1. What are viruses? Name some common diseases in human caused by virus.

Viruses are tiny infectious agents that are smaller than bacteria and consist of genetic material (either DNA or RNA) surrounded by a protein coat called a capsid. They cannot replicate or carry out metabolic functions on their own and rely on infecting host cells to reproduce. Once inside a host cell, a virus hijacks the cell's machinery to replicate itself, often causing harm to the host cell in the process.

Some common diseases in humans caused by viruses include:

1. Influenza (Flu): Influenza viruses cause seasonal flu outbreaks, leading to symptoms such as fever, cough, sore throat, muscle aches, fatigue, and respiratory issues. There are several strains of influenza viruses, including influenza A, B, and C.

2. Common Cold: The common cold is caused by various viruses, including rhinoviruses, coronaviruses, and adenoviruses. It results in symptoms such as a runny or stuffy nose, sneezing, sore throat, cough, and mild fatigue.

3. Human Immunodeficiency Virus (HIV/AIDS): HIV is a retrovirus that attacks the immune system, specifically targeting CD4 T cells. If left untreated, HIV can lead to acquired immunodeficiency syndrome (AIDS), a condition characterized by a weakened immune system and an increased susceptibility to opportunistic infections and cancers.

4. Herpes Simplex Virus (HSV): HSV is a common virus that causes  mouth herpes (cold sores) and genital herpes. It can lead to painful blisters or sores on the lips, mouth, genitals, or other areas of the body.

5. Human Papillomavirus (HPV): HPV is a sexually transmitted virus that can cause genital warts and various types of cancers, including cervical, and oropharyngeal cancers.

6. Varicella-Zoster Virus (VZV): VZV is responsible for causing chickenpox during childhood and can later reactivate to cause shingles (herpes zoster) in adulthood.

7. Hepatitis Viruses: Several viruses, including hepatitis A, B, C, D, and E viruses, can cause inflammation of the liver (hepatitis), leading to symptoms such as fatigue, jaundice, abdominal pain, and liver damage.

8. Ebola Virus: Ebola virus disease (EVD) is a severe and often fatal illness in humans. It is characterized by symptoms such as fever, severe headache, muscle pain, weakness, diarrhea, vomiting, and internal and external bleeding.

These are just a few examples of the many diseases caused by viruses in humans. Vaccination, antiviral medications, and other preventive measures are often used to manage and prevent viral infections.