Page 191 - Concise Pathology for Exam Preparation ( PDFDrive )

176 SECTION I General Pathology

infections are commonly referred to by the term ‘tinea’ followed by area of the body
affected (eg, tinea pedis: ‘athlete’s foot’; tinea capitis: ‘ringworm of the scalp’). Certain
fungal species invade the subcutaneous tissue, causing abscesses or granulomas, (eg,
sporotrichosis and tropical mycoses).
• Deep fungal infections can spread systemically and invade tissues, destroying vital
organs in immunocompromised hosts, but usually heal or remain latent in otherwise
normal hosts, eg, Histoplasma, opportunistic fungi like Candida, Aspergillus, Mucor, Cryp-
tococcus and Pneumocystis jiroveci (carinii).

Candida

• It is a part of normal flora (commensal) of the skin, mouth, gastrointestinal tract and
vagina, and does not usually produce any disease. However, some Candida species, most
often C. albicans, can cause human fungal infections, particularly in immunocompro-
mised persons (diabetics, AIDS patients, burn patients, patients receiving transplants
and those with haematolymphoid malignancies).
• Candida can be directly introduced into the blood by intravenous lines and catheters,
during peritoneal dialysis, cardiac surgery or intravenous drug abuse.
Pathogenesis
• Candida can shift between different phenotypes in a reversible manner. Phenotypic
switching provides a way for Candida to adapt to changes in host environment.
• They produce adhesins that aid in its adherence to host cells, and enzymes that contribute
to invasiveness, such as proteinase (degrades extracellular matrix proteins) and catalase
(resists oxidative killing by phagocytic cells).
• Candida also secretes adenosine, which blocks neutrophil oxygen radical production
and degranulation.

Clinical Manifestations
• Candida can cause superficial to disseminated deep mycosis (vaginitis; oral thrush; dia-
per rash; endocarditis; meningitis; osteomyelitis; and renal, intracerebral and hepatic
abscesses).
• In immunocompetent persons, candidiasis is usually a localized infection of the skin or
mucosal membranes. Most common type of superficial candidiasis is infection of oral
mucosa (thrush), which is characterized by formation of a dirty-looking pseudomem-
brane composed of colonies of organisms and inflammatory debris. Other forms of
oropharyngeal candidiasis include thrush, glossitis, stomatitis and angular cheilitis (per-
leche). Candida esophagitis presents with dysphagia, and endoscopy demonstrates
white plaques (pseudomembranes) on oesophageal mucosa.
• Mucocutaneous candidiasis includes intertrigo, diaper candidiasis, paronychia and
onychomycosis.
• Candida vaginitis is a common form of vaginal infection in women; especially, those
who are diabetic or pregnant or on oral contraceptive pills. It is usually associated with
intense itching and a thick, curd-like discharge.
• Severe disseminated candidiasis is associated with severe immunosuppression. Candidal
sepsis can eventually cause shock and DIC.

Morphology
Candida exists as a yeast form (small, thin-walled ovoid cells of 4–6 microns that re-
produce by budding) as well as pseudohyphae, which are best demonstrated by Silver
Methenamine and PAS stains (Fig. 7.9). Pseudohyphae are important diagnostic clue
for C. albicans and represent budding yeast cells joined end-to-end at constrictions,
thus simulating true fungal hyphae. Three types of histopathological reactions may
be seen:
• No cellular response
• Suppurative response
• Granulomatous response

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