Discuss
infections caused by Candida albicans under the following headings:
(a)
types of infection.
(b)
predisposing factors.
(c)
laboratory diagnosis
Suggested
Answer:
(a)
Candida albicans is an oval yeast with a single bud. It is part of
the normal flora of mucous membranes of the upper respiratory, gastrointestinal,
and female genital tracts. In tissues it may appear as budding yeasts or as
elongated budding ‘pseudohyphae’.
The infections caused by Candida albicans are known as
candidiasis. Candidiasis may be classified as superficial or deep. Superficial
candidiasis may involve the epidermal and mucosal surfaces, including those of
the oral cavity, pharynx, esophagus, intestines, urinary bladder, and vagina.
The alimentary tract and intravascular catheters are the major portals of entry
for deep (or visceral) candidiasis. The kidneys, liver, spleen, brain, eyes,
heart, and other tissues are the major organ sites involved in deep or visceral
candidiasis.
Cutaneous
candidiasis: These superficial infections of moist epidermal surfaces are
associated with moist surfaces subject to regular friction: most commonly the
submammary folds in obese women and the groins and buttocks of babies (napkin
dermatitis). In both cases, satellite lesions can be observed at a distance from
the primary lesion.
Chronic
mucocutaneous candidiasis: A clinical syndrome characterized by development,
usually in infancy or childhood, of a chronic, often widespread candidiasis of
skin, nails, and mucous membranes. It may be secondary to one of the
immunodeficiency syndromes, inherited as an autosomal recessive trait, or
associated with defects in cell-mediated immunity, endocrine disorders, dental
stomatitis, or malignancy.
Oral candidiasis, or thrush is a common clinical feature in
immunocompromised patients, consisting of dense white plaques lying the oral
mucosa.
Esophageal candidiasis: The presenting symptoms are dysphagia and
retrosternal pain. Diagnosis is by microscopy of a potassium hydroxide or
Gram-stained preparation of white plaque scraped from affected mucosa.
Candida infections of the gastrointestinal tract include peritonitis and
hepatosplenic candidiasis which may spread to the gallbladder.
Vaginal discharge. Vaginitis caused by Candida albicans is typically
associated with a thick, creamy discharge and a white, curd-like inflammatory
exudate. This condition is not necessarily transmitted sexually and is often
caused by local factors such as tight underwear, ecological disturbances
resulting from antibiotic use or variation in hormonal background during
particular phases of the menstrual cycle.
Urinary tract infections with Candida albicans can lead to
cystitis and prostatitis. Haematogenous or ascending infections is a dangerous
complication, resulting in formation of fungal balls in renal tissue,
perinephric abscess and papillary necrosis.
In immunocompromised individuals, Candida albicans may disseminate
through the blood, causing septicaemia and spread to many organs. Ocular
endophthalmitis is inflammation of the uveal tract or posterior chamber, usually
caused by an intraocular infection. Candida endophthalmitis is spread by
blood-borne infection following intravascular cannulation or parenteral
infection. Symptoms are visual blurring, pain and a floating
scotomata.Intravenous drug abuse and hyperalimentation can lead to right-sided
endocarditis. Spread of infection in other parts of the body can also result in
myocarditis, purulent pericarditis and osteomyelitis. Central nervous system
involvement affects the brain parenchyma and meninges with formation of
abscesses. Clinical manifestations are fever, headache, stiff neck, seizures and
focal neurologic deficits.
(b)
Infections by Candida albicans are often the result of impaired
local or systemic host defenses. Vulvovaginitis with itching and discharge is
favored by high pH, diabetes, or use of antibiotics. Skin invasion occurs in
warm, moist areas, which become red and weeping. Fingers and nails become
involved when repeatedly immersed in water; persons employed as dishwashers in
restaurants and institutions are commonly affected. The predisposing factors for
candida endocarditis are underlying heart disease, intravenous drug abuse,
cancer chemotherapy, prosthetic valves and prolonged use of intravenous
catheters/ Antibiotic use and indwelling catheters also predispose to candida
urinary tract infections while hepatosplenic candidiasis is common in recovering
neutropenic patients.
The
principal risk factors predisposing to deeply invasive candidiasis are
protracted courses of broad spectrum antibiotics, cytotoxic chemotherapy,
corticosteroids, neutropenia, vascular catheters and intravenous drug abuse.
(c)
Laboratory confirmation of the diagnosis of infections by Candida
albicans is by microscopy of a saline-mounted preparation of exudate and
fungal culture on Sabouraud’s medium. In exudates or tissues, budding yeast
and pseudohyphae are seen microscopically. Such specimens grow typical yeasts
when cultured. Germ tubes form in serum at 37C, which serves to distinguish Candida
albicans from other candida species.