Cryptococcus gattii infections: contemporary aspects of epidemiology, clinical manifestations and management of infection

Comparison of mNGS with conventional methods for diagnosis of cryptococcal meningitis: a retrospective study

The application of metagenomic next-generation sequencing (mNGS) in the diagnosis of cryptococcal meningitis is relatively under characterized. Here, we retrospectively evaluated data from cryptococcal meningitis patients who were tested using mNGS and/or routine testing, including fungal culture, India ink staining, and cryptococcal antigen (CrAg) testing. The performance of mNGS was then assessed. Initial cerebrospinal fluid (CSF) samples were collected from 65 patients with suspected central nervous system (CNS) infection and tested using conventional tests and/or mNGS. mNGS offers a culture-independent approach, facilitating a rapid and unbiased detection of a broad spectrum of pathogens. Patients with bacterial tuberculous or viral meningitis were used as mNGS-positive controls and one autoimmune encephalitis patient was used as an mNGS-negative control. In the 45 patients diagnosed with cryptococcal meningitis, the sensitivity, specificity, positive predictive value, negative predictive value, and concordance rate of mNGS were 92%, 100%, 100%, 90.9%, and 95.6%, respectively. Compared to conventional methods, the sensitivity of mNGS was slightly lower than CrAg tests (96.7%) but higher than India ink (79.5%) and culturing (63.4%). Of the two negative mNGS cases (2/25, 8.0%), one was positive by India ink staining, culture, and CrAg testing, while the other was positive only by CrAg testing. A combination of mNGS and conventional methods enhanced the detection rate to 100%. Our study demonstrates that both CrAg and mNGS offer excellent diagnostic accuracy for cryptococcal meningitis, and utilizing both tests can enhance clinical assessment and patient management.

Clinical treatment of cryptococcal meningitis: an evidence-based review on the emerging clinical data

Cryptococcal meningitis (CM) is a fatal fungal central nervous system (CNS) infection caused by Cryptococcus infecting the meninges and/or brain parenchyma, with fever, headache, neck stiffness, and visual disturbances as the primary clinical manifestations. Immunocompromised individuals with human immunodeficiency virus (HIV) infection or who have undergone organ transplantation, as well as immunocompetent people can both be susceptible to CM. Without treatment, patients with CM may have a mortality rate of up to 100% after hospital admission. Even after receiving therapy, CM patients may still suffer from problems such as difficulty to cure, poor prognosis, and high mortality. Therefore, timely and effective treatment is essential to improve the mortality and prognosis of CM patients. Currently, the clinical outcomes of CM are frequently unsatisfactory due to limited drug choices, severe adverse reactions, drug resistance, etc. Here, we review the research progress of CM treatment strategies and discuss the suitable options for managing CM, hoping to provide a reference for physicians to select the most appropriate treatment regimens for CM patients.

Pulmonary Cryptococcosis

Pulmonary cryptococcosis describes an invasive lung mycosis caused by Cryptococcus neoformans or Cryptococcus gattii complex. It is often a high-consequence disease in both immunocompromised and immunocompetent populations, and may be misdiagnosed as pulmonary malignancy, leading to a delay in therapy. Epidemiology follows that of cryptococcal meningoencephalitis, with C. gattii infection more common in certain geographic regions. Diagnostic tools include histopathology, microscopy and culture, and the detection of cryptococcal polysaccharide antigen or Cryptococcus-derived nucleic acids. All patients with lung cryptococcosis should have a lumbar puncture and cerebral imaging to exclude central nervous system disease. Radiology is key, both as an adjunct to laboratory testing and as the initial means of detection in asymptomatic patients or those with non-specific symptoms. Pulmonary cryptococcomas (single or multiple) may also be associated with disseminated disease and/or cryptococcal meningitis, requiring prolonged treatment regimens. Optimal management for severe disease requires extended induction (amphotericin B and flucytosine) and consolidation therapy (fluconazole) with close clinical monitoring. Susceptibility testing is of value for epidemiology and in regions where relatively high minimum inhibitory concentrations to azoles (particularly fluconazole) have been noted. Novel diagnostic tools and therapeutic agents promise to improve the detection and treatment of cryptococcosis, particularly in low-income settings where the disease burden is high.

Sterylglucosides in Fungi

Sterylglucosides (SGs) are sterol conjugates widely distributed in nature. Although their universal presence in all living organisms suggests the importance of this kind of glycolipids, they are yet poorly understood. The glycosylation of sterols confers a more hydrophilic character, modifying biophysical properties of cell membranes and altering immunogenicity of the cells. In fungi, SGs regulate different cell pathways to help overcome oxygen and pH challenges, as well as help to accomplish cell recycling and other membrane functions. At the same time, the level of these lipids is highly controlled, especially in wild-type fungi. In addition, modulating SGs metabolism is becoming a novel tool for vaccine and antifungal development. In the present review, we bring together multiple observations to emphasize the underestimated importance of SGs for fungal cell functions.

Clinical performance of the IMMY cryptococcal antigen lateral flow assay in dogs and cats

BACKGROUND

Cryptococcal lateral flow antigen assays (CLFAs) have been assessed in comparison to the latex cryptococcal antigen agglutination test but their clinical performance is unknown.

OBJECTIVE

Determine clinical performance of IMMY CLFA (Immuno-Mycologics Inc, Oklahoma) using patients with and without cryptococcosis as the reference standard.

ANIMALS

One-hundred ninety-seven serum samples from client-owned dogs and cats.

METHODS

Review of medical records of a referral population of dogs and cats that had CLFA performed between 2012 and 2020. Animals were classified as cryptococcosis positive (Cr+) or negative (Cr-) based on clinical information. Clinical diagnosis was used to calculate positive and negative percent agreement of the CLFA.

RESULTS

Twelve specimens (4 canine, 8 feline) were obtained from Cr+ animals and had positive CLFA results. One-hundred eighty-five specimens (139 canine, 46 feline) were collected from Cr- animals. Negative CLFA results were recorded in 129 canine and 44 feline Cr- samples. Positive CLFA results were noted for 10 canine and 2 feline Cr- samples. Positive percent agreement of CLFA was 100% (confidence interval [CI], 39.8%-100% dogs; 63.1%-100% cats). Negative percent agreements were 92.8% (CI, 87.2%-96.5%) for dogs and 95.7% (CI, 85.2%-99.5%) for cats.

CONCLUSIONS AND CLINICAL IMPORTANCE

A negative IMMY CLFA result enables reliable exclusion of cryptococcal infection in dogs and cats. By contrast, a positive result must be interpreted cautiously and further testing should be performed to verify a diagnosis of cryptococcosis.

Comparison of features and outcomes between HIV-negative patients with Cryptococcus gattii meningitis and Cryptococcus neoformans meningitis in South China

OBJECTIVES

To compare the epidemiologic, clinical, laboratory, and imaging features, and outcomes in patients with Cryptococcus gattii meningitis (CGM) and Cryptococcus neoformans meningitis (CNM).

METHODS

We performed a retrospective study of HIV-negative patients with CGM and CNM (2015-2021) distinguished by metagenomic next-generation sequencing in cerebrospinal fluid in South China.

RESULTS

81 patients (17 CGM, 64 CNM) were enrolled (72.8% male, median age 49 years, range 21-77 years), and CGM patients were younger (median, 43 vs 53 years, p = 0.005). Of 17 CGM, VGI and VGII accounted for 70.6% and 29.4%, respectively. CGM patients had less underlying diseases (7/17 [41.2%] vs 48/64 [75%], p=0.018) and focal neurologic deficit (3/17 [17.6%] vs 35/64 [54.7%], p = 0.022), had higher intracranial pressure (15/17 [88.2%] vs 25/64 [39.1%], p=0.002), more meningeal enhancement (14/17 [82.4%] vs 32/64 [50%], p = 0.034), less parenchymal involvement (median, 1 vs 3, p = 0.018), more lung cryptococcomas (6/12 [50%] vs 6/47 [12.8%], p = 0.014), faster CSF fungal clearance (p = 0.004), less complications (median, 1 vs 3, p < 0.001), and more favorable outcomes (16/17 [94.1%] vs 41/64 [64.1%], p =0.035).

CONCLUSIONS

This study demonstrated that species identification helps to guide therapy and predict outcomes.

Performance of Metagenomic Next-Generation Sequencing for the Diagnosis of Cryptococcal Meningitis in HIV-Negative Patients

Objectives

Metagenomic next-generation sequencing (mNGS) has been applied more and more widely for the diagnosis of infectious diseases, but its performance in the diagnosis of cryptococcal meningitis (CM) remains unclear.

Methods

Cerebrospinal fluid (CSF) samples from 197 HIV-negative patients with suspected central nervous system infections were tested simultaneously by mNGS and routine methods [India ink staining, fungal culture, or cryptococcal antigen (CrAg) tests]. The performance of mNGS was evaluated.

Results

Of the 197 enrolled cases, 46 (23.4%) cases were finally diagnosed with CM, including 43 (93.5%) Cryptococcus neoformans infections and 3 (6.5%) Cryptococcus gattii infections. The sensitivity, specificity, positive predictive value, negative predictive value, and concordance rate of mNGS were 93.5% [95% confidence interval (CI) at 86.4%~100.0%], 96.0% (95% CI at 92.9%~99.1%), 87.8%, 98.0%, and 95.4%, respectively. Comparing to the conventional diagnostic methods, the sensitivity and concordance rate of mNGS were slightly lower than those of CrAg tests (97.4%) but higher than those of India ink (63.0%) and culture (76.7%). Besides, mNGS had a sensitivity of 100.0% against culture. It should be noted that mNGS could identify Cryptococcus at species level; C. gattii of the 3 cases was only distinguished by mNGS.

Conclusions

CSF mNGS can be considered as a supplementary test to diagnose CM and directly distinguish C. gattii from C. neoformans in clinical specimens.

The aetiology and clinical characteristics of cryptococcal infections in Far North Queensland, tropical Australia

Cryptococcal infections are an important cause of morbidity and mortality in tropical Australia. This retrospective audit was conducted to characterise the aetiology, temporospatial epidemiology, and clinical course of 49 cryptococcal infections in Far North Queensland between 1 January 1999 and 31 December 2019. Cryptococcus gattii was identified in 15/32 (47%) in whom it was possible to speciate the organism. Among these 15 patients, 13 (87%) had a rural residential address, 10 (67%) were Indigenous Australians and 11 (73%) presented during the May-November dry season. When compared to the 17 patients with Cryptococcus neoformans infection, patients with C. gattii were less likely to be immunocompromised (0/15 versus 8/17 (47%), p = 0.003). Neurosurgery was necessary in 5/15 C. gattii cases and 3/17 (18%) C. neoformans cases (p = 0.42). Outcomes were generally good with 42/49 (86%) cases—and 14/15 (93%) with C. gattii infection—surviving to hospital discharge. These positive outcomes are likely to be explained by the development of standardised treatment guidelines during the study period, low rates of comorbidity in the patients with C. gattii infection and access to liposomal amphotericin and neurosurgical support in the well-resourced Australian healthcare system.

A forkhead transcription factor contributes to the regulatory differences of pathogenicity in closely related fungal pathogens

Cryptococcus neoformans and its sister species Cryptococcus deuterogattii are important human fungal pathogens. Despite their phylogenetically close relationship, these two Cryptococcus pathogens are greatly different in their clinical characteristics. However, the determinants underlying the regulatory differences of their pathogenicity remain largely unknown. Here, we show that the forkhead transcription factor Hcm1 promotes infection in C. neoformans but not in C. deuterogattii. Monitoring in vitro and in vivo fitness outcomes of multiple clinical isolates from the two pathogens indicates that Hcm1 mediates pathogenicity in C. neoformans through its key involvement in oxidative stress defense. By comparison, Hcm1 is not critical for antioxidation in C. deuterogattii. Furthermore, we identified SRX1, which encodes the antioxidant sulfiredoxin, as a conserved target of Hcm1 in two Cryptococcus pathogens. Like HCM1, SRX1 had a greater role in antioxidation in C. neoformans than in C. deuterogattii. Significantly, overexpression of SRX1 can largely rescue the defective pathogenicity caused by the absence of Hcm1 in C. neoformans. Conversely, Srx1 is dispensable for virulence in C. deuterogattii. Overall, our findings demonstrate that the difference in the contribution of the antioxidant sulfiredoxin to oxidative stress defense underlies the Hcm1-mediated regulatory differences of pathogenicity in two closely related pathogens.

Cryptococcal meningoencephalitis: time for action

Cryptococcal meningoencephalitis was first described over a century ago. This fungal infection is preventable and treatable yet continues to be associated with excessive morbidity and mortality. The largest burden of disease resides in people living with HIV in low-income and middle-income countries. In this group, mortality with the best antifungal induction regimen (7 days of amphotericin B deoxycholate [1·0 mg/kg per day] and flucytosine [100·0 mg/kg per day]) in a clinical trial setting was 24% at 10 weeks. The world is now at an inflection point in terms of recognition, research, and action to address the burden of morbidity and mortality from cryptococcal meningoencephalitis. However, the scope of interventional programmes needs to increase, with particular attention to implementation science that is specific to individual countries. This Review summarises causes of excessive mortality, interventions with proven survival benefit, and gaps in knowledge and practice that contribute to the ongoing high death toll from cryptococcal meningoencephalitis. TRANSLATIONS: For the Vietnamese and Chichewa translations of the abstract see Supplementary Materials section.

Animal Models of Cryptococcus neoformans in Identifying Immune Parameters Associated With Primary Infection and Reactivation of Latent Infection

Cryptococcus species are environmental fungal pathogens and the causative agents of cryptococcosis. Infection occurs upon inhalation of infectious particles, which proliferate in the lung causing a primary infection. From this primary lung infection, fungal cells can eventually disseminate to other organs, particularly the brain, causing lethal meningoencephalitis. However, in most cases, the primary infection resolves with the formation of a lung granuloma. Upon severe immunodeficiency, dormant cryptococcal cells will start proliferating in the lung granuloma and eventually will disseminate to the brain. Many investigators have sought to study the protective host immune response to this pathogen in search of host parameters that keep the proliferation of cryptococcal cells under control. The majority of the work assimilates research carried out using the primary infection animal model, mainly because a reactivation model has been available only very recently. This review will focus on anti-cryptococcal immunity in both the primary and reactivation models. An understanding of the differences in host immunity between the primary and reactivation models will help to define the key host parameters that control the infections and are important for the research and development of new therapeutic and vaccine strategies against cryptococcosis.

Expansion of the Emerging Fungal Pathogen Cryptococcus bacillisporus Into America: Linking Phylogenetic Origin, Geographical Spread and Population Under Exposure Risk

In 2018 the fungal pathogen Cryptococcus bacillisporus (AFLP5/VGIII) was isolated for the first time in Chile, representing the only report in a temperate region in South America. We reconstructed the colonization process of C. bacillisporus in Chile, estimating the phylogenetic origin, the potential spread zone, and the population at risk. We performed a phylogenetic analysis of the strain and modeled the environmental niche of the pathogen projecting its potential spread zone into the new colonized region. Finally, we generated risk maps and quantified the people under potential risk. Phylogenetic analysis showed high similarity between the Chilean isolate and two clonal clusters from California, United States and Colombia in South America. The pathogen can expand into all the temperate Mediterranean zone in central Chile and western Argentina, exposing more than 12 million people to this pathogen in Chile. This study has epidemiological and public health implications for the response to a potential C. bacillisporus outbreak, optimizing budgets, routing for screening diagnosis, and treatment implementation.

Treatment of invasive fungal diseases in cancer patients-Revised 2019 Recommendations of the Infectious Diseases Working Party (AGIHO) of the German Society of Hematology and Oncology (DGHO)

BACKGROUND

Invasive fungal diseases remain a major cause of morbidity and mortality in cancer patients undergoing intensive cytotoxic therapy. The choice of the most appropriate antifungal treatment (AFT) depends on the fungal species suspected or identified, the patient's risk factors (eg length and depth of granulocytopenia) and the expected side effects.

OBJECTIVES

Since the last edition of recommendations for 'Treatment of invasive fungal infections in cancer patients' of the Infectious Diseases Working Party (AGIHO) of the German Society of Hematology and Medical Oncology (DGHO) in 2013, treatment strategies were gradually moving away from solely empirical therapy of presumed or possible invasive fungal diseases (IFDs) towards pre-emptive therapy of probable IFD.

METHODS

The guideline was prepared by German clinical experts for infections in cancer patients in a stepwise consensus process. MEDLINE was systematically searched for English-language publications from January 1975 up to September 2019 using the key terms such as 'invasive fungal infection' and/or 'invasive fungal disease' and at least one of the following: antifungal agents, cancer, haematological malignancy, antifungal therapy, neutropenia, granulocytopenia, mycoses, aspergillosis, candidosis and mucormycosis.

RESULTS

AFT of IFDs in cancer patients may include not only antifungal agents but also non-pharmacologic treatment. In addition, the armamentarium of antifungals for treatment of IFDs has been broadened (eg licensing of isavuconazole). Additional antifungals are currently under investigation or in clinical trials.

CONCLUSIONS

Here, updated recommendations for the treatment of proven or probable IFDs are given. All recommendations including the levels of evidence are summarised in tables to give the reader rapid access to key information.

Cryptococcus gattii infection complicated by immune reconstitution inflammatory syndrome in three apparently immunocompetent children

BACKGROUND

Paediatric Cryptococcus gattii disease is rare, with only two previous cases recorded in the Northern Territory (NT) over the last 54 years. Immune reconstitution inflammatory syndrome (IRIS) is a recognised complication of C. gattii infection, even in the absence of an identified immunodeficiency syndrome; however, limited paediatric data exist. We present a series of three paediatric patients treated for C. gattii infection in the NT during 2016/2017.

CASE DISCUSSIONS

All three cases were males aged 8-13 years at the time of presentation. Two were Aboriginal Australians from remote NT communities, and the third was a Timorese child from a remote district in Timor-Leste. All cases had evidence of brain cryptococcomas, and two had associated pulmonary lesions. Each child was treated with a 6-week induction phase of intravenous liposomal amphotericin and flucytosine and then continued on a 2-year course of eradication oral fluconazole. Persistent high intracranial pressure (ICP) complicated each case, requiring serial lumbar punctures and, in two cases, insertion of ventriculoperitoneal shunts. All three cases were diagnosed with IRIS between 5 and 10 weeks after commencement of antifungal treatment and were managed with high-dose corticosteroids, which were weaned slowly (6-20 months post-commencement).

CONCLUSIONS

Paediatric C. gattii disease is rare, although three recent cases in the NT highlight some of the challenges involved in managing the infection, including persistent raised ICP and complications such as IRIS. There is a need for further collaborative research into paediatric C. gattii disease.

Apparent performance of metagenomic next-generation sequencing in the diagnosis of cryptococcal meningitis: a descriptive study

INTRODUCTION

In recent years, metagenomic next-generation sequencing (mNGS) has become widely used in medical microbiology to detect pathogen infection.

AIM

We aimed to assess the diagnostic performance of mNGS of cerebrospinal fluid (CSF) for prediction of cryptococcal meningitis (CM).

METHODOLOGY

A comparative evaluation of mNGS (performed on CSF samples) and conventional methods, including India ink staining, culture for fungi and cryptococcal-antigen (CrAg) detection by enzyme immunoassay, was performed on 12 consecutive non-HIV-infected patients with chronic or subacute CM.

RESULTS

India ink staining and culture of the CSF were positive for Cryptococcus in 83.33 % (10/12) of the samples; 100 % (11/11) were positive via CrAg EIA. The mNGS results of the CSF identified DNA sequences corresponding to Cryptococcus in 75 % of samples (9/12). However, the DNA of both C. neoformans s.l. and C. gattii s.l. was detected concurrently in 33.33 % (4/12).

CONCLUSION

mNGS is helpful for identifying Cryptococcus species. The application of mNGS, together with India ink staining, culture methods, and CrAg, may significantly improve the diagnostic precision in CM, thereby informing choice of appropriate antifungal treatment courses.

Targeting the Immune System with Plant Lectins to Combat Microbial Infections

The arsenal of drugs available to treat infections caused by eukaryotic and prokaryotic microbes has been declining exponentially due to antimicrobial resistance phenomenon, leading to an urgent need to develop new therapeutic strategies. Host-directed immunotherapy has been reported as an attractive option to treat microbial infections. It consists in the improvement of host defenses by increasing the expression of inflammatory mediators and/or controlling of inflammation-induced tissue injury. Although the in vitro antimicrobial and immunomodulatory activities of lectins have been extensively demonstrated, few studies have evaluated their in vivo effects on experimental models of infections. This review aims to highlight the experimental use of immunomodulatory plant lectins to improve the host immune response against microbial infections. Lectins have been used in vivo both prophylactically and therapeutically resulting in the increased survival of mice under microbial challenge. Other studies successfully demonstrated that lectins could be used in combination with parasite antigens in order to induce a more efficient immunization. Therefore, these plant lectins represent new candidates for management of microbial infections. Furthermore, immunotherapeutic studies have improved our knowledge about the mechanisms involved in host–pathogen interactions, and may also help in the discovery of new drug targets.

Equine Pulmonary Cryptococcosis: A Comparative Literature Review and Evaluation of Fluconazole Monotherapy

Cryptococcus is the most common fungal respiratory pathogen in Australian horses, manifesting primarily as pulmonary granulomas. Disease severity at presentation is dependent on the athletic use of the horse. The diagnosis and estimation of disease severity are centred around clinical findings, cytological evaluation of respiratory tract secretions, diagnostic imaging, and antigen titre testing. Both the lateral flow assay and the latex cryptococcal antigen titre are used, and important similarities and differences between species are discussed. Cryptococcus gattii occurs with greater frequency than Cryptococcus neoformans in equine pulmonic cryptococcosis and can be successfully treated with enteral fluconazole monotherapy, with disease severity determining treatment length.

A Zebrafish Model of Cryptococcal Infection Reveals Roles for Macrophages, Endothelial Cells, and Neutrophils in the Establishment and Control of Sustained Fungemia

Cryptococcal meningoencephalitis is a fungal infection that predominantly affects immunocompromised patients and is uniformly fatal if left untreated. Timely diagnosis is difficult, and screening or prophylactic measures have generally not been successful. Thus, we need a better understanding of early, asymptomatic pathogenesis. Inhaled cryptococci must survive the host immune response, escape the lung, and persist within the bloodstream in order to reach and invade the brain. Here we took advantage of the zebrafish larval infection model to assess the process of cryptococcal infection and disease development sequentially in a single host. Using yeast or spores as infecting particles, we discovered that both cell types survived and replicated intracellularly and that both ultimately established a sustained, low-level fungemia. We propose that the establishment and maintenance of this sustained fungemia is an important stage of disease progression that has been difficult to study in other model systems. Our data suggest that sustained fungemia resulted from a pattern of repeated escape from, and reuptake by, macrophages, but endothelial cells were also seen to play a role as a niche for cryptococcal survival. Circulating yeast collected preferentially in the brain vasculature and eventually invaded the central nervous system (CNS). As suggested previously in a mouse model, we show here that neutrophils can play a valuable role in limiting the sustained fungemia, which can lead to meningoencephalitis. This early stage of pathogenesis-a balanced interaction between cryptococcal cells, macrophages, endothelial cells, and neutrophils-could represent a window for timely detection and intervention strategies for cryptococcal meningoencephalitis.

Cryptococcus neoformans var. grubii-Induced Arthritis with Encephalitic Dissemination in a Dog and Review of Published Literature

This article describes the clinical, pathological, and immunohistochemical findings associated with Cryptococcus neoformans var. grubii in a 4-year-old female Boxer dog from Uberlândia, Minas Gerais, Southeastern Brazil. Clinically, there was a swelling at the right metatarsal region and the hock joint with enlargement of regional lymph nodes. Radiographical evaluation revealed lysis of the tarsal bone; cytology demonstrated cryptococcal intralesional organisms at the swollen joint. Despite empirical antifungals therapeutic, the animal developed neurological cryptococcosis and died spontaneously. Significant pathological alterations included arthritis, lymphadenitis, and encephalitic cryptococcomas associated with numerous intralesional narrow-necked budding encapsulated yeasts. Immunohistochemistry utilising monoclonal antibodies that label C. neoformans sp. complex capsule, characterised the yeasts as C. neoformans var. grubii. Collectively, the pathological and immunohistochemical findings of this dog indicate that the intralesional organisms observed within the articular surface of the hock joint, lymph nodes, and the brain were C. neoformans var. grubii, confirming the participation of this fungal pathogen in the development of cryptococcal arthritis. In this case, the most likely pathogenesis was percutaneous inoculation with resultant abscess-like lesion, which resulted in the draining sinus, swelling of the right hind limb with progression to the articular disease. Thereafter, the fungal pathogen probably compromised the adjacent lymph nodes with subsequent haematogenous distribution to the brain, terminating with cryptococcal arthritis, lymphadenitis, and encephalitis.

Cryptococcal meningitis initially presenting with eye symptoms in an immunocompetent patient: A case report

Although cryptococcal meningitis (CM) typically occurs in immunocompromised hosts, immunocompetent humans are susceptible to CM. In humans with an intact immune system, CM presents with signs and symptoms typical of meningitis, including fever, headache and neck stiffness. The present study reported the case of a female immunocompetent patient who presented visual blurring in both eyes and bilateral papilledema for ~1 month. Following hospital admission, the patient was diagnosed with optic nerve inflammation and was treated with intravenous methylprednisolone and oral prednisone. However, the initial symptoms failed to improve and the patient developed a headache. The microscopic examination and India ink test performed using the cerebrospinal fluid of the patient showed the presence of Cryptococcus neoformans. Following combined treatment with amphotericin B and fluconazole, the patient made a full recovery with total resolution of the initial symptoms. This case demonstrates that CM in immunocompetent patients may initially include eye symptoms, which may result in a delayed diagnosis of CM.

Cryptococcosis-the impact of delay to diagnosis

Cryptococcosis is a mycotic disease caused by the yeast Cryptococcus sp. It is associated with significant mortality and morbidity, including long-term neurological sequelae. It is not known whether the high morbidity observed is related to a delay in diagnosis. A retrospective chart review of all cryptococcal infections that had been diagnosed in the region between 1997 and 2015 was performed. Twenty-nine cases were identified. Overall mortality rate was 10.3%, with an attributable mortality rate of 6.9%. Forty-five per cent of patients with central nervous system involvement developed long-term neurological deficits. Significant associations were noted between those with and without long-term neurological deficits and in both time from onset of symptoms to diagnosis (median of 45.5 days versus 18.5 days, respectively) and time from presentation to diagnosis (median 14.5 days versus 7 days, respectively). In addition, raised intracranial pressure (p 0.03) and female gender (p 0.02) were significantly associated with poor neurological outcomes. This highlights the importance of early diagnosis and the need to limit raised intracranial pressure to minimize long-term neurological deficits.

Approach to the Solid Organ Transplant Patient with Suspected Fungal Infection

In solid organ transplant (SOT) recipients, invasive fungal infections (IFIs) are associated with significant morbidity and mortality. Detection of IFIs can be difficult because the signs and symptoms are similar to those of viral or bacterial infections, and diagnostic techniques have limited sensitivity and specificity. Clinicians must rely on knowledge of the patient's risk factors for fungal infection to make a diagnosis. The authors describe their approach to the SOT recipient with suspected fungal infection. The epidemiology of IFIs in the SOT population is reviewed, and a syndromic approach to suspected IFI in SOT recipients is described.

Fluconazole Susceptibility in Cryptococcus gattii Is Dependent on the ABC Transporter Pdr11

Cryptococcus gattii isolates from the Pacific Northwest have exhibited higher fluconazole MICs than isolates from other sites. The mechanism of fluconazole resistance in C. gattii is unknown. We sought to determine the role of the efflux pumps Mdr1 and Pdr11 in fluconazole susceptibility. Using biolistic transformation of the parent isolate, we created a strain lacking Mdr1 (mdr1Δ) and another strain lacking Pdr11 (pdr11Δ). Phenotypic virulence factors were assessed by standard methods (capsule size, melanin production, growth at 30 and 37 °C). Survival was assessed in an intranasal murine model of cryptococcosis. Antifungal MICs were determined by the M27-A3 methodology. No differences in key virulence phenotypic components were identified. Fluconazole susceptibility was unchanged in the Mdr1 knockout or reconstituted isolates. However, fluconazole MICs decreased from 32 μg/ml for the wild-type isolate to <0.03 μg/ml for the pdr11Δ strain and reverted to 32 μg/ml for the reconstituted strain. In murine models, no difference in virulence was observed between wild-type, knockout, or reconstituted isolates. We conclude that Pdr11 plays an essential role in fluconazole susceptibility in C. gattii. Genomic and expression differences between resistant and susceptible C. gattii clinical isolates should be assessed further in order to identify other potential mechanisms of resistance.

Cryptococcus gattii-Induced Infections in Dogs from Southern Brazil

Cryptococcus gattii-induced cryptococcosis is an emerging infectious disease of humans and animals worldwide, with rare descriptions of this infection in domestic animals from Brazil. This study presents the findings associated with C. gattii in dogs from Londrina, Paraná, Southern Brazil. Two dogs, a 3-year-old, female German shepherd and a 6-year-old, male Boxer, were evaluated by a combination of pathological, mycological, and molecular diagnostic techniques. Significant pathological alterations included cryptococcal lymphadenitis, meningoencephalitis, tonsillitis, and rhinitis with nasal cryptococcomas in the German shepherd dog, while cryptococcal lymphadenitis and pneumonia were observed in the Boxer; both dogs had pseudocystic cryptococcosis. The mucicarmine histochemical stain readily identified the intralesional cryptococcal budding organisms in all affected tissues. Mycological culture and isolation confirmed the yeasts as C. gattii due to positive reaction with the L-canavanine glycine bromothymol blue agar. A PCR assay using the internal transcribed spacers (ITS)1 and ITS2 primers, which target the ITS1 and 2 regions including the 5.8S rRNA gene, amplified the desired amplicons; direct sequencing confirmed the isolate as C. gattii. ITS nucleotide differentiation demonstrated that the isolate forms part of the ITS type 4 Cryptococcus organisms which corresponds to the C. gattii VGII molecular subtype or the RAPD type 2 Cryptococcus organisms. Collectively, these findings confirmed the participation of C. gattii in the etiopathogenesis of the lesions observed in these dogs and expanded the epidemiological niche of this important mycotic agent to include Southern Brazil. It is noteworthy to mention that previous epidemiological studies have suggested that C. gattii-induced cryptococcosis is more frequently diagnosed in Northern relative to Southern Brazil, so these findings might suggest an expansion of the distribution of this agent within continental Brazil.

Accurate and sensitive real-time PCR assays using intergenic spacer 1 region to differentiate Cryptococcus gattii sensu lato and Cryptococcus neoformans sensu lato

In this work, two accurate and sensitive real-time polymerase chain reaction (PCR) assays to differentiate pathogenic Cryptococcus gattii sensu lato (s.l.) and C. neoformans sensu lato (s.l.) targeting the intergenic spacer 1 (IGS1) region from rDNA locus were developed. Specific primers were designed based on their IGS1 sequence analyses and the optimal real-time PCR assays showed that the dissociation curves generated two different melting peaks, at 82.8 and 84.2ºC for C. gattii s.l. and C. neoformans s.l., respectively. No amplifications were observed in the negative template control. The minimum limit of detection of both primers was 100 plasmid copies per reaction, and they were highly specific when tested with a range of fungal DNAs. Overall, the results showed that the designed primers completely differentiated C. gattii s.l. and C. neoformans s.l. from clinical and environmental sources with great accuracy when compared to phenotypic identification, with no cross-reactivity to other fungal DNA.

Cryptococcus gattii infections

Understanding of the taxonomy and phylogeny of Cryptococcus gattii has been advanced by modern molecular techniques. C. gattii probably diverged from Cryptococcus neoformans between 16 million and 160 million years ago, depending on the dating methods applied, and maintains diversity by recombining in nature. South America is the likely source of the virulent C. gattii VGII molecular types that have emerged in North America. C. gattii shares major virulence determinants with C. neoformans, although genomic and transcriptomic studies revealed that despite similar genomes, the VGIIa and VGIIb subtypes employ very different transcriptional circuits and manifest differences in virulence phenotypes. Preliminary evidence suggests that C. gattii VGII causes severe lung disease and death without dissemination, whereas C. neoformans disseminates readily to the central nervous system (CNS) and causes death from meningoencephalitis. Overall, currently available data indicate that the C. gattii VGI, VGII, and VGIII molecular types more commonly affect nonimmunocompromised hosts, in contrast to VGIV. New, rapid, cheap diagnostic tests and imaging modalities are assisting early diagnosis and enabling better outcomes of cerebral cryptococcosis. Complications of CNS infection include increased intracranial pressure, severe neurological sequelae, and development of immune reconstitution syndrome, although the mortality rate is low. C. gattii VGII isolates may exhibit higher fluconazole MICs than other genotypes. Optimal therapeutic regimens are yet to be determined; in most cases, initial therapy with amphotericin B and 5-flucytosine is recommended.

Heteroresistance to Itraconazole Alters the Morphology and Increases the Virulence of Cryptococcus gattii

Cryptococcus gattii is the main etiological agent of cryptococcosis in immunocompetent individuals. The triazole drug itraconazole is one of the antifungals used to treat patients with cryptococcosis. Heteroresistance is an adaptive mechanism to counteract the stress of increasing drug concentrations, and it can enhance the ability of a microorganism to survive under antifungal pressure. In this study, we evaluated the ability of 11 C. gattii strains to develop itraconazole heteroresistance. Heteroresistant clones were analyzed for drug susceptibility, alterations in cell diameter, capsule properties, and virulence in a murine model. Heteroresistance to itraconazole was intrinsic in all of the strains analyzed, reduced both the capsule size and the cell diameter, induced molecular heterogeneity at the chromosomal level, changed the negatively charged cells, reduced ergosterol content, and improved the antioxidant system. A positive correlation between surface/volume ratio of original cells and the level of heteroresistance to itraconazole (LHI) was observed in addition to a negative correlation between capsule size of heteroresistant clones and LHI. Moreover, heteroresistance to itraconazole increased the engulfment of C. gattii by macrophages and augmented fungal proliferation inside these cells, which probably accounted for the reduced survival of the mice infected with the heteroresistant clones and the higher fungal burden in lungs and brain. Our results indicate that heteroresistance to itraconazole is intrinsic and increases the virulence of C. gattii. This phenomenon may represent an additional mechanism that contributes to relapses of cryptococcosis in patients during itraconazole therapy.