Fungal Infection

Introduction

Fungi are distinct from bacteria and viruses as pathogens that can cause illness in humans.

These micro-organisms are ubiquitous and exist in the environment that we live in. They are mostly outdoors but can be indoors as well, entering the indoor environment through air circulation, windows, physical objects, clothing, pets, etc The commonest fungus that most of us know is Candida, of which Candida albicans is the most common fungus causing disease. The layman term for Candida infection or Candidiasis is “thrush”, which is a common infection affecting both sick patients and otherwise healthy people.

Epidemiology

Certain fungal infections also follow specific geographic distributions and can be “endemic” in certain parts of the world eg coccidioimycosis, blastomycosis, penicilliosis in some countries. Some of these fungi are related to occupational exposure and exposure to birds, cave bats, etc.

Clinical Presentation

The spectrum of fungal infection is very broad. It ranges from mild skin infection to severe life threatening disease in immunocompromised patients. Patients who are at risk for life threatening invasive fungal disease are in the following risk groups:

  1. HIV/AIDS patients
  2. Patients on long term steroid use
  3. Patients on immunosuppressive drugs eg chemotherapy, biologics (anti-TNF monoclonal Ab)
  4. Transplant patients
  5. Patients with congenital immunodeficiency syndromes
  6. Intensive care patients with indwelling devices, central lines on prolonged antibiotic use, intravenous nutrition and other comorbidities

Common fungal infections:

  • A group of fungi known as Dermatophytes cause infections involving the skin and nails. The layman term for skin dermatophytoses is “ring worms” because of the appearance of a reddish ring on the skin.
  • Oral thrush : affects those who take prolonged antibiotics or steroids
  • Vaginal thrush and Urinary infection
  • Severe oral thrush can progress to gastrointestinal infection, candida esophagitis,etc

Uncommonly, Candida can cause invasive disease affecting the lungs, bones, bloodstream and gastrointestinal tract. These patients are usually immunocompromised or may have implants.

Other adverse health effects of fungal infections include :

  • Colonisation of paranasal sinuses
  • Hypersensitivity syndromes or “allergic disease”
  • Toxic/irritant effects of fungal toxins ( mycotoxins ) : Aflatoxin from Aspergillus has been associated with liver cancer
  • Allergic reaction like asthma, rhinitis, hypersensitivity pneumonitis and allergic rhinosinusitis have been described
  • Occupational hazards : granary workers are exposed to fungal elements/toxins which causes ‘organic dust toxic syndrome’ which is a flu-like illness
  • Invasion into internal organs such as pneumonia, brain, liver and spleen. Most invasive fungal infections occur in patients who are immunocompromised. Rarely patients who are otherwise healthy can develop invasive fungal infection due to Cryptococcus (meningitis, lung disease), Histoplasma (lung disease, adrenal glands causing adrenal failure, bone marrow involvement), Coccidioidomyces (meningitis) etc.

Diagnosis

Usually the “typical” appearance of thrush and ringworm is sufficient for a clinical diagnosis to be made by the doctor. Invasive fungal infections will require tissue biopsy and cultures. Serological tests and PCRs are also available for certain fungi of clinical importance.

Treatment

Treatment is according to the type of fungi identified and the site of infection. The common non-invasive infections are treated with topical applications ( creams and paints) and oral suspensions (oral thrush)

The common oral medications used are fluconazole, itraconazole, voriconazole and posaconazole. An older oral agent, ketoconazole which has been often used in fungal infections in the past is now avoided because of concerns for adverse effects to the liver (hepatotoxicity). For severe invasive fungal infections, we have to use intravenous formulations such as Liposomal amphotericin B, intravenous echinocandins (caspofungin, anidalufungin, micafungin) and intravenous azoles (fluconazole, voriconazole, posaconazole).

Prevention

In general for otherwise healthy people, we can prevent fungus infection by maintaining good hygiene in the environment and of ourselves. The living environment should be well ventilated, with adequate sunshine and prevent dampness by fixing leaks and controlling humidity. In immunocompromised patients especially those going for chemotherapy and transplants, drugs are used for “prophylaxis” against invasive fungal infections.

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