The human immunodeficiency virus (HIV) is a lentivirus (a subgroup of retrovirus) that causes HIV infection and acquired immunodeficiency syndrome (AIDS).AIDS is a condition in humans in which progressive failure of the immune system allows life-threatening opportunistic infections and cancers to thrive.he human immunodeficiency virus (HIV) is a lentivirus (a subgroup of retrovirus) that causes HIV infection and acquired immunodeficiency syndrome (AIDS).
The definition of optimal is the most favorable. An example of optimal used as an adjective is in the phrase optimal score, which means the highest score someone can get on a game. most favorable or desirable; best; optimum. Origin of optimal.
Optimal conditions refers to several conditions which optimise the growth of saprotrophic organisms, such as; 1  Presence of water: 80â90% of the fungi is composed of water by mass, and requires excess water for absorption due to the evaporation of internally retent water.