Which of the following causes AIDS?

Retrovirus

The correct answer is Option (1) -Retrovirus

The virus that causes AIDS is a retrovirus, specifically the Human Immunodeficiency Virus (HIV). Retroviruses are a group of RNA viruses that have the ability to convert their RNA genome into DNA using an enzyme called reverse transcriptase. HIV primarily infects and attacks immune cells, particularly CD4+ T lymphocytes, which are crucial for the proper functioning of the immune system.

When HIV enters the body, it attaches to specific receptors on the surface of CD4+ T cells and other immune cells. It then enters the cells and uses its reverse transcriptase enzyme to convert its RNA genome into DNA. This viral DNA is integrated into the host cell's DNA, allowing the virus to replicate and produce new viral particles. As the virus replicates, it gradually destroys the infected immune cells, leading to a progressive weakening of the immune system.

Over time, as the immune system becomes more compromised, the individual becomes susceptible to various opportunistic infections, cancers, and other complications. This advanced stage of HIV infection, characterized by a severely weakened immune system and the presence of specific clinical symptoms, is known as Acquired Immunodeficiency Syndrome (AIDS).

It's important to note that HIV is primarily transmitted through certain body fluids, including blood, semen, vaginal fluids, and breast milk. It can be transmitted through sexual contact, sharing contaminated needles, mother-to-child transmission during childbirth or breastfeeding, and less commonly through blood transfusions (which can be prevented through proper screening of blood donations).