Experimental animal models of coccidioidomycosis

Galleria mellonella Model of Coccidioidomycosis for Drug Susceptibility Tests and Virulence Factor Identification

Coccidioidomycosis (CM) can manifest as respiratory and disseminated diseases that are caused by dimorphic fungal pathogens, such as Coccidioides species. The inhaled arthroconidia generated during the saprobic growth phase convert into multinucleated spherules in the lungs to complete the parasitic lifecycle. Research on coccidioidal virulence and pathogenesis primarily employs murine models typically associated with low lethal doses (LD100 < 100 spores). However, the Galleria model has recently garnered attention due to its immune system bearing both structural and functional similarities to the innate system of mammals. Our findings indicate that Coccidioides posadasii can convert and complete the parasitic cycle within the hemocoel of the Galleria larva. In Galleria, the LD100 is between 0.5 and 1.0 × 106 viable spores for the clinical isolate Coccidioides posadasii C735. Furthermore, we demonstrated the suitability of this model for in vivo antifungal susceptibility tests to validate the bioreactivity of newly discovered antifungals against Coccidioides. Additionally, we utilized this larva model to screen a Coccidioides posadasii mutant library showing attenuated virulence. Similarly, the identified attenuated coccidioidal mutants displayed a loss of virulence in a commonly used murine model of coccidioidomycosis. In this study, we demonstrated that Galleria larvae can be applied as a model for studying Coccidioides infection.

Coccidioidomycosis Osteoarticular Dissemination

Valley fever or coccidioidomycosis is a pulmonary infection caused by species of Coccidioides fungi that are endemic to California and Arizona. Skeletal coccidioidomycosis accounts for about half of disseminated infections, with the vertebral spine being the preferred site of dissemination. Most cases of skeletal coccidioidomycosis progress to bone destruction or spread to adjacent structures such as joints, tendons, and other soft tissues, causing significant pain and restricting mobility. Manifestations of such cases are usually nonspecific, making diagnosis very challenging, especially in non-endemic areas. The lack of basic knowledge and research data on the mechanisms defining susceptibility to extrapulmonary infection, especially when it involves bones and joints, prompted us to survey available clinical and animal data to establish specific research questions that remain to be investigated. In this review, we explore published literature reviews, case reports, and case series on the dissemination of coccidioidomycosis to bones and/or joints. We highlight key differential features with other conditions and opportunities for mechanistic and basic research studies that can help develop novel diagnostic, prognostic, and treatment strategies.

Characterization of the Growth and Morphology of a BSL-2 Coccidioides posadasii Strain That Persists in the Parasitic Life Cycle at Ambient CO2

Coccidioides is a dimorphic fungus responsible for Valley Fever and is the cause of severe morbidity and mortality in the infected population. Although there is some insight into the genes, pathways, and growth media involved in the parasitic to saprophytic growth transition, the exact determinants that govern this switch are largely unknown. In this work, we examined the growth and morphology of a Coccidioides posadasii strain (C. posadasii S/E) that efficiently produces spherules and endospores and persists in the parasitic life cycle at ambient CO2. We demonstrated that C. posadasii S/E remains virulent in an insect infection model. Surprisingly, under spherule-inducing conditions, the C. posadasii S/E culture was found to be completely hyphal. Differential interference contrast (DIC) and transmission electron microscopy (TEM) revealed unexpected cellular changes in this strain including cell wall remodeling and formation of septal pores with Woronin bodies. Our study suggests that the C. posadasii S/E strain is a useful BSL-2 model for studying mechanisms underlying the parasitic to saprophytic growth transition—a morphological switch that can impact the pathogenicity of the organism in the host.

FDA Public Workshop Summary-Coccidioidomycosis (Valley Fever): Considerations for Development of Antifungal Drugs

Coccidioidomycosis is a fungal disease endemic to the southwestern United States, Mexico, and Central and South America. Prevalence rates are increasing steadily and new endemic areas of Coccidioides are emerging. Standard treatment is often administered for months to decades, and intolerance to medications and treatment failures are common. No new treatments for coccidioidomycosis have been approved in the U.S. in nearly 40 years. On August 5, 2020, the U.S. Food and Drug Administration convened experts in coccidioidomycosis from academia, industry, patient groups and other government agencies to discuss the disease landscape and strategies to facilitate product development for treatment of coccidioidomycosis. This paper summarizes the key topics concerning drug development for coccidioidomycosis presented by speakers and panelists during the workshop, such as unmet need, trial designs, endpoints, incentives, research and development support, and collaborations to facilitate antifungal drug development.

A Chronic Murine Disease Model of Coccidioidomycosis Using Coccidioides posadasii, Strain 1038

Murine infections with most Coccidioides spp. strains are lethal by 3 weeks, limiting the study of immune responses. Coccidioides posadasii, strain 1038 (Cp1038), while slowly lethal, resulted in protracted survival of C57BL/6 (B6) mice. In resistant (B6D2)F1/J mice, lung fungal burdens stabilized by week 4 without progression through week 16, better modeling human coccidioidal infections after their immunologic control. Immunodeficient tumor necrosis factor (Tnf) α knockout (KO) and interferon (Ifn) γ receptor 1 (Ifn-γr1) KO mice survived a median of 22.5 and 34 days, compared with 70 days in B6 mice (P = .001 and P < .01, respectively), though 14-day lung fungal burden studies showed little difference between Ifn-γr1 KO and B6 mice. B6 mice showed peak concentrations of key inflammatory lung cytokines, including interleukin 6, 23, and 17A, Tnf-α, and Ifn-γ, only after 4 weeks of infection. The slower progression in B6 and the acquired fungal burden stability in B6D2 mice after Cp1038 infection greatly increases the array of possible immunologic studies.

The clinical laboratory evolution in coccidioidomycosis detection: Future perspectives

Coccidioidomycosis is a systemic disease caused by the fungi Coccidioides immitis and C. posadasii. It is a prevalent disease in arid regions with high temperatures and low precipitations in America. Coccidioidomycosis is a highly endemic disease of US-Mexico border states but commonly underdiagnosed. The diagnosis of coccidiomycosis is not easy due to the lack of specific symptoms; it is usually an integral approach, including clinical laboratory tests as an essential part of the diagnosis. Nevertheless, despite various laboratory tests available, affordability can be a limitation, mainly in developing countries. This review's objectives are 1) to learn the different laboratory approaches that arose and their application for clinical diagnosis; 2) to discuss their advantages and weaknesses, and finally, 3) propose what is on the horizon for future advances in clinical laboratory diagnosis of coccidioidomycosis. It has been a long way in laboratory tests evolution to detect coccidioidomycosis from tissue microscopy to Real-Time PCR. However, there is a delay in technology adoption for Coccidioides spp. detection in the clinical laboratory. The molecular Point of Care Testing (POCT) technology has reached us in our trench while research in PCR variants stills on-going. None of the currently existing scientific literature in coccidioidomycosis research has mentioned it. However, this trend in infectious and non-infectious disease diagnosis will continue in that way in order to offer better options for an easy and fast diagnosis. Undoubtedly, the implementation of molecular POCT for Coccidioides spp. would save resources in health care attention and improve access to diagnostic tools.

Advances in Molecular Tools and In Vivo Models for the Study of Human Fungal Pathogenesis

Pathogenic fungi represent an increasing infectious disease threat to humans, especially with an increasing challenge of antifungal drug resistance. Over the decades, numerous tools have been developed to expedite the study of pathogenicity, initiation of disease, drug resistance and host-pathogen interactions. In this review, we highlight advances that have been made in the use of molecular tools using CRISPR technologies, RNA interference and transposon targeted mutagenesis. We also discuss the use of animal models in modelling disease of human fungal pathogens, focusing on zebrafish, the silkworm, Galleria mellonella and the murine model.

Early Events in Coccidioidomycosis

Since its description nearly 130 years ago, hundreds of studies have deepened our understanding of coccidioidomycosis, also known as valley fever (VF), and provided useful diagnostic tests and treatments for the disease caused by the dimorphic fungi Coccidioides spp. In general, most of the literature has addressed well-established infections and has described patients who have experienced major complications. In contrast, little attention has been given to the earliest consequences of the pathogen-host interaction and its implications for disease manifestation, progression, and resolution. The purpose of this review is to highlight published studies on early coccidioidomycosis, identify gaps in our knowledge, and suggest new or former research areas that might be or remain fertile ground for insight into the early stages of this invasive fungal disease.

Effects of Pregnancy, Outdoor Access, and Antifungal Medication on Hair Loss in Breeding-age Female Pigtailed Macaques (Macaca nemestrina)

Over 18 mo, adult female pigtailed macaques (Macaca nemestrina) housed at a breeding facility in Arizona were monitored every 6 mo for alopecia. The study period coincided with the movement of a majority of animals from primarily outdoor housing to continuous indoor housing and a corresponding decrease in available space. These changes were made due to the newly recognized prevalence of coccidioidomycosis at this site. The effects of pregnancy status, changes in outdoor access or space, and administration of fluconazole for the treatment of coccidioidomycosis on alopecia were explored. In this group of pigtailed macaques pregnancy did not appear to affect alopecia, in contrast to findings from a closely related species, rhesus macaques. Fluconazole administration increased alopecia in older animals but not in the youngest age group. Conversely, the effects of limited outdoor access or decreased space on increasing alopecia were greatest in the youngest group of animals.

Coccidioidomycosis in Nonhuman Primates: Pathologic and Clinical Findings

Coccidioidomycosis in nonhuman primates has been sporadically reported in the literature. This study describes 22 cases of coccidioidomycosis in nonhuman primates within an endemic region, and 79 cases of coccidioidomycosis from the veterinary literature are also reviewed. The 22 cases included baboons ( n = 10), macaques ( n = 9), and chimpanzees ( n = 3). The majority died or were euthanized following episodes of dyspnea, lethargy, or neurologic and locomotion abnormalities. The lungs were most frequently involved followed by the vertebral column and abdominal organs. Microscopic examination revealed granulomatous inflammation accompanied by fungal spherules variably undergoing endosporulation. Baboons represented a large number of cases presented here and had a unique presentation with lesions in bone or thoracic organs, but none had both intrathoracic and extrathoracic lesions. Although noted in 3 cases in the literature, cutaneous infections were not observed among the 22 contemporaneous cases. Similarly, subclinical infections were only rarely observed (2 cases). This case series and review of the literature illustrates that coccidioidomycosis in nonhuman primates reflects human disease with a varied spectrum of presentations from localized lesions to disseminated disease.

Intranasal Antifungal Vaccination Using DNA-Transfected Dendritic Cells

Dendritic cells are the most potent antigen-presenting cells, and are critical for the generation of an antigen-specific immune response and protective immunity. These unique features have been applied to dendritic cell-based immunization in a number of disease conditions. Our published results have demonstrated that the immunity induced by intranasal immunization with DNA-transfected dendritic cells results in reduced fungal burden, and alleviated lung tissue damage in a mouse model of pulmonary fungal infection. In this article, approaches for the preparation and characterization of DNA-transfected dendritic cells and intranasal immunization in mice are described.

Preclinical identification of vaccine induced protective correlates in human leukocyte antigen expressing transgenic mice infected with Coccidioides posadasii

There is an emerging interest to develop human vaccines against medically-important fungal pathogens and a need for a preclinical animal model to assess vaccine efficacies and protective correlates. HLA-DR4 (DRB1∗0401 allele) transgenic mice express a human major histocompatibility complex class II (MHC II) receptor in such a way that CD4⁺ T-cell response is solely restricted by this human molecule. In this study HLA-DR4 transgenic mice were immunized with a live-attenuated vaccine (ΔT) and challenged by the intranasal route with 50-70 Coccidioides posadasii spores, a potentially lethal dose. The same vaccination regimen offers 100% survival for C57BL/6 mice. Conversely, ΔT-vaccinated HLA-DR4 mice displayed 3 distinct manifestations of Coccidioides infection including 40% fatal acute (FAD), 30% disseminated (DD) and 30% pulmonary disease (PD). The latter 2 groups of mice had reduced loss of body weight and survived to at least 50days postchallenge (dpc). These results suggest that ΔT vaccinated HLA-DR4 mice activated heterogeneous immunity against pulmonary Coccidioides infection. Vaccinated HLA-DR4 mice displayed early expansion of Th1 and Th17 cells and recruitment of inflammatory innate cells into Coccidioides-infected lungs during the first 9dpc. While contraction rates of Th cells and the inflammatory response during 14-35dpc significantly differed among the 3 groups of vaccinated HLA-DR4 mice. The FAD group displayed a sharply reduced Th1 and Th17 response, while overwhelmingly recruiting neutrophils into lungs during 9-14days. The FAD group approached moribund by 14dpc. In contrast, vaccinated HLA-DR4 survivors gradually contracted Th cells and inflammatory response with the greatest rate in the PD group. While vaccinated HLA-DR4 mice are susceptible to Coccidioides infection, they are useful for evaluation of vaccine efficacy and identification of immunological correlates against this mycosis.

Card9- and MyD88-Mediated Gamma Interferon and Nitric Oxide Production Is Essential for Resistance to Subcutaneous Coccidioides posadasii Infection

Coccidioidomycosis is a potentially life-threatening respiratory disease which is endemic to the southwestern United States and arid regions of Central and South America. It is responsible for approximately 150,000 infections annually in the United States alone. Almost every human organ has been reported to harbor parasitic cells of Coccidioides spp. in collective cases of the disseminated form of this mycosis. Current understanding of the mechanisms of protective immunity against lung infection has been largely derived from murine models of pulmonary coccidioidomycosis. However, little is known about the nature of the host response to Coccidioides in extrapulmonary tissue. Primary subcutaneous coccidioidal infection is rare but has been reported to result in disseminated disease. Here, we show that activation of MyD88 and Card9 signal pathways are required for resistance to Coccidioides infection following subcutaneous challenge of C57BL/6 mice, which correlates with earlier findings of the protective response to pulmonary infection. MyD88(-/-) andCard9(-/-) mice recruited reduced numbers of T cells, B cells, and neutrophils to the Coccidioides-infected hypodermis com pared to wild-type mice; however, neutrophils were dispensable for resistance to skin infection. Further studies have shown that gamma interferon (IFN-γ) production and activation of Th1 cells characterize resistance to subcutaneous infection. Furthermore, activation of a phagosomal enzyme, inducible nitric oxide synthase, which is necessary for NO production, is a requisite for fungal clearance in the hypodermis. Collectively, our data demonstrate that MyD88- and Card9-mediated IFN-γ and nitric oxide production is essential for protection against subcutaneous Coccidioides infection.

Overview of vertebrate animal models of fungal infection

Fungi represent emerging infectious threats to human populations worldwide. Mice and other laboratory animals have proved invaluable in modeling clinical syndromes associated with superficial and life-threatening invasive mycoses. This review outlines salient features of common vertebrate animal model systems to study fungal pathogenesis, host antifungal immune responses, and antifungal compounds.

Mouse models for the study of fungal pneumonia: a collection of detailed experimental protocols for the study of Coccidioides, Cryptococcus, Fusarium, Histoplasma and combined infection due to Aspergillus-Rhizopus

Mouse models have facilitated the study of fungal pneumonia. In this report, we present the working protocols of groups that are working on the following pathogens: Aspergillus, Coccidioides, Cryptococcus, Fusarium, Histoplasma and Rhizopus. We describe the experimental procedures and the detailed methods that have been followed in the experienced laboratories to study pulmonary fungal infection; we also discuss the anticipated results and technical notes, and provide the practical advices that will help the users of these models.

Phenotypic and molecular identification of Coccidioides posadasii in a patient evaluated for bilateral lung transplantation

BACKGROUND

Coccidioidomycosis is an endemic fungal infection caused by Coccidioides immitis and Coccidioides posadasii. It can be particularly severe in transplant recipients that have a current or a previous coccidioidal infection. Fatal case of coccidioidomycosis has been described in this group of patients.

AIMS

We report a severe case of pneumonia caused by C. posadassi in a 29 year-old white woman that had been admitted to hospital as part of the evaluation for bilateral lung transplantation. The patient was a native and resident of Catamarca, Argentina. Molecular methodologies contributed to the species identification.

METHODS

Clinical, laboratory records and microbiological tests were carried out to diagnose the infection and to identify C. posadasii.

RESULTS

A fungus was isolated from BAL culture. Phenotypic characterization, specific PCR and experimental animal inoculation demonstrated the presence of C. posadasii. The patient responded well to amphotericin B deoxycholate. Lung transplantation was postponed.

CONCLUSIONS

Specific PCR can be an important alternative for the correct identification of C. immitis or C. posadasii in laboratories with implemented molecular biology tools. This case emphasizes the need for a systematic assessment in organ transplant units of patients inhabiting endemic areas of coccidioidomycosis.

Quantitation of cytokine mRNA by real-time RT-PCR during a vaccination trial in a rabbit model of fascioliasis

Use of the rabbit as disease model has long been hampered by a lack of immunological assays specific to this species. In the present study we developed a SYBR Green-based, real-time RT-PCR protocol to quantitate cytokine mRNA in freshly harvested rabbit peripheral mononuclear cells. The method was validated in the course of a vaccination trial in which animals vaccinated with the recombinant antigen FhSAP2 were challenged with Fasciola hepatica metacercariae. Changes in the levels of rabbit interleukin (IL)-2, IL-4, IL-6, IL-10, tumor necrosis factor-alpha (TNFalpha), and interferon-gamma (IFNgamma) mRNA were determined. Messenger RNA from the universally expressed housekeeping gene GAPDH was used as an amplification control and allowed for correction of variations in the efficiencies of RNA extraction and reverse transcription. Rabbits vaccinated with FhSAP2 showed an 83.3% reduction in liver fluke burden after challenge infection when compared to non-vaccinated controls. All cytokine mRNAs were found at detectable levels; however, the levels of IFNgamma, TNFalpha, IL-2 and IL-10 were significantly higher in the vaccinated group compared to the non-vaccinated group. These results suggest that protection conferred by FhSAP2 protein could be associated with a mixed Th1/Th2 immune response in which Th1 cytokines are dominant. The real-time RT-PCR method described herein can be a useful tool for monitoring changes in basic immune functions in the rabbit model of fascioliasis and may also aid in studies of human diseases for which the rabbit is an important experimental model.

Saccharomyces cerevisiae as a vaccine against coccidioidomycosis

Disseminated coccidioidomycosis is a life-threatening infection. In these studies, we examined protection against systemic murine coccidioidomycosis by vaccination with heat-killed Saccharomyces cerevisiae (HKY). CD-1 mice received HKY subcutaneously or by oral gavage with or without adjuvants once weekly beginning 3 or 4 weeks prior to infection; oral live Saccharomyces was also studied. All HKY sc regimens were equivalent, prolonging survival (P<or=0.005) and reducing fungal burden versus controls. Oral live Saccharomyces, but not HKY, prolonged survival (P=0.03), but did not reduce fungal burden. Survival of mice given HKY was equivalent to vaccination with formalin-killed spherules, but inferior in reduction of fungal burden. HKY was superior to a successful recombinant vaccine, PRA plus adjuvant. This novel heterologous protection afforded by HKY vaccination offers a new approach to a vaccine against coccidioidomycosis.

Twelve years of coccidioidomycosis in Ceará State, Northeast Brazil: epidemiologic and diagnostic aspects

Coccidioidomycosis is an endemic infection in the Americas caused by the dimorphic fungi Coccidioides immitis and Coccidioides posadasii. Although the disease occurs in Brazil in sporadic form, little information about these cases is available. In this study, we summarize the most important clinical, epidemiologic, and diagnostic features of coccidioidomycosis in Ceará State (Northeast Brazil) during the past 12 years. In this period, 19 cases of coccidioidomycosis were diagnosed. All the patients were young males and came from semiarid areas of the state. The majority of cases were associated to armadillo hunting, and pulmonary disease was the most common clinical presentation. In our laboratory, coccidioidomycosis was confirmed by culture, serology, and polymerase chain reaction tests, which together were very suitable for the diagnosis of this disease. Based on our local experience, we believe many cases of this disease are misdiagnosed or not diagnosed in our region. Therefore, some strategies for improvement of diagnosis should be encouraged by local authorities.

Coccidioidal pericarditis: a rapid presumptive diagnosis by an in-house antigen confirmed by mycological and molecular methods

Coccidioidal pericarditis is a condition found in approximately 1-5% of patients infected by Coccidioides species. It is associated with widely diverse clinical symptoms. This paper reports a case of coccidioidal pericarditis diagnosed by an in-house Coccidioides posadasii antigen and confirmed with mycological and molecular methods. From February to September 2005, the patient suffered from fever, weight loss, a non-productive cough, thoracic pain and tachycardia. He received a positive diagnosis of coccidioidal pericarditis only in October 2005. The macromorphological examination of the culture showed a whitish felt-like colony, which became brownish with age. Preparations in lactophenol cotton blue stain showed hyaline septate hyphae with fragmentation and thin arthroconidia-like structures. Pericardial fluid and sera samples were positive for Coccidioides antibodies by immunodiffusion and ELISA with a C. posadasii in-house antigen preparation. The C. posadasii identification was confirmed by nested PCR of the antigen 2/proline-rich antigen (Ag2/PRA) encoding gene.