Fungal diseases

 

Fungal diseases

Fungi are eukaryotic; have rigid cell wall containing chitin, mannan, etc and have true nucleus with chromosomes.  They divide asexually, sexually or by both processes.

Most fungi are soil saprophytes and act as human opportunistic pathogens. Fungal diseases are common and a few are fatal

Depending on cell morphology – fungi are of 4 types

1. Yeasts or unicellular fungi – spherical or ellipsoidal cells – Cryptococcus neoformans
2. Yeast like fungi – grow partly as yeast and partly as elongated cells resembling hyphae – candida albicans
3. Moulds or filamentous fungi – forms true mycelia and spores – dermatophytes
4. Dimorphic fungi – grow as filaments in soil and in cultures at 22^oC and as yeast in human body and in cultures at 37^oC. Most fungal pathogens. Sporothrix shenckii

Lab identification – microscopic examination of material from lesion.  Tissue specimens are put in 10% KOH to digest cells and tissue materials and stained with lactophenol cotton blue or periodic acid Schiff or methanamine silver stains

Slide culture – media used are sabourauds dextrose agar/ czapeck dox medium / corn meal agar.  Antibiotics may be added to prevent bacterial contamination.  Incubation for weeks at room temperature or at 37^oC.  Observation of colony morphology, spore morphology, etc helps in identification.

Fungus infections or mycoses

      1. Superficial mycoses – tinea or ringworm affecting nail, skin or hair, digest keratin, chronic mild disease

2. Systemic or deep seated mycoses – asymptomatic to fatally severe disease

3. Opportunistic Mycoses – avirulent fungi cause infection in immune compromised persons

Superficial mycoses

1. Surface infections – fungi grow on the dead layer of skin, no contact with living tissue and cause no immune response, cause cosmetic effect only. Tinea versicolor, Tinea nigra, Piedra
2. Cutaneous infections – Dermatophytosis caused by dermatophytes, infection is confined to skin or mucosa but result in allergic and inflammatory responses.  Another example is candida albicans infection which may sometimes cause systemic infection and thus act as a bridge between superficial and deep mycoses

1. Tinea versicolor or Pityriasis versicolor – chronic, asymptomatic infection of stratum corneum (the outermost layer of the epidermis).  Discolouration or depigmentaion of skin of chest, abdomen, upper limb or back.  Causative agent is pityrosporum orbiculare or Malassezia furfur.  Diagnosis by observation of yeast like cells in skin scraping

2. Tinea nigra - Localized infection of stratum corneum of palm and cause black or brownish lesions.  Caused by Cladosporum wernickii or Hortaea wernickii. Diagnosis by observation of branched septate hyphae and budding cells in skin scraping

3. Piedra – Infection of hair, appearance of firm, irregular nodules along the hair. Two types - black piedra caused by Piedraia hortae and white piedra caused by Trichosporon beigelii

4. Dermatophytosis – infection by filamentous fungi that infect hair, nail and skin.  Dermatophytosis is also known as tinea or ringworm.  Grow in the keratinized layers of skin and donot penetrate living tissues.  The fungal products cause inflammatory response and the resulting hypersensitivity is responsible for the lesions and is known as dermatophytids or the id reaction.

Hair infection is of two types – Ectothrix spores are seen within the hair shaft and Endothrix where spores are seen as a sheath surrounding the hair

Based on the location of infection –

Tinea corporis – smoot nonhairy skin of body

Tinea imbricata – papulosquamous scaly patches

Tinea cruris – in groin and perineum

Tinea pedis or athletes foot – affects foot

Tinea capitis – scalp

Favus – hair follicles

Three genera – Trichophyton, Microsporum and Epidermophyton.

Trichophyton rubrum cause chronic treatment resistant skin lesions.  Form powdery velvety or waxy colonies on culture and form micro and macroconidia. 

Microsporum canis - Infect hair and skin.  Form cotton like, velvety or powdery colonies and form microconidia

Epidermophyton flocosum infects skin and nail.  Powdery colonies with macroconidia. 

Diagnosis – microscopic examination of KOH mounts or by UV light exposure analysis of infected hair which will be fluorescent.

Dermatophytosis is anthropophilic, zoophilic or geophilic. 

Anthropophilic – human beings are only host, cause mild chronic lesions - Trichophyton rubrum, Epidermophyton flocosum  

Zoophilic – naturally animal parasites, cause severe inflammation in human beings, Microsporum canis

Geophilic – naturally present in soil, less pathogenic towards human beings, Microsporum gypseum

5. Candidosis by candida albicans – infection of skin, mucosa, and rarely of internal organs, is pportunistic infection. candida albicans  is ovoid or spherical budding cell with pseudomycelia

Cutaneous candidosis – intertriginous (area where two skin areas may touch or rub together) or paronychial (Inflammation of the tissue surrounding a fingernail or toenail) with scaling or moist lesions and will be erythematous. 

Vaginitis – acidic discharges and found commonly during pregnancy

Oral thrush – in bottle fed infants and in aged debilitated persons where creamy white patches are formed in tongue or buccal mucosa

Intestinal candidosis – as diarrhea in person weak from antibiotic treatment

Bronchopulmonary candidosis, septicemia, endocarditis, mengitis, etc

Candida granuloma and chronic mucocutaneous candidiasis in immunodeficient persons

Diagnosis by microscopy and culture

Deep mycoses

Two types -     Subcutaneous mycoses - Infections that affect the subcutaneous tissue

Systemic mycoses - Infections that affect the internal organs

Subcutaneous mycoses

1.      Mycotic mycetoma

2.      Chromoblastomycosis

3.      Sporotrichosis

4.      Rhinosporidiosis

5.      Subcutaneous phycomycosis

Systemic mycoses

1.      Cryptococcosis

2.      Blastomycosis

3.      Paracoccidioidomycosis

4.      Coccidioidomycosis

5.      Histoplasmosis

Mycotic mycetoma – chronic, slowly progressing disease of subcutaneous tissue of foot and rarely other part of the body caused by actinomycetes and filamentous fungi.  Similar situation botryomycosis is caused by Staphylococcus aureus

The fungi enter through minor trauma and disease begin as subcutaneous swelling of foot which grow deep inside and discharge viscid, seropurulant fluid containing granules (granules are microcolonies of the fungi)

Chromoblastomycosis or verrucous dermatitis – warty cutaneous nodules which resemble florets of cauliflower, mainly in lower leg and feet. Caused by Fonsecaea species, Cladosporium species

Phaeohyphomycosis – by Cladosporium in Cutaneous, subcutaneous or organs such as brain and lung in immunodeficient patients

Sporotrichosis – by Sporothrix shenckii, cause nodules in skin, subcutaneous tissues and lymph nodes which soften and break down to form ulcers.  Infection acquired through thorn pricks as the fungus is a saprophyte found on plants.  The fungus is dimorphic and this feature aids in identification

Rhinosporidiosis – caused by Rhinosporidium seeberi.  chronic granulomatous infection of the mucous membranes that usually manifests as vascular friable polyps on nasal mucosa or external structures of the eye.

Subcutaneous phycomycosis – caused by Basdibolus haptosporus.  Painless subcutaneous nodule develops which enlarges to a whole limb or large areas of body and the infection is supposed to be acquired through insect bites

Cryptococcosis – Also known as European Blastomycosis.  Subacute or chronic disease caused by Cryptococcus neoformans.   Ovoid cells with polysaccharide capsule and commonly found in pigeon or other bird fecal matter.

Infection is through inhalation or through skin or mucosa.  Pulmonary infection may be asymptomatic or with a mild pneumonitis.  Sometimes results in Cutaneous or meningeal disease, bones and joints may be involved.   Cryptococcal meningitis is serious disease which is often seen in AIDS.

Diagnosis by microscopic observation of capsulated yeast in lesions, or by culture, inoculation into mice.

Blastomycosis – Also known as North American Blastomycosis. Caused by Blastomyces dermatitidis.  Cause formation of suppurative or granulomatous lesions in any part of the body, especially in lungs and skin. Soil is the source of fungi.  Initial lesion is a papule around which nodules develop and joins together to form a large ulcerative lesion.

Paracoccidioidomycosis – caused by Paracoccidioides brasileinsis and known as South American Blastomycosis.  Symptoms are ulcerative granulomas of the buccal and nasal mucosa. The fungus is dimorphic which helps in its lab diagnosis

Coccidioidomycosis – caused by coccidioides immitis.  The infection is asymptomatic, severe or fatal.  Infection is through inhalation. The fungus is dimorphic.

Histoplasmosis – caused by Histoplasma capsulatum.  Fungus is present in soil and in bird feces.  Infection is acquired through inhalation and is asymptomatic. Some persons develop symptoms similar to tuberculosis.  Sometimes results in lymphadenopathy, hepatosplenomegaly, anemia and may be fatal.  The fungus is dimorphic and in tissues it is present inside phagocytes.

Diagnosis by microscopy of blood smear, lesions, biopsy, etc. serological tests like agglutination, complement fixation, etc are also useful. 

African histoplasmosis is caused by Histoplasma duboisii which affects mainly skin, subcutaneous tissues and bones

Opportunistic infections – Normally harmless fungi that cause infection in persons who are immunologically weak. 

Examples are Aspergillosis caused by Aspergillus species, Penicillosis caused by Penicillium marneffei, Mucormycosis caused by Mucor, Rhizopus and Absidia, Otomycosis (infection of ear) caused by Aspergillus, Oculomycosis (infection of eyes) caused by Aspergillus, Fusarium, Candida, etc

 

Mycotic Poisoning