When a 3-year-old boy with herpes comes to school to find that his classmates and teacher have remained at home, it is time for a sober, scientific and understandable explanation of herpes.

Fortunately, Dr. Henry H. Balfour Jr., a clinician and virus researcher at the University of Minnesota, and Ralph C. Heussner, a medical writer at the university, provide one in their new book.

Balfour gives the reader two good reasons to keep reading right in the preface: "Because you almost certainly have one of the five human herpes viruses in your own body right now, and you should know what that means."

The reader learns about the prevalence and transmission of herpes simplex types I and II, which cause genital and oral herpes; Epstein-Barr virus, which causes mononucleosis; the usually quiet cytomegalovirus; and the varicella-zoster virus, which causes chicken pox and shingles.

The authors explain that herpes simplex viruses don't survive in the open air, so classmates of the Anne Arundel County child with herpes would have to come into direct contact with his open sores to contract the disease. More likely, the boy's classmates will encounter the virus somewhere else: The authors note that 30 to 50 percent of higher socioeconomic groups and 80 to 100 percent of lower socioeconomic groups show evidence of having been infected by herpes simplex type I.

The book has some minor problems. Many of the graphs are overloaded with information, and wind up not getting any point across. There's probably more herpes research going on outside of the University of Minnesota than the book lets on, and one can only hope the antiviral drug acyclovir is as good as the book claims.

But overall, Balfour and Heussner tell their story fluidly, simply and remarkably thoroughly. They guide the reader into visualizing what goes on in the body during a viral attack, how and where each of the viruses hide, and how antiviral drugs work. "The disease," they note, "is much less intimidating when you learn the facts."

Despite some alarming statistics on prevalence, they soothe with their take-home message: "The majority of herpes diseases can be treated, and treated again if they recur." For those frustrated by the seemingly glacial pace of medical progress, the authors detail the process of establishing a treatment. And for herpes victims and those trying to avoid being herpes victims, they predict the introduction of vaccines and new antiviral drugs in the 1980s and 1990s.

Many of us remember all the questions we should have asked the doctor only when we get home. And some people are too embarrassed to ask about social diseases. This book is a handy, ready reference that answers nearly every question about the viruses except why they exist in the first place.