Infections caused by fungi are referred to as mycoses or mycosis (singular). Despite the fact that there are hundreds of fungal species, only a small number of them cause illness in humans. Superficial, Cutaneous, Subcutaneous, Systemic, and Opportunistic mycoses are the five forms of mycoses characterized by the type of affected tissues present in the host.
Since the fungal causative are only present on the external surface of hair and skin, they are referred to be superficial. Because skin, scalp, and nail disorders were once thought to be originated by burrowing worms that produced ring-shaped markings in the skin, the name tinea (Latin for “worm”) was assigned to each illness, combined with a Latin term for the anatomical site.
Malassezia globosa, Malassezia restricta, and other members of the Malassezia furfur complex enter the stratum corneum epidermidis and produce hypopigmentation or hyperpigmentation on the body. Malassezia are lipophilic yeasts that require lipid in their environment to grow. The diagnosis is confirmed by direct microscopic inspection of scrapings of infected skin treated with 10-20% potassium hydroxide (KOH) or stained with calcofluor white. There are short unbranched hyphae and spherical cells visible. The lesions glow as well under Wood’s light.
Tinea nigra is a superficial infection of the stratum corneum epidermidis caused by Exophiala werneckii, a dematiaceous fungus. Infection is indicated by brown to black, nonscaly patches on the palms of the hands. Microscopic examination of skin scrapings from the lesion’s perimeter reveals branched, septate hyphae and budding yeast cells with melanized cell walls. Keratolytic solutions, salicylic acid, or azole antifungal medications can be used to treat Tinea nigra.
Piedra is an infection of the hair shaft that causes hair damage. In immunocompromised patients, illnesses spreads fast. Piedraia hortae causes black piedra, a nodular inflammation of the hair shaft. Infection with Trichosporon species results in white piedra, which appears as bigger, softer, yellowish nodules on the hairs. Infected hair can be detected on the axillary, pubic, mustache, and scalp. The infected hair is removed, and a topical antifungal drug is used to treat all types of infections.
Dermatophytic fungi cause cutaneous mycoses by attacking exclusively keratinized tissue (skin, hair, and nails). The most significant of them are the dermatophytes, a collection of roughly 40 related fungi grouped into three genera: Microsporum, Trichophyton, and Epidermophyton. Most dermatophytes are likely limited to nonviable skin because they cannot grow at 37°C or in the presence of serum. Ringworm is a term used to describe dermatophytic infections. Microconidia and macroconidia may be observed on the fungus when prepared under a microscope. A fungus may produce all or only one form of conidia.
Tinea capitis (head) is a dermatophyte-caused scalp infection. Tinea capitis is a highly infectious condition that primarily affects infants. The causative is M. audouinii, which fluoresces when exposed to a Wood’s lamp. Children are predisposed to zoophilic tinea capitis. Contamination comes from animals. The most prevalent cause is Microsporum canis, which has few microconidia but numerous rough, thick-walled, spindle-shaped macroconidia with 6 to 15 cells. Trichophyton mentagrophytes is the causal agent of zoophilic tinea capitis. Trichophyton tonsurans is the cause of adult black-dot tinea capitis, a persistent illness. Trichophyton schoenleinii is the cause of favus (tinea favosa), a severe tinea capitis.
Tinea barbae is a beard, neck, or face fungus. Tinea barbae is caused by Trichophyton verrucosum, Trichophyton rubrum, and Trichophyton mentagrophytes.
Tinea corporis is a kind of dermatophytosis that involves the skin’s inner folds. Candida species are frequently identified as the cause of this infection. Other causatives include T. rubrum, T. mentagrophytes, and T. violaceum.
Tinea cruris is a fungus-caused groin dermatophytosis. The pathogens are Epidermophyton floccosum, Trichophyton rubrum, Trichophyton mentagrophytes, and Candida species.
Tinea pedis is a foot infection also known as athlete’s foot. The most prevalent causes of athlete’s foot and plague tinea pedis are T. rubrum, T. mentagrophytes, and E. floccosum.
Tinea Unguium is followed by chronic tinea pedis and or nail infection. As a result of hyphal invasion, the nails become yellow, brittle, thickened, and crumbly. It is possible if one or two fingernails or toe nails are affected.
Subcutaneous mycoses involve mycoses of the deeper skin layers, such as muscle, connective tissue, and bone. Inoculation of infectious material by trauma causes it to infiltrate the skin or subcutaneous tissue. For example, a superficial cut or abrasion might introduce an environmental mold that can infiltrate the exposed dermis. Furthermore, the lesions develop granulomatous and eventually extend outwards from the portal of entry. Except with sporotrichosis, lymphatic expansion from the lesion is sluggish. These mycoses are often restricted to subcutaneous tissues, but they can spread throughout the body and cause life-threatening infection.
Sporotrichosis, often known as Rose Gardener’s Disease, is caused by the thermally dimorphic fungus Sporothrix schenckii. It is similar with grass, vines, sphagnum moss, rose bushes, and other horticultural plants. At room temperature, it forms a mold with branching, septate hyphae and conidia, and at 35-37°C, it grows as a tiny budding yeast. After parenteral entry into the skin, S. schenckii causes sporotrichosis, a reoccurring granulomatous disease. After the first occurence, secondary dissemination, including the draining lymphatics and lymph nodes, is common.
Eumycotic mycetoma, commonly known as madura foot, is characterized by swelling, sinus tract formation, and the presence of sulfur granules. There is no swelling or bone degeneration. Many saprophytic fungi and actinomycetous bacteria found in soil cause local swelling of infected tissue and frequently draining sinuses or fistulae that produce granules, which are microcolonies of the agent implanted in tissue material. Pseudoallescheria boydii, the sexual stage of Scedosporium apiospermum, is the most common cause of mycetoma. Madurella species have been linked to mycetoma in Africa. To treat eumycetoma, surgical debridement or excision, as well as chemotherapy, are employed.
Chromoblastomycoses begin with the spore being parenterally inoculated into a limb. The condition develops stiff and dry cauliflower-like lesions. Elephantiasis, deformity, and abnormal expansion of the diseased arm come from drainage blocking lymphatic channels. Black patches known as sclerotic skeletons can be noticed in the deepest sections of the tumors. Secondary bacterial infections can be a sign of the condition. Infections are caused by dematiaceous fungus such as Phialophora verrucosa, Fonsecaea pedrosoi, Fonsecaea compacta, Rhinocladiella aquaspersa, and Cladophialophora carrionii. Long-term infection is characterized by the progressive growth of granulomatous lesions, which finally lead to epidermal hyperplasia.
Phaeohyphomycosis can range from a minor infection to a multi-organ infection. The causal agents are Phialophora, Exophiala, and Wangiella, all of which form slow-growing, black, yeasty colonies with a short mycelium.
Except for Cryptococcus neoformans, which has only a yeast form, the fungi that cause systemic or deep mycoses are dimorphic, which means they have a parasitic yeastlike phase (Y) and a saprophytic mold or mycelial phase (M). Most systemic mycoses are acquired through inhaling spores from soil containing the mold-phase of the fungus. If a vulnerable person inhales enough spores, an infection begins as a lung lesion, persists, and spreads through the bloodstream to other organs.
Blastomycosis is a systemic mycosis caused by the fungus Blastomyces dermatitidis that spreads in individuals as a budding yeast on culture medium or as a mold in the environment. It is typically found in the soil of the Mississippi and Ohio River basins. The disease has three clinical manifestations: cutaneous, coronary, and disseminated. Infection develops when blastospores are inhaled into the lungs. The fungus will then rapidly spread, particularly to the skin, producing cutaneous ulcers and abscesses. B. dermatitidis may be extracted from pus and biopsy samples. Amphotericin B, itraconazole, or ketoconazole are the drugs of choice for treatment.
Because of the fungus’s geographic distribution, coccidioidomycosis is sometimes known as valley fever, San Joaquin fever, or desert rheumatism. In North, Central, and South America, Coccidioides immitis can be found in sandy, alkaline soils. In 60% of people, arthroconidia inhalation generates a primary infection that is asymptomatic. The sole symptoms of infection are the formation of serum precipitins and the conversion to a positive skin test after 2-4 weeks. Miconazole, Amphotericin B, Itraconazole, and Ketoconazole are the drugs of choice for treatment.
Histoplasmosis is caused by the intracellularly developing parasitic fungus Histoplasma capsulatum var. capsulatum. It grows as a tiny budding yeast in people and on culture medium at 37°C. At 25°C, it grows as a mold and produces microscopic microconidia (1-5 μm in diameter) that are carried individually at the tips of short conidiophores. Histoplasmosis is spread to people by airborne microconidia that grow under optimum circumstances.
Microconidia are most prevalent in locations where bird droppings, or guanos, have accumulated, particularly from starlings, crows, blackbirds, cowbirds, seagulls, turkeys, and chickens. Because histoplasmosis is a condition of the monocyte-macrophage system, it can affect many different organs. More than 95% of “histo” patients have no symptoms or very minor ones like as coughing, fever, and knee discomfort. Most infections resolve on their own; nevertheless, calcified lesions in the lungs might form. The disease is unlikely to spread. The most often used therapies are amphotericin B, ketoconazole, or itraconazole.
Individuals with weaker host defenses are vulnerable to fungi that are ubiquitous in the environment but to which healthy patients are generally immune. The underlying predisposed condition of the host also influences the kind of fungus and the natural history of a mycotic infection. Candida and related yeasts are endogenous opportunists that are found in the normal mammalian microbiome. Other opportunistic mycoses are caused by exogenous fungi prevalent in soil, water, and air all around the world. Candida, cryptococcosis, aspergillosis, mucormycosis, Pneumocystis pneumonia, and penicilliosis are the most frequent infections and illnesses caused by them.
Candidiasis is a fungal disease that can affect the lips, vaginal area, skin, nails, bronchi, lungs, gastrointestinal system, bloodstream, and urinary tract. Candida albicans is the most prevalent causal agent, but additional Candida species are emerging as opportunistic infections. Candida albicans is naturally present in the skin, mucous membranes, and gastrointestinal system as part of the flora.
Oral thrush is a yeast infection characterized by white curd-like spots on the oral mucosa. Vulvovaginitis is characterized by a thick yellow-white discharge. Diabetes, antibiotic therapy, oral contraceptives, and lactation have all predisposed the patient to this condition. Candidaemias are caused mostly by C. parapsilosis in patients with indwelling catheters.
Cryptococcus neoformans and Cryptococcus gattii are environmental basidiomycetous yeasts. Unlike other harmful fungi, yeast cells contain enormous polysaccharide capsules. Cryptococcus neoformans may be easily isolated from dry pigeon excrement, plants, soil, and other sources found in nature. Cryptococcus gattii is a tropical parasitic fungus that is less frequent. In both species, cryptococcosis is caused by inhaling dried yeast cells or maybe smaller basidiospores. Meningoencephalitis is caused by neurotropic yeasts migrating from the lungs to the central nervous system. Patients with HIV/AIDS, hematogenous cancers, and other immunocompromised conditions are more susceptible to get Cryptococcus neoformans. Cryptococcosis induced by C. gattii is uncommon and usually affects healthy people.
Aspergillosis is a group of infections caused by different Aspergillus species. Aspergillus species are frequent saprobes in nature, and aspergillosis may be found everywhere. Aspergillus fumigatus is the most frequent human pathogen, but other pathogens such as Aspergillus flavus, Aspergillus niger, Aspergillus terreus, and Aspergillus lentulus can also cause disease. This mold produces a vast number of small conidia that float around in the air. Individuals with hypersensitivity have severe allergic responses to conidial antigens after breathing these conidia. Aspergilloma is treated with itraconazole or amphotericin B, as well as surgery sometimes.
Mucormycosis (zygomycosis) is an opportunistic mycosis caused by molds from the Phylum Glomerulomycota and Subphylum Mucoromycotina’s order Mucorales. These fungi are thermotolerant saprobes and may be found all around the world. The most prevalent pathogens in this genus include species of the genera Rhizopus, Rhizomucor, Lichtheimia, Cunninghamella, Mucor, and others. Rhizopus oryzae is the most prevalent pathogen. Acidosis, including those linked with diabetes mellitus, leukemias, lymphomas, corticosteroid treatment, serious burns, and immunodeficiencies, depending on the sporangial structures, are all illnesses that put patients at risk.
Pneumocystis jiroveci causes pneumonia in immunocompromised people; consequently, transmission is infrequent. For many years, P jiroveci was thought to be a protozoan, but molecular biologic research revealed that it is a fungus with linkages to ascomycetes. Many animals (rats, rodents, lambs, cats, ferrets, and rabbits) carry Pneumocystis organisms in their lungs, but they seldom cause sickness unless the host is immunocompromised.
Penicillium, Scopulariopsis, and Paecilomyces, fungi that produce penicillus, cause penicilliosis. Otomycosis (outer ear infection), keratomycosis (corneal infection), and nail infections are other potential ailments. Dissemination occurs in incapacitated individuals as a result of spore inhalation and the spread of an early pulmonary disease.
- Sherris Medical Microbiology 6th Edition, by Ryan KJ and Ray CG
- Textbook of Diagnostic Microbiology 5th Edition, by Mahon CR, Lehman DC, Manuselis G
- Prescott Harley Klein’s Microbiology 5th Edibion by Prescott LM
- Jawetz, Melnick & Adelberg’s Medical Microbiology 26th Edition by Mc Graw Hill Pub
- A concise Review of Clinical Labortory Science by Hubbard JD