|Classification and external resources|
Oral candidiasis (thrush)
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Candidiasis, thrush, or yeast infection is a fungal infection (mycosis) of any species from the genus Candida (one genus of yeasts). Candida albicans is the most common agent of candidiasis in humans. It is also technically known as candidosis, moniliasis, and oidiomycosis.
Candidiasis encompasses infections that range from superficial, such as oral thrush and vaginitis, to systemic and potentially life-threatening diseases. Candida infections of the latter category are also referred to as candidemia or invasive candidiasis, and are usually confined to severely immunocompromised persons, such as cancer, transplant, and AIDS patients, as well as nontrauma emergency surgery patients.
Superficial infections of skin and mucosal membranes by Candida causing local inflammation and discomfort are common. While clearly attributable to the presence of the opportunistic pathogens of the genus Candida, candidiasis describes a number of different disease syndromes that often differ in their causes and outcomes.
Candidiasis may be divided into these types:
- Mucosal candidiasis
- Oral candidiasis (thrush, oropharyngeal candidiasis)
- Pseudomembranous candidiasis
- Erythematous candidiasis
- Hyperplastic candidiasis
- Denture related stomatitis — Candida organisms are involved in about 90% of cases
- Angular stomatitis — Candida species are responsible for about 20% of cases, mixed infection of C. albicans and Staphylococcus aureus for about 60% of cases.
- Median rhomboid glossitis
- Candidal vulvovaginitis (vaginal yeast infection)
- Candidal balanitis, infection of the glans penis, almost exclusively occurring in uncircumcised males.
- Esophageal candidiasis (Candid esophagitis).
- Oral candidiasis (thrush, oropharyngeal candidiasis)
- Cutaneous candidiasis
- Onychomycosis (nail infection) caused by Candida
- Invasive candidiasis
- Antibiotic candidiasis (iatrogenic candidiasis)
Signs and symptoms
Symptoms of candidiasis vary depending on the area affected. Most candidial infections result in minimal complications such as redness, itching, and discomfort, though complications may be severe or even fatal if left untreated in certain populations. In immunocompetent persons, candidiasis is usually a very localized infection of the skin or mucosal membranes, including the oral cavity (thrush), the pharynx or esophagus, the gastrointestinal tract, the urinary bladder, the fingernails or toenails (onychomycosis), and the genitalia (vagina, penis).
Candidiasis is a very common cause of vaginal irritation, or vaginitis, and can also occur on the male genitals. In immunocompromised patients, Candida infections can affect the esophagus with the potential of becoming systemic, causing a much more serious condition, a fungemia called candidemia.
Thrush is commonly seen in infants. It is not considered abnormal in infants unless it lasts longer than a few weeks.
Infection of the vagina or vulva may cause severe itching, burning, soreness, irritation, and a whitish or whitish-gray cottage cheese-like discharge. These symptoms are also present in the more common bacterial vaginosis. In a 2002 study, only 33% of women who were self-treating for a yeast infection actually had a such an infection, while most had either bacterial vaginosis or a mixed-type infection. Symptoms of infection of the male genitalia (balanitis thrush) include red skin around the head of the penis, swelling, irritation, itchiness and soreness of the head of the penis, thick, lumpy discharge under the foreskin, unpleasant odour, difficulty retracting the foreskin (phimosis), and pain when passing urine or during sex.
Candida yeasts are generally present in healthy humans, particularly on the skin, but their growth is normally limited by the human immune system, by competition of other microorganisms, such as bacteria occupying the same locations in the human body, and in the case of skin, by the relative dryness of the skin, as Candida requires moisture for growth.
C. albicans was isolated from the vaginas of 19% of apparently healthy women, i.e., those who experienced few or no symptoms of infection. External use of detergents or douches or internal disturbances (hormonal or physiological) can perturb the normal vaginal flora, consisting of lactic acid bacteria, such as lactobacilli, and result in an overgrowth of Candida cells, causing symptoms of infection, such as local inflammation. Pregnancy and the use of oral contraceptives have been reported as risk factors. Diabetes mellitus and the use of antibacterial antibiotics are also linked to increased rates of yeast infections. Diets high in simple carbohydrates have been found to affect rates of oral candidiases, and hormone replacement therapy and infertility treatments may also be predisposing factors. Wearing wet swimwear for long periods of time is also believed to be a risk factor.
A weakened or undeveloped immune system or metabolic illnesses such as diabetes are significant predisposing factors of candidiasis. Diseases or conditions linked to candidiasis include HIV/AIDS, mononucleosis, cancer treatments, steroids, stress, and nutrient deficiency. Almost 15% of people with weakened immune systems develop a systemic illness caused by Candida species. In extreme cases, these superficial infections of the skin or mucous membranes may enter into the bloodstream and cause systemic Candida infections.
In penile candidiasis, the causes include sexual intercourse with an infected individual, low immunity, antibiotics, and diabetes. Male genital yeast infections are less common, and incidences of infection are only a fraction of those in women; however, yeast infection on the penis from direct contact via sexual intercourse with an infected partner is not uncommon.
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 the Western Hemisphere, about 75% of females are affected at some time in their lives.
Diagnosis of a yeast infection is done either via microscopic examination or culturing. For identification by light microscopy, 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 added to the specimen. The KOH dissolves the skin cells, but leaves the Candida cells intact, permitting visualization of pseudohyphae and budding yeast cells typical of many Candida species.
For the culturing method, a sterile swab is rubbed on the infected skin surface. The swab is then streaked on a culture medium. The culture is incubated at 37°C for several days, to allow development of yeast or bacterial colonies. The characteristics (such as morphology and colour) of the colonies may allow initial diagnosis of the organism causing disease symptoms.
A one-time dose of fluconazole is 90% effective in treating a vaginal yeast infection. Local treatment may include vaginal suppositories or medicated douches. Other types of yeast infections require different dosing. Gentian violet can be used for thrush in breastfeeding babies, but when used in large quantities, it can cause mouth and throat ulcerations, and has been linked to mouth cancer in humans and to cancer in the digestive tract of other animals. C. albicans can develop resistance to fluconazole, this being more of an issue in those with HIV/AIDS who are often treated with multiple courses of fluconazole for recurrent oral infections.
For vaginal yeast infection in pregnancy, topical imidazole or triazole antifungal is considered the therapy of choice owing to available safety data. Systemic absorption of these topical formulations is minimal, posing little risk of transplacental transfer. In vaginal yeast infection in pregnancy, treatment with topical azole antifungals is recommended for 7 days instead of a shorter duration.
Not enough evidence is available to determine if probiotics, either as pills or as yogurt, have an effect on the rate of occurrence of vaginal yeast infections. No benefit has been found for active infections.
Oral candidiasis is the most common form, by far the most common fungal infection of the mouth, and it also represents the most common opportunistic oral infection in humans. Candida septicemia is rare.
Esophageal candidiasis is the most common esophageal infection in persons with AIDS, and accounts for about 50% of all esophageal infections, often coexisting with other esophageal diseases. About two-thirds of people with AIDS and esophageal candidiasis also have oral candidiasis.
The colloquial term "thrush" refers to the resemblance of the white flecks present in some forms of candidiasis (e.g. pseudomembranous candidiasis) with the breast of the bird of the same name. The term candidosis is largely used in British English, and candidiasis in American English. Candida is also pronounced differently, in American English, the stress is on the "i", whereas in British English the stress is on the first syllable.
The genus Candida and species C. albicans were described by botanist Christine Marie Berkhout in her doctoral thesis at the University of Utrecht in 1923. Over the years, the classification of the genera and species has evolved. Obsolete names for this genus include Mycotorula and Torulopsis. The species has also been known in the past as Monilia albicans and Oidium albicans. The current classification is nomen conservandum, which means the name is authorized for use by the International Botanical Congress (IBC).
The genus Candida includes about 150 different species; however, only a few are known to cause human infections. C. albicans is the most significant pathogenic species. Other species pathogenic in humans include C. tropicalis, C. glabrata, C. krusei, C. parapsilosis, C. dubliniensis, and C. lusitaniae.
The name Candida was proposed by Berkhout. It is from the Latin word toga candida, referring to the white toga (robe) worn by candidates for the Senate of the ancient Roman republic. The specific epithet albicans also comes from Latin, albicare meaning "to whiten". These names refer to the generally white appearance of Candida species when cultured.
What has been described as "a large pseudoscientific cult" has developed around the topic of Candida, with claims up to one in three people are affected by conditions with terms such as systemic candidiasis, "candidiasis hypersensitivity", fungal type dysbiosis, Candida-related complex, the yeast syndrome, yeast allergy, yeast overgrowth, or simply "Candida" or "yeast problem". Some practitioners of alternative medicine have promoted these purported conditions and sold dietary supplements as supposed cures; a number of them have been prosecuted.
In 1990, alternative health vendor Nature's Way signed an FTC consent agreement not to misrepresent in advertising any self-diagnostic test concerning yeast conditions or to make any unsubstantiated representation concerning any food or supplement's ability to control yeast conditions, with a fine of $30,000 payable to the National Institutes of Health for research in genuine candidiasis.
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