We have the Fourth Edition (2001) and it lists the following as "NEW"
—Thoroughly revised and expanded information on animal and reptile bites...
—Many new illustrations bringing the total to more than 1,400...
—Totally new information on injury prevention, pain management, seasonal allergies, nutrition, bear attacks... .
...as well as a list of other additional material.
Maybe one of the on-line book venders has a synopsis of the differences of the Fourth Ed.
Allen R