Candida | Medical Science Optional Notes for UPSC PDF Download

Candida - Morphology

• Among the 150 species, human pathogens include C. albicans, C. guilliermondii, C. krusei, C. paropsilosis, C. tropicalis, C. kefyr, C. lusitcmiae, C. dubliniensis, C. glabrata, and C. auris.
• Candida is a small, thin-walled, unicellular, ovoid yeast with a diameter of 4-6 μm, reproducing through budding.
• Both yeast and pseudo-hyphae exhibit gram-positive characteristics.
• Encapsulated and diploid, they can also form true hyphae and biofilms.
• Under normal conditions, it exists as yeast, while under specific conditions (pH, temperature), it forms pseudo-hyphae.
• Approximately 80-90% of the cell wall is composed of carbohydrates.

Candida - Clinical Manifestations

Candida - Pathogenesis

Factors Responsible for Invasive Candida Infection

• Antibacterial medications
• Abdominal and thoracic surgical procedures
• Placement of indwelling intravenous catheters
• Cytotoxic chemotherapy treatments
• Administration of hyperalimentation fluids
• Use of indwelling urinary catheters
• Administration of parenteral glucocorticoids
• Severe burn injuries
• HIV-associated low CD4+ T cell counts
• Use of immunosuppressive agents for organ transplantation
• Utilization of respirators
• Presence of neutropenia
• Low birth weight in neonates
• Diabetes

The advent of antifungal agents has led to a shift in the causes of Candida infections, moving from a near-exclusive prevalence of C. albicans to the frequent involvement of C. glabrata and other aforementioned species. Non-albicans species currently contribute to around fifty percent of all cases of candidemia and hematogenously disseminated candidiasis. Acknowledging this shift is clinically significant, given the distinct susceptibilities of the various species to the newer antifungal agents.

Lab Diagnosis of Candida

Beta - Glucan Assay

How to Find out Hematogenous Dissemination to Multiple Organs

• The most challenging aspect of diagnosis involves determining which patients with Candida isolates are experiencing hematogenously disseminated candidiasis.
• For example, the recovery of Candida from sputum, urine, or peritoneal catheters may indicate colonization rather than a deep-seated infection. Candida isolation from the blood of patients with indwelling intravascular catheters may reflect inconsequential seeding of the blood from or the growth of organisms on the catheter.
• Despite extensive research on both antigen and antibody detection systems, there is currently no widely available and validated diagnostic test to differentiate patients with inconsequential seeding of the blood from those with positive blood cultures representing hematogenous dissemination to multiple organs.
• Numerous studies are underway to establish the utility of the β-glucan test; presently, its greatest value lies in its negative predictive value (approximately 90%).
• Meanwhile, the presence of ocular or macronodular skin lesions strongly suggests widespread infection of multiple deep organs.

After combining the pretreated sample with the LAL solution, the (1→3)-β-D-glucan in the sample activates Factor G, triggering cascade reactions that result in gelation. The duration required for the transmittance to reach the threshold value is also recorded. This period is referred to as gelation time (Tg).

Prophylaxis for Candida Infections

The use of antifungal agents for preventing Candida infections has been a subject of debate, but certain general principles have been established. Employing prophylaxis for almost all patients in general surgical or medical intensive care units is not a common and recommended practice for three main reasons:

• the occurrence of disseminated candidiasis is relatively low,
• the cost-benefit ratio is suboptimal, and
• concerns about increased resistance with widespread prophylaxis are valid.

In most centers, recipients of allogeneic stem cell transplants receive prophylactic fluconazole (400 mg/d). High-risk liver transplant recipients are also commonly provided with fluconazole prophylaxis. Posaconazole (200 mg three times daily) has received approval from the U.S. Food and Drug Administration for prophylaxis in neutropenic patients, gaining popularity and potentially replacing fluconazole.

Prophylaxis is occasionally administered to surgical patients facing a very high risk.
Prophylaxis for oropharyngeal or esophageal candidiasis in HIV-infected patients is not advised unless there are frequent recurrences.

Candida - Repeats

• Candidiasis: Pathogenesis, Laboratory Diagnosis, and Prophylaxis (2009)
• Morphology, Pathogenicity, and Laboratory Diagnosis of Candidiasis: A Discussion (2013)
• Candida albicans: Pathogenesis and Laboratory Diagnosis (2015)
• Factors Contributing to Invasive Candida Infection and a Brief Overview of the Laboratory Diagnosis of Bloodstream Candida Infection (2017)