The genus Candida encompasses more than 150 species, only a few of which cause disease in humans. With rare exceptions, the human pathogens are C. albicans, C. krusei, C. parapsilosis, C. tropicalis, and C. glabrata.

These organisms are found on inanimate objects, in foods, and on animals and are normal commensals of humans.

They inhabit the gastrointestinal tract including the mouth and oropharynx, the female genital tract, and the skin.

Although cases of candidiasis have been described since antiquity in debilitated patients, the advent of Candida species as common human pathogens dates to the introduction of modern therapeutic approaches that suppress normal host defense mechanisms.

With the introduction of antifungal agents, the causes of Candida infections shifted from an almost complete dominance of C. albicans to the common involvement of C. glabrata and the other species listed above.

The non-albicans species now account for approximately half of all cases of candidemia and hematogenously disseminated candidiasis.

Recognition of this change is clinically important, since the various species differ in susceptibility to the newer antifungal agents.

In developed countries, where medical therapeutics are commonly used, Candida species are now among the most common nosocomial pathogens.

Candida is a small, thin-walled, ovoid yeast that measures 4-6 micrometers in diameter and reproduces by budding.

Pathogenesis
In the most serious form of Candida infection, the organisms disseminate hematogenously and form micro abscesses and small macro abscesses in major organs. Although the exact mechanism is not known, Candida probably enters the bloodstream from mucosal surfaces after growing to large numbers as a consequence of bacterial suppression by antibacterial drugs; alternatively, in some instances, the organism may enter from the skin.

PREDISPOSING FACTORS:
Numerous reviews of cases of hematogenously disseminated candidiasis have identified the following predisposing factors or conditions:

– Antibacterial agents
– Indwelling intravascular catheters
– Hyper alimentation fluids
– Indwelling urinary catheters
– Parenteral gluco corticoids
– Respirators
– Neutropenia
– Abdominal and thoracic surgery
– Cytotoxic chemotherapy
– Immunosuppressive agents for organ transplantation.
– Patients with severe burns
– Low-birth-weight neonates
– Persons using illicit IV drugs are also susceptible.
– HIV-infected patients with low CD4+ T cell counts
– patients with diabetes

These patients are susceptible to mucocutaneous infection, which may eventually develop into the disseminated form when other predisposing factors are encountered.

Women who receive antibacterial agents may develop vaginal candidiasis.

Clinical Manifestations

Mucocutaneous Candidiasis

Thrush is characterized by white, adherent, painless, discrete or confluent patches in the mouth, tongue, or esophagus, occasionally with fissuring at the corners of the mouth.

This form of Candida disease may also occur at points of contact with dentures.

Organisms are identifiable in gram-stained scrapings from lesions

. The occurrence of thrush in a young, otherwise healthy-appearing person should prompt an investigation for underlying HIV infection.

More commonly, thrush is seen as a nonspecific manifestation of severe debilitating illness.

Vulvovaginal candidiasis is accompanied by pruritus, pain, and vaginal discharge that is usually thin but may contain whitish “curds” in severe cases.

Other Candida skin infections include
1. Paronychia, a painful swelling at the nail-skin interface
2. Onychomycosis, a fungal nail infection rarely caused by this genus
3. Intertrigo, an erythematous irritation with redness and pustules in the skin folds
4. Balanitis, an erythematous-pustular infection of the glans penis
5. Erosio interdigitalis blastomycetica, an infection between the digits of the hands or toes
6. Folliculitis, with pustules developing most frequently in the area of the beard
7. Perianal candidiasis, a pruritic, erythematous, pustular infection surrounding the anus
8. Diaper rash, a common erythematous-pustular perineal infection in infants.

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