Cryptococcal meningitis in India

Pushpa Yadav; Manodeep Sen; Anupam Das; Tanushri Chaterji

doi:10.4103/mgmj.mgmj_14_20

REVIEW ARTICLE

Year : 2019 | Volume : 6 | Issue : 4 | Page : 194-203

Cryptococcal meningitis in India

Pushpa Yadav¹, Manodeep Sen¹, Anupam Das¹, Tanushri Chaterji²
¹ Department of Microbiology, Dr. Ram Manohar Lohia Institute of Medical Sciences, Lucknow, Uttar Pradesh, India
² Department of Microbiology, Babu Banarasi Das College of Dental Sciences, Babu Banarasi Das University, Lucknow, Uttar Pradesh, India

Date of Submission	27-Jan-2020
Date of Acceptance	13-Feb-2020
Date of Web Publication	29-Apr-2020

Correspondence Address:
Dr. Manodeep Sen
Department of Microbiology, Dr. Ram Manohar Lohia Institute of Medical Sciences, Vibhuti Khand, Gomti Nagar, Lucknow 226010, Uttar Pradesh.
India

Source of Support: None, Conflict of Interest: None

DOI: 10.4103/mgmj.mgmj_14_20

Abstract

Cryptococcal meningitis caused by the environmental yeast Cryptococcus neoformans has emerged as a significant pathogen in immunocompromised and immunocompetent patient especially in human immunodeficiency virus (HIV) or acquired immune deficiency syndrome (AIDS). Recent advances in the diagnosis and management of cryptococcal meningitis are promising and have been improving long-term survival. Point-of-care testing has made diagnosing cryptococcal meningitis rapid, practical, and affordable. Cryptococcus neoformans var. neoformans is predominantly found in Cerebro Spinal Fluid sample. Although the diagnostic testing and the antifungal treatment of cryptococcal infections have become firmly established in clinical practice, new developments and the areas of ambiguity merit further consideration. Early diagnosis followed by the institution of specific therapy, where possible, has effectively reduced mortality. This review aims to present status of cryptococcosis in India. Fortunately, new approaches have been leading the way toward improving care for cryptococcal meningitis patients. New trials using different combinations of antifungal therapy are reviewed, and we summarize the efficacy of different regimens.

Keywords: Acquired immune deficiency syndrome, antifungal therapy, cryptococcal meningitis, high active antiretroviral therapy, human immunodeficiency virus, immune reconstitution inflammatory syndrome

How to cite this article:
Yadav P, Sen M, Das A, Chaterji T. Cryptococcal meningitis in India. MGM J Med Sci 2019;6:194-203

How to cite this URL:
Yadav P, Sen M, Das A, Chaterji T. Cryptococcal meningitis in India. MGM J Med Sci [serial online] 2019 [cited 2023 Mar 28];6:194-203. Available from: http://www.mgmjms.com/text.asp?2019/6/4/194/283455

Introduction

Cryptococcus neoformans var. neoformans is an opportunistic fungal pathogen that causes cryptococcal meningitis, which is mostly in human immunodeficiency virus (HIV)-infected and immunocompromised/immunocompetent patients.^[1] Cryptococcosis is an important opportunistic fungal infection causing an estimated 1 million cases and 625,000 deaths per year due to central nervous system (CNS) disease among patients with HIV worldwide.^[2]Cryptococcus neoformans is a human fungal pathogen that causes life-threatening meningoencephalitis in immunocompromised and, in some cases, immunocompetent hosts.^[3] Two C. neoformans serotypes are currently recognized: the most common causative agent of cryptococcosis is serotype A (C. neoformans var. grubii), and the relatively less virulent is serotype D (C. neoformans var. neoformans).^[4],[5]Cryptococcus gattii has been classified into two additional serotypes, B and C, but these are currently considered to be sibling species.^[4],[5],[6]

The vast majority of cases globally were caused by C. neoformans, compared to the more geographically restricted C. gattii. Although cryptococcosis is most often associated with HIV infection, in many centers, especially in more developed countries, the majority of cases occur among non-HIV-infected individuals including transplant recipients; patients who are receiving immunosuppressive agents such as glucocorticosteroids, cytotoxic chemotherapy, tumor necrosis factor-alpha (TNF-α) inhibitors, and other disease-modifying agents; and a heterogeneous group of patients with underlying disorders such as organ failure syndromes, innate immunologic problems, common variable immunodeficiency, and hematologic disorders.^[7]Cryptococcus neoformans is a heterothallic encapsulated yeast. Microscopically the unicellular cells of the fungus are spherical to oval in shape. Individual cells are surrounded by a polysaccharide capsule. The diameter of the cell can vary from 2–5 m (capsule deficient) to 30–80 m in heavily encapsulated cells.^[8] Recognition of variants in the morphology of the organisms is important in laboratory confirmation of the disease. Characteristic morphology of C. neoformans does not pose any difficulty in recognizing the fungus. But unusual forms may be produced in clinical material, which can give rise to diagnostic dilemmas. Cruickshank et al.^[9] have reported a case of primary cryptococcosis of lungs where giant cells of C. neoformans were observed in the pleural fluid. They showed thick capsules. The average size of the isolates was >40 m and it was associated with enlargement of the cytoplasm, cell wall, and capsule. However, upon culturing in artificial media, the organism reverted to normal size. A rare morphology of hand mirror appearance in direct microscopic examination of both cerebrospinal fluid (CSF) and sputum from a patient with acquired immune deficiency syndrome (AIDS) has been reported by Anandhi et al.^[10]Cryptococcus neoformans grows vegetatively as budding yeast and can be frequently found in tree hollows and pigeon guano. During the sexual cycle [Figure 1], Cryptococcus switches from yeast growth to hyphal growth. Despite this dramatic morphological transition, Cryptococcus is not considered by some to be a dimorphic fungus because yeast cells are the predominant form in the environment and in the human host, and it is likely that the morphological transition is not involved in infection. However, there are at least three important reasons why the development of Cryptococcus is relevant to its pathogenicity. First, spores that result from hyphal development during mating are infectious propagules. Upon inhalation, spores (in addition to desiccated yeast) can colonize the lungs of a host. Cryptococcus neoformans propagate to the bloodstream and cross the blood–brain barrier, ultimately colonizing brain tissue and leading to fatal consequences if not treated. Second, sexual reproduction contributes to the genotypic variability of Cryptococcus species, which may lead to increased fitness and virulence. Third, some genes located within the mating between strains locus are important during mating and during infection. Therefore, the development of Cryptococcus is not only an interesting paradigm for biologists, but also is important in the study of cryptococcal pathogenicity.^[4]

Figure 1: Depiction of a Cryptococcus neoformans cell. (The Science Creative Quarterly, 2003, drawn by Jane Wang)

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When immunity wanes as in HIV infection in the host is kept under control by active cell-mediated immunity (CMI). Virulence factors of cryptococci are the polysaccharide capsule. Phenoloxidases reacts the capsule and produce infection and spread it hematogenously to extrapulmonary tissues. They usually settle in the brain to cause meningoencephalitis, which may be fatal if left untreated.

HIV-infected patients are also susceptible to other mycoses associated with impaired cell-mediated immunity, such as mucosal candidiasis and histoplasmosis, in contrast to mycosis for which neutrophil is the crucial host defense, such as systemic candidiasis, mucormycosis, and aspergillosis during the initial HIV infection.^[9] The incidence of cryptococcal meningitis has declined signiﬁcantly with the use of early antiretroviral treatment and effective antifungal therapy.^[11]

Classification

Cryptococcus neoformans has undergone numerous nomenclature revisions since its first description in 1894. For instance, it once contained two varieties (var.): C. neoformans var. neoformans and C. neoformans var. grubii. A third variety, C. neoformans var. gattii, was defined as a distinct species, C. gattii. The most recent classification system divides organisms into seven species,^[12]Cryptococcus neoformans refers to C. neoformans var. grubii. A new species named C. deneoformans is used for the former C. neoformans var. neoformans. Cryptococcus gattii is divided into five species.^[13] Fungal cells are packed in a rigid, pore-containing cell wall consisting of polysaccharides, proteins, and pigments.^[14],[15]

Remarkably, Cryptococcus is the only eukaryotic pathogen that produces a polysaccharide capsule, which serves as the major virulence factor.^{[16],[17],[18]} This capsule consists of glucuronoxylomannan (GXM) and galactoxylomannan (GalXM), as well as mannoproteins.^[19] GXM is the major capsular polysaccharide; the structural differences of its polymer are the antigenic basis for the C. neoformans serotype classification system described above.^[4] Morphologically, the polysaccharide capsule is not readily visible under light microscopy. Visualization is realized with the help of India ink or with immunofluorescence. Fungal cells produce unique sterols, which are the binding target of amphotericin B as well as extracellular vesicles that are secreted across the cell wall.^[20] GXM is packed in these vesicles and exported to the extracellular milieu^[20] together with other molecules associated with fungal survival and host pathogenicity, including urease and acid phosphatase.^[21]The pigment melanin provides protection against oxidative mechanisms of host defense.^[22]Chitin is another important fungal cell wall component that contributes to its strength and integrity.^[23] The structure of C. neoformans is shown in [Figure 1].

Cryptococcus neoformans grows as a yeast (unicellular) and replicates by budding. It makes hyphae during mating and eventually creates basidiospores at the end of the hyphae before producing spores. Under host-relevant conditions, including low glucose, serum, 5% carbon dioxide, and low iron, among others, the cells produce a characteristic polysaccharide capsule^[12] [Figure 2]A. The recognition of C. neoformans in Gram-stained smears of purulent exudates may be hampered by the presence of the large gelatinous capsule that apparently prevents definitive staining of the yeast-like cells. In such stained preparations, it may appear either as round cells with Gram-positive granular inclusions impressed upon a pale lavender cytoplasmic background or as Gram-negative lipoid bodies.^[24] When grown as yeast, C. neoformans has a prominent capsule composed mostly of polysaccharides. Under the microscope, the India ink stain is used for easy visualization of the capsule in cerebral spinal fluid [Figure 2]B.^[25] The particles of ink pigment do not enter the capsule that surrounds the spherical yeast cell, resulting in a zone of clearance or “halo” around the cells. This allows for quick and easy identification of C. neoformans. Unusual morphological forms are rarely observed.^[26] For identification in tissue, mucicarmine stain provides specific staining of polysaccharide cell wall in C. neoformans. Cryptococcal antigen (CrAg) from the CSF is thought to be the best test for the diagnosis of cryptococcal meningitis in terms of sensitivity, although it might be unreliable in HIV-positive patients.^[27]

Figure 2: (A) Cryptococcus neoformans stained by Gram stain. (B) C. neoformans stained by India ink stain

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The diagnosis of cryptococcosis includes direct examination of the fungus in body fluids with India ink examination, histopathology of infected tissue with specific stains to identify capsule (mucicarmine and alcian blue) or presence of melanin (Fontana-Masson), serology from body fluids and culture of fluids and/or tissues. Despite these multiple strategies to make the diagnosis, the clinician, without risk factor assessments and with its nonspecific symptoms of the disease, can fail to make an early diagnosis of disseminated cryptococcosis that might be critical to outcome. For example, it has been shown that from the beginning time of symptoms both HIV-infected and transplant patients are diagnosed with cryptococcal meningitis within 2–3 weeks. On the contrary, those without these risk factors may take twice as long to make the diagnosis and patient outcome with treatment is worse.^[28] Therefore, despite our diagnostic tools, the critical factor for best outcome will be the clinician’s risk assessment and consideration of cryptococcal meningitis in the diagnosis during early symptoms to then apply these diagnostic strategies.^[29] The diagnostic methods such as histopathology and cultures are well-described in a series of reviews and books.^[30],[31]

The diagnostic area with the most recent evolution has been the serological diagnosis of cryptococcosis. The diagnostic use for detection of cryptococcal capsular polysaccharide in serum and CSF by latex agglutination or enzyme-linked immunosorbent assay (ELISA) has been available for over 35 years and this testing system has an overall sensitivity and specificity of 93%–100% and 93%–98%, respectively. The false positive rate is less than 1% and generally is explained by technical issues or other infections (including a cross reaction with antigens from Trichosporon species). These tests can occasionally yield a false negative output in early infections, but more commonly can be positive before the detection of viable cryptococcal colonies obtained through cultures. A lateral flow assay (LFA) was recently introduced into the diagnostic repertoire for cryptococcosis.^[32],[33]

The semiquantitative LFA offers many advantages including rapid turnaround time, minimal requirements for a specialized laboratory with potential use at “point of care,” and low costs. The LFA has been compared to latex agglutination, ELISA, and cultures with excellent concordance. It works well in resource-limited settings and can even pick up some C. gattii infections not detected by the other serological tests. This LFA is now being instituted in clinical practice and studies have begun as a “point-of-care” testing for preemptive administration of antifungals in resource-limited settings with a high incidence of HIV and cryptococcal diseases. With an accurate “point-of-care” test, these early, precise strategies of diagnostic intervention and preemptive therapy should be considered, implemented, and/or tested.

Polysaccharide antigen testing has two other important principles. First, a baseline high titer of polysaccharide antigen in serum or CSF carries prognostic significance, in that a high titer (>1:1024) is associated with a large burden of yeasts and a high viable quantitative yeast count in CSF is a predictor of death during systemic antifungal therapy.^[34]

Second, the elimination kinetics of polysaccharide in the host is not precise and it is important to recognize that the use of changing polysaccharide antigen titers to make therapeutic decisions should be carried out with caution and in relationship to other clinical factors. Another test in cryptococcal meningitis is the viable quantitative CSF yeast count, which may allow both appreciation of fungal burden and even be used for therapeutic monitoring by measurement of the early fungicidal activity (EFA) with serial quantitative CSF yeast measurements during antifungal treatment.^[35] This test has been used as an effective research tool but has not yet been integrated into routine clinical practice. As we consider more useful and precise follow-up lumbar punctures, this measurement could be insightful for management. Furthermore, the ongoing evaluation of EFA as a potential surrogate marker in cryptococcal meningitis is important if it is to be used in the process of regulatory approval of novel anti-cryptococcal agents.^[29] The sensitivity of CrAg in blood is ≥99% when positive in CSF.^[36] CrAg LFA can be tested in either serum or plasma.^[37] The presence of serum antigenemia in any HIV-infected patient with CNS symptoms should provoke a lumbar puncture with measurement of opening intracranial pressure.^[38],[39]

In a recent study in Uganda, there was perfect agreement between finger-stick whole blood, serum, and plasma CrAg LFA suggesting that testing from finger-stick whole blood is a viable option for detecting antigen CrAg, particularly in settings where phlebotomy is not available, or in patients with difficult venous access.^[40] The CrAg LFA has also been evaluated in both urine and saliva, but agreement with serum LFA was not sufficient to recommend routing screening using these fluids.^[41],[42]

The use of semiquantitative CrAg LFA titers has been shown to correlate with pretreatment quantitative cultures but has not been found to be useful for monitoring treatment response. CrAg titers can also be used as a prognostic marker as titers >1:1024 are associated with greater mortality at two and ten weeks.^[43] However, performing CrAg titers can be labor intensive, requiring extra diluent, and increasing the cost.^[44]

Pathology

Infection with C. neoformans is termed cryptococcosis. Most infections with C. neoformans occur in the lungs.^[45] However, fungal meningitis and encephalitis, especially as a secondary infection for AIDS patients, are often caused by C. neoformans, making it a particularly dangerous fungus. Infections with this fungus are rare in those with fully functioning immune systems, so C. neoformans is sometimes referred to as an opportunistic fungus.^[46] It is a facultative intracellular pathogen^[47] that can use host phagocytes to spread within the body.^[48],[49] In human infection, C. neoformans is spread by inhalation of aerosolized basidiospores and can disseminate to the CNS, where it can cause meningoencephalitis^[50] [Figure 3].

Figure 3: Diagrammatic view of Cryptococcus from the environment to hosts. (Adapted and reprinted with permission from Lin and Heitman^[5])

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In the lungs, C. neoformans cells are phagocytosed by alveolar macrophages.^[51] Macrophages produce oxidative and nitrosative agents, creating a hostile environment, to kill invading pathogens.^[52] However, some C. neoformans cells can survive intracellularly in macrophages.^[51] Intracellular survival appears to be the basis for latency, disseminated disease, and resistance to eradication by antifungal agents. One mechanism by which C. neoformans survives the hostile intracellular environment of the macrophage involves the upregulation of expression of genes involved in responses to oxidative stress.^[51] Traversal of the blood–brain barrier by C. neoformans plays a key role in meningitis pathogenesis.^[53] However, precise mechanisms by which it passes the blood–brain barrier are still unknown; one recent study in rats suggested an important role of secreted serine proteases.^[54] The metalloprotease (Mpr1) has been shown to be critical in blood–brain barrier penetration.^[55]

Serious complications

The infection starts in the lungs [Figure 4], disseminates via blood to meninges, and then to other parts of the body. Capsule inhibits phagocytosis. It can cause a systemic infection, including fatal meningitis known as meningoencephalitis in normal, diabetic and immunocompromised hosts. The infection from C. neoformans in the brain can be fatal if untreated. CNS infection may also be present as a brain abscess known as cryptococcosis, subdural effusion, dementia, isolated cranial nerve lesion, spinal cord lesion, and ischemic stroke. If cryptococcal meningitis occurs, the mortality rate is between 10% and 30%.^[56]

Figure 4: Cryptococcus neoformans observed in the lung of a patient with AIDS. The inner capsule of the organism stains is in red in this photomicrograph

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Radiology

For other published data, we attempted to categorize the computed tomography abnormalities. Although no reported radiological changes in cryptococcal meningitis seem to be specific or unique for the infection, some findings are common and thought to be cryptococcal related. These are, firstly, dilated Virchow–Robin spaces (VR), defined as small hypodense or cystic, non-enhancing, lesions with a diameter of 2–3mm on axial slices. Secondly, gelatinous pseudocysts, presenting as low-density and non-enhancing lesions, but because of accumulation of the yeast, are bigger than VR spaces (>3mm) and are often located in the basal ganglia and periventricular areas. Cryptococcomas are a third specific finding and consist of masses also mostly located in the basal ganglia, with or without enhancement and surrounding edema.^{[57],[58],[59],[60],[61]}

In the setting of confirmed, active cryptococcal meningitis we would also define meningeal enhancement and hydrocephalus (dilated a ventricular system with ballooning of third ventricle recess and temporal horns of the lateral ventricles, not attributed to atrophy) as cryptococcal-related radiological findings. Other nonspecific findings included global cerebral atrophy and symmetrical confluent white matter changes in keeping with HIV encephalopathy.^[62]

The term immune reconstitution inflammatory syndrome (IRIS) has been used to describe a group of clinical syndromes associated with immune reconstitution that has been observed most commonly for mycobacterial infection, but also for other opportunistic infections (OIs), including pneumocystis jirovecii pneumonia (PCP), toxoplasmosis, hepatitis B and hepatitis C viruses, cytomegalovirus (CMV) infection, varicella-zoster virus (VZV) infection, and cryptococcal infection.^[63] Despite improved immune function in antiretroviral therapy (ART)-treated HIV-infected patients in low- and middle-income countries, a significant proportion of patients with a new HIV diagnosis still present with advanced disease (CD4⁺ T cells <200/µL) and are at risk for OI such as cryptococcal meningitis.^[64] ART suppresses HIV replication and CD4⁺ T-cell loss by apoptosis allowing immune reconstitution to occur. However, in addition to its benefits, immune reconstitution with ART can also be detrimental. A proportion of patients treated with ART experience a constellation of symptoms and signs in which subclinical or preexisting infections trigger an exaggerated inflammatory response that leads to clinical deterioration, presenting as IRIS.^[65] IRIS can present as unmasking or paradoxical phenomena. In unmasking IRIS, subclinical infections become overtly symptomatic with a first episode of the OI after ART initiation. Conversely, in paradoxical IRIS, there is usually evidence of initial microbiological and clinical response to treatment of the OI pre-ART, which evolves into the recrudescence of symptoms following ART without microbiological evidence of the associated OI following ART initiation. Depending on the site and activity, IRIS can present with a range of symptoms from minor to severe inflammation resulting in organ failure, hospitalization, or death.^{[66],[67],[68],[69]}

Whether the current shift to a “Test and Treat” ART strategy with limited screening and treatment of OIs prior to ART will increase the incidence of unmasking IRIS remains to be observed. Reversal of CD4⁺ T-cell lymphopenia and increased T-cell activation have been associated with the development of IRIS.^[70] Studies in vitro have shown that attenuated Cryptococcus-specific interferon-γ (IFN-γ) responses prior to starting ART are associated with cryptococcal meningitis-IRIS when patients who developed CM-IRIS were compared to HIV-infected controls who did not develop IRIS.^[71] However, the ontogeny of antigen-specific T-cell responses prior to and during cryptococcal IRIS are not well defined. In previous study showed that CSF leukocytes count and CSF protein level, IFNY-y, interleukin-6 (IL-6), IL-8, and TNF-α were predictors for developing cryptococcal IRIS.^[72] It has mostly been described in HIV-infected patients under highly active antiretroviral therapy (HAART).^[69],[73]Cryptococcus neoformans-associated IRIS has also been described in solid-organ transplant (SOT) patients, with an estimated incidence of 4.8% in all SOT recipients^[74] and 5.5% in the subpopulation of renal transplant recipients,^[75] and usually occurred shortly after antifungal treatment’s initiation. Cryptococcus neoformans-associated IRIS has also been described after recovery from alemtuzumab therapy for T-cell prolymphocytic leukemia.^[76] Singh et al.^[74] report that patients receiving tacrolimus, mycophenolate mofetil, and corticosteroids as our patients are more likely to develop C. neoformans-associated immune reconstitution inflammatory syndrome (IRIS). IRIS consists in the paradoxical worsening of infection-related symptoms after an initial improvement despite appropriate antimicrobial therapy and most often culture-negative microbial investigations.^[69] Clinical manifestations associated with C. neoformans IRIS may consist in worsening of neurological symptoms, and myositis in SOT patients.^[74] Of note, cellulitis with necrotic adenitis as a manifestation of cryptococcosis-related IRIS has already been reported in the setting of AIDS.^[73] In our case, as for those recently reported, negative bacterial and fungal cultures associated with granuloma surrounding unculturable encapsulated yeasts were highly evocative of IRIS in the context of the recent reduction of IS therapy and his CD4⁺ lymphocytes increase.^[77] The absence of positive fungal culture, worsening condition after antifungal therapy, and broad-spectrum antibiotherapy and improvement with corticosteroids are consistent with IRIS, but not with a microbiologically active fungal or bacterial infection. It has been suggested that antifungal therapy and IRIS withdrawal reverse the T helper type 2 (Th2)-predominant immune profile induced by the fungus in combination with the IS therapy toward a Th1/pro-inflammatory leading to the overwhelming granulomatous reaction defining IRIS.^[74] Renal transplant recipients with cryptococcosis-related IRIS are more likely to experience graft rejection and/or loss, which occurred in up to 66% in a recent series.^[75] Corticosteroid therapy has been successful for the control of cryptococcosis-related IRIS in patients with HIV.^[73] In conclusion, short-term steroid therapy can be helpful for severe aseptic cellulitis ascribed to cryptococcosis-related IRIS in SOT recipients.^[78] Experimental studies have shown that C. neoformans has immunomodulatory characteristics and preferentially inhibits Th1 while inducing Th2 responses.^{[79],[80],[81]}

The exact relevance of these data in vitro and in animals for human disease is incompletely discerned. Nevertheless, several reports have shown that patients with cryptococcal meningitis have defective production of IFN-γ and TNF-α,^[82] with or without high interleukin-10 (IL-10) concentrations in the CSF.^{[83],[84],[85]}

Furthermore, higher IFN-γ concentrations in the CSF correlated with an improved clinical response during treatment of CNS cryptococcosis.^[86] However, the receipt of antifungal therapy in a patient with C. gattii meningitis was associated with a pronounced reversion of Th2 to Th1 response with an exacerbation of clinical inflammatory manifestations, although the yeast was ultimately eradicated from the site.^[87] In addition to antigen-specific responses, C. neoformans is capable of eliciting an innate T-lymphocyte response as a mitogen.^[88] Mitogen-activated T cells could potentially lead to potent pro-inflammatory responses and therefore IRS. Even specific antibody responses to the invading fungus may contribute to an inflammatory imbalance during immune reconstitution. A phenomenon, similar to a prozone-like effect, whereby too much antibody enhances disease, has been described in cryptococcosis.^[89],[90]

In fact, in experimental cryptococcosis, antibody-mediated immunity may be protective, non-protective, or even harmful to the host, depending on its concentration relative to the inoculum of C. neoformans.^[90] For instance, concentrations of immunoglobulin M and immunoglobulin G antibodies specific to GXM, a component of the cryptococcal polysaccharide capsule, were higher in transplant recipients who developed cryptococcosis than in those who did not?^[91] The precise contribution of this immunoglobulin dysregulation to IRS remains to be elucidated, but it shows the potential ability of the fungus to directly drive an inappropriate immune response.^[77] The optimum management of IRS is dependent on the awareness by health-care providers of its existence. Recognition that IRS is a manifestation of a poorly controlled inflammatory response rather than direct treatment failure of antifungal agents to eradicate or kill the fungus is crucial in avoiding unnecessary modifications in therapy. Currently, no readily available markers exist that can reliably establish the diagnosis of IRS. However, on the basis of published data.^{[74],[92],[93]}

The criteria outlined (panel) might be thought as representing the IRS and provide some reference in the discussion or study of this entity. In therapy-naive HIV-infected patients with OIs, consideration should be given to deferring the start of ART for 4–10 weeks until the infection seems to be microbiologically controlled. This approach has been proposed for the treatment of Mycobacterium tuberculosis and C. neoformans in these patients.^[94],[95] Similar rationales can also be applied to the management of immunosuppression in transplant recipients with these infections. Withdrawal of immunosuppression in transplant recipients with OIs is a common practice and is intuitively logical. However, concurrent withdrawal of immunosuppression and initiation of antifungal therapy has been shown to predispose not only to IRS but also allograft loss. Thus, it is plausible that spacing or separating the reduction in posttransplant immunosuppression and initiation of antifungal therapy is a more prudent approach to the management of transplant recipients with cryptococcosis.^[75] More-severe cryptococcal disease, including fungemia, an extremely low CD4 cell count, cryptococcosis revealing initial HIV infection, lack of previous ART, lack of CSF sterilization at week 2, the introduction of HAART during the early part of induction therapy, and rapid initial decrease in HIV load in response to HAART have all been recognized as risk factors for IRIS.^[73] Presence of cerebral lesions during the initial treatment phase of the disease is not predictive of the subsequent occurrence of symptomatic cerebral IRIS.^[57] IRIS may either occur early (i.e., within a few days) or late after the introduction of HAART, sometimes up to several months thereafter. Time of occurrence appears shorter in cases of cerebral IRIS. In SOT recipients, IRIS has been described as a mean of 6 weeks after the initiation of antifungal therapy. Manifestations of IRIS consist frequently of fever with peripheral or mediastinal/abdominal lymphadenitis or CNS signs and/or symptoms of the disease (meningitis or cerebral abscesses and their clinical consequences with or without an increase of CSF opening pressure), and these new symptoms can be construed as signs of treatment failure. Furthermore, in kidney transplant recipients, graft loss has appeared as a consequence of IRIS. Severe manifestations of IRIS can be lethal if not taken into consideration.^[69]

False negative test results are unusual and can be due to a prozone effect or immune complexes, or low production of antigen.^[97] One of the most important advances in the post-culture identification of fungi is that of matrix-assisted laser desorption ionization-time of flight (MALDI-TOF) mass spectrometry (MS).^[98],[99]

MALDI-TOF MS uses species-specific patterns of peptides and protein masses to identify microorganisms. It has been shown to be highly accurate in identifying a broad array of bacteria and recently has been shown to provide a rapid and reliable method for the identification of yeasts, yeast-like fungi, and some molds.^[99] The technique involves the use of whole-cell preparations or an extract of proteins from the fungal cells, spotting of the specimen on a grid and overlaying the spot with a matrix. The proteins are ionized by a laser and migrate through a charged field in a vacuum tube towards a detector. The spectrum is generated rapidly (~10min per specimen) and is compared to a reference database. Currently, there are two commercial systems based on this method available in the USA that are able to identify yeast and mold species. Studies evaluating their performances are promising, showing that this method is able to accurately and rapidly identify Candida spp. and Cryptococcus spp., including C. gattii, from positive cultures, with a high concordance (>90%) in comparison to both conventional and molecular methods.^[99],[100]

In some instances, MALDI-TOF MS has been shown to be superior to conventional methods.^[99] Cryptococcal meningitis is treated in three phases: induction, consolidation, and maintenance. Combination antifungal therapy treatment is induction. Liposomal amphotericin B and flucytosine are preferred because of improved survival with this regimen.

Alternative induction regimen is as follows:

Amphotericin B lipid complex 5mg/kg intravenous (IV) q 24h + flucytosine 25mg/kg orally (PO) q 6 h

Amphotericin B (liposomal or deoxycholate, dosed as above) + fluconazole 800mg PO or IV q 24h amphotericin B (liposomal or deoxycholate, dosed as above) monotherapy

Fluconazole (400mg or 800mg PO or IV q 24h) + flucytosine 25mg/kg PO q 6 h

Fluconazole 1200mg PO or IV daily monotherapy

Induction therapy should be continued for 2 weeks but increased to 4 weeks in the case of amphotericin B monotherapy. Many experts obtained a CSF fungal culture at the end of induction to document clearance of viable organisms, continuing induction therapy until the cultures have cleared. In consolidation therapy, patients take fluconazole 400mg by PO or IV daily for 8 weeks. At least 1 year of maintenance therapy with fluconazole 200mg daily is recommended.^[101] With the advent of ART, AIDS-related cryptococcal infection has been declining. A similar regime that can be used in immunocompetent individuals through standard therapy recommended is to extend the intensive phase to 6–10 weeks followed by consolidation with fluconazole. Treatment of cryptococcal meningitis in immune-compromised individuals consists of amphotericin B 0.7mg/kg/day along with flucytosine 100mg/kg/day for 2 weeks followed by consolidation with fluconazole 400mg/day for 10 weeks.^[102],[103]

Conclusion

A high index of suspicion and routine mycological surveillance is required to help early diagnosis and adequate treatment with an appropriate antifungal agent after susceptibility testing may save the lives of these unfortunate patients.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

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