Modern historians and others have suggested many possible causes of Alexander's death, including alcoholism, and even AIDS. It seems most likely, however, that he died of malaria, aggravated by the heavy drinking of the Macedonian court, although a strong case for typhoid has been made by the combined team of an ancient historian, Eugene Borza, a specialist in the study of Alexander, and an infectious-disease physician, David Oldach.

The argument can be found in the October 1998 issue of Discover Magazine:
http://discovermagazine.com/1998/oct/alexandertheinfe1521

A collection of sites on the possible causes of Alexander's death (typhoid, poisoning, AIDS, West Nile virus, etc.) can be found at:
http://www.grahamphillips.net/Alexander/Alexander_2.htm