Topic 6.2 Non-bacterial pathogens

Question 1

What adaptions of malaria mean that an effective vaccine has not been made yet?

Answer 1

• parasite spends a lot of time hidden from immune system in bodily cells
• antigens on its surface change frequently (hard for immune system to recognise them)

Question 2

What causes antigen variability?

Answer 2

• random genetic mutation changes DNA base sequence
• results in different sequences of codons on mRNA
• different primary structure of antigen = H-bonds, ionic bonds, disulfide bridges form in different places in tertiary structure
• different shape of antigen

Question 3

Explain how antigen variability affects the incidence of dieases?

Answer 3

• memory cells no longer complimentary to antigen (individual not immune and can catch the disease more than once/ can’t recognise pathogen e.g. HIV)
• many varieties of a pathogen so difficult to develop a vaccine containing all antigen types

Question 4

Why is it so difficult to control the spread of antibiotic resistant bacteria?

Answer 4

horizontal conjunction transfers plasmids with resistance allele from one bacterium to another rapidly

Question 5

Define modes of transmission

Answer 5

the different ways a pathogen is spread from one host to another

Question 6

What’s a zoonotic infection?

Answer 6

an infection in a person caused by a pathogen that can cross the species barrier from other animals

Question 7

Define the mode of infection

Answer 7

the way a pathogen causes infection

Question 8

What’s the pathogenic effect of a microorganism?

Answer 8

the symptoms of disease it causes

Question 9

Why do fungal pathogens have a large effect on humans even if they rarely cause human diseases?

Answer 9

many plant diseases that threaten human food security are caused by fungal infections

Question 10

Give another name for stem rust fungus

Answer 10

Puccinia graminis

Question 11

What are the modes of transmission of stem rust fungus?

Answer 11

• wind carries spores from infected plants

- infected plant fragments in the soil

Question 12

State the mode of infection for stem rust fungus

Answer 12

• spores germinate in water on plant
• hyphae enter through stomata of the leaves
• enzymes like cellulase digest the plant cells (secreted from the hyphae)
• nutrients are then absorbed into the fungus
• hyphae branch to form mycelium that feed and grows, hidden in the plant

Question 13

Define hyphae (single-hypha)

Answer 13

thread-like fungal structures that are single units of the mycelium

Question 14

Define mycelium

Answer 14

a fungal body made up of a mass of thread-like hyphae

Question 15

What are the pathogenic effects of stem rust fungus?

Answer 15

• nutrients lost to the fungus
• pustules break the epidermis so it is difficult to control transpiration
• stem weakened and may collapse in the wind (cannot be harvested effectively)
• mycelium grows into vascular tissue, absorbing water and nutrients

Question 16

In what ways does modern farming encourage the growth of stem rust fungus?

Answer 16

• high nitrate levels favour the fungus (fertilisers)
• irrigate regularly which provides water for stem rust spores to germinate
• not disturbing the soil means bits of infected plants are more likely to be on top of the plant to infect the new crop

Question 17

How can stem rust fungus be controlled and reduced?

Answer 17

• bigger spaces in between plants to reduce moisture and increase distance for spore to travel
• reducing application of fertilisers
• use of earlier-maturing crops which avoid time of max spread
• remove any wild Berberis so part of lifecycle is interrupted
• fungicides control growth of stem rust but expensive

Question 18

What are the optimum conditions for stem rust fungus?

Answer 18

• hot days (25-30 degrees)
• mild nights (15-20 degrees)
• wet leaves (from wither rain, dew or irrigation)

Question 19

What type of pathogen is influenza?

Answer 19

viral pathogen

Question 20

What are the modes of transmission for influenza?

Answer 20

• droplet infection
• direct contact with animal droppings
• direct contact with virus-filled mucus
• direct contact with surfaces contaminated with virus

Question 21

State the mode of infection for influenza

Answer 21

• infects ciliated epithelial cells of the lungs
• viral RNA takes over the biochemistry of the cell
• cell produces new virus particles
• the cell lyses, releases viruses and dies

Question 22

What are the pathogenic effects of influenza?

Answer 22

• fever, shivering, sweating
• loss of appetite
• severe headaches
• shortness of breath
• sore throats
• disease lasts for around 5-7 days
• lungs and heart can be severely affected
• secondary bacterial infection may occur where epithelial tissue is damaged
• full recovery 6-12 weeks

Question 23

Why does having the flu make people more susceptible to secondary infections?

Answer 23

the death of ciliated epithelial cells of the trachea and bronchi leave the airways open to infection (secondary bacterial infection)

Question 24

What is the malaria parasite?

Answer 24

Plasmodium spp.

Question 25

Define Plasmodium spp.

Answer 25

the parasitic protozoa that cause malaria. they have a life cycle split between 2 different hosts, female Anopheles mosquitoes and people

Question 26

Define vectors

Answer 26

living organisms or environmental factors that transmit infection from one host to another

Question 27

Define Anopheles mosquitoes

Answer 27

the type of mosquitoes that carry the malarial parasite from one host to another

Question 28

How is malaria/Plasmodium spp. transmitted?

Answer 28

• by a mosquito vector

- transmission to human host occurs when an infected mosquito takes a blood meal

Question 29

State the stages of the life cycle of the malaria parasite

Answer 29

1) Malarial parasite transmitted to person from infected Anopheles mosquito
2) Parasites travel to liver
3) Next stage of malarial parasite released from the liver into the blood where they invade the red blood cells
4) Parasites reproduce asexually and burst out of red blood cells, destroying them, every 48-72 hours
5) Malarial parasite transmitted to mosquito taking a blood meal where they go through more life cycle stages before being transmitted to another person

Question 30

How is influenza treated?

Answer 30

• antiviral medication
• antibiotics to treat secondary bacterial infection
• management of symptoms e.g. painkillers

Question 31

What are the pathogenic effects of malaria?

Answer 31

• malaria parasites burst out of the red blood cells every 2-3 days causing fever, sweating, shaking, muscle pains and headaches
• liver damage and anaemia (due to lack of red blood cells)

Question 32

Define an endemic disease

Answer 32

one in which the active disease, or the pathogen that causes the disease, is constantly present in a particular country or area

Question 33

Why are endemic diseases difficult to control?

Answer 33

• disease is often widespread, so any eradication programme covers a large area
• pathogen is widespread in the environment so difficult to track down and remove sources of infection
• requires cooperation from large numbers (to eradicate pathogen/vector, vaccinations or effective drugs)
• very expensive to provide treatment

Question 34

What are the treatments for malaria?

Answer 34

• drug treatment: quinine, chloroquinine and artemisinin can kill parasite + prevent it recurring but only effective if given very soon after infection
• WHO advice is to take a combination of drugs including artemisinin to avoid resistance problems

Question 35

What are the ways to avoid contact with mosquitoes?

Answer 35

• mosquito screens on doors and windows
• mosquito nets impregnated with insecticide
• insect repellents + insecticides in the home and on people
• long clothing to cover skin

Question 36

What control measures can be used to prevent mosquitoes breeding?

Answer 36

• remove standing water and sewage so that mosquitoes won’t lay their eggs
• biological control by introducing predators that feed on mosquito larvae
• chemical control by spraying water sources with pesticides that kill the eggs and larvae

Question 37

State the ethical implications of malaria control methods

Answer 37

• reservations about safety of vaccinations
• informed consent difficult where understanding of medical trials is poor
• spraying mosquitoes with insecticides will affect other organisms
• money spent on developing effective vaccine could be spent on education or preventing famine

Question 38

State the social implications of malaria control methods

Answer 38

• people have to be persuaded to change their behaviour e.g. sleeping under mosquito nets
• social changes to reduce infection are very difficult to bring about
• vaccines need to become acceptable

Question 39

State the economic implications of malaria control methods

Answer 39

• treatment, control and prevention of endemic disease is very expensive
• many affected countries are poor
• malnutrition may be more of a threat than malaria which results in difficulty choosing where to place resources

Question 40

What guidelines do WHO provide based on scientific evidence for malaria control?

Answer 40

• diagnosis: accurate diagnosis, using microscopes, avoids inappropriate use of expensive drugs (for diseases that cause similar symptoms)
• insecticide-impregnated mosquito nets can reduce malaria cases by up to 50%
• spraying with insecticide significantly reduces the risk of infection
• using drugs like quinine in combination with artemisinin provides very effective treatment