World of Microbiology and Immunology | Candidiasis

Candidiasis is an infection that is caused by members of the fungal genus Candida.

The two most common species associated with Candidiasis are Candida albicans and Candida glabrata. Less commonly, but still able to cause the infection, are Candida tropicalis, Candida parapsilosis, Candida guilliermondi, and Candida krusei.

The fungus is a normal resident of the body, typically in the mouth and the gastrointestinal tract. In these habitats, the microorganism normally colonizes the cell surface. In healthy people in the United States, Candida species colonize more than half of these individuals. The presence of the fungus is beneficial. Invading bacteria are recognized by the Candida cells and are destroyed. Thus, the fungi complement the immune system and other defenses of the body against infection.

When the body is in proper balance with respect to the microbial flora, the fungi exist as a so-called yeast form. These are not capable of invasion. However, Candida can infect areas of the body that are warm and moist. These include the eye (conjunctivitis), fingernails, rectum, folds in the skin, and, in infants, the skin irritation in infants known commonly as diaper rash. Typically, such infections are more of an inconvenience than a dangerous health concern.

However, in people whose immune systems are compromised in some way, or when the normal balance of the microbial flora has been disrupted by, for example, antibiotic therapy, Candida can establish an infection. For example, an infection of the mouth region, which is referred to as oropharyngeal infection, was a very common infection in those whose immune system was deficient due to infection with the Human immunodeficiency virus. More aggressive antiviral therapy has reduced the incidence of the infection.

Such infections are associated with the change from the Candida cells from the yeast form to a so-called mycelial fungal form. The mycelia produce long, root-like structures that are called rhizoids. The rhizoids can penetrate through the mucous cells that line the inside of the mouth and vagina, and through the epithelial cells that line the intestinal tract. This invasion can spread the infection to the bloodstream. As well, the microscopic holes that are left behind in the cell walls can be portals for the entry of toxins, undigested food, bacteria, and yeast.

In countries around the world where fungal infections are widespread in the populations, Candida species have over-taken Cryptococcus species as the most common cause of infections that affect the central nervous system of immunocompromised people.

Besides the oropharyngeal infection, Candida can also commonly cause a vaginal infection. Both infections are evident by the development of a fever and chills that, because of the fungal genesis of the infections, are unaffected by antibacterial therapy. Visually, white patches appear on the surface of the cells lining the mouth and oral cavity and the vagina. More rarely, the infections may spread to the bloodstream. Examples of the infections that can result include the kidney, spleen, nerve cells (meningitis), heart (endocarditis). Arthritis may even develop. Immunocompromised individuals are especially susceptible to these infections.

The contamination of the bloodstream by Candida occurs most commonly in the hospital setting, where a patient is being treated for Candidiasis or other malady. Indeed, this type of bloodstream infection is the fourth most common cause of hospital-acquired bloodstream infections in the United States. The death rate from the infection can approach 40 per cent.

Treatment for Candida infections consist of the administration of antifungal drugs. Examples of the drugs of choice include amphotericin B, fluconazole, ketoconazole, and nystatin. The real possibility of the development of irritative side effects makes monitoring during therapy a prudent precaution.

See also Fungi; Immunodeficiency