Candidal Infections – causes, symptoms, diagnosis, treatment, pathology

Candidal Infections – causes, symptoms, diagnosis, treatment, pathology


Candida is a yeast, not the maple syrup-loving
country in North America – although Candida can be found in Canada as well! Candida sometimes causes a mild yeast infection,
but in some situations, can get into the bloodstream and cause severe illness. Now, there are various types of Candida species,
and over twenty of them cause disease in humans – C. albicans, C. parapsilosis, C. tropicalis,
C. glabrata, C. krusei, C. auris, the list goes on. Of these, the most common one is C. albicans. Candida is found throughout the body; it likes
warm, moist environments like the mouth, the diaper region of babies, and in women it can
be found in the vagina. Now, it’s normal for microbes – bacteria,
fungi, and viruses – to live all over the body, but each microbe is slightly different
in terms of whether it’s colonizing the body – in other words just living and not
causing any problems, or whether it’s infecting the body, causing some degree of tissue damage
or destruction. An important factor is exactly how much of
a microbe is present. Candida is considered an opportunistic microbe. When the amount of Candida is relatively low,
it’s harmless. But if a person’s immune system is weakened
or if there’s less competition for the Candida, then the amount of Candida can increase – and
that’s called Candida overgrowth. Now, Candida can exist in multiple forms – it’s
a bit like a chameleon. Sometimes the cells can appear round or oval
and these are called yeast cells, other times it can appear like hyphae where it looks like
long thin filaments – kind of like a segmented cactus plant. It can also take an in-between appearance
called pseudohyphae. Each of these morphologies or “looks”
reflect the same Candida cells that are expressing different protein profiles, and they give
the cells different properties. When the Candida is in “yeast mode” it’s
better at moving from one part of the body to another, whereas when it’s in “filamentous
mode” it’s better at invading tissues. Candida typically lives on the skin or mucous
membranes, and when it starts to overgrow it can damage nearby tissue. There are a few patterns of injury, the most
common one is pseudomembranous candidiasis, and it’s primarily due to a weakened immune
system that allows for Candida overgrowth. The result is destruction of the stratified
squamous epithelium layer, which is the outermost layer of the skin or mucous membranes. This causes accumulation of the destroyed
cells and the keratin protein that fills that outermost layer, forming a white lesion, called
a pseudomembrane, that looks kind of like “cottage cheese”. The white lesions aren’t typically painful
and they can be scraped away with a tongue depressor, leaving behind a red mucosal base
which sometimes bleeds. Since the underlying cause is a weakened immune
system, it’s fairly common in young infants and the elderly, both groups that have a relatively
weak immune system. It can also be related to an immunosuppressive
condition like diabetes or HIV, or from immunosuppressive medical treatments like steroids – including
inhaled steroids, as well as radiotherapy or chemotherapy. Another pattern of injury is called erythematous
candidiasis and that typically results from a change in the levels of microbial competition
keeping Candida in check. For example, a course of antibiotics or tobacco
smoking, which both selectively destroy certain bacterial populations more than they affect
Candida. The opposite is true as well, sometimes there
are mechanical devices like braces that favor Candida growth more than the growth of other
microbes. In either situation, the result is an overgrowth
of Candida which causes increased blood flow to the affected tissue with red painful lesions. In a lot of situations there’s a mixed pattern
of injury with both a pseudomembranous and erythematous component. Candidal infections can affect various parts
of the body. The most common location is in the mouth where
it causes thrush – which is usually a pseudomembranous candidiasis, so classically it looks like
white cottage cheese on the buccal and gingival mucosa. Candida can also affect the esophagus, resulting
in an esophagitis that can cause pain with swallowing. Candida can affect the diaper region of babies,
causing a diaper rash with redness surrounded by scattered red spots that are called satellite
lesions because they look like tiny red satellites that are not contiguous with the rest of the
rash. Another common one is vulvovaginitis, commonly
called a yeast infection in women, and it can cause vaginal itching and discharge as
well as pain while urinating. Now in addition to local infections, Candida
can cause more serious invasive infections, and these often develop in individuals that
have underlying immunodeficiencies. Other risk factors for serious candidal infections
include hyperglycemia and reduced stomach acidity. The most common situation is an infection
of a prosthetic device like a central venous catheter. In these settings, Candida forms a biofilm
which is where the yeast lives within a jelly like matrix of proteins and behaves more like
a large colony than like a collection of individual cells. Candida is able to infect devices and if the
infection isn’t treated, then over time, small clumps of the yeast-laden biofilm can
break away, get into the blood, and can cause infections in other locations – like on the
heart valves. From the blood, Candida can also cause infections
in the liver and spleen as well as the bones and joints. It also likes to cause infections in the kidney;
the Candida can reach the kidneys from the blood, as well as by going up the ureters
after a urinary tract infection. Candida can also cause meningitis, in particular
if it infects a device in that space – like a ventricular shunt. What’s more is that Candida can cause particularly
worrisome infections of the eye. Diagnosis of oral candidiasis can be confirmed
with a culture, and ultimately a tissue biopsy might be done in some cases as well. For invasive infections, antigen testing can
also be done – for example one test looks for a cell wall component called beta-D-glucan
which is found in Candida and a few other fungal species. Another test is Candida PCR which detects
candidal DNA. Treatment of candidiasis depends on the location
and severity of the infection. Oral thrush is treated with oral nystatin
suspension, whereas vulvovaginitis and skin infections are treated with topical antifungals. Resistant infections are often treated with
azole antifungal medications. In severe infections, especially when there’s
a prosthetic device like a catheter or a ventricular shunt that’s infected with a biofilm, it’s
often necessary to remove the device. Severe infections are often treated with a
medication like amphotericin, azole antifungals, or echinocandins like Micafungin. Alright recap: Candida is an opportunistic
fungus that can overgrow in situations where there are fewer competitive microorganisms
or a weakened immune system. Common sites of infection include the mouth,
the esophagus, the vulvovaginal region, and the groin in infants. These superficial infections are usually treated
with nystatin or topical antifungals. Severe infections include those where a biofilm
forms over a prosthetic device, and typically require removal of the infected device.

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