Black Fungus an Add on Epidemic to Cosvid-19 Pandemic

COVID-19 patients have lower immunosuppressive CD4+ T and CD8+ T cells and henceforth patients in intensive care units (ICU) need mechanical ventilation, henceforward they stay in hospitals. These patients have been exposed to advances in fungal co-infections. COVID-19 patients progress towards mucormycosis a black fungal infection that is deadly leading to loss of sight and hearing and eventually death. This article discusses the clinical manifestations, risk factors and emphases on virulence traits and management of black fungus.


INTRODUCTION
COVID-19 pandemic is an outbreak of coronavirus disease that was first acknowledged in December 2019. As the infection is asymptomatic and the severity of the disease leads to respiratory failure and death [1]. The most significant challenges increasing day by

Review Article
day is patient's morbidity and mortality which is caused by secondary fungal or bacterial infections [2]. Candidiasis and pulmonary aspergillosis have been common fungal infections that were reported as superinfections in COVID-19 patients [2,3]. On the other hand, it has been presumed that the oral manifestations which have been reported in association with  has the primary pathway for infection, precisely the ones of fungal origin [1][2][3].
Mucormycosis or Zygomycosis, also entitled Phycomycosis, is an unusual, aggressive, invasive, speedily progressive, and lifethreatening fungal infection. Triple strain corona virus is considerably high on patients those are in need of ICU advancing them to suffer from mucormycosis. Hence fatality rate is estimated to be high [2]. The infection they cause, mucormycosis "black fungus," can infect the sinuses and bones of the face and invade the brain or cause patients to lose an eye [4]. Generally, patients reported problems to the physicians not only breathless, feverish yet had pain and pressure behind their cheekbones and around their eyes. The black fungus has painted the country red in the second wave [5].
The epidemic of mucormycosis is yet another of the unpleasant surprises produced by the COVID pandemic following MIS-C, a severe inflammatory syndrome that seems to mostly affect children, and "long COVID," which is a complex of symptoms that continue to distress patients months after initial infection [6]. Mucormycosis is one of the violent fungal diseases that have attacked COVID patients, including a lethal yeast called "Candida Auris" and a spate of infections with Aspergillus fungi which is also known as CAPA (for COVIDassociated pulmonary aspergillosis) [7].
Mucormycosis has been a centre of attention all around the globe. But there seems difference in species and effects on the human body differing from a developed country and developing nations [8]. In developed nations this disease in less common and seen only in patients with haematological malignancies (HM). The developing countries paint a different picture, it is common in patients with uncontrolled diabetes mellitus or trauma. In India, mucormycosis is seen in 14 out of 100000 patients. In Europe and US, it is seen in 0.01 per 100000 population [6][7].
As the maxillofacial region consists of rich vascularity due to its anatomy, therefore it is more prone to the opportunistic infections [9]. Mucormycosis has the potential for virulence to escape the defense mechanism [10]. The attributable risk factors comprise uncontrolled diabetes mellitus, long-term steroid therapy, Acquired Immune Deficiency Syndrome (AIDS), haematological conditions like leukemia and lymphomas, renal failure [11]. In the body the mucromycosis infection can easily invades into the body through nose, breached skin surface and tooth extraction sockets. Primary infection spots include the skin, ears, gastrointestinal tract, and there could be disseminated forms involving multiple locations like pulmonary and rhinoorbito-cerebral [10] Contingent on the site of infection and underlying inclining factors, mortality rates may vary from 10% to 100% [12]. Here, we review the black fungus regarding mucormycosis in immunocompromised patients and uses the evidence to provide recommendations and management for black fungus treatment.

Search Strategy
Electronic databases were explored (PubMed, Embase, Scopus, Dentistry and Oral Science Source, and Google Scholar) to maximize the identification of relevant primary studies published over the last 1 year (September 2020 -July 2021). During the initial search, the following MeSH and keywords were employed: "Mucormycosis", "Rhino-orbital mucormycosis" and "Black fungus" written in the English language.

Data Collection Process
The necessary available information was extracted from each initially included article, through different case reports.

Microbiology
Mucormycosis is caused by fungi which belongs to the order Mucorales. These ubiquitous fungi reside in the soil and organic debris. They cultivate rapidly and sporulate quickly and abundantly. The only term mucormycosis arise from the "Mucoraceae" family of the Mucorales order, which is substituted commonly from the term zygomycosis which is the prime suspect for the mucormycosis infection in the human. Rhizopus arrhizus species is frequently encounter, but some other mucor species also includes are Lichtheimia species (formerly known as Absidia species), and Cunninghamella species [13].

Virulence Traits
Mucoromycotina able to grow at 37 0 C known as a thermotolerant but some of them proliferates even at higher temperatures. However, in 2012 Schwartze et al [14] concluded the different virulence potential but there is no association has been observed among the growth speed at host temperature.
The second, virulence factor is iron acquition, which acts as a vital role for development and fungal cell growth, as it has three general mechanisms for the uptake of iron and which has been identified in fungi. It encompasses for the reduction of iron uptake, siderophoresequestered iron uptake which has been facilitated by the siderophorepermease and acquiring iron from haem in the uptake system [15].
Fungal isolates such as Rhizopus and Lichtheimia corymbifera along with Mucor species were found in children in some cases [16]. Keeping the factors of Hematological malignancies, organ transplant, surgery, diabetes mellitus and underlying various medical conditions. The fungus targets the compromised medical conditions and attacks lungs, skin, soft tissues, sino orbital and rhino cerebral region. Mortality rate for such cases were more than 60%. In Children it was 15% with certain infection [13,14].
Recently, another factor, has been identified i.e; glucose regulated protein 78 (GRP78) which enables the invasion of the pathogen through endocytotic mechanism. One more aspect contributing to virulence of a pathogen is its ability to evade recognition and elimination by the host immune system [17].

EPIDEMIOLOGY
As a group, Mucoraceae represent the third most common cause of invasive fungal infection after Candida and Aspergillus species [18]. As increasing incidence of mucormycosis has been recommended by epidemiologic studies [19]. Numerous factors contribute in the increase, incidences for including antifungal prophylaxis by agents without Mucor mycosis activity [1].
Pandemic has rapidly spread to 212 countries and caused nearly 5 million laboratory-confirmed cases and more than 310,000 deaths globally [20].

COVID-19
patients always have immunosuppression with a decrease in CD4 +T and CD8 +T cells. 3 Critically ill patients admitted to the intensive care unit (ICU) with more extended stays were more likely to develop fungal co-infections [4]. It is crucial to notice that COVID-19 patients can develop fungal infections [18][19]].

Risk Factors
The immune dysfunction or immunodeficiency primary risk factor for the invasive diseases. The primary immunodeficiency form is not characteristically accompanying with the mucormycosis infection [20]. The substantial risk factor is associated with the hematologic malignancy, as the presence of hematopoietic stem cell transplant or solid organ transplant recipient. Solid organ malignancy (without transplant) is not commonly associated with mucormycosis [21].
Diabetes also is a commonly identified risk factor, with 9% to 36% of cases occurring in diabetics [7][8][9]. In human monocytes, elevated glucose levels directly increase SARS-CoV-2 replication, and glycolysis sustains SARS-CoV-2 replication via the production of mitochondrial reactive oxygen species and activation of hypoxia-inducible factor 1α20. Therefore, hyperglycaemia might support viral proliferation. In concurrence with this assumption, hyperglycaemia or a history of T1DM and T2DM were found to be independent predictors of morbidity and mortality in patients with SARS [21].
Furthermore, comorbid T2DM in mice infected with MERS-CoV resulted in a dysregulated immune response, leading to severe and extensive lung pathology [22]. Patients with diabetes mellitus typically fall into higher categories of SARS-CoV-2 infection severity than those without [23,24], and poor glycaemic control predicts an increased need for medications and hospitalizations, and increased mortality [18,25].

Pathogenesis
These organisms are spread by air borne asexual spores and invade into the tissues in reduced host defences via respiratory tract, wounded skin or via transcutaneous route [25]. Due to its high affinity towards the plasma these fungal hyphae enter the arterial blood vessels of the internal elastic lamina and resulting into the thromboembolism and cause ensuing thrombotic infarction [26]. In the blood vessels they proliferate mainly in the lungs, paranasal sinuses and it leads to the infarction & necrosis of the blocked vessels towards the distal end of the tissue [21,22]. In the medically compromised patients like in diabetic patients the free iron level increases which enhances the growth of the these organisms [17].

Clinical Manifestations
This disease habitually presents with signs of acute sinusitis, fever, nasal congestion, purulent nasal discharge, and headache. Sinuses involvement with contiguous spread to adjacent structures such as the palate, orbit, brain results in clinical symptoms [27]. The disease spreads from the ethmoid sinus to the frontal lobe results in obtundation. Clinical suspicion and initial treatment with surgical debridement are vital in averting the morbidity of this often-fatal condition [28]. The clinical hallmark of mucormycosis is vascular invasion resulting in thrombosis and tissue infarction/necrosis. The most common clinical presentation of mucormycosis is a rhinoorbital cerebral infection [20][21][22][23][24][25][26][27][28]. It is believed to be secondary to inhalation of spores into the paranasal sinuses of a susceptible host. Predisposing mucormycosis factors are diabetes, systemic corticosteroid use, neutropenia, hematologic malignancies, stem cell transplant, and immunocompromised individuals.
Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection resulting in tissue hypoxia, which persuades interstitial lung damage and acute respiratory distress syndrome [15][16][17][18][19][20][21]. Patients with diabetes mellitus and coronavirus disease 2019 (COVID-19) exhibits dysregulation of glucose homeostasis, exacerbation of inflammation and impairment in the function of the immune system. These conditions increase oxidative stress, cytokine production and endothelial dysfunction leading to increased risk of thromboembolism [12] and damage to vital organs. All these factors contribute to increased severity of COVID-19 and rapid progression to cardiorespiratory failure in patients with diabetes mellitus.
 The grown research evidence demonstrated that saprophytic zygomycetes are rarely seen in the tissue of immune compromised patients. On the contrary, diabetes both type I and type II, tumor, and metabolic inflammation such fungal infections these chronic diseases significantly enhance the depletion of immunity. The fungal infection caused by Rhizopus, mucor, and zygomycetes primarily enter into blood vessels and trigger thrombosis as one of major hallmark of chronic fungal infections. The thrombosis cases are more common in para nasal sinus and lower respiratory tissue such as lungs causing ischemic cascade along with self -induce tissue damage.

Diagnosis
Mucormycosis in early diagnosis is critical which enables the early initiation of active antifungal therapy. The symptoms, signs and radiographic manifestations of mucormycosis are nonspecific and a definitive diagnosis requires direct identification of the characteristic hyphae or the recovery of organism in culture from specimens obtained from the site of infection. Specificity is also an issue, because isolation from nonsterile sites is sometimes indicative of contamination rather than disease. Culture of a clinically relevant isolate enables identification and susceptibility testing of the pathogen [16].

 Cytopathology
The hyphae may be difficult to observe on an unenhanced Potassium hydroxide wet mount and may not stain well with conventional Gram stain. The use of chitin binding stains, such as Calcoflour, Fungi-flour, or Blancoflour, may be used with a fluorescent microscope to identify hyphal elements on Potassium hydroxide wet mounts [24].

 Histopathology
The culture still forms the basis of diagnosis in most cases, although molecular techniques are being used increasingly to complement traditional methods [17]. Molecular testing improves the accuracy of species identification compared to phenotypic identification of culture isolates [15]. Nucleic acid amplification techniques that target the ribosomal DNA gene targets 18S, 28S, and Internal Transcribed Spacer (ITS) region are all used. The sensitivity and specificity of molecular diagnosis performed directly on fresh or frozen tissue depend on the DNA-extraction method used [15]. Fresh material is preferred over paraffin-embedded tissue, because formalin damages DNA [16].

Radiography/ Imaging Techniques
Computed tomography (CT) is useful in preoperative procedure which defines the extent of the disease. Scan displays the edematous mucosa, fluid filling the sinuses and destruction of the peri-orbital tissue and bony margins, even though sinus CT is preferred in imaging modality, bony destruction is often existing in the course of the disease. Magnetic Resonance Imaging (MRI) is useful in identifying the intradural and intracranial extent of the disease, cavernous sinus thrombosis, or thrombosis of the cavernous portion of the internal carotid artery. Perineural spread of the disease can also be demonstrated with contrast enhanced MRI scan [26].

TREATMENT
Multimode approach is necessary to cure mucormycosis. Early dosage of anti-fungal agents, rapid correction of metabolic abnormalities are mandatory features. The global pandemic of COVID-19 has accelerated the race to find effective prevention and treatment for SARS-CoV-2 infection [27]. Currently, more than 1,800 clinical trials targeting viral entry and replication and immune responses to infection are ongoing; however, the efficacy of most drugs has not yet been proven (Clinical Trials. gov database of COVID-19 interventional studies) [28]. Candidates for COVID-19 therapy can affect glucose metabolism pharmacologically or through the modulation of inflammation and the immune system.
Thrombosis of blood vessel resulting in tissue necrosis during mucormycosis results in deprived penetration of antifungal agents to the site of infection. Therefore, the complete eradication of mucormycosis the debridement of necrotic tissues should be done [27]. Aggressive medical treatment with conventional antifungals and non-conventional therapeutics are corner stone for successful treatment [29]. Polyenes like Amphotericin-deoxycholates and lipid complex are primary therapeutic agents for mucormycosis. The dosage varies from 0.5-1.0mg/kg body weight once daily for not less than 4 weeks [30]. There should be close monitoring of serum electrolytes, as polyenes are known to cause potassium imbalance [29,31]. Salvage therapy by Posaconazole or deferasirox are reasonable options for patient's refractory to or intolerant to polyene therapy [32]. Non-conventional therapeutic agents like antidiabetics, iron chelating agents, statins, granulocyte transfusions, cytokines, and hyperbaric oxygen have increased the survival rates to 94%. Prevention always remains a gold standard [33].
Both medication and surgical management strategies are active in mucormycosis cases. Amphotericin B (liposomal) is the most frequently used drug in the management of mucormycosis [28][29][30][31][32][33]. Combination of liposomal amphotericin B and Posaconazole management manifests the synergistic effects against fungal hyphae formation [34][35]. Neutropenic patients or individuals with graft-versus-host disease should be indorsed for oral Posaconazole medication as prophylactic management against mucormycosis, although mucormycosis cases in neutropenia or graft-versus-host disease patients managed by oral administration of fluconazole, while itraconazole and voriconazole are administered as prophylactic doses [36][37][38][39].

CONCLUSION
The COVID-19 is accompanying with a significant incidence of secondary infections, both bacterial and fungal, perhaps due to deterioration of immunity. The key fragment for the treatment of COVID-19 is the widespread use of steroids/monoclonal antibodies/broadspectrum antibiotics which exacerbates into the fungal diseases. The pre-existing factors gives a prospective of invasive secondary fungal infections in patients with COVID-19 infection. The early diagnosis and treatment of black fungus with rhino-orbital mucormycosis successively reduces the mortality and morbidity rates.

CONSENT
It is not applicable.

ETHICAL APPROVAL
It is not applicable.