Non Bacterial Pathogens

Question 1

Why are viral infections often specific to particular tissues?

Answer 1

Due to the presence or absence of antigenic markers of the surface of host cells. Each type of cell has its own markers and each type of virus can only bind to particular antigens on the host cell. The presence or absence of these antigens can effect the vulnerability of whole groups of living organisms to attack by viruses

Question 2

Why does the flu cause huge epidemics and sometime even extensive pandemics?

Answer 2

Because the virus mutates frequently so it can overcome the immune response of the body

Question 3

What is an epidemic?

Answer 3

When a higher than average number of people are infected with a disease in a particular area or country

Question 4

Why is a pandemic?

Answer 4

When a higher than average number of people are infected with a disease across a number of countries

Question 5

What are three major strains of the influenza virus and which in particular causes severe disease?

Answer 5

Influenza A, B and C

A often causes a severe disease

Question 6

What are modes of transmission?

Answer 6

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

Question 7

What are the main modes of transmission of the flu?

Answer 7

• largely linked to droplet infection
• transmitted by direct contact with animal droppings or with virus filled mucous from tbe nose
• surfaces which have been contaminated by the virus
• skin contact with viral filled mucous

Question 8

What is zoonotic infection?

Answer 8

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

Question 9

What is the mode of infection?

Answer 9

The way a pathogen causes infection

Question 10

What is the mode of infection of the flu virus?

Answer 10

To infect the ciliated epithelial cells of the respiratory system. The viral RNA reaches the nucleus of the host cell and takes over the biochemistry producing new viral particles. Eventually the cell lyses, releasing more viruses amd dying in the process. The reaction of the body to the lysis of the cell causes the symptoms of disease.

Question 11

Why are many of the deaths associated with the flu from severe secondary bacterial imfections on top of the original infection?

Answer 11

Because the death of the ciliated epithelial cells of the trachea and bronchi leaves the airway open to infection

Question 12

Who is most likely to die of flu?

Answer 12

The young who have no prior immunity, the old who have weaked immune systems and are very vulnerable to secondary infections and anyone that is prone to asthma or heart disease

Question 13

What does the pathogenic effect of an microorganism describe?

Answer 13

The symptoms of disease it causes

Question 14

What are the symptoms of flu?

Answer 14

Fever, shivering, sweating, feeling very unwell and unable to do anything, loss of appetite, aching muscles, painful joints, severe headaches, sore throats, shortness of breath

Question 15

What is best to do when you have the flu?

Answer 15

Rest, stay warm, have plenty of fluids to avoid dehydration and mild painkillers

Question 16

What is best to do when you have the flu?

Answer 16

Rest, stay warm, have plenty of fluids to avoid dehydration and mild painkillers

Question 17

Is there a vaccine virus?

Answer 17

Yes but it has to be continually modified due to the changing nature of the flu virus

Question 18

Give some features of fungi

Answer 18

• they have cell ealls made of chitin and glucans
• yeasts are single-celled fungi but mant fungi grow as hyphae (long thread like filaments) and reproduce using spores
• fungi cannot photosynthesise, they are all saprophytes of parasites
• many live in mutalistic symbiotic relationships

Question 19

Despite the fact the few human diseases a43 caused by fungi why do fungal diseases have an enourmous impact on human existence?

Answer 19

Because many of the plant diseases that threaten human food security around the world are caused by fungal infections

Question 20

What is puccunua graminis/ stem rust fungus?

Answer 20

The fungus that causes wheat stem and barley rust

Question 21

Puccinia graminis is a parasitic fungus. What does this mean?

Answer 21

It feeds on the living tissue of its host

Question 22

What have been the different hosts of puccinia graminis?

Answer 22

Cereal plants such as wheat and barley and berberis, a genus of shrub which grow freely in temperate and subtropical regions

Question 23

How many different types of spores does puccinia graminis form?

Answer 23

5

Question 24

How is puccinia graminis transmitted?

Answer 24

When spores from either infected wheat plants or infected Berberis are carried to young crop plants by the wind. They pay become infected from parts of infected plants left in the soil after harvest, feom Berberis bushes growing near the field or from infected crops growing thousands of miles away

Question 25

What happens when spores of puccinia graminis land on the host plant?

Answer 25

They need water to germinate. Then a thread like hypha emerges from the spore and penetrates one of the stomata of the leaves or stem. This gives the fungus a way into the internal tissues of the plant. The hypha secretes enzymes such as cellulase which digest the plant cells and the nutrients are then absorbed into the fungus. The hyphae branch out to form a myceliym that feeds and grows, hidden in the stem or leaves of the healthy looking plant

Question 26

Under what conditions does stem rust fungus grow best?

Answer 26

When it has hot days (25-30°c) and mild nights (15-20°c) and wet leaves from either rain, dew or irrigation. The spore needs the water to germinate

Question 27

What happens 7-15 days after the plant has become infected by stem rust fungus?

Answer 27

Rusty - red pustules break through the epidermis of the stem or leaf. These contain up to 100 000 rusty-red spores. This stage can be repeated many times during the growth of the wheat crop until finally black spores which can survive over winter are formed and the crop becomes blackened

Question 28

What are the ways puccinia graminis affects the plant?

Answer 28

• it absorbs nutrients from the plant, reducing the yield of the grain
• the pustules break the epidermis, making it more difficult for the plant to control transpiration. This results in less efficient metabolism, makes the plant more likely to dry out and gives entry to other pathogens.
• the mycelium grows into the vascular tissue, absorbing water and nutrients and interfering with the supply to the growing wheat grains
• it weakens the stem so the plants are more likely to fall over in heavy winds and rain, so they cannot be harvested effectively

Question 29

Why do fertilisers help puccinia graminis thrive?

Answer 29

Because high nitrate levels favour the fungus

Question 30

What are the ways in which puccinia graminis can be controlled or reduced?

Answer 30

• bigger spaces between plants to reduce moisture and increase distance for spore to travel
• reducing the application of fertiliser
• remove any wild Berberis
• fungicides will control the growth of stem rust but cost of this control measure is prohibitive - the crop becomes unecenomic to produce

Question 31

Give features of the protozoa

Answer 31

• group of unicellular organisms
• part of the kingdom Protista
• many live singly but some exist in huge colonies
• feed in every way
• reproduce sexually and asexually

Question 32

What are plasmodium spp.?

Answer 32

The parasitic protozoa that cause malaria. They have a life cycle split between two different hosts: female Anopheles mosquitoes and people

Question 33

Why does malaria have a massive economic impact on the countries where it is present?

Answer 33

because many millions of adults are weakened by the disease which affects their ability to work

Question 34

What are vectors?

Answer 34

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

Question 35

What are anopheles mosquitoes?

Answer 35

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

Question 36

When is plasmodium spp. transmitted to the human host?

Answer 36

When an infected mosquito takes a blood meal. Femalw anopheles mosquitoes need two blood meals to provide them with plenty of protein for their developing eggs. The female mosquito has piercing mouthparts that go through human skin and her saliva containd an anticoagulant that prevents blood clotting as it passes up her body. It is during the blood meal that transmission occurs in both directions. If a person has malaria the gametocytes (one stage of the parasite lige cycle) pass into the mosquito ready for the next stage of their life cycle. When an infected mosquito pumps saliva into her host before the blood meal the spirozoutes (another stage of the parasite life cycle) pass directly into the human blood stream

Question 37

What happens when the malaria parasite enters the blood of the human host?

Answer 37

It travels to the liver. It remains in the liver for a time before releasing the next stage of its life cycle into the blood. At this stage the parasite invades red blood cells and reproduces asexually. At regular intervals of about 48-72 hours the parasites burst out of the red blood cells, destroying them before moving on to affect more. This continues in cycles. Some of the parasites become gametocytes and are taken into a female mosquito during a blood meal where they complete their life cycle

Question 38

What is the pathogenic effect of the malaria?

Answer 38

• when the malaria parasites burst out of the red blood cells they cause the flu like symptoms. The fever, sweating, shaking, muscle pain and headaches that result are linked to the response of the body to the lysis of the blood cells
• there is long tern damage to the liver and a steady reduction in the number of blood cells and this leads to weakness, severe anaemia and eventually death
• people who are affected by diseases such as HIV/AIDS are particularly badly affected

Question 39

How is the plasmodium parasites lifestyle well adapted to ensure it’s survival?

Answer 39

• It can take advantage of two different hosts and can survive in a dormant form for a long time in either
• when the parasite is in the human body it spends most of the time inside either liver cells or red blood cells so it is hidden from the immune system
• althought it eventually kills the human host ut takes a long time providing many more opportunities for it to be passed on to the mosquito

Question 40

Malaria is an endemic disease. What are the problems treating an endemic disease raises?

Answer 40

• the disease is often widespread so the eradication programme covers a large area
• the pathogen is widespread in the environment so it can be particularly difficult to track down and remove sources of infection
• it requires the cooperation of large population numbers to eradicate a pathogen or vector, protect a community by vaccination or deliver and use effective drugs
• it costs lot of moneg to treat or control endemic diseases becayse they involve many areas

Question 41

How is malaria treated?

Answer 41

The drugs Quibine, chloroquinine and arteminism can kill the parasite and prevent it from recurring but are only effective if given very soon after infection. The parasite is now developing resistance to drugs such as chlorquinine so the advice by the WHO is to take a combination of drugs if infected

Question 42

Why is it hard to make a vaccine for malaria?

Answer 42

• the malarial parasite spends its time hidden away from the immune system inside body celle
• it has many different stages in it’s life cycle
• the antigens on it’s surface change regularly making it less likely to be recognised by the immune system

Question 43

What do the simplest and most effective ways of controlling malaria involve?

Answer 43

Controlling the mosquito that transmits the disease

Question 44

How can avoiding contact with mosquitoes be achieved?

Answer 44

• Have mosquito screens on doors and windows
• sleep under mosquito nets - preferably nets impregnated with insecticide
• use insect repellents and insecticides in the home and on people
• wear clothes with long sleeves and legs to cover up as much skin as possible

Question 45

What are the control methods to prevent mosquitoes from breeding?

Answer 45

• mosquitoes will lay eggs in any standing water. Communities should be encouraged to remove possible breeding sites by removing rubbish and disposing of it properly
• proper duspisal of sewage - managing human waste so foul water is not left standing for mosquitoes to breed in
• biological control - seeding local water supplies with organisms that feed on mosquito larvae
• chemical co trol - spraying local water sources with pesticides that kill the eggs and the larvae

Question 46

What are the issues raised wuth methods used to control endemic diseases?

Answer 46

• social implications: people have to be persuaded to change their behaviour to reduce endemic disease
• economic implications: the treatment, control and prevention of endemic diseases all involve a lot of economic investment. People have to decide whether the cost of a particular course of action is worth the gain. May of the countries affected by malaria are very poor and aid agencies have to weigh up providing mosquito nets for example against providing food and antibiotics
• ethucal implications: the autonomy or choices of a few people may be sacrificed for the good of many. Some peiple have reservations about vaccinations. There are always issues of informed consent in medical trials, especially in different countries and cultures. The potential benefits and risks must be clearly explained. Actions such as spraying insecticide on water to kill malaria mosquitoes will also affect other species of fish, insect and birds. This needs to be discussed and determined by local people

Question 47

How does the scientific community play an important role in the validation of different approaches to the control of malaria?

Answer 47

Data on different aspects of maaria are used by the WHO to produce international guidelines for all countries

Question 48

What do the international guidelines on aspects of malaria control based on scientific evidence include?

Answer 48

• diagnosis: evidence shows that accurate diagnosis using microscopes to see the protozoa in the blood avoids treating diseases which cause similar symptoms with expensive antimalarial drugs. This saves money and helps reduce the build up of resistance. Guidelines are created to help people use microscopes accurately
• prevention: evidence shows that insectice impegnated mosquito nets can reduce malaria cases by up to 50 % in areas where it’s common. So the use of long lasting insecticide treated nets which give protection for yo to 3 years is being introduced in as many malaria infected countries as possible. Evidence shows that spraying the homes with insecticide significantly reduces the risk of malarial infection too
• treatment: evidence shows that although quinine and chloroquinine are becoming increasingly ineffective to the resistance parasites when combined with arteminism they provide a very effective treatment. The guidelines recommend that only cases of malaria which are diagnosed under a microscope of blood smears are treated with anti-malarial drugs and that those causes are all treated with different combinations of antimalarial drugs