CANDIDA & CANDIDIASIS

Candida causes lots of different diseases from superficial diseases that only involve the skin to deep seated and systemic infections. Candida has over 200 species, about 20 of which have been associated with human diseases. C. albicans is the major cause of disease, but since the 90’s there has been a shift. C. glabrata has become important because it’s relatively resistant to fluconazole. C. parapsilosis is also frequently associated with catheter-associated infections. Other important candidas are C. tropicalis and C. krusei.

Candida infections are really really common. We’ll all see these infections often in our practices. About 5% of women (probably more) have yeast infections, 5% of babies have thrush, 10% of old people, 20-50% of AIDS patients have thrush. Candida is also the 3^rd or 4^th most common blood isolate from hospitalized patients.

Candida are eukaryotic dimorphic yeasts. This means they can change forms and form pseudohyphae. They are different from dimorphs that live free in nature because both yeast and mold forms appear in the human tissue. At 25 degrees you can see the candida as yeasts, but at 37 degrees you see hyphae formation and yeast. Candida are part of the normal flora but they can be pathogenic. If you see hyphae, it is probably an infection and not just normal colonization. Hyphae are harder to kill because they’re bigger and the tips have enzymes that can eat into tissue. It is the most important fungal pathogen and can cause two types of infections:

Mucocutaneous

1. 1. Mucosal  most common sites are vulvo-vaginitis and oral thrush (thrush is an old English term describing a fungal infection in the oral cavity. Small gray, whitish patches and it can disturb food intake and can be painful)

   2. Cutaneous  diaper rash, intertrigo (skin between fingers), and basically areas where there are skin folds.

   3. Nail Infections  can be onychomycosis (just the nail) or paronychia (around the nail).

2. Deep-seated and systemic  can occur anywhere, but especially likes the CNS (meningitis), circulatory system (endocarditis and sepsis), respiratory, digestive system (esophagitis), and the urinary system (UTI and renal infections).

CMC (Chronic Mucosal Candidiasis), is a genetic defect and the patient will have recurring infections for life.

Virulence Factors:

1. Attachment  organisms attach to the tissue and there is crosstalk between the host and yeast. Candida can also bind to contacts, dentures, IV catheters and urinary catheters

2. Secreted Aspartic Proteinases (SAP)  there are 9 known enzymes in this group, encoded on 10 genes. Each different SAP is associated with a different clinical condition.

3. Phospholipases  encoded on 3 genes, C. albicans secretes it during infection and it has been associated with C. albicans virulence.

4. Transition  yeast  hyphae

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5. Immunomodulation  overcome host defenses

In order for the host to defend herself against the evil yeast attackers, she must have intact skin and mucosa, complement system, and transferin (keeps the iron away from the fungi so they can’t grow). Cell mediated immunity is important against T cells, while PMNs and mononuclear phagocytes are important against systemic infections.

Predisposing factors 

1. Physiological conditions:

   1. Age  both edges of life are at more risk for oral thrush,

   2. Pregnancy  actually any change in hormone puts people at risk, including birth control pills, diabetes and hypothyroidism

2. Trauma: surgery, burns, skin abrasion

3. Foreign bodies: catheter, prosthetic valves

4. Immune defects: AIDS, CGD

5. Neutropenia: leukemia

6. Debilitating diseases: cancer

7. Nosocomial:

   1. Antibiotics – they kill all the bacteria and the fungi have a party and grow outta control.

   2. Drugs – cytotoxic drugs,immunosuppressive, corticosteroids, IV alimentation

Lab Diagnoses

This can be tricky because candida are also part of the normal flora, so seeing it in a culture doesn’t really mean much. You get samples and culture them, and see what comes up. You also look at the patient. You can also use immunodetection, detection of antigen works better than antibody. PCR is at the developmental stages right now.

Treatment

For muco-cutaneous you use topical creams like nystatin and azoles, but nails require systemic treatment. For systemic and deep-seated forms you use systemic treatment like Amphotericn B (AMB), Liposomal AMB, Fluorocytosine, Flucanoazole, and the newest is Caspofungin.

Category: Microbiology Notes