Candida species are primarily saprophytic eukaryotic organisms and only occasional opportunistic pathogens. Many species exhibit a bitrophic existence, spending much of their life as common commensals of the gastrointestinal (GI) tract and mucous membranes of humans only to become pathogenic because of debilitation of the host. Indeed, the most significant source of Candida causing candidosis is endogenous.
Despite the main cause of invasive candidosis (IC; Candida albicans) being considered as an obligatory animal saprophyte,Candida species, including C. albi-cans, are frequently isolated from nonanimal environments. Indeed, Candida is an important cause of nosocomial bloodstream infections, with 97% of candide-mias attributed to C. albicans, Candida glabrata, Candida parapsilosis, Candida tropicalis, and Candida krusei.
For an informative review of superficial candidosis including the symptoms, predisposing factors, and treatment for oral, genital, cutaneous, and chronic mucotaneous candidosis, and candidosis of the nail, then refer to the comprehensive book by Odds. The following text represents a summary of some of the information available.
Oral candidosis (OC) is one of the most frequent human fungal infections. Commonly affecting the young, the aged, and the immunosuppressed, it has various clinical forms [pseudomembranous candidosis (oral thrush), atrophic candidosis, hyperplastic candidosis, and angular cheilitis]. Its diagnosis can be complicated by a lack of culture or symptoms; however, because Candida species are regular human commensals (30-50% of the normal population), then an oral culture of Candida does not confirm a case of OC and only histological evidence can validate an infection.
C. albicans is the most prevalent cause of OC (60-80% of yeasts isolated from the mouth), with at least eight other species documented as causative agents of OC and with non-C. albicans emerging as relatively common causes of OC. Furthermore, novel species of Candida (Candida dubliniensis) have been, and will continue to be, isolated over time. The treatment regime is usually topical; however, oral fluconazole has proven successful with acquired immunodeficiency syndrome (AIDS) patients, although monitoring for fluconazole-resistant strains is essential.
Candida species are common organisms of the female genital tract, which are isolated from 20% of normal women. C. albicans is the most common cause of vaginal candidosis (VC) (up to 89% of infections), although C. glabrata is emerging as an important pathogen that could become resistant to fluconazole
Affecting 75% of women during their lifetime, VC is a common problem. As the prevalence of Candida detected by culture is the same in women with or without symptoms, meaningful diagnosis is difficult and both culture and clinical symptoms should be evaluated to define the condition.
VC can be a severe source of irritation and discomfort to the patient, but the condition can have more serious consequences. Infection with VC has been considered as a risk factor for human immunodeficiency virus (HIV) infection and gynecological surgery performed on patients with VC has led to systemic candidal infec-tions. VC has also been transmitted congenitally from mother to child, with some research indicating that treatment for VC during pregnancy actually reduced the opportunity for premature births.
Penile candidosis is far less common than vaginal infection, although it can be a result of sexual transmission. It is usually an uncomplicated infection that responds to topical antifungal therapy.
IC (deep-seated candidosis) is a worldwide disease that targets the immunocompromised population, with Candida species able to infect virtually every deep organ. Localized systemic candidosis is the term given to an infection of an individual organ, whereas disseminated candidosis (Candida septicemia, candidemia) involves the infection of several organs where the disease has been propagated by the bloodstream. This classification is not rigid and the diagnosis of systemic candidosis in one organ may be the initial sign of disseminated candidosis observed earlier at that particular site.
The population at risk for IC will generally be immunocompromised, usually as a result of treatment for cancer, organ transplantation, HIV, or intensive care unit (ICU) treatment. However, surgery, antibiotic use, a central venous line, prematurity, parenteral nutrition, damage to the GI mucosal membrane, and neutropenia have been indicated as predisposing factors to infec-tion. Furthermore, several of these risk factors may be combined in certain case scenarios.
C. albicans is the most common cause of IC, although the contribution of non-C. albicans species causing IC is rising. There are distinct geographical and patient group distributions to the species causing non-C. albicans infections, and recent publications have highlighted the diagnosis of polycandidal IC, which could be significant when initiating the correct antifungal therapy. With high mortality rates associated with IC (up to 40%), early diagnosis and treatment of IC are essential. However, the diagnosis of IC can be problematical, with up to 50% of patients with autopsy-proven IC having multiple negative blood cultures. The British Society for Medical Mycology has produced a review article highlighting the problems and proposing standards that should be met to provide optimal surveillance and diagnostic programs for invasive fungal infections.
Treatment for IC involves the use of a systemic antifungal agent, such as fluconazole or amphotericin B, with or without flucytosine, plus the removal of central venous catheters. Fluconazole should not be used with C. krusei or C. glabrata infections. Recent developments in antifungal therapy have seen the emergence of a new triazole ''voriconazole'' and a novel group of drugs, the echinocandins, of which ''caspofungin'' is the first licensed drug. Both of these have given promising results in treating IC, with the added benefit of being effective against Aspergillus infections.
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