Species of aspergilli are common in man's environment and are responsible for a wide spectrum of human and animal disease, ranging in animals from mycotic abortion to aflatoxicosis and in humans from localized colonization of the ear or skin to life-threatening systemic infection of neutropenic patients. In recent times, invasive aspergillosis has become increasingly important as a cause of morbidity and death, initially in patients receiving immunosuppression prior to organ transplantation, and latterly in haematologic patients rendered neutropenic by underlying disease or chemotherapy. In some centres, the condition has been recorded in more than 40% of patients dying with acute leukaemia. Laboratory diagnostic procedures are not always helpful and the diagnosis depends largely on clinical parameters. The clinician is faced with yet another problem, that of management. At present, antifungal therapy of invasive aspergillosis can be largely ineffectual, and the mortality rate remains unacceptably high. Since Aspergillus fumigatus was first described almost 125 years ago, several other pathogenic species have been recognized. The marked biosynthetic abilities and varied mechanisms of gene recombination of aspergilli have long commanded attention in food technology and genetics. Their equally varied abilities to cause disease have attracted the interest of toxicologists, allergists and physicians concerned with infectious diseases.

Species of aspergilli are common in man's environment and are responsible for a wide spectrum of human and animal disease, ranging in animals from mycotic abortion to aflatoxicosis and in humans from localized colonization of the ear or skin to life-threatening systemic infection of neutropenic patients. In recent times, invasive aspergillosis has become increasingly important as a cause of morbidity and death, initially in patients receiving immunosuppression prior to organ transplantation, and latterly in haematologic patients rendered neutropenic by underlying disease or chemotherapy. In some centres, the condition has been recorded in more than 40% of patients dying with acute leukaemia. Laboratory diagnostic procedures are not always helpful and the diagnosis depends largely on clinical parameters. The clinician is faced with yet another problem, that of management. At present, antifungal therapy of invasive aspergillosis can be largely ineffectual, and the mortality rate remains unacceptably high. Since Aspergillus fumigatus was first described almost 125 years ago, several other pathogenic species have been recognized. The marked biosynthetic abilities and varied mechanisms of gene recombination of aspergilli have long commanded attention in food technology and genetics. Their equally varied abilities to cause disease have attracted the interest of toxicologists, allergists and physicians concerned with infectious diseases.

Fungal dimorphism is a topic that sounds inherently too rarified to attract more than a specialist audience. Yet some 230 individuals representing an eclectic mixture of interests, from basic science to medical practice, gathered in Churchill College, Cambridge in Semptember 1992 for a meeting devoted only to this subject. The symposium was the fourth in a series "Topics in Mycology" to be jointly organized by the Janssen Research Foundation and the International Society for Human and Animal Mycology. The participants enjoyed a rich and varied diet of oral presentations and poster displays in the field of fungal morphogenesis. This book sets down in print the material presented at the dimorphism symposium. We think that the high quality of these papers conveys very well the flavor of what was an excellent meeting. The selection of contributions in this volume covers very wide ground indeed. Chapters devoted to some non-pathogenic fungi are included, because the scientific basis of morphological development belongs to the fields of cellular and molecular biology: it does not recognize the boundary imposed by considerations of virulence of a fungus for a human host. Yet morphogenetic change in those fungi that do cause human disease frequently appears to be a component of the pathological process: many important pathogens change from a hyphal form in the external environment to a round form in infected tissues. This relationship between dimorphism and pathogenicity is the point of contact between pure biology and medicine.

The World Health Organization estimates that at least five million people worldwide are infected with human immunodeficiency virus (HIV) Of these about 100,000 are in Asia and Oceania, 500,000 in Europe, 2 million in the Americas and 2.5 million in Africa (Mann, 1989). The acquired immunodeficiency syndrome is characterized by a derangement in cell-mediated immunity leading to opportunistic infections with for example Mycobacterium spp., Candida spp., Cryptococcus neoformans, Pneumocystis carinii, Toxoplasma gondii and Cryptosporidium. The third symposium on "Topics in Mycology" brought together 265 experts from 32 countries to discuss the epidemiology, immmunological and pathogenetic aspects of AIDS and its opportunistic infections in general and fungal infections in particular. Pneumocystis carinii pneumonia is by far the commonest opportunistic infection in AIDS patients. The nature and classification of P. carinii is still controversial. In search for its true taxonomic affinities an introductory paper formulates a number of key questions. Candidosis is another frequent opportunistic infection. A number of papers discuss the possibility that selective pressures may operate on Candida albicans within the AIDS population and influence its nature: this might have an impact on prophylaxis and curative and/or suppressive therapy.