I have been reading a lot of medical papers linked to candida recently, specially about the link between the pathogen with immune suppression.
I have found interesting information that is giving me a better picture to understand why this infection is so difficult to cure.
You should know that persistent mucosal fungal infections (vaginal, intestinal, etc) are associated to a deficient immune response, specially to an noneffective T lymphocyte response.
Science has been studying the role of candida albicans inducing the immune suppression that doesn't allow the immune system to clear the pathogen. It is a this point where mannan shows up.
Mannan is a protein present in candida cell wall that the yeast release during an intestinal infection.
This fragments of the cell wall goes to the bloodstream and is thought to be what cause an strong cell mediated immunity suppression.
What is interesting about it is that experiments "in vitro" demonstrate that native mannan, in fact, stimulates the immune system. The problem is that released mannan bind with cooper in blood creating a variant of mannan with an strong immune suppression power.
The other interesting finding during my reading was that mannan catabolizes very slow, meaning that break down takes time. It implies that the blood will be contaminated with mannan for a while even after clearing the fungus in the intestines with an intensive antifungal therapy.
I am creating a classic scenery here. Normal people take a long course of Antibiotics that triggers an intestinal yeast overgrowth. Candida colonies release mannan that is absorbed by the gut epithelium and circulates in the blood suppressing cell-mediated immunity. When the infected person gets a diagnosis, he/she begins antifungal treatments and diet but the immune suppression mechanism created by the same pathogen impedes that cell-mediated immunity clear the infection.
The second scenery is the case of a person that after heroic efforts following a diet and taking strong antifungals reduced the yeast colonies in the gut to a point most or all symptoms have disappeared. That person believes he is cured releasing the diet and relapses.
What happens here is that there is still mannan circulating in the blood since it takes a lot of time to break down it, so an immune restoration has not been achieved.
All this allow me to understand why is extremely difficult to achieve a final cure. You need to consider that eliminating the symptoms don't mean your immune system has re-activated. Until the immune system doesn't re-activate, a diet and treatment must be followed even if you are symptom free. The blood must be clear of mannan to release the diet. Remember, it is cell-mediated immunity what controls the yeast growth on mucosal tissues.