A new ""First Book,"" graced with large print, well-explicated color photos, and comprehensible scientific explanations. With clarity and accuracy--no simple task--Greenberg explains the causes, transmission, diagnosis, and lines of defense against the virus. Along the way, he includes interesting facts (e.g., viruses are so small that they're measured in nanometers--billionths of a meter), plus information on current research toward arrest and cure that gives a hopeful tone. There's an especially nice photo of a healthy child in a day-care center playing with and touching an HIV-infected infant. Glossary; bibliography; resources; index.