In this issue of Mycopathologia, Loperana-Alvarez et al. [1] report that they have isolated the pathogenic yeast Cryptococcus gattii from trees and succulent plants in Puerto Rico, a tropical island in the Caribbean.

Until a decade ago the basidiomycetous yeast Cryptococcus gattii was a rare cause of cryptococcosis in humans and animals that occurred mainly in the subtropical and tropical regions in South America, Africa and Australia. However, this distribution pattern changed by an unprecedented outbreak of this yeast which emerged in 1999 in the temperate climate of British Columbia (Canada) and that subsequently expanded to the Pacific Northwest [2, 3]. In contrast to its opportunistic relative Cryptococcus neoformans, C. gattii has a preference to cause disease in apparently healthy humans and animals [2, 3]. However, it became obvious that also immunocompromised patients, like individuals receiving immunosuppressive therapy, organ transplant recipients and patients with hematological malignancies, are likely to acquire cryptococcosis caused by C. gattii [2]. Furthermore, several cases of activated dormant C. gattii infections have been described [4]. In a recent study by Litvintseva et al. [5], C. gattii was identified as the cause of cryptococcal disease in more than 13% of the studied HIV-positive humans in the sub-Saharan region. These examples suggest that C. gattii can no longer be regarded as a primary pathogenic yeast [4].

In most cases, C. gattii and C. neoformans enter the body via the respiratory system from where it disseminates to the central nervous system to cause meningitis, which frequently has a fatal course [2, 6]. It is generally accepted that airborne basidiospores produced by Filobasidiella bacillispora, the teleomorph of C. gattii or small-sized desiccated C. gattii cells are the infectious propagules since encapsulated vegetative yeast cells are too large to pass through the lung alveoli [6]. Nevertheless, the sexual phases of both pathogenic Cryptococcus species are only known to be produced under laboratory circumstances and have not yet been found in nature or in clinical samples [6].

The natural habitat of C. neoformans and C. gattii has been intensively studied, especially in those areas where the incidence of cryptococcosis is relatively high [7]. The primary ecological niche of C. neoformans has been determined to be bird excreta, especially pigeon droppings, and trees [8]. Two decades ago, C. gattii was isolated from plant debris under a Eucalyptus camaldulensis tree in Australia [8]. The distribution pattern of E. camaldulensis has been associated with the relatively high proportion of C. gattii infections among rural aboriginals, compared to other areas where C. gattii was known from clinical sources [8]. However, shortly after this finding, Ellis and Pfeiffer, as well as other Australian investigators isolated C. gattii from a wide variety of Eucalyptus species and Syncarpia glomulifera, which is also a native Australian tree species [7, 9]. Eucalyptus trees have been exported from Australia to many countries, especially those with a subtropical or tropical climate, which is the preferred environment for Eucalyptus trees [7–9]. It has been speculated that the export of Eucalyptus seeds and trees had contributed to the dispersal of C. gattii [7, 8]. However, the finding of C. gattii in a hollow of a native Guettarda acreana tree in Ilha de Maracá, an unaffected area in the Northern Brazilian Amazon rainforest, indicated that probably not Eucalyptus but (decomposing) plant material in general is the most probable ecological niche for C. gattii [7, 9].

This idea became more evident after a large environmental sampling study to determine the environmental source of the ongoing Vancouver Island C. gattii outbreak [2, 3, 7, 9]. This study revealed that C. gattii was abundantly present on a broad range of native Canadian tree species, especially alder (Alnus spp.), cedar (Thuja spp.), Douglas fir (Pseudotsuga menziesii), grand fir (Abies grandis) and Garry oak (Quercus garryana), but that it was absent on several imported tree species such as Eucalyptus spp. [9].

The search for the presence of C. gattii in the environment is usually initiated after the emergence of clinical and veterinary cases [2, 3, 7, 9]. Since C. gattii has been isolated from a wide variety of natural habitats in North and South America, the presence of C. gattii in the Caribbean could be expected [7]. Earlier attempts to isolate C. gattii from the environment in Puerto Rico and Cuba were unsuccessful [10, 11]. Loperana-Alvarez and colleagues investigated the same regions in Puerto Rico that were sampled two decades ago, but this time both pathogenic Cryptococcus species were found [1, 11]. Trees that were known to be positive for C. gattii, like the almond (Terminalia cattapa) and mango tree (Mangifera indica), were found to yield C. gattii [1, 7, 9]. Strikingly, the majority of C. gattii strains were isolated from lesions on Cephalocereus royenii cacti. This cactus species belong to a group of succulent plants that are known to harbor non-pathogenic Cryptococcus yeasts [1]. With the knowledge that C. gattii can survive in lesions of succulent plants, it may be a matter of time before cacti in other geographic regions of the world will be found to harbor C. gattii.

The question remains how C. gattii has colonized the cacti lesions. Loperana-Alvarez et al. [1] suggested that invasive insects, causing lesions on plants, could be the mode of transfer for C. gattii. This hypothesis deserves to be investigated since C. gattii has been isolated from several insect-related sources in the past [1, 12]. The current investigations clearly demonstrate that our understanding of the ecology of C. gattii is only partly known. What will be the next surprise?