Methods of using azide-modified biomolecules, such as fatty acids, carbohydrates and lipids, to treat a plant or an animal infected with a virus or to inhibit infectivity of a virus, such as the human immunodeficiency virus, are provided. Also provided are methods of labeling a human immunodeficiency virus with an azide-modified biomolecule, such as a fatty acid, a carbohydrate, or an isoprenoid lipid. The azide-modified biomolecules may be combined with a pharmaceutically acceptable excipient to produce a pharmaceutical composition, optionally containing another anti-viral agent and/or a delivery agent, such as a liposome.