3.1.2 Viral diseases

• Viral diseases: measles, HIV and tobacco mosaic virus (TMV)
• Disease: Measles

  Symptoms:

  ● Fever

  ● Red skin rash

  How is it spread?

  Inhalation of droplets from sneezes / coughs from infected people

  How can spread be reduced or prevented?

  ● Most young children vaccinated against measles

  ● Isolation

  Other info

  ● A serious illness

  ● Can be fatal if complications arise eg. pneumonia
• Disease:HIV

  Symptoms:

  ● Initially a flu-like illness

  ● Often no symptoms for years

  ● If AIDS develops - recurrent infections + longer recovery

  How is it spread?

  ● Sexual contact

  ● Exchange of body fluids eg. blood when drug users share needles

  How can spread be reduced or prevented?

  ● Antiretroviral drugs control HIV (to stop AIDS developing)

  ● Avoid sexual intercourse / use a condom

  ● Do not share needles

  Other info

  ● HIV attacks immune cells ● AIDS (late stage HIV infection) - immune system becomes so badly damaged that it can no longer deal with other infections
• Disease:Tobacco mosaic virus (TMV)

  Symptoms:

  ● ‘Mosaic’ pattern of discolouration on leaves

  ● Restricted growth due to lack of photosynthesis

  How is it spread?

  Direct contact between diseased / healthy plants.

  How can spread be reduced or prevented?

  ● Remove infected plants / leaves ● Wash tools in disinfectant after using on infected plant

  Other info

  ● A widespread plant pathogen

  ● Affects many species of plants including tomatoes
• why is this statement wrong?

  “AIDS is a virus.”

  HIV is an infection caused by a virus whereas AIDS is the consequences in the body from HIV infection
• why is this statement wrong?

  "HIV always leads to AIDS.”

  HIV can be controlled with antiretroviral drugs. These stop HIV replicating, so the immune system doesn’t get so damaged that AIDS develops. These drugs do not eliminate HIV completely though, so are not considered a cure
• why is this statement wrong?

  "Viral diseases can be treated with antibiotics.” Antibiotics are only effective against bacteria.
• Explain why TMV causes restricted growth in plants. (4)

  ● Less chlorophyll so less photosynthesis

  ● So less glucose produced

  ● So less energy released for growth as glucose is needed for respiration

  ● Less proteins / cellulose for growth as glucose needed for making these
• Explain why antibiotics do not cure HIV / measles / TMV. (1)

  ● Antibiotics are only effective against bacteria / do not kill viruses
• Suggest reasons for the decrease in the number of new HIV cases in recent years. (2)

  ● Better education (into prevention of spread of HIV)

  ● Condoms more widely available / easier to source / cheaper

  ● New / better drugs / antiretrovirals to prevent HIV spread

  ● Better / more testing / identification of people with HIV