"The discovery of a drug for the treatment of, or vaccination against, a disease is greatly facilitated if there is an animal model (an animal that mimics the behavior or responses of the human body) for testing the effectiveness of the drug. But animals are generally not susceptible to the diseases that afflict humans. AIDS is a good example. HIV, the virus that causes AIDS, either does not infect or does not cause the same disease symptoms in laboratory animals that it does in humans. It is therefore difficult to test vaccines or therapies for their potential to alleviate the symptoms of the disease. Cloning technology may be utilized to produce useful genetically modified animal models, which would greatly facilitate the development of treatments or innoculations for many diseases. Scientists are already at work developing a genetically modified rabbit model that expresses the human receptor for the virus and is susceptible to infection.