Systemic Mycoses

Conditions that favor Opportunistic Mycoses: Recall that "opportunistic" pathogens are micro-organisms that are commonly found in the environment, even our own microbiomes, that cause infection when the "opportunity" arises – for example, in immunosuppressed individuals or when trauma permits access to a novel niche within the body. The fungi responsible for opportunistic mycoses cause disease when normal host defenses are impaired. Thus, populations with increased risk of infection include the following: Patients with immunosuppression, especially due to underlying disease, such as HIV infection, hematological malignancies, or diabetes mellitus. Immune suppressing treatments, such as chemotherapy, organ transplants, antibiotics and corticosteroids, also increase risk for opportunistic mycoses. Additionally, the very young and elderly are more vulnerable. Some patients are at risk due to increased exposure to the fungi: For example, hospital settings, surgery, and medical devices or implants increase risk of infection. Be aware that, as the number of people living with immunosuppressive disorders and therapies has increased, so, too, has the frequency of opportunistic mycoses. Recent research indicates a possible link between host genetics and susceptibility to opportunistic infections. Candidiasis is the most common opportunistic mycosis. It is caused by species of Candida, especially Candida albicans; other important species include C. glabrata, C. parapsilosis, C. tropicalis, and C. krusei. Microbiology Thermally dimorphic: They exist as budding yeast and pseudohyphae at 20 degrees Celsius, and form germ tubes at 37 degrees Celsius. Candida albicans colonies comprise yeast-like cells with filamentous cells on top. Pathology Candida are commonly found in our gastrointestinal and urogenital tracts, and on the skin; thus, most infections are endogenous. Exogenous infections are less common, and are more likely in health care settings. Candidiasis can manifest in several forms throughout the body. Superficial candidiasis is the result of localized overgrowth. On mucosal surfaces, overgrowth is visible as whitish plaques and pseudomembranes; On the skin, overgrowth produces erythematous and/or vesiculopustular lesions. Mucosal and cutaneous forms are typically easy to treat. Chronic muco-cutaneous candidiasis is rare, but difficult to treat; this form of candidiasis is the result of T-lymphocyte defects. Invasive candidiasis occurs as the result of hematological dissemination or trauma that introduces fungi to a novel site. Infection can be focal, for example, localized within the heart, lungs, brain, bones, or other organ system, or, can be systemic. Candidemia and dissemination to the viscera is more likely in neutropenic and hospitalized patients. Candida species are major causes of central-line associated bloodstream infections. # Oropharyngeal overgrowth can produce thrush, which manifests as whitish plaques or pseudomembranes over the palate, buccal surfaces, and tongue. These lesions are generally painless, though they can cause a "cottony" feeling in the mouth and loss of taste. Oropharyngeal candidiasis can also produce angular cheilitis, which are painful fissures at the corners of the mouth. Adults who wear dentures can develop a form of oral candidiasis, called denture stomatitis, which is characterized by uncomfortable erythema without plaques. Esophageal candidiasis produces plaques or pseudomembranes in the esophagus, and produces pain upon swallowing (odynophagia); this is most common in HIV patients with low CD4+ T-cell counts (thus, it is an AIDS-defining illness). Intra-abdominal overgrowth is associated with hospitalized patients, especially those who have had abdominal surgery. Infection can involve the peritoneum and/or any of the abdominal viscera. Cutaneous candidiasis tends to occur in the body folds, where conditions are warm and moist, such as the armpits, under the breasts, and groin area. The red rash is often itchy, and can become painful. Diaper rash can also be caused by Candida overgrowth; the red, itchy rash tends to appear in the folds of the groin, buttocks, and external genitalia. Vulvovaginal candidiasis (aka, vaginal yeast infections) is characterized by whitish plaques, itching, and a foul-smelling discharge. Infections of the CNS and pulmonary system caused by Cryptococcus neoformans and Cryptococcus gattii. These fungi are found in bird droppings, and, by association, soil and trees. They are encapsulated, spherical yeast; the outer "halo" is the polysaccharide capsule and the inner yeast cell has melanin in its cell wall. Cryptococcus is inhaled into the respiratory system, followed by dissemination to and localization within the CNS. Cryptococcus neoformans is a major opportunistic pathogen in AIDS patients. Cryptococcosis typically manifests as CNS infections, meningitis and encephalitis; in the image, we can see the characteristic "soap bubble" lesions of Cryptococcal encephalitis. Cryptococcus neoformans CNS infection is associated with immunosuppressed patients. Cryptococcus gattii tend to produce infection in relatively immunocompetent individuals. These patients tend to have more granuloma formation Some authors suggest that so-called immunocompetent patients actually have complicating illnesses or histories of immunosuppression. Cryptococcosis can also manifest as pulmonary infection, sometimes following CNS involvement. In the lungs, severity ranges from asymptomatic to pneumonia with pulmonary infiltrates. Cryptococcus gattii tends to produce larger pulmonary lesions than Cryptococcus neoformans. Caused by species of Aspergillus, especially Aspergillus fumigatus. Additional important species include A. flavus, A. niger, and A. terreus. Aspergillus forms hyaline molds with abundant conidia production. Conidia are the asexual spores that are ubiquitous in our environment, both outside and inside, including hospitals. We are constantly inhaling these spores, which, in the immunocompetent, are typically harmless. Spores can colonize and/or invade individuals who have immune abnormalities. Hypersensitivity i.e., allergic reactions to Aspergillus: Allergic Aspergillus sinusitis is a form of chronic rhinosinusitis that can obstruct the sinuses and produce asymmetrical swelling around the orbit and/or nasal sinuses. Allergic bronchopulmonary aspergillosis occurs in patients with asthma and cystic fibrosis. In these individuals, the fungi colonize the bronchopulmonary tissue. This can lead to obstruction or, upon damage to the vasculature, hemoptysis (coughing up blood). Treatment: Because allergic sinusitis and bronchopulmonary aspergillosis are the result of hypersensitivity reactions, corticosteroids are often recommended. Patients with other conditions: Specifically, those with underlying chronic pulmonary illnesses and/or immunosuppression. Aspergillomas, aka, fungus balls (or mycetomas), can form within pre-existing cavities within the lungs or sinuses. For example, in a patient with a history of tuberculosis, fungal balls can form within cavities produced by TB infection. These masses comprise fungal hyphae as well as tissue debris and inflammatory cells. Chronic pulmonary aspergillosis occurs in patients with chronic lung disease. In these individuals, localized lung tissue invasion occurs, which can lead to cavitation with or without formation of fungal balls, or even fibrosis. Invasive aspergillosis occurs in patients with severe immunodeficiency, and, because of the invasive nature, has a high mortality rate. In addition to pulmonary tissue invasion and destruction, the fungus may disseminate to other organs and cause invasive damage. Aspergillosis can also be a cutaneous mycosis, typically following a wound. Learn about Mucormycoses