MUCORMYCOSIS (THE BLACK FUNGUS) ASSOCIATED WITH COVID-19 PATIENTS- EPIDEMIOLOGY, PATHOGENESIS, DIAGNOSIS AND TREATMENT REGIMESHTML Full Text
MUCORMYCOSIS (THE BLACK FUNGUS) ASSOCIATED WITH COVID-19 PATIENTS- EPIDEMIOLOGY, PATHOGENESIS, DIAGNOSIS AND TREATMENT REGIMES
Pranay Jain * and Ram Kumar Pundir
Department of Biotechnology, University Institute of Engineering and Technology, Kurukshetra University, Kurukshetra, Haryana, India.
ABSTRACT: Mucormycosis is an opportunistic fungal infection caused by a member of the order Mucorales. It is an angio-invasive fungal infection because of its propensity to invade blood vessel walls, resulting in catastrophic tissue ischemia (restriction in blood supply to tissues, causing a shortage of oxygen that is needed for cellular metabolism), infarct (tissue death that is necrosis) due to inadequate blood supply to the affected area. Mucorales fungi are distributed worldwide and found in soil and decaying organic substrates. The most common microbiologically confirmed infecting members of the order Mucorales are Rhizopus, Mucor, Cunninghamella bertholletiae, Apophysomyces elegans, Absidia, Saksenaea and Rhizomucor pusillus. The incidence of mucormycosis has increased significantly in patients with diabetes which is the commonest underlying risk factor globally. Recently, COVID-19 caused by SARS CoV-2 has further worsened the incidence of this disease. Diagnosis of mucormycosis remains challenging. The clinical approach to diagnosis has a low sensitivity and specificity; however, it helps raise suspicion and prompt the initiation of laboratory testing. Histopathology, direct examination, and culture remain essential tools, although the molecular methods are improving. The review highlights the current status on epidemiology, pathogenesis diagnosis and treatment regime available for mucormycosis.
Keywords: Mucormycosis, Epidemiology, Pathogenesis, Diagnosis, SARS CoV-2, COVID-19
INTRODUCTION: Mucormycosis or commonly called black fungus disease, is a rare, emerging fungal infection with high morbidity and mortality. Mucormycosis typically occurs in patients with diabetes mellitus, patients who have received an organ or hematopoietic stem cell transplant, patients with neutropenia, i.e., a person having lower-than-normal levels of neutrophils, a type of white blood cell, in the blood, or patients with malignancy (presence of cancerous cells).
The prevalence of mucormycosis in India is about 80 times the prevalence in developed countries, being approximately 0.14 cases per 1000 population. The true incidence of mucormycosis is not known and probably underestimated because of difficulties in antemortem diagnosis.
The most common microbiologically confirmed infecting members of the order Mucorales are Rhizopus (47%), Mucor (18%), Cunning-hamella bertholletiae (7%), Apophysomyces elegans (5%), Absidia (5%), Saksenaea (5%), and Rhizomucor pusillus (4%). 1, 2 Rhizopus oryzae is the most common organism isolated from patients with mucormycosis and is responsible for nearly 70% of all cases of mucormycosis 3, 4, 5. The classic risk factors for mucormycosis include hematologic malignancy, hematopoietic stem cell or solid organ transplantation, poorly controlled diabetes mellitus, chronic acidemia, prematurity, iron overload, profound chronic debilitation, trauma, burns and intravenous drug use. Nosocomial cutaneous infections can develop in surgical wounds and at intravenous catheter insertion sites. The disease was first described in 1876 when Fürbinger 6 described in Germany a patient who died of cancer and in whom the right lung showed a hemorrhagic infarct with fungal hyphae and a few sporangia 7. Currently, Mucorales fungi are the next most common mold pathogens after Aspergillus species that causes Aspergillosis, leading to invasive fungal disease in patients with malignancies or transplantation 8.
The incidence of mucormycosis has also increased significantly in diabetes 9, which is the commonest underlying risk factor globally. The coronavirus disease 2019 (COVID-19) infection caused by the novel severe acute respiratory syndrome coronavirus 2 (SARS CoV-2) has been reported to be associated with a wide range of bacterial and fungal infections, especially mucormycosis10. The aim of this review is to present an update on the epidemiology, pathogenesis, the available diagnostic methods, prevention, and treatment management for this potentially lethal disease.
Epidemiology: The most common causative agents of mucormycosis are Rhizopus spp., Mucor spp., and Lichtheimiaspp, Rhizomucor, Saksenaea, Cunninghamella, and Apophysomyces 11, 12. In India, although Rhizopus species are the most common cause of the disease, Apophysomyces elegans, A. variabilis, and Rhizopus homothallicus are emerging species, and uncommon agents such as Mucor irregularis and Thamnostylum lucknowense are also being reported 13, 14. Most cases of mucormycosis result from inhalation of fungal sporangiospores that have been released in the air or from direct inoculation of organisms into disrupted skin or gastrointestinal tract mucosa. Seasonal variations affect the incidence of mucormycosis, with most infections occurring from August to November 15. Necrotizing fasciitis due to Apophysomyces variabilis or A.elegans 14 and Saksenaea erythrospora 16 after intramuscular injections, have also been reported from India. The incidence of mucormycosis has been increasing in recent decades, mainly due to the growth of the number of severely immune-compromised patients 5. The most important conditions that predispose to mucormycosis include diabetes mellitus, with or without ketoacidosis, hematological malignancies, other malignancies, transplantation, prolonged neutropenia, over use of corticosteroids, trauma, iron overload, illicit intravenous drug use, neonatal prematurity and malnourishment 12. Diabetes mellitus is the leading underlying disease in patients with mucormycosis globally 5. The number of people aged 20–79 years with diabetes in 2011 was 61.3 million in India, and it is estimated to rise to 101.2 million in 2030 17. A great rise in the diabetic population is also predicted for China, Brazil, Japan, Mexico, Egypt, and Indonesia 18.
Accordingly, the cases of mucormycosis are expected to increase. Hematological malignancies and hematopoietic stem cell transplantation are the most common underlying diseases in mucormycosis in Europe, USA, and Australia. In India haematological malignancy has been reported a risk factor in 1–9% 9. Solid-organ malignancies and solid organ transplantation, although not as common as hematological malignancy and hematopoietic stem cell transplantation, are also important risk factors for mucormycosis.
Chronic administration of corticosteroids and other immunosuppressive agents is an important risk factor for mucormycosis. They are used in the treatment of malignancies, transplantation, and autoimmune diseases 7. Corticosteroids impair migration, ingestion, and phagolysosome fusion in macrophages. In addition, they may lead to drug-induced diabetes. Prolonged (>3 weeks) high-dose systemic corticosteroids are risk factors for mucormycosis 19. Increased serum iron is a risk factor for mucormycosis, as iron plays a crucial role in the pathogenesis of this infection 20. Iron is normally attached to transferrin and ferritin and is not available to the Mucorales fungi. In patients with diabetic ketoacidosis or other forms of acidosis, these proteins have decreased affinity to bind iron 21. Another factor that may predispose to mucormycosis is the use of antifungal prophylaxis or treatment, which is effective against Aspergillus but not Mucorales(voriconazole and echinocandins) 22. Other diseases associated with mucormycosis are intravenous drug use, AIDS, renal failure, liver diseases, chronic alcoholism, malnutrition, and low birth weight infants 23. Despite aggressive surgical intervention and intensive antifungal treatment, mortality of mucormycosis is high, ranging from 50–100% depending on the disease form 3. By comparison, mortality rates for candidiasis and aspergillosis range from 20–50% and 35–45%, respectively 24. Successful management of mucormycosis requires early diagnosis, reversal of underlying predisposing risk factors, surgical debridement, and prompt administration of Amphotericin B. However, besides these measures, mucormycosis is not always amenable to cure because of the challenging obstacles that lead to difficulties in managing mucormycosis 24. In developed countries, the disease remains uncommon and is mostly seen in patients with hematological malignancies. In contrast, in developing countries, especially in India, mucormycosis is more common and cases occur mainly in patients with uncontrolled diabetes mellitus or trauma 13.
Based on clinical presentation and the involvement of a particular anatomic site, mucormycosis can be divided into the following clinical categories: rhino-orbito-cerebral (34%), pulmonary (21%), cutaneous (20%), and disseminated (14%), respectively 25.
Pathogenesis: Pathogenic microorganisms use several strategies to establish virulence, the relative ability of a pathogen to harm the host. The mechanism of microbial pathogenesis is the process by which microorganisms cause disease.
Microbial pathogenesis begins with exposure and adherence of the microorganisms to host cells, followed by invasion, colonization, and infection or growth. The unchecked growth of the pathogen can result in host damage and disease 7, 41. The steps of pathogenesis are as follows:
- Exposure of Fungal spores via inhalation (Rhino-Orbito-Cerebral Mucormycosis (ROCM), Pulmonary Mucormycosis) /ingestion (Gastrointestinal Mucormycosis) / implantation (Renal Mucormycosis) / inoculation through a needle (Disseminated Mucormycosis).
- Body defense mechanisms work on pathogenic exposure (Predisposing factors play an important role in case of mucormycosis).
- Adherence and invasion.
- Colonization and growth (fungal proliferation enhanced with iron overload).
- Invasiveness (further growth at original and distinct cells causes further exposure to new cells).
- Tissue damage that causes disease.
A recently identified prominent clinical feature is the increased susceptibility to mucormycosis of patients with elevated available serum iron. To cause disease, the members of mucorales must scavenge from the host sufficient iron for growth, evade host phagocytic defense mechanisms, and access vasculature to disseminate. Moreover, the ability of inhaled sporangiospores to germinate and form hyphae in the host is critical for establishing infection.
The skin barrier represents a host defence against cutaneous mucormycosis, as evidenced by the increased risk for developing mucormycosis in persons with disruption of this barrier. The agents of mucormycosis are typically incapable of penetrating intact skin. However, burns, traumatic disruption of the skin and persistent maceration of skin enable the organism to penetrate deeper tissues 20. In a normal healthy individual, a primary defense mechanism against mucormycosis include sequestration of iron in serum by specialized iron-binding proteins, phagocytes including circulating neutrophils and tissue macrophages, and endothelial cells, which regulate vascular tone and permeability.
Acting in concert, these mechanisms prevent the establishment of infection in the tissue and subsequent endovascular invasion. On the contrary, in susceptible hosts, normal defense mechanisms break down. For example, in patients suffering from diabetic ketoacidosis, the acidic pH of the serum causes dissociation of free iron from sequestering proteins. This release of free iron allows rapid fungal growth. Defects in phagocytic defense mechanisms, for example, deficiency in cell number (neutropenia) or functional defects caused by corticosteroids or the hyperglycemia and acidosis of diabetic ketoacidosis, allow proliferation of the fungus 7. Moreover, adherence to and damage of endothelial cells by the fungus allows fungal angio-invasion and vessel thrombosis and subsequent tissue necrosis and dissemination of the fungal infection 4. This angio-invasion likely contributes to the capacity of the organism to hematogenously disseminate to other target organs. Consequently, damage of and penetration through endothelial cells or the extracellular matrix proteins lining blood vessels is likely to be a critical step in the pathogenetic strategy of mucormycosis fungi 20.
Diagnosis: Early diagnosis of mucormycosis is of utmost importance since it increases survival, and it may also reduce the need for or extent of surgical resection, disfigurement and suffering 26. Diagnosis of this disease comprises recognition of risk factors, assessment of clinical manifestations, early use of imaging modalities and prompt initiation of diagnostic methods based on histopathology, cultures and advanced molecular techniques.
Clinical Diagnosis: The clinical approach to diagnosis has low sensitivity and specificity. The salient feature of mucormycosis is tissue necrosis resulting from angioinvasion and thrombosis, the absence of a necrotic scab does not preclude the diagnosis. Necrotic cutaneous lesions in immuno-compromised patients may be due to mucormycosis, but the differential diagnosis includes other pathogens, such as Aspergillus, Fusarium, Pseudallescheria, and Scedosporium species 26. A patient with diabetes and sinusitis should be thoroughly examined for possible mucormycosis. The prominent symptoms of mucormycosis are cranial nerve palsy, diplopia, sinus pain, proptosis, periorbital swelling, orbital apex syndrome, or a palatine ulcer. The finding of any of these signs should prompt immediate further testing, including blood tests, imaging, ocular and sinus surgery or endoscopic revision, and initiation of antifungal treatment. Prolonged fever, not responding to broad-spectrum antibiotics, is usually present in this disease 7. A non-productive cough is a common symptom, whereas hemoptysis, pleuritic chest pain, and dyspnea are less common. Radiologically, multiple (≥10) nodules and pleural effusion are more common in mucormycosis. Another indication of mucormycosis is the reversed halo sign on computerized tomography (CT) scan 27.
Laboratory Identification: After specimen collection, various routine laboratory identification, detection and diagnostic methods of mucormycosis causing fungi are performed as shown in Fig. 1.
FIG. 1: METHODS FOR IDENTIFICATION AND DETECTION OF MUCORMYCOSIS CAUSING FUNGI
Histopathology: A definitive diagnosis is based on the presence of fungal hyphae typical for mucormycetes in biopsies of affected tissues. Histopathology is a very important diagnostic tool since it distinguishes the presence of the fungus as a pathogen in the specimen from a culture contaminant and is indispensable to define whether there is blood vessel invasion. It can furthermore reveal coinfections with other molds. Mucorales genera produce typically non-pigmented, wide (5–20 µm), thin-walled, ribbon-like hyphae with no or few septations (pauciseptate) and right-angle branching 3. Stains that can help highlight the fungal wall include Grocott methenamine-silver and periodic acid-Schiff stains 28. Tissue histopathology is dominated by inflammation that may be neutrophilic or granulomatous; inflammation seems absent in a few cases, particularly in immunosuppressed patients 4. Prominent infarcts and angio-invasion characterize the invasive disease. Key features of mucorales, clinical isolates grow at 4°C, one-celled, globose to ovoid, echinulate sporangiola borne on the swollen terminal or lateral globose to clavate fertile vesicles. In cases where nerve structures are involved, a perineural invasion may be present. Neutropenic patients display a more extensive angioinvasion when compared to nonneutropenic patients 29.
Culture: The culture of specimens is essential for the diagnosis of mucormycosis since it allows identification to the genus and species level and eventually antifungal susceptibility testing. Most medically important Mucorales are thermo tolerant and are able to grow rapidly at temperatures of 37 °C. They grow on virtually any carbohydrate substrate, colonies usually appearing within 24 to 48 h and identification is based on colonial and microscopic morphology and growth temperature 26.
Direct Microscopy: Potassium hydroxide (KOH) wet mounts can be used for a rapid presumptive diagnosis of mucormycosis in the case of direct microscopy. It can be applied using fluorescent brighteners such as Blankophor and Calcofluor White together with KOH, which enhances the visualization of the characteristic fungal hyphae, requiring a fluorescent microscope 26. Direct microscopy of fresh material is an inexpensive yet invaluable method to rapidly give a presumptive diagnosis and to define clear surgical margins for invasive fungal infection intraoperatively 30.
These methods, however are not able to identify a fungus to the genus or species level. Another method, immunohistochemistry, using monoclonal antibodies against members of mucorales can aid in the diagnosis when cultures are negative and has been proven useful for differentiating aspergillosis from mucormycosis 31. The cultural characteristics of Mucor and Rhizopus spp. are shown in Fig. 2. The colonial and microscopical characteristics of important mucormycosis causing fungi are shown in Table 1.
FIG. 2: (A) MUCOR SPECIES (B) RHIZOPUS SPECIES (C) SPORANGIOPHORE (STALK) BEARING SPORANGIUM AND SPORANGIUM BEARS SPORANGIOSPORES (CAPPUCCINO AND WELSH, 2018.)
TABLE 1: COLONIAL AND MICROSCOPIC CHARACTERISTICS OF IMPORTANT MUCORMYCOSIS CAUSING FUNGI
|Name of mucormycosis causing fungi||Cultural/ colonial characteristics||Microscopic characteristics|
|Mucor spp.||Colonies grow to several centimeters in height. Older colonies become grey to brown in colour due to the development of spores. Reverse pigmentation is white to yellow. Dense cottony-fluffy growth with a flossy texture||Columellate sporangiophores arise singly from the aseptate mycelium; sporangium is spherical, gray to black in colour. Columella may be of various shapes; sporangiospores are grayish or brownish, hyaline smooth-walled, and globose to ellipsoids in shape. Spores or sporangiospores can be simple or branched and form apical, globular sporangia that are supported and elevated by a column-shaped columella|
|Rhizopus stolonifer||Colonies are initially white and turns grey to yellowish-brown as culture matures. Reverse pigmentation is white to pale.||Columellate sporangiophores arise in the cluster just opposite to the rhizoids (pale to brown), sporangia colourless when young and black at maturity. Columella subglobose to oval, pale brown, sporagiospores gray, subglobosebiconical to oval|
|Lichtheimia spp.||Colonies are fast-growing, floccose, white at first becoming pale grey with age, and up to 1.5 cm high||Sporangiophores are hyaline to faintly pigmented, simple or sometimes branched, arising solitarily or in groups. Sub-sporangial septa are absent or rare. Rhizoids are very sparingly produced and may be difficult to find without the aid of a dissecting microscope to examine the colony on the agar surface. Sporangia are small (10-40 µm in diameter) and are typically pyriform with a characteristic conical-shaped columella and pronounced apophysis, often with a short projection at the top. Sporangiospores vary from subglobose to oblong-ellipsoidal, hyaline to light grey and smooth-walled. Intercalary giant cells may also be present|
|Rhizomucor spp.||The texture is typically cotton-candy-like. From the front, the color of the colony is white initially and turns grey to yellowish-brown in time. The reverse is white to pale
|The microscopic morphology of Rhizomucor appears to be intermediate between that of Rhizopus and Mucor. Nonseptate or sparsely septate broad hyphae, rudimentary rhizoids, sporangiophores, sporangia, and sporangiospores are visualized. Rudimentary rhizoids, if they exist, are few in number and are located on stolons between the sporangiophores. Sporangiophores are irregularly branched and end in sporangia at their apices. Sporangia are brown in color and round in shape. Columellae, on the other hand, are prominent and spherical to pyriform in shape. Sporangiospores (3-4 µm in diameter) are small, unicellular, and round to ellipsoidal in shape|
|Saksenaea spp.||Colonies are fast-growing, downy, white with no reverse pigment, and made up of broad||Non-septate hyphae are typical of a mucormycetous fungus.
Sporangia are typically flask-shaped with a distinct spherical venter and long-neck, arising singly or in pairs from dichotomously branched, darkly pigmented rhizoids. Collumellae is prominent and dome-shaped. Sporangiospores are small, oblong, and are discharged through the neck following the dissolution of an apical mucilaginous plug
|Cunninghamella spp.||Colonies are very fast-growing, white at first, but becoming dark grey and powdery with sporangiola development||Sporangiophores straight, with verticillate or solitary branches. Vesicles subglobose to pyriform, Sporangiola are globose or ellipsoidal verrucose or short-echinulate, hyaline singly but brownish in mass|
|Apophysomyces spp.||Colonies are white to creamy white to buff with age||Filamentous, contain sporangiophore bearing sporangium contains sporangiospores|
Serology: Enzyme-linked immunosorbent assays 32, immunoblots 32 and immunodiffusion tests 32 have been used to examine the fungal specimen in several cases.
Molecular Assays: Molecular assays have evolved as a useful tool to confirm the infection and identify the strains involved in mucormycosis. There are assays, therefore, developed on the one hand to accurately identify the species level strains that already have grown in cultures and, on the other hand, assays to detect mucormycetes in tissues. Matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF) identification of cultured Mucorales has been regarded as a promising method 33. The ITS region is the most widely sequenced DNA region for fungi in general. ITS sequencing is a reliable method and has typically been the most useful for molecular systematics at the species level and even within species. It is recommended as a first-line method for species identification of Mucorales 34. For the detection in tissues, several methods have been developed, including Polymerase Chain Reaction based techniques such as nested PCR, real-time PCR (qPCR), nested PCR combined with Restriction Fragment Length Polymorphism (RFLP) 35, PCR coupled with electrospray ionization mass spectrometry (PCR/ESI-MS) 36 and PCR/high-resolution melt analysis (HRMA) 37. Many of these methods have been reportedly successfully applied and perform better on fresh or deep-frozen samples than on paraffin-embedded tissues. Target selection for the PCR is a key determinant of the success of the method 38, 39.
Treatment: Successful management of mucor-mycosis is based on multiple approaches, including reversal or discontinuation of underlying predisposing factors, early administration of active antifungal agents at the optimal dose, complete removal of all infected tissues, and the use of various adjunctive therapies 40. Early diagnosis is crucial to promptly initiate therapeutic interventions necessary for preventing progressive tissue invasion and its devastating sequelae, minimizing the effect of disfiguring corrective surgery, and improving outcome and survival 26.
Mucoraceous fungi are resistant to most antifungals in-vitro, including Fluconazole and Voriconazole. Amphotericin B is the most active drug, except for some Cunninghamella and Apophysomycesspecies 41, Posaconazole and isavuconazole are also active, while itraconazole and terbinafine show some activity against certain strains as reported by Borman et al. 42. The response of mucormycosis to antifungal agents is host and site-dependent and is particularly problematic in patients with hematological disorders and hematopoietic stem cell transplant recipients 5. Members of Mucorales have many common characteristics with other molds, including portals of entry (airways as well as disrupted mucosal and skin barriers), innate host defenses (polymorphonuclear neutrophil and mononuclear phagocytes, specific ligands in fungal spores such as pathogen-associated molecular patterns, and immune cells as well as histopathological and clinical features 11.
However, Rhizopus oryzae, Lichtheimia, Rhizomucor, and Mortierella species are characterized by distinctive virulence factors that enable them to infect patients with diabetic ketoacidosis or other forms of acidosis and exert unique host-pathogen interactions compared to other fungi, thus facilitating host evasion and disease progression despite treatment 11. In addition, mucormycosis is characterized by extensive angio-invasion that leads to vessel thrombosis and tissue necrosis 43. Angioinvasion results in hematogenous dissemination of the organism, whereas necrosis of the affected tissues prevents penetration of immune cells and antifungal agents to the infection focus 44. Certain Mucorales, such as R. oryzae, have reduced susceptibility to innate host defense as compared to other fungi, such as Aspergillus or Candida, making them more difficult to treat and therefore associated with increased mortality 27. The optimal doses for antifungal agents are still an issue of controversy, as in the case of Posaconazole and isavuconazole, which are used as salvage or maintenance therapy. The advent of the intravenous and tablet forms of Posaconazole has enhanced bioavailability and increased drug exposure. This may strengthen the position of this triazole in the antifungal armamentarium, especially against difficult-to-treat mucormycosis 45.
Isavuconazole is a recently developed triazole, with a wide spectrum of antifungal activity, including Mucorales 47. The duration of treatment with active antifungal agents has not been determined. Active agents that have oral formulations such as Posaconazole and isavuconazole are preferred because they can be administered for several months if needed 32. Surgery when needed and possible must be very aggressive. Not only necrotic tissues but also surrounding infected healthy-looking tissues should be removed, as the speed of the extension of the infection by the Mucorales hyphae is enormous. Surgery is particularly useful in rhino-orbitocerebral infection and in soft tissue infection 32.
Other adjunctive therapies are the use of hyperbaric oxygen to make a more-oxygen enriched cell environment and administration of cytokines at the same time with antifungal therapy. There are in-vitro, and some preclinical data showing that granulocyte-macrophage colony-stimulating factor and/or interferon-γ may enhance the immune response against certain Members of Mucorales and thus potentially help treat the infection 47.
Natural Antimicrobials for Treatment of Mucormycosis: Mucorales are resistant to most antifungals, except to toxic agents such as polyene amphotericin B and triazole Posaconazole, and even these agents are relatively inefficient unless administered very early in the invasive stage when fungal infection is often very difficult to recognize 48. The genomic sequencing of the most common cause of invasive mucormycosis, Rhizopus oryzae, has revealed that Mucorale's innate resistance to therapy is the result of duplication within the genome of ergosterol biosynthesis pathway genes and mitochondrial protein complexes associated with respiratory electron transport chains 11. Hence, the development of new antifungal agents with distinct mechanisms of action against mucormycosis, especially those targeting the above-mentioned pathways, remains a major unmet need of contemporary medicine.
Medicinal Plants: The plant kingdom has always been a hub for many natural compounds with novel structures. This keeps the investigators interested in researching many plants species till today. The results of new researchers showed that plants enrich many bioactive secondary metabolites such as flavonoids, saponins, alkaloids, and terpenoids characterized by antifungal properties. Depending on that, these plants can be considered as a potential future source for antifungal drugs 49. With the challenges like morbidity and mortality, there always lies the difficulty in antifungal treatment for patients receiving therapy for AIDS, diabetes, chemotherapy or organ transplant and recently systematic acquired respiratory syndrome coronavirus-2 infection as some of the molecular processes of fungus are similar to humans, so toxicity to fungal cells could affect human cells too 50.
The spread of multidrug-resistant strains of fungus and the reduced number of drugs available make it necessary to discover new classes of antifungals from natural products, including medicinal plants. Medicinal plants have also been reported in traditional systems of medicine for the treatment of both human and animal mycoses. They are considered to be a valuable source for the discovery of new antifungal drugs. Table 2 lists some medicinal plants used for treating fungal infections caused by the members of Mucorales medicinal plants reported for antifungal activity against Mucorales.
TABLE 2: MEDICINAL PLANTS REPORTED FOR ANTIFUNGAL ACTIVITY AGAINST MUCORALES
|Botanical Name||Family||Part Used||Chemical Constituents||Microorganisms evaluated|
|Rubia tinctorum||Rubiaceae||Root||Triterpene||Mucor mucedo|
|Diterpemoids and Triterpenoids||Rhizopus sp., Mucor sp, Rhizomucor sp.|
|Ocimum gratissimum||Lamiaceae||Leaves||Flavonoids and Terpenoids||Rhizopus sp., Mucor sp, Rhizomucor sp|
|Carica papaya||Caricaceae||Seeds||Immune-stimulating and oxidizing agents||Rhizopus sp., Mucor sp, Rhizomucor sp|
|Thymus vulgaris||Lamiaceae||Spice||Linalool and p-cymene||Mucor sp. Rhizopus sp.|
|Cinnamomum zylanicum||Lauraceae||Barks, leaves, flowers and fruit||Phenols||Mucor sp. Rhizopus sp.|
|Allium sativum||Amaryllidaceae||Bulb||Allicin, ajoene||Mucor mucedo, Rhizopus sp.|
alkaloids, senkirkine and doronine
|Acacia catechu||Fabaceae||Seed||Catechin, Epicatechin||Mucor heimalis|
|Sida cordifolia||Malvaceae||Seed||β-phenthylamine, tryptamine||Mucor heimalis|
Essential Oils as Controlling Agents: The essential oil of Thymus vulgaris and its constituents thymol and p-cymene, has strong inhibitory effects on Rhizopus oryzae mycelial growth and germination of sporangiospores and interaction with ergosterol, supporting the possible use of these products in the treatment of mucormycosis51. The essential oils of Syzygium aromaticum (clove), Cymbopogon citrates (lemongrass), and Mentha piperata (menthe) have also been shown to exhibit very high antifungal activity against R. Oryzae 52. In a study, ethanolic turmeric extract showed activity against Rhizopus stolonifer and Mucor sp. with percent mycelial growth inhibition ranging between 25% and 30% 53. In another study, Syzygium aromaticum (clove) ethanolic extract showed 100% percent mycelial growth inhibition against food associated R. Stoloniferand 90% against Mucor sp. Allium sativum(garlic) ethanolic extract showed 50% percent mycelial growth inhibition against food-associated R. stoloniferand 40% inhibition against Mucor sp.54.
The essential oils can deactivate the fungus by disrupting the structure and function of membranes or organelles of fungal cells and/or inhibiting the nuclear material or protein synthesis in the following ways 55. Cell membrane disruption- Ergosterols play an essential role in preserving the integrity and function of the fungal cell membrane. If antifungal drugs bind such sterols or inhibit their biosynthesis by specific inhibitors, the cell membrane integrity will be disrupted. Inhibition of cell wall formation- The integrity of the cell wall can be disrupted by blocking the formation of β-glucans. Dysfunction of the fungal mitochondria- Antifungal agents can inhibit the function of the mitochondrial electron transport chain, reducing mitochondrial membrane potential. The inhibition can also occur through the inhibition of the proton pumps in the respiratory chain, reducing ATP production and subsequent cell death. Inhibition of efflux pumps- Efflux pumps, present in all living cells, remove toxic substances from the cell. The transport often includes the transport of accumulated drugs out of the fungal cell. Thus, the over-expression of these efflux pumps can lead to drug resistance. On the contrary, their inhibition can reduce drug resistance.
CONCLUSION: Mucormycosis poses an important burden on immunocompromised patients due to its persistently high mortality. The development of newer, more effective immunosuppressive medications has been associated with an increase in its incidence. Diabetics are also susceptible to this potentially lethal disease, especially in developing countries. The diagnosis and treatment of mucormycosis remain a challenge. The clinical symptoms are nonspecific, and when it becomes apparent that the patient most probably has mucormycosis, it is often too late to administer effective treatment. Early diagnosis is thus crucial and is the main target of current research. Direct examination, culture, and histopathology are the cornerstones of diagnosing mucormycosis, but they are time-consuming and lack sensitivity. Newer molecular diagnostic techniques, such as in-situ hybridization and PCR, offer an alternative that may lead to earlier diagnosis and prompt initiation of treatment. The management of mucormycosis is multimodal, including reversing underlying risk factors, administering antifungal agents, surgical intervention, and various adjunctive therapies. Timely and adequately dosed antifungal therapy is necessary. Amphotericin B and Posaconazole are the most often used medications. Isavuconazole is a new triazole with activity against the agents of mucormycosis, but it does not seem to offer an increased chance of survival compared to older treatments. Immunologic and metabolomic profiling of the host targeted immunotherapy and reversal of tissue hypoxia, natural antifungals derived from plants and their essential oils may evolve in the future, leading to better treatment of this devastating disease.
ACKNOWLEDGEMENT: The authors are grateful to the Vice-Chancellor (Kurukshetra University, Kurukshetra, Director (UIET, KUK) and University Institute of Biotechnology, Chandigarh University, Mohali, India for encouraging us to write this valuable manuscript.
CONFLICTS OF INTEREST: The authors declare no conflicts of interest.
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How to cite this article:
Jain P and Pundir RK: Mucormycosis (the black fungus) associated with Covid-19 patients- Epidemiology, pathogenesis, diagnosis and treatment regimes. Int J Pharm Sci & Res 2021; 12(12): 6270-80. doi: 10.13040/IJPSR.0975-8232.12(12).6270-80.
All © 2021 are reserved by International Journal of Pharmaceutical Sciences and Research. This Journal licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported License.
Pranay Jain * and Ram Kumar Pundir
Department of Biotechnology, University Institute of Engineering and Technology, Kurukshetra University, Kurukshetra, Haryana, India.
28 August 2021
24 October 2021
09 November 2021
01 December 2021