Fungi-caused infections are called mycoses or mycosis (singular). Despite the fact that there are thousands of fungal species in the world, only a small percentage of them cause disease in humans. Superficial, Cutaneous, Subcutaneous, Systemic, and Opportunistic mycoses are the five types of mycoses classified by the type of infectious tissue found in the host.

SUPERFICIAL MYCOSES

Since the fungi responsible are only found on the outer surface of hair and skin, they are referred to as superficial. Since skin, scalp, and nail diseases were once thought to be caused by burrowing worms that left ring-shaped marks in the skin, the word tinea (Latin for “worm”) was applied to each illness, along with a Latin term for the body location.

Pityriasis versicolor is caused by Malassezia globosa, Malassezia restricta, and other members of the Malassezia furfur complex infiltrate the stratum corneum epidermidis and induce hypopigmentation or hyperpigmentation on the trunk of the body. Malassezia yeasts are lipophilic yeasts that require lipid in their environment to develop. Direct microscopic examination of scrapings of contaminated skin treated with 10–20 percent potassium hydroxide (KOH) or stained with calcofluor white confirms the diagnosis. There are short unbranched hyphae and spherical cells visible. Under Wood’s lamp, the lesions also fluoresce.

Tinea nigra is a superficial infection of the stratum corneum epidermidis caused by the dematiaceous fungus, Exophiala werneckii. Brown to black, nonscaly spots appear on the palms of the hands, indicating infection. Branched, septate hyphae and budding yeast cells with melanized cell walls can be seen on microscopic inspection of skin scrapings from the lesion’s periphery. Tinea nigra can be treated with keratolytic solutions, salicylic acid, or azole antifungal drugs.

Piedra is a hair-shaft infection that causes hair breakage. Infected hairs are trimmed or shaved, and topical antifungals are applied. In immunocompromised people, infections will spread quickly. Piedraia hortae causes black piedra, a nodular inflammation of the hair shaft. Infection with Trichosporon species causes white piedra, which appears as larger, softer, yellowish nodules on the hairs. Infected hair can be found on the axillary, pubic, mustache, and scalp. The affected hair is removed and a topical antifungal agent is applied on all forms of infections.

CUTANEOUS MYCOSES

Dermatophytic fungi affect only the keratinized tissue, causing cutaneous mycoses (skin, hair, and nails). The most prominent of these are the dermatophytes, a group of about 40 related fungi classified into three genera: Microsporum, Trichophyton, and Epidermophyton. Since most dermatophytes are unable to develop at 37°C or in the presence of serum, they are likely limited to nonviable skin. Dermatophytic diseases are also known as ringworm. Microconidia and macroconidia can be seen on the fungi under a microscope. A fungus can show all types of conidia or just one type.

Tinea capitis (head) is a scalp infection caused by dermatophytes. Tinea capitis is a contagious infection that affects infants. M. audouinii, which fluoresces when exposed to a Wood’s lamp, is the causative. Children are more susceptible to zoophilic tinea capitis. Animals are the source of contamination. Microsporum canis, which has few microconidia but many rugged, thick-walled, spindle-shaped macroconidia with 6 to 15 cells, is the most common cause. Trichophyton mentagrophytes is a zoophilic tinea capitis causative agent. Trichophyton tonsurans causes adult black-dot tinea capitis, which is a chronic infection. Trichophyton schoenleinii causes favus (tinea favosa), which is a serious 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 form of dermatophytosis that affects the inside folds of the skin. Candida species are often found to be the source of this infection. T. rubrum, T. mentagrophytes, and T. violaceum are among the other causatives.

Tinea cruris is a groin dermatophytosis caused by the fungi below. Epidermophyton floccosum, Trichophyton rubrum, Trichophyton mentagrophytes, and Candida species are the causatives.

Tinea pedis, also known as athlete’s foot, is a foot infection. T. rubrum, T. mentagrophytes, and E. floccosum are the most common causes of athlete’s foot and plague tinea pedis, respectively.

Tinea Unguium (Onychomycosis) Long-term tinea pedis can lead to nail infection. The nails turn yellow, brittle, thickened, and crumbly as a result of hyphal invasion. It’s possible if one or two fingernails or toe nails are involved.

Dermatophytosis; Unstained Microscopic KOH preparation of skin scraping from infected lesion (Copyright; clinicalsci)

SUBCUTANEOUS MYCOSES

Mycoses of the deeper skin layers, such as muscle, connective tissue, and bone, are affected by subcutaneous mycoses. Traumatic inoculation of infected material allows them to penetrate the skin or subcutaneous tissue. A superficial cut or abrasion, for example, can introduce an environmental mold that can invade the exposed dermis. In addition, the lesions become granulomatous and eventually spread outwards from the implantation site. Except in sporotrichosis, extension via the lymphatics draining the lesion is slow. These mycoses are normally limited to the subcutaneous tissues, but they will also spread across the body and cause life-threatening disease.

Sporotrichosis or Rose Gardener’s Disease is caused by Sporothrix schenckii. a thermally dimorphic fungus. Grass, vines, sphagnum moss, rose bushes, and other horticultural plants are all synonymous with it. It develops as a mold at room temperature, forming branching, septate hyphae and conidia, and as a small budding yeast in tissue or in vitro at 35–37°C. S. schenckii develops sporotrichosis, a recurring granulomatous infection, after a painful entry into the skin. Secondary distribution, including the draining lymphatics and lymph nodes, is common after the initial episode.

Eumycotic mycetoma, or madura foot, Swelling, sinus tract forming, and the presence of sulfur granules are all symptoms of madura foot, which normally affects the extremities. There isn’t any inflammation or bone deterioration. Local swelling of infected tissue and interconnecting, frequently draining, sinuses or fistulae that produce granules, which are microcolonies of the agent embedded in tissue material, are caused by many saprophytic species of fungi or actinomycetous bacteria that are commonly present in soil. The most frequent cause of mycetoma is Pseudoallescheria boydii, the teleomorph or sexual stage of Scedosporium apiospermum. In Africa, Madurella species are also known to cause mycetoma. Surgical debridement or excision, as well as chemotherapy, are used to treat eumycetoma.

Chromoblastomycoses Start by traumatically implanting the spore into a limb.The disease causes cauliflower-like lesions that are stiff and dry. Drainage blocks lymphatic pathways, resulting in elephantiasis, deformity, and abnormal enlargement of the infected arm. In the deepest areas of the tumors, black spots, called sclerotic skeletons, can be seen. A symptom of the disease may be secondary bacterial infections. Phialophora verrucosa, Fonsecaea pedrosoi, Fonsecaea compacta, Rhinocladiella aquaspersa, and Cladophialophora carrionii are dematiaceous fungi that cause infections. The infection is long-term and is characterized by the gradual progression of granulomatous lesions that eventually lead to epidermal hyperplasia.

Phaeohyphomycosis can range from a superficial infection to one that affects several organs. Phialophora, Exophiala, and Wangiella are the causative agents, all of which develop slow-growing, black, yeasty colonies with a short mycelium.

SYSTEMIC MYCOSES

With the exception of Cryptococcus neoformans, which only has a yeast form, the fungi that cause systemic or deep mycoses are dimorphic, meaning they have a parasitic yeastlike phase (Y) and a saprophytic mold or mycelial phase (M). Inhalation of spores from soil containing the mold-phase of the fungus is how most systemic mycoses are acquired. An infection starts as a lung lesion, becomes persistent, and travels through the bloodstream to other organs if a susceptible individual inhales enough spores (the target organ varies with the species).

Blastomycosis is a systemic mycosis caused by the fungus Blastomyces dermatitidis, which spreads in humans as a budding yeast either as a mold on culture media and in the atmosphere. It is mostly found in the Mississippi and Ohio River basins’ soil. There are three clinical manifestations of the disease: cutaneous, coronary, and disseminated. When blastospores are inhaled into the lungs, the infection begins. The fungus will then spread quickly, especially to the skin, causing cutaneous ulcers and abscesses. From pus and biopsy bits, B. dermatitidis may be removed. The medications of choice for therapy are amphotericin B, itraconazole, or ketoconazole.

Coccidioidomycosis caused by Coccidioides immitis, also known as valley fever, San Joaquin fever, or desert rheumatism due to the fungus’s geographic spread. C. immitis can be found in sandy, alkaline soils in North, Central, and South America. Arthroconidia inhalation causes a primary infection that is asymptomatic in 60 percent of people. The production of serum precipitins and conversion to a positive skin test within 2–4 weeks are the only signs of infection. The medications of choice for therapy are Miconazole, Amphotericin B, Itraconazole, or Ketoconazole.

Histoplasmosis is caused by Histoplasma capsulatum var. capsulatum, an intracellularly growing facultative parasitic fungus. In humans and on culture media at 37°C, it occurs as a small budding yeast. It develops as a mold at 25°C and produces small microconidia (1–5 um in diameter) that are borne singly at the tips of short conidiophores. Histoplasmosis is transmitted to humans by airborne microconidia that are formed in ideal conditions.

Microconidia are most common in areas where bird droppings, or guanos, have collected, especially from starlings, crows, blackbirds, cowbirds, sea gulls, turkeys, and chickens. Since histoplasmosis is a disorder of the monocyte-macrophage system, it may affect a variety of body organs. More than 95% of “histo” patients have no signs or only minor symptoms including coughing, fever, and knee pain. Most infections recover on their own; however, lesions in the lungs can occur and display calcification. The illness is very unlikely to spread. Amphotericin B, ketoconazole, or itraconazole are now the most common treatments.

OPPORTUNISTIC MYCOSES

Patients with weakened host defenses are vulnerable to fungi that are common in the environment but to which healthy patients are normally immune. The underlying predisposing state of the host also determines the form of fungus and the natural history of a mycotic infection. Candida and associated yeasts are endogenous opportunists, as part of the natural mammalian microbiota. Exogenous fungi found worldwide in soil, water, and air cause other opportunistic mycoses. Candida, cryptococcosis, aspergillosis, mucormycosis, Pneumocystis pneumonia, and penicilliosis are the most common pathogens and diseases they cause. However, the number of fungal species causing severe mycotic infections in people with weakened immune systems is rising.

Candidiasis is a fungal infection that may affect the lips, vaginal area, skin, nails, bronchi, lungs, gastrointestinal tract, bloodstream, and urinary tract. Candida albicans is the most common causative agent, but other Candida species are emerging as opportunistic pathogens. Candida albicans is found in the skin, mucous membranes, and gastrointestinal tract as part of the natural flora.

Oral thrush is a yeast infection that causes white curd-like patches on the mucosa of the mouth. Vulvovaginitis, also known as vaginal thrush, is characterized by a thick yellow-white discharge. The patient is predisposed to this disease by diabetes, antibiotic treatment, oral contraceptives, and breastfeeding. Patients with indwelling catheters develop candidemias, which are caused mainly by C. parapsilosis.

CRYPTOCOCCOSIS; Cryptococcus neoformans and Cryptococcus gattii are basidiomycetous yeasts that live in the environment. This yeast cells, unlike other pathogenic fungi, have large polysaccharide capsules. Cryptococcus neoformans is found in nature all over the world and can be easily isolated from dry pigeon waste, plants, soil, and other sources. Cryptococcus gattii is a less common parasitic fungus found in tropical areas. Inhalation of desiccated yeast cells or perhaps the smaller basidiospores causes cryptococcosis in both species. This neurotropic yeasts normally migrate from the lungs to the central nervous system, causing meningoencephalitis. Patients of HIV/AIDS, hematogenous malignancies, and other immunosuppressive disorders are more likely to contract Cryptococcus neoformans. Cryptococcosis caused by C. gattii is less common and normally occurs in healthy people.

Aspergillosis refers to a group of diseases caused by various Aspergillus species. Aspergillus species are common saprobes in nature, and aspergillosis is found all over the world. The most common human pathogen is Aspergillus fumigatus, although other pathogens such as Aspergillus flavus, Aspergillus niger, Aspergillus terreus, and Aspergillus lentulus may also cause disease. This mold creates a large number of tiny conidia that are readily dispersed in the air. Atopic individuals also experience serious allergic reactions to the conidial antigens after inhaling these conidia. Itraconazole or amphotericin B, as well as surgery, are used to treat aspergilloma.

Mucormycosis (zygomycosis) is an opportunistic mycosis caused by a variety of molds belonging to the Phylum Glomerulomycota and Subphylum Mucoromycotina’s order Mucorales. This fungi are thermotolerant saprobes that are found all over the world. Species of the genera Rhizopus, Rhizomucor, Lichtheimia, Cunninghamella, Mucor, and others are the most common pathogens in this genus. Rhizopus oryzae is the most common pathogen. Acidosis, including that associated with diabetes mellitus, leukemias, lymphoma, corticosteroid therapy, extreme burns, and immunodeficiencies, depending on the sporangial structures, are all conditions that put patients at risk.

Pneumocystis pneumonia; In immunocompromised patients, Pneumocystis jiroveci develops pneumonia; however, transmission is uncommon. P jiroveci was believed to be a protozoan for several years, but molecular biologic experiments have shown that it is a fungus with similar ties to ascomycetes. Many animals (rats, rodents, sheep, cats, ferrets, and rabbits) have Pneumocystis organisms in their lungs, but they seldom induce illness unless the host is immunocompromised.

Peniillosis; The penicillus-producing fungi Penicillium, Scopulariopsis, and Paecilomyces cause penicilliosis. Otomycosis (infection of the outer ear), keratomycosis (infection of the cornea), and nail infections are also possible infections. In debilitated patients, dissemination happens due to spore inhalation and the propagation of an initial pulmonary illness.

References:

  1. Sherris Medical Microbiology 6th Edition, by Ryan KJ and Ray CG
  2. Textbook of Diagnostic Microbiology 5th Edition, by Mahon CR, Lehman DC, Manuselis G
  3. Prescott Harley Klein’s Microbiology 5th Edibion by Prescott LM
  4. Jawetz, Melnick & Adelberg’s Medical Microbiology 26th Edition by Mc Graw Hill Pub
  5. A concise Review of Clinical Labortory Science by Hubbard JD
Default image
clinicalsci

A tech enthusiast medical molecular technologist, biotechnologist and now also a blogger.

Articles: 66

Leave a Reply