12.2 - Animal and plant diseases

Question 1

Plant disease: Ring rot

Answer 1

• Bacterial disease of potatoes, tomatoes, and aubergines
• Caused by gram-positive bacterium: Clavibacter michiganensis
• Damagees leaves, tubers and fruit
• Can destroy up to 80% of the crop with no cure
• Once a field is infected, it is out of use for at least 2 years

Question 2

Plant disease: Tomato mosaic virus

Answer 2

• Virus that infects tobacco plants and around 150 other species including tomatoes, peppers, cucumbers, petunias and delphiniums
• Damages leaves, flowers and fruit, stunting growth and reducing leaves
• Can result in total crop loss
• Resistant crop strains are available but there is no cure

Question 3

Plant disease: Potato/tomato/late blight

Answer 3

• caused by the fungus-like protoctist oomycete Phytophthora infestans.
• The hyphae penetrate host cells, destroying leaves, tubers and fruit
• causes millions of pounds worth of crop damage each year.
• There are resistant strains but no cure
• Chemical treatments can reduce infection risk

Question 4

Plant disease: Black sigatoka

Answer 4

• Banana disease
• Caused by fungus: Mycosphaerella fijiensis, which attacks and destroys the leaves
• The hyphae penetrate and digest cells, turning the leaves black
• 50% reduction in yield in infected plants
• Resistant strains are being developed - good husbandry and fungicide treatment can control the spread of the disease but there is no cure.

Question 5

Animal disease: tuberculosis (TB)

Answer 5

• Bacterial disease of humans, cows, pigs, badgers, and deer
• caused by Mycrobacterium tuberculosis and M.bovis.
• Damages and destroys lung tissue and supresses the immune system, so the body is less able to fight off other diseases.
• In 2012, 8.6 million people had TB of which 1.3 million died
• The global rise of HIV/AIDS are more likely to develop TB infections
• TB is curable (by antibiotics) and preventable (improving living standards and vaccination)

Question 6

Animal disease: bacterial meningitis

Answer 6

• Bacterial infection of the meininges of the brain (protective membranes on the surface of the brain), which can spread into the rest of the body causing septicaemia and rapid death.
• caused by streptococcus pneumoniae or Neisseria meningitidis
• Mainly affects very young children and teenagers aged 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 medical treatment is needed
• 10% of people infected will die
• 25% of those who recover have some permanent damage
• Antibiotics will cure the disease if delivered early
• Vaccines can protect against some forms of bacterial meningitis

Question 7

Animal disease: HIV/AIDS (acquired immunodeficiency syndrome)

Answer 7

• Caused by HIV, which targets T helper cells in the immune system
• 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 wih RNA as its genetic material
• It contains the enzyme reverse transcriptase, which transcribes the RNA to a single strand of DNA to produce a single strand of 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, commonly through unprotected sex, shared needles, contaminated blood products and from mothers to their babies during pregnancy, birth, or breastfeeding.
• In 2012, 35 million people worldwide were living with HIV infections and 1.6 million died of the disease.
• No vaccine and no cure, but anti-retroviral drugs slow the progress 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 FGM increase infection rte - if the same equipment is used multiple times, then this can spread the infection.
• 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 it - 70% of the population

Question 8

Animal disease: Influenza (flu)

Answer 8

• viral infection of the ciliated epithelial cells in the gas exchange system. It kills them, leaving the airways open to secondary infection.
• Caused by orthomyxoviridae
• Flu can be fatal, especially to young children old people and people with chronic illnesses.
• Deaths caused by flu are from severe secondary bacterial infections such pneumonia on top of the original viral infection
• Flu affects mammals, including humans, pigs, and birds.
• There are 3 main strains: A, B and C.
• Flu viruses mutate regularly
• The change is usually quite small, so having the flu one year leaves you with some immunity for the next.
• Every so often, 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

Question 9

Animal disease: Malaria

Answer 9

• Caused by the protoctista Plasmodium and spread by bites of infected Anopheles mosquitoes
• The plasmodium parasite has . complex life cycle with two hosts, mosquitoes and people
• They reproduce inside the female mosquito
  -The female needs to take two blood meals to provide her with protein before she lays her egg - this is when plasmodium is passed onto people
• It invades red blood cells, liver, and even the brain
  -Around 200 million people are reported to have malaria, and each year over 600 000 die
• The disease recurs, making people weak and vulnerable to other infections
  -There is no vaccine against malaria and limited cures, but preventative measures can be effective
• They key is to control the vector.
  Anopheles mosquitoes can be destroyed by insecticides and by removing the standing water where they breed.
  -Simple measures such as mosquito nets, window and door screens and long sleeved clothing can prevent them biting people and spreading the disease.

Question 10

Animal disease: Ring worm

Answer 10

• Fungal disease affecting mammals, including cattle, dogs, cats and humans
• Different fungi infect different species
• In cattle, ring worm is usually caused by Trichophyton verrucosum
• It causes grey-white, crusty, infectious, circular areas of the skin
• It is not damaging but it looks unsightly and may be itchy
• Antifungal creams are and effective cure

Question 11

Animal disease: Athlete’s foot

Answer 11

• Human fungal disease
• Caused by Tinia pedia
• A human form of ring worm that grows on and digests the warm, moist skin between the toes
• It causes crackling and scaling, which is itchy and may become sore
• Anti-fungal creams are an effective cure