As scientists gained a better understanding of the virus, they developed drugs that target different stages of viral replication. Protease inhibitors, which interfere with the ability of newly formed viruses to mature and become infectious, were introduced in 1995. At the same time, scientists recognized that treating patients with a combination of drugs that attack the virus in different ways reduces the opportunity for HIV to mutate and develop resistance.


The introduction of these drug combinations, called highly active antiretroviral therapy, led to dramatic improvements in the survival of HIV-infected patients. As a result, the number of AIDS deaths fell by more than half between 1996 and 1998 and has continued to decline since then. Americans have little chance of being exposed to BSE in the United States. Restrictions have been introduced that prohibit importation of live ruminants, such as cattle, sheep, and goats, except from Canada, which also implemented stricter feed regulations.


Although there was controversy about whether enough is being done to protect American cattle from BSE, only four cases have been identified in American cows since 2003. No cases of CJD have been attributed to consumption of American beef. Other prion diseases have been identified in humans and animals. Two of them, Gerstmann Strausler Schenk syndrome and fatal familial insomnia, are extremely rare genetic diseases.