Fungal infections and laboratory tests

Sh. Nilica Devi *

Fungal infections represent the invasion of tissues by one or more species of fungi. They range from superficial, localised skin conditions to deeper tissue infections to serious lung, blood (septicaemia) or systemic diseases. Some fungi are opportunistic while others are pathogenic, causing disease whether the immune system is healthy or not.

Fungi – What are they?

Fungi are one of the four major groups of microorganisms (bacteria, viruses, parasites and fungi). They exist in nature in one of two forms: as unicellular yeasts or as moulds. Some fungi are dimorphic – they change from one form to another depending on their environment. While yeasts cannot be seen with the naked eye, moulds can be seen as the fuzzy splotches on overripe fruit or stale bread, as mildew in bathroom shower, and as mushrooms growing on a rotted log.

There are more than 50,000 species of fungi in the environment, but less than 200 species are associated with human disease. Of these, only about 20 to 25 species are common causes of infection. Most fungal infections occur because a person is exposed to a source of fungi such as spores on surfaces, in the air, soil, or bird droppings.

Anyone can have a fungal infection, but certain populations are at an increased risk of fungal infections and recurrence of infections. These include organ transplant recipients, people who have HIV/AIDS, those who are on chemotherapy or immune suppressants, and those who have an underlying condition such as diabetes or lung disease.

Superficial fungal infections of skin, nail and hair

Superficial fungal infections are very common. They may cause nail infections or itchy red scaly skin infections such as those commonly known as athlete’s foot, jock itch, and ringworm, or yeast infections that cause white patches in the mouth (oral thrush) or vaginal itching and discharge.

– Oral thrush causes redness and white patches inside the mouth, especially in children.
– Yeast infection in women causes genital itching and discharge.
– Athlete’s foot is found between the toes and sometimes covers the bottom of the foot.
– Jock itch may extend from the groin to the inner thigh.
– Scalp and hair infection affects hair shaft, primarily in children.
– Finger or toenail infection.
– Ringworm of the body can be found anywhere on the body.
– Barber’s itch affects the bearded portion of the face.

Deep tissue, blood, lung and systemic fungal infections

Though less common in occurrence, in deep, systemic infections, fungi may spread from their original location to penetrate deeper tissues or may cause serious lung infections and septicaemia. Systemic infections can affect any organ in the body. Fungal lung infections typically start with the accidental inhalation of microscopic fungal spores.

While anyone can get serious lung or systemic fungal infection, most affected people will only experience mild to moderate flu-like symptoms. Common deep or systemic infections include:
– Aspergillosis – cause fungal masses in the sinuses and lungs, and in some cases, can spread to the brain and bones.
– Blastomycosis – fungal infection of humans and other animals, most notably, dogs and occasionally, rats.
– Coccidioidomycosis, also called Valley Fever.
– Histoplasmosis that typically affects lungs.
– Candidiasis – infections occur in the moist mucous membranes of the body.
– Pneumocystis pneumonia – commonly affecting those with compromised immune systems, including those with HIV/AIDS.

LABORATORY TESTS

For superficial infections: Many fungal skin infections are diagnosed by the doctor based on a clinical evaluation and experience.

A few laboratory tests that may be useful in detecting and confirming a fungal infection include:
-Microscopic examinations, such as potassium hydroxide (KOH) preparation.
– Fungal culture and susceptibility testing.

For deep and systemic infections: With lung and systemic fungal infections, the symptoms are frequently nonspecific and may be confused with those due to other microorganisms or to another disease process. Laboratory testing is primarily used to diagnose these serious fungal infections, to identify the microorganism responsible, and to determine its disease process.

Testing may include:
– Microscopic examinations of the sample using techniques such as KOH preparation.
– Fungal culture –primary test used to diagnose fungal infection; many fungi are slow-growing and may require up to several weeks for detection and identification.
– Susceptibility testing – a follow-up test to the fungal culture that is sometimes done to help guide treatment.
– Antigen and antibody testing – available for a variety of fungi but only for deep or systemic infections; may be performed on blood or other body fluids, or on a sample of the microorganism grown in culture.
In some cases, imaging such as x-rays may be done to detect fungal mass, such as in the lungs, and to evaluate the extent of tissue damage.

How is the sample collected?

The sample collected depends upon the suspected location of the infection. For superficial infections, the sample may include scrapings of the skin, clipped or shaved hair or nail, vaginal secretions collected with a swab, or a urine sample. For deeper tissue, organ or systemic infections, the sample may involve the collection of urine, blood from vein, sputum from the lungs, and the collection of a tissue biopsy.

Preparation for the test

No special preparation is needed.