Understanding Viruses and Viral Diseases

Introduction to Viruses

• Viruses are not cells and are not considered living organisms.
• They are typically regarded as organisms.
• Viruses are about 10,000 times smaller than animal cells.
• Cannot reproduce independently; require a host cell to replicate.
• Use the host cell's machinery to replicate and eventually burst the host cell, releasing new viruses.
• This cell damage is a primary reason why viruses cause illness.

Diseases Caused by Viruses

• Focus on three viral diseases: Measles, HIV, and Tobacco Mosaic Virus (TMV).

Measles

• Spread via droplets from coughs or sneezes of infected individuals.
• Symptoms include a red rash and fever.
• Can be serious or fatal, but is rare in the UK due to widespread vaccination.

HIV (Human Immunodeficiency Virus)

• Transmitted through sexual contact or exchange of bodily fluids (e.g., blood from shared needles).
• The virus affects the immune system, leading to immune deficiency.
• Initial symptoms resemble flu, including fever and tiredness, but individuals may feel better temporarily.
• Over time, it severely weakens the immune system, leading to AIDS.
• AIDS is characterized by vulnerability to unusual infections and certain cancers due to immune system failure.
• Antiretroviral drugs can prevent viral replication, allowing individuals to live normal lives if medication is accessed early.

Tobacco Mosaic Virus (TMV)

• Affects plants, specifically tobacco and tomato plants.
• Causes discoloration in a mosaic pattern on leaves, hindering photosynthesis.
• Results in decreased sugar production, leading to stunted plant growth.

Additional Resources

• Videos, questions, flashcards, exam-style questions, and past papers available at Cognito's website.
• Progress tracking is offered to guide study efforts.