Pneumonia occurs when the air sacs and small airways in the lungs fill with liquid and cannot function properly. When gas exchange is impeded, the body cannot take in oxygen as it normally would.
Oxygen is vital to the body’s cells, where it is needed for aerobic respiration; the breakdown of glucose to obtain energy for cellular work.
Causes of Pneumonia
Pneumonia can have many different causes: viral, bacterial, fungal, or, in the case of aspiration pneumonia, may result from the inhalation of substances such as caustic chemicals, food or vomit.
Opportunistic Fungal Pneumonia
Fungal pneumonia is an infection in the lungs caused by any one or a combination of endemic or opportunistic fungi. Opportunistic fungal organisms cause pneumonia in immune-compromised patients.
Pathophysiology: Infection occurs following the inhalation of spores, or by the reactivation of a latent infection. Dissemination through the circulatory system can occur, especially in the immunocompromised.
Diagnosis & Treatment: Usually diagnosis is made by identifying the fungus in a sputum sample, performing a blood or urine test to detect the organism, or by examining the blood for certain antibodies. Treatment typically consists of taking an antifungal drug. The following are some of the main types of opportunistic fungal infections and pathogens.
Pulmonary Candidiasis
Organism: Candida species
Candida are ubiquitous yeast-like fungi and the most common fungal pathogens to affect humans. Candida species inhabit the digestive tracts of 40-80% of healthy individuals, and also frequently colonize the upper respiratory tract without causing any symptoms. However, when an opportunistic infection does occur, Candida Pneumonia is one of the most challenging of all the Candida infections.
Primary Candida Pneumonia refers to infections limited to the lungs. Secondary Candida Pneumonia indicates lung involvement due to the movement of invasive Candida from other areas of the body.
Clinical indications of Candida Pneumonia consist of generalized, nonspecific symptoms and often remain undiagnosed until autopsy. Because of this, it is impossible to know the true incidence of this type of pneumonia.
Aspergillosis
Organism: Aspergillus spp.
Aspergillosis is not a single disease, but several which are caused by the inhalation of spores of the fungus Aspergillus.
Aspergillus are ubiquitous, frequently found in compost heaps, air vents, and airborne dust. More than 100 species have been identified; however, the majority of human illness is caused by Aspergillus fumigatus and A. niger and occurs in individuals who are immune compromised in some way.
The fungus primarily affects the lungs, causing three clinical pulmonary diseases:
Hypersensitivity Aspergillosis
This variety of Aspergillosis manifests as asthma or allergic symptoms, which may be mild or become chronic with recurrent episodes leading to permanent lung damage.
Noninvasive Aspergillomas
Usually asymptomatic, this type of Aspergillosis manifests as ball-like fungal masses in lung cavities that had been created by pulmonary tuberculosis.
Acute Invasive Pulmonary Aspergillosis
This is the most serious form of Aspergillosis. Symptoms may appear as a mild pneumonia with fever, cough and pain. This condition can lead to necrosis (tissue death) in the lungs and significant respiratory impairment.
Cryptococcosis
Organism: Cryptococcus neoformans
The causative agent of Cryptococcosis is a fungus ordinarily found in soil. Once inhaled, infection may heal on its own, remain localized in the lungs, or spread throughout the body.
Most cases occur in people whose resistance to infection is lowered. In those with normal immune systems, there may be no symptoms. Some individuals experience a mild, self-limiting pneumonia marked by a low fever, cough and mild chest pain.
In some cases, invasive pulmonary Cryptococcosis may occur, resulting in chronic pneumonia in which cough and pulmonary lesions progressively worsen. Cryptococcosis is one of the most common life-threatening fungal infections in AIDS patients, in whom the Cryptococcus organism may spread to the brain.
Mucormycosis
Organism: Mucor species
Mucormycosis is caused by a common fungus frequently found in the soil and decaying vegetation. Most of us are exposed to these fungi on a daily basis; however people with immune disorders are more susceptible to infection.
Medical conditions most commonly associated with Mucormycosis include diabetes, chronic steroid use, metabolic acidosis, organ transplantation, leukemia, lymphoma, and AIDS.
The primary treatment is early surgical intervention to remove all dead and infected tissue, with supportive intravenous antifungal therapy. Chances of survival are greatly decreased without this aggressive intervention.
Even with aggressive surgical intervention, Mucormycosis has an extremely high mortality rate. Death rates range from 25-80% depending on the site involved and the underlying immune problems.
Pneumonia Resources
For more information on pneumonia, see the Mayo Clinic: Infectious Diseases or Science Prof Online, or the Suite101.com articles Gram Positive Bacterial Pneumonia, Gram Negative Bacterial Pneumonia and Primary Atypical Pneumonia.
This article is a summary of opportunistic fungal pneumonia. It is not meant to be used for self-diagnosis or as a substitute for professional medical care.
Sources
Bauman, R. (2005) Microbiology.
Park Talaro, K. (2008) Foundations in Microbiology.
Tami Port - Tami Port is a college professor of cell and microbiology and creator of ScienceProfOnline.com, a free science education website.
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