Table 1.

A comprehension of the Mucorales group causing mucormycosis in humans

Pathogens	Route of transmission	Site of infection	Virulence factors	Susceptible hosts and associated risk factors	Disease manifestations	References
Rhizopus spp.	Respiratory, oral, gastrointestinal (GI), and percutaneous	Sinuses, brain, lungs, skin, and GI tract. Disseminated infection involves the central nervous system, heart, liver, kidney, and spleen	Thermotolerance, Ergot alkaloids (agroclavine, ergosine, and ergotamine), Mycotoxin like rhizonin A, hydroxamate siderophores, glycosidic, lipolytic and proteolytic enzymes, antigenic extracellular polysaccharides, alkaline Rhizopus protease enzyme (Arp) ketone reductase system	Patients with predisposed illness, diabetes, compromised immune system, steroid or broad-spectrum antibiotics, iron overload, hyperglycemia,	Angioinvasion, infarction, thrombosis, necrosis, and less often acute inflammation	(Morace and Borghi 2012; Binder et al. 2014; Walther et al. 2019)
Mucor spp.	Respiratory, oral, gastrointestinal (GI), cutaneous and subcutaneous	Skin, nails, ear, sinuses, brain, eyes, liver, kidney, and heart	Calcineurin (CaN), ADP-ribosylation factor (Arf), rodlet hydrophobins, ferroxidases	Immunosuppressed individuals, patients with leukemia, aplastic anemia, bone/organ transplants, diabetes mellitus, asthma, burns, corticosteroid treatment, Hepatitis/HIV infection	Cutaneous infections with necrotic and hemorrhagic lesions with typical black eschars or gangrenous cellulitis and erythema, nail infections with punctate erosions, invasive organ damage in immunocompromised hosts. It is also responsible for mastitis in cattle	(Petrikkos et al. 2012; Binder et al. 2014; Petrikkos and Tsioutis 2018; Hassan and Voigt 2019)
Rhizomucor spp.	Respiratory, percutaneous	Skin, lungs, or disseminated disease. Very rarely heart is involved	Thermotolerance, acid-proteases, lipases, ethanol, acids, and mycotoxins	Patients with immunosuppressive treatment like antibiotics and steroids, profound neutropenia, aplastic anemia, myelofibrosis, diabetes	Mostly associated with animal disease and rare in humans with pulmonary or disseminated disease	(Wickline et al. 1989; Severo et al. 1991; St-Germain et al. 1993; Weitzman et al. 1995)
Lichtheimia corymbifera (formerly Absidia corymbifera)	Respiratory, oral, gastrointestinal, percutaneous	Sinuses, brain, GI tract, lungs, and skin	Ability to survive in extreme environmental conditions, dihydrolipoyl dehydrogenase, serine and aspartate proteases, and siderophores,	Immunocompromised individuals, patients with organ transplants and tissue grafts, diabetes, and cystic fibrosis Coinfection may occur with cytomegalovirus (CMV), HIV, hepatitis C virus (HCV), and pulmonary tuberculosis. Risk factors include Hyperglycemia, Hyperferritinemia, low pH, and decreased phagocytic defense	Cutaneous infections with grey-black plaques, extensive necrosis. Rhino-cerebral infections involve typical black necrotic nasal turbinate, swelling, inflammation, and rarely direct trauma	(Scalise et al. 1999; Ribes et al. 2000; Rickerts et al. 2006; Blomberg et al. 2007)
Apophysomyces elegans	Respiratory, Percutaneous, postoperative surgical wounds	Skin, sinuses, bone, muscles, fat, kidney, bladder, orbital tissue, central nervous tissue, and less frequently disseminated infections	Thermotolerance, proteases, siderophores	Soil-contaminated wounds, immunocompromised (severe burns and organ transplants) and diabetic individuals,	Necrotizing cellulitis, tissue, and angioinvasion, painful swelling, edema, extensive thrombosis, black hemorrhagic or white and friable lesions	(Cooter et al. 1990; Neblett Fanfair et al. 2012; Egge et al. 2018; Rashid et al. 2021)
Saksenaea vasiformis	Open, soil contaminated cutaneous wounds and/or lesions,	Skin, sinuses	No specific virulence factors	Individuals with open wounds together with trauma, immunocompromised hosts due to antibiotics, steroid treatment or with an in-dwelling catheter, leukemia with neutropenia, diabetes, thalassemia, and splenectomy	Cutaneous lesions with painful red blisters and peeling skin with purulent eschar, less frequent evidence of cheesy necrosis or friable tissue Abscess formation in sinuses	(Saksena 1953; Gomes et al. 2011; Pilch et al. 2017; Lumyongsatien et al. 2020)
Cunninghamella bertholletiae	Upper respiratory tract, GI tract, percutaneous, cutaneous, and subcutaneous	Eyes, ears, lungs, skin, sinuses, brain, joints, liver, and kidneys	Thermotolerance	Individuals with a compromised immune system, hematologic malignancies, neutropenia, diabetes, acidosis, nonmalignant hematologic conditions, hyperglycemia, iron overload, treatment with broad-spectrum antibiotics, predisposed infections of HIV, CMV, and HCV	Angioinvasion, hemoptysis, multiple cavities in lower and upper lobes of lungs	(Zeilender et al. 1990; Patrick et al. 1993; Darrisaw et al. 2000; Rickerts et al. 2000; Liu et al. 2019)
Cokeromyces recurvatus	Unknown	Vagina and cervix are the major sites followed by the bladder and the G tract	Extracellular mycotoxins	Patients with compromised or dysfunctional immune system, antibiotic or steroid treatment, and diabetes	No visible sign of fungal invasion but acute and chronic inflammation in case of bladder infection and mucus-laden, watery diarrhoea in the GI tract	(Rippon and Dolan 1979; Kemna et al. 1994; Tsai et al. 1997; Odronic et al. 2012)
Syncephalastrum racemosum	Contamination of open wounds with air-borne or soil-borne fungal spores (cutaneous), respiratory tract, GI tract	Skin, nails, sinuses, eyes, GI tract, lungs	Mycotoxins, thermotolerance	Individuals with a previous history of lung abscess, diabetic ketosis, immunocompromised, post-operative trauma, chronic HBV infection, and nail injury for several months	Intracavitary fungal balls in lungs, arteritis, and osteomyelitis, onychomycosis, and multiple discharging lesions	(Schlebusch and Looke 2005; Gulati et al. 2021)
Mortierella wolfii	Unknown but presumed to be respiratory, through infected semen, GI tract, conjunctiva, skin wounds	Skin, lungs, eyes,	Thermotolerance, A water-soluble, heat- and trypsin-stable toxin (nephrotoxic)	Immunocompromised individuals, patients with organ transplants, and grafting	Chronic granulomatous disease, multiple hypodense lesions in the hepato-splenic parenchyma, keratitis	(Davey et al. 1973; Layios et al. 2014; Therese et al. 2020)