Viral Diseases
Viruses live and reproduce inside cells, causing cell damage.
There are 3 viral diseases that you need to study
1.Measles
2. HIV
3. Tobacco mosaic virus
Measles
Measles is a serious illness. In most cases people will make a good recovery, but in a small number of cases if complications occur it can be fatal. Most cases occur in children.
Symptoms: Fever (temperature >38°C), red skin rash
Transmission is by air, through droplet infection. An infected person will cough or sneeze expelling droplets that contain the measles virus, an uninfected person will breathe in these droplets and become infected. Measles is highly contagious.
Due to how contagious measles is, most children are vaccinated against measles to reduce the transmission and to protect them against the disease.
HIV
HIV stands for Human immunodeficiency virus. This virus will progressively weaken the bodies immune system until the immune system is no longer able to protect the person against other pathogens. At this point the person is said to have AIDS (Acquired immunodeficiency syndrome).
Symptoms: After infection the person experience a flu like virus, which will progress over time to weaken the immune system until it reaches a late stage when the bodies immune system is so damaged that it can no longer deal with other infections or cancers.
Transmission is by direct contact either as:
1.Unprotected sexual contact
2.Exchange of bodily fluids such as blood where drug users share needles, or unscreened blood transfusions
Treatment is with antiretroviral drugs which can slow down the virus and control the HIV.
Tobacco Mosaic Virus
Tobacco mosaic virus (TMV) is a widespread plant pathogen so it affects many plants including tomatoes and other species of plants.
TMV doesn’t usually kill plants, but it reduces growth and productivity, which is economically significant for crops. The TMV will damage the plant cells, reducing the amount of photosynthesis that can occur, leading to reduced growth.
Symptoms: Distinctive ‘mosaic’ pattern of discolouration on the leaves. There are light and dark green patches, giving a “mottled” look.
Transmission: Highly contagious via direct contact—touching infected leaves, tools, or hands.
TMV is a virus, so chemical treatments like fungicides or antibiotics won’t work. Prevention is mainly by using resistant varieties and good field hygiene such as disinfecting tools.
Practice Questions
1.State how measles is transmitted
2. What are the symptoms of an early stage HIV infection
3. How would it be best for a farmer to protect the crops against TMV