As the sun set across the Saigon river and the mosquitoes busily began their evening rounds, the 400-page Exotic Viral Infections, edited by James S. Porterfield, lay rather heavily on my lap. The comments of Harold Ellis came to mind, that the reviewer of a multiauthor textbook need not necessarily read the whole thing from cover to cover. I need not have worried. I opened the book at page one and could not put it down. Here at last is a textbook that fully addresses the exotic viral infections often only given a passing mention in the standard virology and infectious disease texts.

The word exotic derives from the Latin exoticos and Greek ekotikos meaning foreign, not indigenous, from outside. Thus whether you see something as exotic depends entirely on your viewpoint. Dengue fever, for example, which is encountered occasionally in the United Kingdom in returning travelers, is one of the most common causes of hospital admission among children in Southeast Asia. Indeed, many of the diseases covered, although rare in the West, are major causes of morbidity and mortality elsewhere in the world, hence the importance of a book devoted to such infections.

To many physicians virology is somewhat mysterious, and virological classification is something of a nightmare. No viruses support this impression better than those encountered in the tropics. Their classification can only be understood fully in the context of the historical development of the field. The arboviruses provide a good example. In the 1950s they were classified on the basis of the hemagglutination inhibition assay as group A and group B. These were renamed subsequently as the genera Alphavirus and Flavivirus of the family Togaviridae, toga from the Latin for cloak as seen by electron microscopy. However, biochemical and molecular studies showed important differences between alphaviruses and flaviviruses, and the latter were reclassified as the genus Flavivirus within the family Flaviviridae. The term arbovirus itself, though of great practical importance describing the mode of transmission (arthropod-borne), has no taxonomic significance, and several families contain arboviruses. One of the strengths of Exotic Viral Infections is that important historical details such as these are fully explained at the beginning of each chapter.

The array of different tests for diagnosing viral infections can also be bewildering. How does one choose between a hemagglutination inhibition assay, complement fixation tests, neutralization tests and enzyme-linked immunosorbant assay? What does it mean when they give different results, and where do viral culture and nucleic acid hybridization fit in? The reader is taken carefully through these investigations, with an explanation of how they evolved and how to interpret them to get the correct diagnosis.

The book starts with the alphaviruses, including the American arboviruses causing western and eastern equine encephalitis. An overview of the family Flaviviridae follows, with subsequent chapters on yellow fever, dengue and Japanese encephalitis. Yellow fever is still a considerable problem in parts of Africa and South America; dengue is the most widely distributed mosquito-borne virus of humans, and Japanese encephalitis is the most common viral encephalitis worldwide. In the United States, St. Louis encephalitis virus is the most important arboviral infection, and it is included in a chapter with the Rocio virus and West Nile virus, whose wide geographical distribution includes parts of Europe. The Australian mosquito-borne flaviviruses are considered next.

Other members of the Flavivirus genus have evolved to survive in locations without abundant mosquitoes. Chapter nine examines these tick-borne flaviviruses, such as tick-borne encephalitis, formerly known as Russian spring summer encephalitis. The closely related virus, louping ill, a disease of sheep which occasionally spills over into humans is also mentioned. Although louping ill occurs in the United Kingdom, it is included with the exotic viral infections because it is the only flavivirus causing human disease in the United Kingdom. Powassan virus, first isolated from a Canadian child with encephalitis, is the last flavivirus considered before the book moves on to the Arenaviruses. These �rodent-borne� zoonotic viruses are spread to humans via urine droplets and feces. They have a wide distribution, often presenting as hemorrhagic fevers, for example Lassa fever in Africa and Sabia infection in Brazil. The Arenavirus lymphoctyic choreomeningitis virus is an important cause of aseptic meningitis throughout the West, including the United Kingdom.

The very large Bunyaviridae family is described in the next four chapters. The first genus, Bunyavirus, contains the California serogroup agents that cause encephalitis in humans. The Hantavirus genus follows, including Hantaan virus (hemorrhagic fever with renal syndrome) and Sin Nombre virus, cause of the recently described hantavirus pulmonary syndrome. Congo Crimean hemorrhagic fever is described in the chapter on the genus Nairovirus, and the genus Phlebovirus, which includes rift valley fever virus, completes the Bunyaviridae. The last few chapters look at the Filoviridae, Marburg and Ebola, Coltivirus infections, such as Colorado tick fever, and the Rhabdoviridae. The description of rabies is noteworthy for its excellent illustrations and photographs.

The choice of which viruses to include in such a book is going to be somewhat arbitrary and personal. Although trained as a physician, Porterfield�s selection reflects the fact that he is better known as a virologist. Thus rubella, because it happens to be a Togavirus, is included but not measles and mumps. And yet polio virus, still an important cause of illness and death in many parts of the tropics is not included. For many of the exotic viral infections, it becomes clear that our laboratory-based knowledge of the virus far exceeds our clinical knowledge about its effects. Whether this reflects the fact that studying the virus in the laboratory is often easier than investigating the disease in the tropics, or the recent trend for research funding to be directed toward molecular work is not certain. The murine model of lymphocytic choreomeningitis virus (LCMV), for example, has greatly advanced our understanding of immune tolerance, and cytotoxic T-cell function, but the full spectrum of LCMV disease in humans remains unknown. However, there are also many instances where the laboratory science has directly assisted the clinician. Recent work on vaccines provides good examples of this, and in the chapter on alphaviruses it becomes clear how our understanding of the different serological assays has been greatly enhanced by recent molecular work looking at the epitopes involved. In these days of the Internet and electronic access to journals and databases, those who want the most up-to-date information no longer expect textbooks to fulfill this role. This volume gives a full picture of the current state of the art, and the contributors have pointed out the direction in which new developments are likely. Two changes of publisher have meant it has taken several years for completion of this book, which is the third Kass Handbook of Infectious Diseases. The series editors� intention that Exotic Viral Infections will be a gold-standard resource for those interested in this area will, I am sure, be realized. It will also be a useful reference text for physicians working in the tropics. The chapters by those with a clinical as well as virological background are especially good in this respect, as demonstrated, for example, by the tables giving differential diagnoses for Japanese encephalitis and dengue hemorrhagic fever.

The importance of a strong relationship between the clinical and laboratory sciences is increasingly recognized. As the science of virology blossoms, this book provides many examples of how the two complement each other. With the current awareness worldwide on emerging and re-emerging infections, the timing of such a publication could not be better. I am confident that Exotic Viral Infections will do well.