Disease caused by virus are:

Viruses are microscopic organisms that can cause a wide variety of diseases in humans, animals, and plants.

• These diseases vary in severity and can affect different body systems.

Key Points

• The disease caused by a virus is AIDS (Acquired Immunodeficiency Syndrome).
• AIDS is caused by the HIV (Human Immunodeficiency Virus), which attacks the immune system, making the body vulnerable to other infections and diseases.

Hint

• Fever is a symptom, not a specific disease caused by a virus, although many viral infections can cause fever.
• Cancer is primarily caused by mutations in cells and is not a viral disease, although certain viruses, like the human papillomavirus (HPV), can increase the risk of certain cancers.
• Underweight is a condition that can result from malnutrition or other health issues but is not caused by a virus.

Hence, the correct answer is 'AIDS'.