Chapter 12-12.2- Animal and plant disease Flashcards
Why does plant disease threaten people?
Because when crop plants fail, people suffer. They may starve, economies may struggle and jobs are lost. Plant diseases threaten ecosystems too- entire species can be threatened.
Explain about the threat to the English oak trees
Oak trees- Quercus robur can live for centuries and are home to up to 284 species of insects.
As many as 324 different lichens have been identified on a single tree. Future generations, however may not see these trees in the countryside- they are under threat from a new disease.
Acute oak decline first appeared in the UK in the 1980s, having spread from continental Europe. It causes dark fluid to ooze from the bark, with a rapid decline in the tree and often death.
Scientists still don’t know exactly what the cause of this deadly tree disease is- which makes it very difficult to understand how to prevent it spreading.
Some of the evidence so far includes:
- The discovery of previously unknown bacteria in the tree which may play a role in the disease.
- Evidence of oak jewel beetle activity in infected trees- they may be important in disease development. For example, they may act as a vector or their presence may just be a coincidence.
A massive research project is currently under way involving DNA analysis of the microorganisms on infected and healthy oak trees, along with a careful study of the behaviour of the oak jewel beetle.
For now, the advice is to try and avoid spreading the disease by careful hygiene procedures for both people who work in oak woodlands and their machinery.
Plant diseases are caused by a range of pathogens. They include what?
Ring rot
Tobacco mosaic virus (TMV)
Potato blight
Black sigatoka
Explain the disease ring rot
A bacterial disease of potatoes, tomatoes, and aubergines caused by the Gram positive bacterium Clavibacter michiganensis.
It damages leaves, tubers and fruit. It can destroy up to 80% of the crop and there is no cure.
Once bacterial ring rot infects a field it cannot be used to grow potatoes again for at least 2 years.
Explain the disease tobacco mosaic virus (TMV)
A virus that infects tobacco plants and around 150 other species including tomatoes, peppers, cucumbers, petunias and delphiniums.
It damages leaves, flowers and fruit, stunting the growth and reducing yields, and can lead to an almost total crop loss. Resistant crops strains are available but there is no cure.
Explain the disease potato blight
also known as tomato blight and late blight.
Caused by the fungus- like protoctist oomycete, (Phytophthora infestans).
The hyphae penetrate host cells, destroying leaves, tubers and fruit, causing millions of pounds worth of crop damage each year.
There is no cure but resistant strains, careful management and chemical treatments can reduce infection risk.
Explain the disease black sigatoka
A banana disease caused by fungus (Mycosphaerella fijiensis) which attacks and destroys the leaves.
The hyphae penetrate and digest the cells, turning the leaves black.
If plants are infected it can cause a 50% reduction in yield.
Resistant strains are being developed- good husbandry and fungicide (a chemical that kills fungi) treatment can control the spread of the disease but there is no cure.
Explain about the link between banana disease and food security
Food security is one of the biggest issues globally.
In an ideal world everyone would consistently have a balanced diet provided in a sustainable way.
One of the main problems, however, for many people is getting enough to eat. If plant diseases threaten staple crops such as rice, maize, cassava, and bananas then they threaten food security and the survival of the population.
- Bananas are growing in over 130 countries where they are important both as a food crop and economically as a cash crop. they are the 4th most important crop in the developing world after rice, wheat and maize.
- In East Africa bananas (known as plantains) are the staple food for around 50% of the population. People eat around 400kg of bananas per year
- 90% of the bananas cultivated are produced on small farms and eaten locally. In recent years, as a result of Black Sigatoka there has been a 40% fall in banana yield.
- Around 10% of bananas are produced on big plantations for Western supermarkets. These are all from the same clone of a variety similar. Black sigatoka is invading these plantations too.
What is animal disease?
The diseases that affect animals- and in particular human beings- have a profound effect on human health and wellbeing- and on national economies.
Communicable diseases range from mild to fatal.
What are the example of communicable diseases in animals?
Tuberculosis (TB) Bacterial meningitis HIV/AIDS Influenza (flu) Malaria Ring worm Athlete's foot
Explain the communicable disease in animals- Tuberculosis (TB)
A bacterial disease of humans, cows, pigs, badgers, and deer commonly caused by Mycobacterium tuberculosis and M.bovis.
TB damages and destroys lung tissue and supresses the immune system, so the body is less able to fight off other diseases. Worldwide in 2012 around 8.6 million people had TB of which 1.3 million died.
The global rise of HIV/AIDS has had a big impact on the number of people also suffering from diseases such as TB infections.
In people TB is both curable (by antibiotics) and preventable (by improving living standards and vaccination).
How does TB affect animal populations?
TB affects animal pollutions. In 2013 almost 33000 UK cattle were destroyed because they were infected with bovine TB. There is clear evidence that TB is passed from wild animals such as badgers or possums to cattle.
This presents a problem as cattle can be tested and culled, but it is very difficult to prevent them becoming re-infected from wildlife, particularly when they are on pastures.
Scientists are still unsure how this wildlife infections can best be controlled. One method is to cull the wildlife source- in countries where this has been done, TB rates in cattle have fallen substantially, however it must be carried out carefully and thoroughly or it can lead to greater disease spread as animals are dispersed.
Some people, however, feel culling is not an acceptable approach and vaccination of either cattle other wild animals is a better route.
The test for TB cannot currently distinguish between an infected animal and a vaccinated animal, so current EU law bans cattle vaccines.
Research is continuing on an improved version of both the vaccine and test. Vaccinating a population of wild animals is not an easy task, and it is as yet an unproven method to control spread of disease.
The problem of TB in animals will not solved easily, but the research and the debate continues.
Explain the communicable disease in animals- Bacterial meningitis
A bacterial infection (commonly Streptococcus pneumonia/ Neisseria meningitides) of the meninges of the brain (protective membranes on the surface of the brain), which can spread into the rest of the body causing septicaemia (blood poisoning) and rapid death.)
It mainly affects very young children and teenagers 15-19. They have different symptoms but in both, a blotchy red/purple rash that does not disappear when a glass is pressed against it is a symptom of septicaemia and immediate treatment is required.
bout 10% of people infected will die. Up to 25% of those who recover have some permanent damage.
Antibiotics will cure the disease if delivered early. Vaccines can protect some forms of bacterial meningitis.
Explain the communicable disease in animals- HIV/AIDS
HIV/AIDS (acquired immunodeficiency syndrome)- caused by HIV (human immunodeficiency virus), which targets T helper cells in the immune system of the body.
It gradually destroys the immune system so affected people are open to other infections, such as TB and pneumonia, as well as some types of cancer.
HIV/AIDS can affect humans and some non-human primates. HIV is a retrovirus with RNA as its genetic material.
It contains the enzyme reverse transcriptase, which transcribes the RNA to a single strand of DNA to roduce a single strand DNA in the host cell. This DNA interacts with the genetic material of the host cell.
The virus is passed from one person to another in bodily fluids, most commonly through unprotected sex, shared needles, contaminated blood products and from mothers to their babies during pregnancy, birth or breast feeding.
In 2012 around 35 million people worldwide were living with HIV infections and about 1.6 million died of the disease.
There is as yet no vaccine and no cure, but years of anti-retroviral drugs slow the process of the disease to give many years of healthy life.
Girls and women are at particularly high risk of HIV/AIDS in many countries. Traditional practices such as female genital mutilation (FMG) increase the infection rate- if the same equipment is used multiple times then this can spread the infection, in addition, women who have undergone FGM are also more vulnerable to infection during intercourse.
Sub-Saharan Africa is the region worst affected by HIV/AIDS, with 25 million people living with HIV/AIDS- around 70% of the global total.
Tis disease has massive social and economic consequences as well as the personal impact to each person infected.
Explain the communicable disease in animals- Influenza (flu)
A viral infection (Orthomyxoviridae spp.) of the ciliated epithelial cells in the gas exchange system.
It kills them, leaving the airways open to secondary infection. Flu can be fatal, especially to young children, old people and people with chronic illnesses.
Many of these deaths are from severe secondary bacterial infections such as pneuomia on top of the original vira infections.
Flu affects mammals, including humans and pigs, and birds, including chickens. There are three main strains- A,B and C.
Strain A viruses are the most virulent and they are classified further by the proteins on their surfaces, for example, A (HINI) and A (H3N3).
Flu viruses mutate regularly. The change is usually quite small, so having flu one year leaves you with some immunity for the next.
Every so often, however there is a major change in the surface antigens and this heralds a flu epidemic or pandemic as there are no antibodies available.
Vulnerable groups are given a flu vaccine annually to protect against ever changing strains. There is no cure.
