A Spuriously Negative Cryptococcal Antigen Assay Result in Disseminated Cryptococcosis: the Deception of the Postzone Phenomenon.

Cryptococcus is a basidiomycetous yeast responsible for considerable HIV-related morbidity and mortality. A cachectic 26-year-old HIV-positive man with a CD4 count of 103 cells/µl presented with fever, breathlessness, and bilateral lower limb weakness. A brain computed tomography scan could not elucidate the neurological deficit. His blood was sent for culture and serum cryptococcal antigen detection, with the latter testing as negative. By the fourth day of admission, the patient's condition had deteriorated drastically. A lumbar puncture was performed, and like his serum sample, the cerebrospinal fluid also tested negative for cryptococcal antigens. By this time, Cryptococcus neoformans was isolated from the admission blood culture. The laboratory diluted both the serum and cerebrospinal fluid specimens to retest for cryptococcal antigens, and finally, an antigen titer of ≥1:2560 was recorded.

Cryptococcosis in an HIV-negative, HCV positive, immunosenescent patient: a case report.

Cryptococcus species is still a very common opportunistic infection in AIDS patients. However, it is increasingly responsible for disease in otherwise immunocompromised individuals, such as transplant recipients and the heterogeneous group of patients with underlying immunologic diseases, hematologic disorders and organ failure syndromes. Clinical presentation, prognosis, and outcomes are difficult to define given these varied host groups, and tailoring treatments to fit the necessities of each patient is likewise challenging. Our patient was on treatment with steroids and direct-acting antiviral agents (DAAs) for a chronic HCV-related hepatitis, worsened by cryoglobulinemia, membranoproliferative glomerulonephritis and a lowgrade B cells lymphoma. We report a case of systemic cryptococcal infection in an immunosenescent, HIV-negative patient.

Fatores de virulência e susceptibilidade a antifúngicos de Cryptococcus Spp / Virulence factors and susceptibility to Cryptococcus Spp. antifungals

Criptococose é uma doença grave que afeta tanto imunocomprometidos quanto imunocompetentes, com isso analisar a virulência é fundamental para novas terapêuticas. Objetivo: Analisar a capacidade de virulência e susceptibilidade aos antifúngicos de Cryptococcus spp. isolados de líquor de pacientes de hospital do norte do Paraná. Métodos: A partir de dois isolados clínicos C. neoformans e C. gattii, realizou-se a confirmação da identificação. Para a virulência, avaliou-se o tamanho da cápsula, capacidade de sobrevivência após exposição a neutrófilos, produção de melanina e urease. No antifungigrama por difusão em disco utilizou-se: anfotericina B, cetoconazol, voriconazol, itraconazol e miconazol. Resultados: C. gattii destaca-se por maior desenvolvimento da cápsula além da melhor capacidade de sobreviver a fagocitose em relação ao C. neoformans. No antifungigrama, ambos os isolados se apresentam sensíveis às drogas estudadas. Conclusão: Esses achados contribuem para a compreensão das diferentes patogêneses entre C. gattii e C. neoformans.

Cryptococcosis is a serious disease that can affect both immunocompromised and immunocompetent individuals, thus the virulence analysis is fundamental for the development of new treatments. Objective: To analyze the virulence and susceptibility of Cryptococcus spp. isolated from cerebrospinal fluid of patients from a hospital in the north of Paraná. Methods: From two clinical isolates, C. neoformans and C. gattii were confirmed and identified. For virulence, capsule size, survival capacity after exposure to neutrophils, melanin production and urease were evaluated. In the disc-diffusion method, the following antifungals were used: amphotericin B, ketoconazole, voriconazole, itraconazole and miconazole Results: It was observed that C. gattii presents greater results for development of the capsule beside presenting the best ability to survive phagocytosis in relation to C. neoformans. In the disc-diffusion method, both isolates presented sensitivity to the studied drugs. Conclusion: These findings contribute to the understanding of the different pathogens between C. gattii and C. neoformans.

Viral infection triggers interferon-induced expulsion of live Cryptococcus neoformans by macrophages.

Cryptococcus neoformans is an opportunistic human pathogen, which causes serious disease in immunocompromised hosts. Infection with this pathogen is particularly relevant in HIV+ patients, where it leads to around 200,000 deaths per annum. A key feature of cryptococcal pathogenesis is the ability of the fungus to survive and replicate within the phagosome of macrophages, as well as its ability to be expelled from host cells via a novel non-lytic mechanism known as vomocytosis. Here we show that cryptococcal vomocytosis from macrophages is strongly enhanced by viral coinfection, without altering phagocytosis or intracellular proliferation of the fungus. This effect occurs with distinct, unrelated human viral pathogens and is recapitulated when macrophages are stimulated with the anti-viral cytokines interferon alpha or beta (IFNα or IFNß). Importantly, the effect is abrogated when type-I interferon signalling is blocked, thus underscoring the importance of type-I interferons in this phenomenon. Lastly, our data help resolve previous, contradictory animal studies on the impact of type I interferons on cryptococcal pathogenesis and suggest that secondary viral stimuli may alter patterns of cryptococcal dissemination in the host.

Hemophagocytic syndrome in patients living with HIV: a retrospective study.

Various infectious diseases can hyper-stimulate the immune system, causing hemophagocytic syndrome (HPS). Little is known regarding the accuracy of diagnostic criteria and epidemiological triggering factors in the acquired immunodeficiency syndrome (AIDS) setting. We investigated the major infectious disease triggers of HPS in patients living with human immunodeficiency virus (HIV)/AIDS and determined the accuracy of bone marrow aspiration (BMA). The inclusion criteria were (i) confirmed HIV diagnosis, (ii) bone marrow aspiration, and (iii) a minimum of four HPS criteria. Patients were further classified into those with four presumed HPS criteria, or ≥ 5 confirmed criteria. The disease triggers, accuracy of bone marrow aspiration, and prognosis markers were examined. Presumed HPS was observed in 15/36 patients (41%), and confirmed HPS in 58% (n = 21). The major etiological triggers were infection with Mycobacterium (34%), Cytomegalovirus (14%), Cryptococcus neoformans (11%), and hematological or tumoral disease (11%). BMA demonstrated 93% specificity on screening diagnosis (odds ratio [OR] 12.7, 95% confidence interval [CI] 1.4-115.1, P = 0.01). Ferritin > 5000 ng/mL correlated with probability of death in univariate analysis (OR 6.00, 95% CI 1.33-27.05, P = 0.02). Ferritin performance as test of death probability presented area under the curve as 0.74 (95% CI 0.56-0.91, P = 0.016). However, neither cluster of differentiation for lymphocyte count nor HIV viral load correlated with patient deaths. Mycobacterium spp. and Cytomegalovirus were the main factors triggering HPS, followed by Cryptococcus neoformans, and hematological and tumoral diseases. High ferritin levels were associated with increased death probability. High specificity was noted with BMA.

Rapid emergence of cryptococcal fungemia, Mycobacterium chelonae vertebral osteomyelitis and gastro intestinal stromal tumor in a young HIV late presenter: a case report.

BACKGROUND: Highly active antiretroviral therapy has significantly changed the natural history of HIV infection, leading to a dramatic reduction of HIV-related morbidity and mortality. Late Presenters, Very Late Presenters and AIDS presenters still represent, also in Europe, including Italy, a huge challenge in terms of diagnostic and therapeutic management. CASE PRESENTATION: A 35-year-old male with a history of fever and back pain. HIV test resulted positive with a high HIV Viral Load and a very low T-CD4 number of cells (5 cells/mm3). Imaging investigations revealed multiple vertebral and pulmonary lesions together with abdominal and thoracic lymphadenopathy. Blood cultures were positive for Cryptococcus neoformans and for Staphylococcus haemolyticus. Lymphnode biopsy resulted positive in PCR for Non-Tuberculosis Mycobacteria (Mycobacterium chelonae). A gastric biopsy also revealed a GIST. The patient also had CMV DNA positive. Although we performed antiretroviral therapy and specific-therapies for each disease, he was transferred to intensive care unit where he died due to an Acute Respiratory Distress Syndrome. CONCLUSION: The reported case is unusual due to the relevant number of opportunistic diseases (both infectious and tumoral) emerging not long after the HIV infection had been diagnosed. Late presenters HIV patients and AIDS presenters still represent a challenge, which is often too complex for clinicians to deal with. In spite of proper management, the risk of suboptimal results cannot be excluded.

Integrated therapy for HIV and cryptococcosis.

Cryptococcosis has been one of the most common opportunistic infections and causes of mortality among HIV-infected patients, especially in resource-limited countries. Cryptococcal meningitis is the most common form of cryptococcosis. Laboratory diagnosis of cryptococcosis includes direct microscopic examination, isolation of Cryptococcus from a clinical specimen, and detection of cryptococcal antigen. Without appropriate treatment, cryptococcosis is fatal. Early diagnosis and treatment is the key to treatment success. Treatment of cryptococcosis consists of three main aspects: antifungal therapy, intracranial pressure management for cryptococcal meningitis, and restoration of immune function with antiretroviral therapy (ART). Optimal integration of these three aspects is crucial to achieving successful treatment and reducing the mortality. Antifungal therapy consists of three phases: induction, consolidation, and maintenance. A combination of two drugs, i.e. amphotericin B plus flucytosine or fluconazole, is preferred in the induction phase. Fluconazole monotherapy is recommended during consolidation and maintenance phases. In cryptococcal meningitis, intracranial pressure rises along with CSF fungal burden and is associated with morbidity and mortality. Aggressive control of intracranial pressure should be done. Management options include therapeutic lumbar puncture, lumbar drain insertion, ventriculostomy, or ventriculoperitoneal shunt. Medical treatment such as corticosteroids, mannitol, and acetazolamide are ineffective and should not be used. ART has proven to have a great impact on survival rates among HIV-infected patients with cryptococcosis. The time to start ART in HIV-infected patients with cryptococcosis has to be deferred until 5 weeks after the start of antifungal therapy. In general, any effective ART regimen is acceptable. Potential drug interactions between antiretroviral agents and amphotericin B, flucytosine, and fluconazole are minimal. Of most potential clinical relevance is the concomitant use of fluconazole and nevirapine. Concomitant use of these two drugs should be cautious, and patients should be monitored closely for nevirapine-associated adverse events, including hepatotoxicity. Overlapping toxicities of antifungal and antiretroviral drugs and immune reconstitution inflammatory syndrome are not uncommon. Early recognition and appropriate management of these consequences can reinforce the successful integrated therapy in HIV-infected patients with cryptococcosis.

Feasibility and Acceptability of Cryptococcal Antigen Screening and Prevalence of Cryptocococcemia in Patients Attending a Resource-Limited HIV/AIDS Clinic in Malawi.

BACKGROUND: The World Health Organization (WHO) recommends screening patients living with AIDS to detect and treat early cryptococcal infection. METHODS: The authors evaluated a cryptococcal antigen (CrAg) screening and treatment program at an HIV/AIDS clinic in Malawi. Eligible patients were of age >18 years, had a CD4 count <100 cells/µL or WHO clinical HIV/AIDS stage III or IV. RESULTS: Of 552 patients who presented for care, 113 were eligible, and all (100%) agreed to CrAg screening. Of them, 2 (1.8%; 95% confidence interval [CI]: 0-4.2%) patients were CrAg positive. Among those with CD4 count <100 cells/µL or WHO stage IV, the CrAg prevalence was 3.5% (95% CI: 0-8.4%) and 5.0% (95% CI: 0-15%), respectively. CONCLUSION: A CrAg screening program was acceptable to new patients in a Malawian HIV/AIDS clinic. The CrAg prevalence for patients with CD4 count < 100 cells/µL and WHO stage IV was consistent with cost-effectiveness estimates. CrAg screening and treatment programs for patients living with AIDS should be expanded.

Comparison of Etests and Vitek 2 ® to broth microdilution for the susceptibility testing of Cryptococcus neoformans.

We determined the susceptibility of 102 clinical isolates Cryptococcus neoformans from Durban, South Africa, to amphotericin B, fluconazole, flucytosine, and voriconazole using broth microdilution (BMD) according to the Clinical and Laboratory Standards Institute M27-A3 document and compared these results with Etest and Vitek 2(®). Essential agreement (EA) of Etest and Vitek 2(®) compared to BMD was determined. Low MICs that were below the epidemiological cutoff values of the 4 antifungal agents tested were demonstrated by all isolates. The EA of Etests for fluconazole, amphotericin, and voriconazole was 95.1%, 83.3%, and 91.2%, respectively, and for Vitek 2(®) EA for fluconazole, amphotericin, and flucytosine was 97.1%, 95.1%, and 97.1%, respectively. The Vitek 2(®) showed good agreement with BMD and is a suitable alternative. Etests demonstrated good EA for azoles only. Clinical cryptococcal isolates from Durban remain susceptible to current recommended antifungal therapy.

No association of cryptococcal antigenemia with poor outcomes among antiretroviral therapy-experienced HIV-infected patients in Addis Ababa, Ethiopia.

INTRODUCTION: There are limited data on clinical outcomes of ART-experienced patients with cryptococcal antigenemia. We assessed clinical outcomes of a predominantly asymptomatic, ART-experienced cohort of HIV+ patients previously found to have a high (8.4%) prevalence of cryptococcal antigenemia. METHODS: The study took place at All Africa Leprosy, Tuberculosis and Rehabilitative Training Centre and Black Lion Hospital HIV Clinics in Addis Ababa, Ethiopia. A retrospective study design was used to perform 12-month follow-up of 367 mostly asymptomatic HIV-infected patients (CD4<200 cells/µl) with high levels of antiretroviral therapy use (74%) who were previously screened for cryptococcal antigenemia. Medical chart abstraction was performed approximately one year after initial screening to obtain data on clinic visit history, ART use, CD4 count, opportunistic infections, and patient outcome. We evaluated the association of cryptococcal antigenemia and a composite poor outcome of death and loss to follow-up using logistic regression. RESULTS: Overall, 323 (88%) patients were alive, 8 (2%) dead, and 36 (10%) lost to follow-up. Among the 31 patients with a positive cryptococcal antigen test (titers ≥1∶8) at baseline, 28 were alive (all titers ≤1∶512), 1 dead and 2 lost to follow-up (titers ≥1∶1024). In multivariate analysis, cryptococcal antigenemia was not predictive of a poor outcome (aOR = 1.3, 95% CI 0.3-4.8). A baseline CD4 count <100 cells/µl was associated with an increased risk of a poor outcome (aOR 3.0, 95% CI 1.4-6.7) while an increasing CD4 count (aOR 0.1, 95% CI 0.1-0.3) and receiving antiretroviral therapy at last follow-up visit (aOR 0.1, 95% CI 0.02-0.2) were associated with a reduced risk of a poor outcome. CONCLUSIONS: Unlike prior ART-naïve cohorts, we found that among persons receiving ART and with CD4 counts <200 cells/µl, asymptomatic cryptococcal antigenemia was not predictive of a poor outcome.

Cryptococcus gattii in the United States: genotypic diversity of human and veterinary isolates.

BACKGROUND: Cryptococcusgattii infections are being reported in the United States (US) with increasing frequency. Initially, US reports were primarily associated with an ongoing C. gattii outbreak in the Pacific Northwest (PNW) states of Washington and Oregon, starting in 2004. However, reports of C. gattii infections in patients from other US states have been increasing since 2009. Whether this is due to increasing frequency of disease, greater recognition within the clinical community, or both is currently unknown. METHODOLOGY/PRINCIPAL FINDINGS: During 2005-2013, a total of 273 C. gattii isolates from human and veterinary sources in 16 US states were collected. Of these, 214 (78%) were from the Pacific Northwest (PNW) and comprised primarily the clonal C. gattii genotypes VGIIa (64%), VGIIc (21%) and VGIIb (9%). The 59 isolates from outside the PNW were predominantly molecular types VGIII (44%) and VGI (41%). Genotyping using multilocus sequence typing revealed small clusters, including a cluster of VGI isolates from the southeastern US, and an unrelated cluster of VGI isolates and a large cluster of VGIII isolates from California. Most of the isolates were mating type MATα, including all of the VGII isolates, but one VGI and three VGIII isolates were mating type MATa. CONCLUSIONS/SIGNIFICANCE: We provide the most comprehensive report to date of genotypic diversity of US C. gattii isolates both inside and outside of the PNW. C. gattii may have multiple endemic regions in the US, including a previously-unrecognized endemic region in the southeast. Regional clusters exist both in California and the Southeastern US. VGII strains associated with the PNW outbreak do not appear to have spread substantially beyond the PNW.

Solitary cavitary pulmonary nodule may be a common CT finding in AIDS-associated pulmonary cryptococcosis.

BACKGROUND: Previous studies have demonstrated that the most common chest radiologic finding in acquired immune deficiency syndrome (AIDS)-associated pulmonary cryptococcosis (PC) is diffuse interstitial infiltrates. The aim of this study was to provide additional radiologic characterization of PC in AIDS patients. METHODS: AIDS patients from the Second Affiliated Hospital of the Southeast University who were diagnosed with cryptococcosis between February 2009 and May 2012 and who had undergone chest computed tomography (CT) scans before or at the time of diagnosis were retrospectively analyzed. RESULTS: Twelve patients met eligibility criteria. The median CD4 T-cell count was 23 cells/µl (range 2-79 cells/µl). Eleven patients had pulmonary abnormalities on imaging. Initial chest CT scans demonstrated solitary cavitary pulmonary nodules in 9 patients, pleural effusions in 2 patients, bilateral ground-glass opacities in 6 patients, patchy opacities in 1 patient, and bronchiectasis in 1 patient. Bilateral ground-glass opacities appeared to be associated with Pneumocystis pneumonia, while the presence of a pleural effusion was predictive of PC. Of the 9 solitary cavitary pulmonary nodules, 7 were PC and the other 2 were probable cases of PC. These nodules were predominantly in the peripheral lung and were either asymptomatic or caused only mild pulmonary symptoms. CONCLUSIONS: Solitary cavitary pulmonary nodule may be a common CT finding in AIDS-associated PC. All AIDS patients with solitary cavitary pulmonary nodules on chest CT should be screened for Cryptococcus infection.

Evaluation of a newly developed lateral flow immunoassay for the diagnosis of cryptococcosis.

BACKGROUND: Cryptococcosis is a common opportunistic infection of human immunodeficiency virus (HIV)-infected individuals mostly occurring in resource-limited countries. This study compares the performance of a recently developed lateral flow immunoassay (LFA) to blood culture and enzyme immunoassay (EIA) for the diagnosis of cryptococcosis. METHODS: Archived sera from 704 HIV-infected patients hospitalized for acute respiratory illness in Thailand were tested for cryptococcal antigenemia using EIA. All EIA-positive and a subset of EIA-negative sera were tested by LFA, with results recorded after 5 and 15 minutes incubation. Urine from patients with LFA- and EIA-positive sera was tested by LFA. Antigen results from patients with positive cryptococcal blood cultures were compared. RESULTS: Of 704 sera, 92 (13%) were positive by EIA; among the 91 EIA-positive sera tested by LFA, 82 (90%) and 87 (96%) were LFA positive when read after 5 and 15 minutes, respectively. Kappa agreement of EIA and LFA for sera was 0.923 after 5 minutes and 0.959 after 15 minutes, respectively. Two of 373 EIA-negative sera were LFA positive at both time points. Of 74 urine specimens from EIA-positive patients, 52 (70.3%) were LFA positive. EIA was positive in 16 of 17 sera from blood culture-positive patients (94% sensitivity), and all sera were positive by LFA (100% sensitivity). CONCLUSIONS: A high level of agreement was shown between LFA and EIA testing of serum. The LFA is a rapid, easy-to-perform assay that does not require refrigeration, demonstrating its potential usefulness as a point-of-care assay for diagnosis of cryptococcosis in resource-limited countries.

The role of serum cryptococcal antigen screening for the early diagnosis of cryptococcosis in HIV-infected patients with different ranges of CD4 cell counts.

OBJECTIVE: To determine the role of serum cryptococcal antigen (SCA) for the screening of cryptococcosis in HIV-infected patients with different ranges of CD4 cell counts. METHODS: A retrospective cohort study was conducted in antiretroviral-naïve HIV-infected patients who had no symptom and had been screened with SCA in a tertiary-care hospital. Prevalence of positive SCA at different ranges of CD4 cell counts, risk factor of positive SCA, and incidence of cryptococcosis during one-year follow-up period after negative SCA were determined. RESULTS: There were 131 patients with a mean age of 38.5 years; 61.8% were male. Median (range) CD4 was 62 (3-590) cells/mm(3). The overall prevalence of positive SCA was 9.2%. This prevalence in patients with CD4 < 100, 100-199, and >or=200 cells/mm(3) were 12.9%, 3.6%, and 0%, respectively (P = 0.041). In multivariate analysis, CD4 < 100 cells/mm(3) was associated with positive SCA (OR = 6.69; 95% CI, 1.03-23.56). Four (33.3%) of 12 patients with positive SCA had cryptococcosis whereas one (0.8%) of 119 patients with negative SCA developed meningitis at one-year follow-up. CONCLUSIONS: SCA screening has a substantial role for the early detection of cryptococcal infection in HIV-infected patients with low CD4 cell counts. Routine screening with SCA should be performed in patients with CD4 < 100 cells/mm(3).

Cryptococcal disease in patients with or without human immunodeficiency virus: clinical presentation and monitoring of serum cryptococcal antigen titers.

BACKGROUND AND PURPOSE: Cryptococcus neoformans is an encapsulated pathogenic yeast that causes a wide range of clinical manifestations. The serum cryptococcal latex agglutination test is a simple, rapid, and reliable diagnostic test for cryptococcosis. This study was performed to assess the clinical relevance of serum cryptococcal antigen (CRAG) titer in patients with cryptococcosis with or without human immunodeficiency virus (HIV). METHODS: From January 1999 to December 2007, 45 patients with a diagnosis of cryptococcosis made by culture and/or histopathology were enrolled in this retrospective study. Ten patients had HIV and 35 were not infected. RESULTS: Patients with HIV were more likely to have central nervous system (CNS) involvement than patients without HIV (100% vs 37.1%; p = 0.0005), higher serum CRAG titers (median, 1:1024 vs 1:64; p < 0.05), higher positive cerebrospinal fluid (CSF) CRAG (100% vs 37.1%; p = 0.0005), and higher CRAG titers in the CSF (median, 1:1024 vs 1:32; p < 0.001). Patients without HIV were more likely to have pulmonary involvement (62.9% vs 0%; p = 0.0005) and no underlying disease at diagnosis (42.9% vs 0%; p = 0.011). Serum CRAG titers among patients without HIV with CNS or pulmonary cryptococcosis declined during treatment and no relapse was noted when serum CRAG titers were

Concomitant disseminated histoplasmosis and cryptococcosis in a person with AIDS.

A 46-year-old Hispanic male from Ecuador presented with fever, malaise, weight loss, and dyspnea. He was HIV-positive with a CD4+ cell count of 4/microL. He was hospitalized, and therapy for community-acquired pneumonia with broad-spectrum antibiotics was started. Both Histoplasma capsulatum and Cryptococcus neoformans were cultured from bronchial lavage, blood, and bone marrow specimens. Despite aggressive therapy with amphotericin B, the patient died 8 days after admission.

HIV disorders of the brain: pathology and pathogenesis.

Infection with HIV-1 has spread exponentially in recent years to reach alarming proportions. It is estimated than more than 33 million adults and 1.3 million children are infected worldwide. Approximately 16,000 new cases are diagnosed every day and almost 3 million people die every year from AIDS, making it the fourth leading cause of death in the world. Since the introduction of highly active anti-retroviral therapy (HAART) in the mid 1990s, the morbidity and mortality associated with HIV-1 infection has significantly decreased and AIDS has become a chronic disorder. However, neuropathological conditions associated with AIDS are still present in approximately 70 to 90% of patients and can be the result of HIV itself or of opportunistic infections. Here we briefly review the pathology and pathophysiology of AIDS-Encephalopathy, of some of the significant opportunistic infections affecting the brain in the context of AIDS, including Progressive Multifocal Leukoencephalopathy (PML) a demyelinating disease caused by the human neurotropic JC virus, Toxoplasmosis, Cryptococcosis and of primary CNS lymphoma, a brain malignancy frequently associated with HIV-1 infection, all of them considered AIDS defining conditions.

Prevalence of clinical isolates of Cryptococcus gattii serotype C among patients with AIDS in Sub-Saharan Africa.

Cryptococcus gattii is a group of exogenous, neurotropic yeasts that possess the capsular serotype B or C. Isolates of serotype C are extremely rare and, until recently, were known to infect only immunocompetent individuals. We genotyped 176 isolates of Cryptococcus from patients in sub-Saharan Africa who had AIDS; 22 (13.7%) of 161 isolates from Botswana and 2 (13.3%) of 15 isolates from Malawi were C. gattii serotype C strains. All of these serotype C strains belong to the rare VGIV genotype, possess the MAT alpha mating-type allele, and exhibit little genetic diversity.