevalent there

Question 32

infectious diseases, estimated amounts of new people and deaths

Answer 32