Molecular ecology of cryptococcus neoformans in the Maltese Islands

Abstract

Cryptococcosis is the most life-threatening deep seated fungal infection in AIDS patients. In immunocompetent hosts cryptococcosis is rare. However its effects are devastating, in both immunocompetent and immunosuppressed patients resulting in death or permanent brain damage, unless cases are diagnosed and treated at an early stage. In Aids a growing problem in the management of secondary diseases is the recurrence of cryptococcosis due to the reactivation of latent strain of c. neoformans probably from prostatic foci. Many questions related to the ecology and epidemiology of Cryptococcus neoformans, the aetiological agents of cryptococcosis, are still unanswered. This extremely versatile fungus is represented by two varieties and five serotypes with different geographical distributions and different epidemiological significance. C. neoformans variety neoformans serotype A has a world wide distribution and it is prevalent in AIDS patients. The serotype D of the same variety has been isolated in Italy, Denmark and France from clinical samples of AIDS patients. Extreme genetic variability among both serotype A and D has been demonstrated by molecular typing techniques. The variety gatti has been isolated in Africa where it is prevalent, in western Australia and in California, leading to the theory that the distribution of Cryptococcus varieties are related to regional climatic conditions. The isolation of both environmental and clinical strains is correlated for variety gatti with the presence of Eucalyptus tree which is the reservoir for this fungus variety (Ellis and Pfeiffer 1990). Beside a different geographical distribution the two varieties possess a different degree of pathogenicity and a different sensitivity to antifungal therapy. In fact the variety gatti is predominantly a pathogen, the variety neoformans is considered opportunistic. However the opportunistic nature of neoformans variety is still being queried. Information about epidemiology and ecology of C. neoformans is lacking in the Mediterranean area. We chose the Maltese Islands for their secluded and strategic position in the centre of the Mediterranean. Malta being, at the crossroads between Europe and Africa, could be a linking point between the two different ecological patterns of C. neoformans. The isolated position of the two islands represents an ideal restricted geographical area for the study of genetic variability between strains. The aim of these studies is to elucidate the incidence of C. neoformans in the Maltese Islands, the prevalence of serotypes and the distribution of genetic relatedness within strains in a limited geographic area.