Candidiasis, often known in layman’s terms as "thrush", designates an infection caused by yeast of the genus Candida, with Candida albicans being the most common species responsible. Candida species are rarely found in environmental samples, being primarily associated with man or with warm blooded animals. Candida infections are normally transmitted by contact, and invasive candidiasis is a real threat in hospitals and intensive care units. The infection can range from superficial (oral thrush or vaginitis) to systemic, in which case it can be potentially life-threatening. This latter condition is normally restricted to patients that are severely immunocompromised (cancer and AIDS patients, or people receiving a transplant). Since yeasts from the Candida genus are usually present as part of the gastrointestinal flora in humans, candidiasis is considered an opportunistic infection that only occur when the immune system fails to keep the yeast population under control. That is why candidiasis is often referred to as "the disease of the diseased".
Many factors have been advanced to explain why the populations of Candida albicans and other yeasts of the Candida genus grow beyond control and become pathogens of the organism. Long term antibiotic treatment can disrupt the gastrointestinal flora, killing other microorganisms that normally compete with Candida for resources, and thus allowing their numbers to increase dramatically. In general, the "very young, very old or very ill" are considered to be at risk, because their immune system is weakened or undeveloped and could fail to keep Candida yeasts under control. Other conditions such as chronic inflammatory bowel disease, oncological diseases, diabetes mellitus and alcoholism have been associated with an increased risk for candidiasis.
The following are among the most common symptoms of candidiasis in the gastrointestinal tract:
- Difficulty Swallowing
- Food Caught in the Esophagus
- Ulcerated Esophagus
- Weight Loss (a consequence of malnutrition)
- Nausea and Vomiting
- Bloating in the Abdominal Area
- Abdominal Pain
- Persistent Watery Diarrhea
- Unexplained Fatigue
- Lack of Concentration/Poor Memory
- Irritability/Sudden Mood Swings
The diagnosis of candidiasis is normally performed via examination of a scraping or swab of the affected area under the microscope, or by culturing the yeasts from an initial sample obtained from the site of infection. There is still a controversy in the medical community about the best way to diagnose gastrointestinal candidiasis, since Candida is normally present in the gut, and therefore stool samples appear to be unreliable (positive results do not always correlate with symptoms). The clinical signs described above are not exclusive of Candida infection, and therefore cannot be used as diagnostic tools. Moreover, imaging techniques such as tomography or magnetic resonance, which allow physicians to examine the gut directly, are only useful when the infection is very advanced.
Candidiasis is commonly treated with antimycotic agents, drugs that target fungi specifically. Some of the most common antifungal agents used against Candida infections are clotrimazole, nystatin, fluconazole and ketoconazole. For esophagal and gastrointestinal candidiasis, fluconazole is the first choice of treatment. Another commonly used antimytatotic for cases of gastrointestinal candidiasis is nystatin, which is cheaper than fluconazole and has the additional advantage that it causes fewer side effects than this drug. In all cases, the mode of administration varies according to the localization and severity of the Candida infection: it can either be by the oral route or delivered directly to the affected area by injection.
It has been observed that yeasts from the Candida genus can develop resistance to antimycotic drugs, and therefore it is necessary for physicians to have a battery of different antimycotic agents available in case the patient does not respond well to the initial attack. If the infection continues after this first-line of treatment, alternative therapeutic agents include itraconazole, voriconazole, posaconazole or amphotericin B.
In addition to these standard antimycotic agents, ingestion of probiotic microorganisms as part of the diet has been proposed to help prevent the symptoms of candidiasis.
In healthy people, response to the antimycotic agents is good, and the properly treated infection goes away without leaving permanent damage. This may not necessarily be the case in people with chronic illnesses or weakened immune systems. When Candida infections to the gastrointestinal tract are considered specifically, early detection is critical for a favorable outcome. When untreated, this condition can derive into abdominal candidiasis or Candida peritonitis, complications that are potentially lethal and should be aggressively treated. Direct examination of the peritoneal fluid for presence of Candida yeasts is a good predictor of the patient's outcome.
Breaches in the gastrointestinal wall (for example, resulting from a recent surgical procedure) can allow Candida yeasts to infect the bloodstream, a condition known as candidemia. This in turn may lead to the colonization of internal organs (disseminated candidiasis). Both conditions are extremely serious and have a poor prognosis. Mortality rates among patients have been estimated to be between 30% and 50% in these circumstances. The symptoms are similar to bacterial septicaemia, and death may occur before antifungal treatments have had time to work or even be applied. For this reason, antimycotics are often administered as prophylaxis after bone marrow transplant or abdominal surgery.
The prophylactic use of antimycotic agents can be used in those patients who are considered in high risk of developing gastrointestinal candidiasis.
It is known that intestinal microflora can provide protection against Candida infections in the gastrointestinal tract, and therefore many of the efforts to prevent gastrointestinal candidiasis have focused on probiotics. Consuming regularly a preparation of different bacterial strains that are normally present in the human gut prevented Candida colonization and gastric ulceration, and this was demonstrated in patients suffering from pouchitis as well as in elderly patients and premature newborns.
Sometimes a so-called "elimination diet" is recommended as a preventive measure against Candida colonization of the gut. This involves excluding from the diet any food item containing processed sugars that may nourish the yeast population, and fermented products that could contain yeasts. However, the effectiveness of such a measure has been called into question, since it is mainly anecdotal and has not been substantiated by rigorous clinical research.
In patients that have successfully recovered from candidiasis, care should be taken to avoid re-infection by partner contact, or through dental prostheses, tooth brushes, mouthpieces, or dummies. This is commonly known as the "ping-pong effect".
If the Candida infection is limited to the skin and external mucosa, treatment with the right animycotic agent should normally eliminate it within a week. Therefore, there is no need for patients to adapt their lifestyle in any way to cope with candidiasis.
Some people postulate that gastrointestinal overgrowth of Candida yeasts may be a widespread phenomenon, and that a variety of common symptoms with unknown or unspecified causes may result from this unrecognized or"subclinical" infection. These include chronic fatigue syndrome, inflammatory bowel disease, post-menopausal syndrome, asthma, sexual dysfunction, chronic indigestion and muscle pain. This view has been advanced more emphatically by Dr. William Crook in his book"The yeast connection: a medical breakthrough".
Although if proven true, these claims would mean that chronic candidiasis has an enormous impact on the lifestyle of unsuspecting patients, conventional practitioners remain skeptical of widespread Candida infection in the community. This is because the scientific evidence for subclinical systemic candidiasis as a viable diagnosis is very limited and there are no clinical trials that document the efficacy of the therapies proposed against it.
One of the persistent problems in the treatment of gastrointestinal candidiasis are the lack of effective diagnostic tools capable of discriminating between a potentially dangerous infection and the normal presence of Candida yeasts that are part of the gut flora. Therefore, most of the current research is focused in developing more effective methods of diagnosis.
Molecular diagnostic tests for detection of Candida DNA in either blood or tissues have been described. These assays allow for the highly sensitive and specific detection and identification of fungal pathogens, including the several species of the Candida genus that are responsible for the symptoms of candidiasis. Although these assays are certainly promising, relatively few data have been published on their performance and they are not commercially available yet.
Another approach that has received attention is the detection of components of the fungal cell wall such as such as mannan, galactomannan and β-(1,3)-D-glucan. One of this assays for the detection of β-(1,3)-D-glucan is already widely used in Japan and has recently been approved by the US Food and Drug Administration based on its excellent predictive value.
From the point of view of treatment, several novel antifungal agents have become available in recent years, including a brand new class (echinocandins). These new weapons against candidiasis demonstrated an excellent safety profile, with very few adverse effects reported, and showed no cross-resistance with conventional antimycotic agents, making them particularly valuable in those cases where resistance has developed in the infecting Candida population. In addition, lipid formulations of the conventional antimycotic agent amphotericin B have been developed. This alternative formulation is useful in patients who are intolerant to conventional amphotericin B or are unlikely to tolerate it because of altered renal function.