Fungi are important agents of human disease. Amongst the most important fungal pathogens are yeast species belonging to the genus Candida. These species can cause a wide range of human diseases ranging from superficial mucosal infections, such as vulvovaginal (VVC) and oropharyngeal candidosis (OPC), to life-threatening invasive infections. In the majority of cases OPC and systemic infections occur only in individuals who are severely ill and/or immunocompromised. In particular, oropharyngeal infections are very commonly diagnosed in human immunodeficiency virus (HIV)-infected individuals and individuals with acquired immune deficiency syndrome (AIDS), while deep-seated systemic infections are frequently associated with patients with neutropenia, for example as a result of antineoplastic therapy or immunosuppressive therapy associated with organ transplantation. Candidiasis constitutes the majority of fungal infections, and Candida albicans is the major etiologic species.
The most common cause of candidosis is the polymorphic species Candida albicans, which can grow as yeast cells, pseudohyphae and hyphae. It also produces chlamydospores which are refractile spore-like structures that are mainly produced at the termini of hyphae under specific environmental conditions in vitro. However, other Candida species, including Candida glabrata, Candida tropicalis and Candida parapsilosis, are currently also significant human pathogens. Though the incidence of infections caused by non-C. albicans Candida species is increasing for the past 15 years, still the leading agent is Candida albicans. Superficial candidiasis is also caused by C. albicans and/or other Candida species in both healthy and immunocompromised individuals.
Prevalence and Epidemiology
Candida albicans is a commensal pathogen that lives on the skin and mucosal surfaces of the genital and intestinal tracts as well as the oral cavity. This species is one of the most common responsible for nosocomial infections. In immunocompetent persons, candidiasis is usually a very localized infection of the skin or mucosal membranes, including the oral cavity (oral thrush), the pharynx, the esophagus , the navel , the intestines , the urinary bladder , the vagina.
Clinical Significance/Disease Manifestations
Candida albicans is a ubiquitous component of the normal human microflora and a frequent cause of superficial epithelial yeast infections. In immunocompromised individuals, however, this species is capable of invading host tissues, resulting in severe disseminated disease. C. albicans is a leading primary agent in nosocomial mycotic infections, the rate of which has been increasing during the past decade. Further, there is evidence for emerging resistance to widely used antifungal (azole) compounds, which has led to a renewed interest in this organism’s epidemiology and to the understanding of genetic diversity within the species. C. albicans lacks a known sexual cycle and is diploid, containing eight chromosomes. Infections due to Candida spp. have increased dramatically in recent years and are of particular importance because of the rising number of immunocompromised patients.The increasing incidence of acquired immunodeficiency syndrome (AIDS) and recent development of new and more aggressive treatment procedures for patients with malignancies and organ transplants have resulted in an increase in the number of immunocompromized patients. Systemic yeast infections are the major cause of morbidity and mortality in these patients .
Due to the fact that most candidal infections occur in individuals with impaired immunity, these species are often referred to as opportunistic pathogens. Under the right circumstances these yeasts can cause a wide variety of diseases ranging from superficial (e.g. vaginal and oral thrush) to systemic (e.g. candidaemia) infections.
Symptoms include severe itching, burning, and soreness, irritation of the vagina and/or vulva, and a whitish or whitish-gray discharge, often with a curd-like appearance. Many women mistake the symptoms of the more common bacterial vaginosis for a yeast infection. In men, symptoms include red patchy sores near the head of the penis or on the foreskin, severe itching, and/or a burning sensation. Candidiasis of the penis can also have a white discharge, although uncommon. However, having no symptoms at all is common, and usually, a more severe form of the symptoms may emerge later.
For clinical diagnosis of candidiasis, several molecular biology-based techniques, such as polymerase chain reaction (PCR), Southern blotting, random amplification of polymorphic DNA (RAPD) or in situ hybridization (FISH) techniques, PCR-RFLP technique targeting intergenic spacer regions of rDNA have been adapted for the detection and identification of fungal species in clinical specimens.
Medical professionals use two primary methods to diagnose yeast infections microscopic examination and culturing.
1) Microscope method – a scraping or swab of the affected area is placed on a microscope slide. A single drop of 10% potassium hydroxide (KOH) solution is then also placed on the slide. The KOH dissolves the skin cells but leaves the Candida untouched, so that when the slide is viewed under a microscope, the hyphae and pseudo spores of Candida are visible. Their presence in large numbers strongly suggests a yeast infection.
2) Culturing method – a sterile swab is rubbed on the infected skin surface. The swab is then rubbed across a culture medium. The medium is incubated for several days, during which time colonies of yeast and/or bacteria develop. The characteristics of the colonies provide a presumptive diagnosis of the organism that is causing symptoms.
As it is rightly said in the Chapter 95 of Thirukkural,
“Test disease, its cause and cure
And apply remedy that is sure.”
it is important to treat the specific infection caused by Candida spp.
Recently, the incidence of infections caused by Candida species other than C. albicans, some of which show lower susceptibility to azoles, has gradually increased. Therefore, it is important to identify Candida to the species level in order to accurately treat this type of infection. However, it is generally accepted that Candida albicans strains constitute the majority of the etiological agents for superficial candidiasis in both non-immunocompromized and immunocompromized individuals.
It is important to consider that Candida species are frequently part of the human body’s normal oral and intestinal flora. Treatment with antibiotics can lead to eliminating the yeast’s natural competitors for resources, and increase the severity of the condition.
In clinical settings, candidiasis is commonly treated with antimycotics—the antifungal drugs commonly used to treat candidiasis are topical clotrimazole, topical nystatin, fluconazole, and topical ketoconazole. For example, a one-time dose of fluconazole (as Diflucan 150-mg tablet taken orally) has been reported as being 90% effective in treating a vaginal yeast infection. This dose is only effective for vaginal yeast infections, and other types of yeast infections may require different treatments. In severe infections (generally in hospitalized patients), amphotericin B, caspofungin, or voriconazole may be used. Local treatment may include vaginal suppositories or medicated douches.
Treating candidiasis solely with medication may not give desired results, and other underlying causes require consideration. For example, oral candidiasis can also be the sign of a more serious condition, such as HIV infection or other immunodeficiency diseases. Maintaining vulvovaginal health can help prevent vaginal candidiasis.
- It is possible for Candida albicans to develop a resistance to the drugs used to treat it, as seen from research done involving fluconazole, one of the drugs that is used to treat candidiasis. In this case, the recurring infection would have to use a different prescription, and it is possible that resistance is slowly built to many of the available medications used to treat the yeast infection.
- Babies with diaper rash should have their diaper areas kept clean, dry, and exposed to air as much as possible. Sugars assist the overgrowth of yeast, possibly explaining the increased prevalence of yeast infections in patients with diabetes mellitus, as noted above. As many Candida spp. reside in the digestive tract, dietary changes may be effective for preventing or during a Candida infection. Due to its requirement for readily-fermentable carbon sources, such as mono- or dimeric sugars (e.g., sucrose, glucose, lactose) and starch, avoiding foods that contain these nutrients in high abundance may help to prevent excessive Candida growth.