Invasive fungal infections are a significant threat to immunocompromised patients. Recently, reports of systemic mycosis in previously healthy individuals are on the rise [1]. This may be attributed to the evolution of the fungal pathogens with increased virulence. This necessitates a high index of suspicion for fungal infections with atypical presentations.

Cryptococcus neoformans species complex belongs to the phylum Basidiomycota. These group of yeasts can cause fatal infections of the central nervous system, lung and skin not only in humans but also in animals. C. neoformans var. grubii (serotype A) and C. neoformans var. neoformans (serotype D) have been isolated worldwide, causing disease in immunocompromised hosts. C. neoformans var. gattii (serotype B and C), has been recently elevated to species level as Cryptococcus gattii, due to its phenotypic and molecular differences [2] [3]. Moreover, C. gattii infects mainly immunocompetent hosts. It is an environmental fungus, first isolated in Vancouver Islands, British Columbia in 1970. By two decades, it has been associated with 176 cases and 8 deaths worldwide [3] [4] [5]. This fungi is generally restricted geographically to the tropical and subtropical climates [6]. It spreads through the inhalation of spores. It is known to produce large space occupying lesions. The sequencing of the genomes of the two species reveals distinct functional differences in similar genes. The microevolution in the genome of C. gattii has lead to a change in its ecological niche and its virulence factors, which explains reports of sporadic cases of C. gattii infections in non-endemic regions [6]. C. gattii meningitis requires a more aggressive and longer duration of therapy when compared to Cryptococcus neoformans. Though reported rarely, prevalence of C. gattii infections is now on the rise [7].

This paper describes a case of primary central nervous system (CNS) cryptococcosis caused by C. gattii. The infection was diagnosed by detection of Cryptococcal capsular antigen and demonstration of capsulated yeast cells in negative staining microscopy and further confirmed by culture and gene sequencing.

A 24-year-old unmarried male presented to our hospital with chief complaints of headache, bilateral visual disturbance (diplopia), photosensitivity and intermittent fever. He was an engineering graduate by profession, with no history of travel in the previous 5 years. He gave no history of association with animals. His residence was not in proximity to any vegetation which might serve as a source of Cryptococcus infection. He was seronegative for retroviral infection and had no overt immunodeficiency state. It was later found that his CD4 count was below normal (292 cells/mm³). On admission, his systemic examination revealed no abnormalities. Ocular examination showed bilateral lateral rectus palsy and papilledema. Computed tomography (CT) scan and magnetic resonance imaging (MRI) scan of brain were normal. As the patient developed increasing drowsiness and restlessness, he was admitted in the ICU with a provisional diagnosis of meningoencephalitis.

Lumbar puncture was done in which cerebrospinal fluid pressure was high. The CSF parameters showed: sugar-3 mgs/dl, protein 73mg/dl, white blood cells 63 cells/cm3. red blood cells 26 cells/cm3. Gram staining of CSF revealed occasional pus cells and plenty of yeast cells with a clear halo, suggestive of capsule (Figure 1). Negative staining with India ink showed plenty of capsulated yeasts, compatible with Cryptococcus species (Figure 2). Fungal culture of the CSF sample on Sabouraud's dextrose agar yielded cream colored, mucoid colonies, which were identified as Cryptococcus gattii by VITEK 2 (BioMerieux, Inc, Durham NC, USA. panel YST 21 343) (Figure 3). The identification was further confirmed by gene sequencing. The sequence has been submitted to the databank. The accession number is Banklt1828989 Cryptococcus KT027381.

The patient was started on Injection amphotericin B for treatment of meningitis, but since he developed anaphylactic reaction to it, the medication was discontinued. Fluconazole 400 mg per day plus flucytosine100 mg/kg/d in 4 divided doses was given since this patient was unable to tolerate amphotericin B. He was put on mechanical ventilation. A therapeutic lumbar puncture was done to decrease the raised intracranial pressure. A repeat CT brain, done at this point of time, revealed diffuse cerebral edema (Figure 4). A repeat MRI could not be performed. The patient's condition deteriorated through a period of 16 days. Cardiopulmonary decompensation and superadded bacterial infections worsened his condition.

After three weeks of intensive therapy, he succumbed to the infection.

Being an environmental fungus of the tropics and subtropics, Cryptococcus gattii has been reported as an accidental infection in apparently immunocompetent individuals, with history of residing in or recent travel to an endemic area like British Columbian Islands and North West Pacific Coast of America. It has a specialized ecological niche in eucalyptus and almond trees [4] [7]. C. gattii more frequently causes pulmonary infections while C. neoformans has increased cerebral tropism [8]. C. gattii meningitis is characterized by larger space occupying lesions than C. neoformans, and associated with more neurological complications increased incidence of neurosurgical intervention and delayed response to therapy [1] [9]. Radiographic imaging is used to identify mass lesions, which may be the primary finding in this indolent infection. Phenotypically, C. gattii is differentiated from C. neoformans by L-Canavanine-glycine-bromothymol blue agar. Serotypic determination can be by slide agglutination tests. Molecular methods like PCR and gene sequencing aid in the confirmation of the isolate to species level. Cryptococcal meningitis is treated in 3 phases: Induction (AmpB plus Flucytosine for 2 weeks), Consolidation (Fluconazole for 8 weeks) and Maintenance (Fluconazole for 6 months to 1 year).

The first report of C. gattii as a pathogen was in 1896 by pathologist, Ferdinand Curtis. First case of human meningitis by C. gattii was reported in 1999 in Vancouver Islands, British Columbia, Canada [5]. Nearly 60 cases of C. gattii infection have been reported in United States during the outbreak in 2006–2010. Between 2004 and 2011, 96 cases of C. gattii infections were reported from Pacific Northwest. In India, the first case of C. gattii infection in an AIDS patient was documented by Abraham et al. [8]. Chakrabarti et al. reported five isolates of C. gattii from eucalyptus trees in Northern India, and traced the origin of these trees to Australia, thus validating spread of C. gattii infection in nonendemic areas [10]. Marriott et al. recorded five cases of C. gattii meningitis among seven HIV patients with cryptococcal infection [11]. Few reports of C. gattii meningitis among immunocompetent population of India and other countries are tabulated (Table 1) [12]. It is inferred that though there have been sporadic cases of C. gattii infections in immunocompetent individuals, isolated primary cerebral cryptococcosis is found to be rare.

The present report is a case of C. gattii meningitis in a young adult who was seronegative for HIV infection and apparently immunocompetent. He presented with indolent signs of meningitis like intensifying headaches and diplopia of two months duration, which later progressed to acute cryptococcal meningitis. Further, anaphylaxis to amphotericin B posed a hurdle in clearing the cryptococcal infection. Hence, the patient was started on fluconazole combined with flucytosine. However, the combination of fluconazole and flucytosine is clinically inferior to amphotericin B–based therapy. The patient expired after 23 days of stay in the intensive care unit.

This case report heralds the need for suspicion of Cryptococcus gattii infection even in non-endemic regions. It contradicts the popular belief that invasive cryptococcosis is usually caused by Cryptococcus neoformans and not by Cryptococcus gattii. Environmental and clinical surveillance of cryptococcosis is important in preventing under reporting of C. gattii infections in non-endemic areas.

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