Fungal Diseases Notes

Fungal Diseases

Of the large number of known fungi, only a few are infective to human beings. Many of the human fungal infections are opportunistic i.e. they occur in conditions with impaired host immune defenses.

Such conditions include defective neutrophil function, administration of corticosteroids, immunosuppressive therapy, and immunodeficiency states (congenital and acquired).

Read And Learn More: General Pathology Notes

A list of common fungal infections of human beings is given in Table. A few important representative examples are discussed below.

Mycetoma

Mycetoma is a chronic suppurative infection involving a limb, shoulder, or other tissues and is characterised by draining sinuses. The material discharged from the sinuses is in the form of grains consisting of colonies of fungi or bacteria.

Mycetomas are of 2 main types:

1. Mycetoma caused by actinomyces (higher bacteria) also called actinomycetoma comprises about 60% of cases (page 109).
2. Eumycetoma caused by true fungi, Madurella mycetomatis or Madurella grisea, comprises the remaining 40% of the cases.

Eumycetomas are particularly common in Northern and tropical Africa, Southern Asia and tropical America. The organisms are inoculated directly from soil into bare feet, from carrying of contaminated sacks on the shoulders, and into the hands from infected vegetation.

Morphologic Features:

• After several months of infection, the affected site, most commonly the foot, is swollen and hence the name ‘madura foot’.
• The lesions extend deeply into the subcutaneous tissues, along the fascia, and eventually invade the bones.
• They drain through sinus tracts which discharge purulent material and black grains. The surrounding tissue shows granulomatous reaction.

Candidiasis

Candidiasis is an opportunistic fungal infection caused most commonly by Candida albicans and occasionally by Candida tropicalis. In human beings, Candida species are present as normal flora of the skin and mucocutaneous areas, intestines, and vagina.

The organism becomes pathogenic when the balance between the host and the organism is disturbed.

Various predisposing factors are:  Impaired immunity, prolonged use of oral contraceptives, Long-term antibiotic therapy, Corticosteroid therapy, Diabetes mellitus, Obesity, pregnancy etc.

Candidiasis Symptoms – Diseases caused by fungi:

Morphologic Features:

Candida produces superficial infections of the skin and mucous membranes, or may invade deeper tissues as described under:

• Oral thrush:  This is the commonest form of mucocutaneous candidiasis seen especially in early life. Full-fledged lesions consist of a creamy white pseudomembrane composed of fungi covering the tongue, soft palate, and buccal mucosa. In severe cases, ulceration may be seen.
• Candidal vaginitis:  Vaginal candidiasis or monilial vaginitis is characterised clinically by thick, yellow, curdy discharge. The lesions form pseudomembrane of fungi on the vaginal mucosa. They are quite pruritic and may extend to involve the vulva (vulvovaginitis) and the perineum.
• Candidal balanoposthitis:  Candidal inflammation of the penile foreskin in uncircumcised males is common. It is often seen more commonly in diabetics and pre-diabetics.
• Cutaneous candidiasis:  Candidal involvement of nail folds producing a change in the shape of the nail plate (paronychia) and colonization in the intertriginous areas of
  • The skin
  • Axilla
  • Groin
  • Infra- and
  • Inter-mammary
  • Intergluteal folds, and
  • Interdigital spaces.
• These are some of the common forms of cutaneous lesions caused by Candida albicans.
• Systemic candidiasis:  Invasive candidiasis is rare and is usually a terminal event of an underlying disorder associated with an impaired immune system. The organisms gain entry into the body through an ulcerative lesion on the skin and mucosa or may be introduced by iatrogenic means such as via intravenous infusion, peritoneal dialysis or urinary catheterization.

The lesions of systemic candidiasis are most commonly encountered in the kidneys as ascending pyelonephritis and in the heart as candidal endocarditis.

Cutaneous Superficial Mycosis

Dermatophytes cause superficial mycosis of the skin, the important examples being Microsporum, Trichophyton, and Epidermophyton. These superficial fungi are spread by direct contact or by fomites and infect tissues such as the skin, hair and nails.

Examples of diseases pertaining to these tissues are as under:

1. Tinea wapitis characterized by patchy alopecia affecting the scalp and eyebrows.
2. Tinea barbae is acute folliculitis of the beard.
3. Tinea corporis is dermatitis with formation of erythematous papules.

The diagnosis of dermatophytosis is made by light microscopic examination of skin scrapings after addition of sodium or potassium hydroxide solution.

Other methods include fungal culture and demonstration of fungus in tissue sections.

Cutaneous Superficial Mycosis Fungal Diseases:

Opportunistic fungi occur in conditions with impaired host immunity. Mycetoma is a chronic suppurative infection caused by actinomyces (higher bacteria) also called actinomycetes, or eumycetomas caused by true fungi (Madura foot).

Candidiasis is an opportunistic fungal infection caused commonly by Candida albicans and produces superficial infections of the skin and mucous membranes for example, Oral thrush, Candidal vaginitis, Cutaneous candidiasis.

Superficial mycosis of the skin are caused by dermatophytes and produce tinea of various tissues