Aids is a disease

Yes, but I believe it is still preferentially written AIDS-- it is an acronym for Acquired Immune Deficiency Syndrome.

AIDS - immune system disease: a disease of the immune system caused by infection with the retrovirus HIV, which destroys certain white blood cells and is transmitted through blood or bodily secretions such as *****. Patients lose the ability to fight infections, often dying from secondary causes such as pneumonia or Kaposi’s sarcoma.

Thank you friends.

Also can I say, "AIDS is a viral infection".

It is not a viral infection. It is the result of Human immunodeficiency virus (HIV) = a retrovirus that can lead to Acquired Immunodeficiency Syndrome.

I would avoid using AIDs and HIV in your examples. Stick to the simpler diseases and illnesses.