Lecture 6: Systemic Fungal Infection PDF

Lecture 6: Systemic fungal infection  Learning Objectives At the end of the lecture, you will be capable to: 1. Identify different types of Systemic fungal infection. 2. Understand laboratory diagnosis methods of systemic mycoses. 3. Recognize Subcutaneous mycoses. 4. Syste...

Lecture 6: Systemic fungal infection  Learning Objectives At the end of the lecture, you will be capable to: 1. Identify different types of Systemic fungal infection. 2. Understand laboratory diagnosis methods of systemic mycoses. 3. Recognize Subcutaneous mycoses. 4. Systemic mycoses caused by : fungi of soil, which are inherently virulent and cause disease in healthy humans. Fungal diseases coccidioidomycosis, paracoccidioidomycosis, histoplasmosis, blastomycosis, and cryptococcosis. Systemic Mycoses 1) Coccidioidomycosis Disease: Coccidioides immitis (causing coccidioidomycosis) Saprobic Phase Parasitic Phase Properties: C. immitis is a dimorphic fungus that exists as a mold in soil and as a spherule in tissue (Spherules are multinucleate). Systemic Mycoses Coccidioidomycosis Symptoms More than half of the cases are asymptomatic. Primary coccidioidomycosis, which is an acute, self-limited respiratory disease. Progressive coccidioidomycosis, which is a chronic, malignant and disseminated disease involving cutaneous, subcutaneous , visceral central nervous system (CNS) and bones. The condition is uncommon, but is highly fatal. Systemic Mycoses Coccidioidomycosis Systemic Mycoses Coccidioidomycosis Infection symptoms Primary pulmonary coccidioidomycosis Non-pulmonary coccidioidomycosis The organism is inhaled with dust in endemic Verrucous growth on the back of neck. The lesion areas, upper respiratory infection symptoms, remains localized for 8 years, and then spread to appear after an incubation period of 10 to 14 days. other parts of the body Systemic Mycoses Coccidioidomycosis lesions in subcutaneous tissue Systemic Mycoses Laboratory Diagnosis of Coccidioide The blood count during the first week of disease shows an initial leukocytosis, followed by increase in the eosinophils. Sputum, gastric contents, pleural fluid, pus from subcutaneous abscesses and exudates of cutaneous lesionsstained by calcofluor white and in biopsy material stained by hematoxylin and eosin, silver, or periodic acid-Schiff stains, should be examined microscopically. C.immitis appears as a non- budding, spherical, thick-walled structure, 20 to 80 μ in diameter, (spherules)which is filled with numerous small endospores. Systemic Mycoses Laboratory Diagnosis of Coccidioide In tissue specimens, spherules are seen microscopically. Cultures on Sabouraud’s dextrose agar (SDA) incubated at 25 °C show hyphae with arthrospores within 5 days. (Caution: Cultures are highly infectious; precautions against inhaling arthrospores must be taken.) Systemic Mycoses Coccidioidomycosis Systemic Mycoses Coccidioidomycosis Systemic Mycoses Coccidioidomycosis Systemic Mycoses Coccidioidomycosis Systemic Mycoses Coccidioidomycosis Systemic Mycoses Laboratory Diagnosis of Coccidioide Immunology and Serology : complement fixation and precipitin tests are positive in patients with severe infections. The antibody titer is highest in patients with dissemination of the infection DNA probe is a recent method used for accurate identification of the fungus. Skin test Using coccidioidal antigens is used for diagnosis of coccidioidomycosis. It is a delayed-type hypersensitivity reaction that appears 2–21 days after the onset of symptoms. Skin test has limited diagnostic utility because of its low sensitivity and specificity in endemic areas. Systemic Mycoses 2) Paracoccidiodomycosis Disease: Paracoccidioides brasiliensis (causing paracoccidiodomycosis) Saprobic Phase Parasitic Phase Properties: Thermally Dimorphic with mold to yeast transition when infecting susceptible species. Yeast cells have multiple buds Infection occurs by inhalation of conidia or mycelial fragments. The lungs are the primary site of infection. From this site, the fungus then disseminates to other organs through the venous and lymphatic systems. Systemic Mycoses Paracoccidiodomycosis chronic granulomatous disease of the skin, mucous membranes, lymph nodes and internal organs caused by Coccidioides brasiliensis. The disease occurs most frequently in manual laborers Systemic Mycoses Paracoccidiodomycosis Infection symptoms The most characteristic clinical feature is the enlargement of lymph nodes. The clinical type of infection is determined largely by the site of infection. i. Mucocutaneous Coccidiodomycosis: ulcerative papules on the mucosal surface of the tongue, palate, gums, cheeks, lips or nose. ii. Lymphangitic Coccidiodomycosis: massive lymph node enlargement, particularly in the neck region iii. Visceral Coccidiodomycosis: The liver, spleen and other organs become enlarged as the infection becomes generalized Systemic Mycoses Laboratory Diagnosis of Paracoccidiodomycosis Laboratory diagnosis depends on Microscopic examination of large, multiple budding yeasts (blastoconidia) in 30% KOH wet mount preparation of sputum. Gomori’s methenamine silver (GMS) staining of biopsy (of tissues with exudate from the mucous membranes of the mouth and lips) specimens shows yeast cells measuring 2–30 um in diameter. The organism is isolated by culture on SDA at 37°C after 20–30 days. Pus should be aspirated from fluctuant nodules Systemic Mycoses Laboratory Diagnosis of Paracoccidiodomycosis Complement fixing antibodies can be demonstrated in the sera of patients ELlSA (sensitivity of 95% and a specificity of 93%. The test shows cross-reactivity with sera from patients of histoplasmosis or Lobo disease) Western blot. Hypersensitivity : (skin tests are rarely helpful) The intracutaneous injection of antigens from cultures produce focal reactions with redness, pain and burning, and some patients react with generalized symptoms such as malaise and fever Systemic Mycoses Paracoccidiodomycosis Systemic Mycoses 3) Histoplasmosis Disease: is primarily a disease of reticuloendothelial system caused by an intracellular fungus Histoplasma capsulatum. Properties: H. capsulatum is a dimorphic fungus, which occurs in two stages: as a mold in soil and as yeast at body temperature in mammals. On SDA medium at 37°C, this fungus produces cottony mycelial growth. H. capsulatum infection is acquired by inhalation of conidia and mycelial fragments from contaminated soil. Once inhaled, it is deposited in alveoli of the lung and transformation from the mycelial to the pathogenic yeast form occurs intracellularly inside the macrophages. The yeast inside the macrophages multiplies in approximately 15–18 hours.  Clinical feature of Histoplasmosis Most infected individuals are asymptomatic. H. capsulatum causes: -acute pulmonary histoplasmosis. -chronic pulmonary histoplasmosis. -progressive disseminated histoplasmosis. Fever, headache, malaise, myalgia, abdominal pain, and chills are common symptoms. Cough, hemoptysis, dyspnea, and/or chest pain may be present. Chronic pulmonary histoplasmosis is seen in patients with underlying pulmonary disease. Progressive disseminated histoplasmosis is seen in patients who are immunocompromised, such as patients with AIDS.  Laboratory diagnosis of Histoplasmosis Demonstration of oval yeast cells within macrophages in bone marrow aspirates and in tissue biopsy specimens (oropharyngeal ulcers ). Culture of sputum and blood on SDA at 25°C shows hyphae with tuberculoid macroconidia and at 37°C shows yeasts. Complement-fixation test (CFT) and immunodiffusion (ID) are useful serological tests for demonstration of specific antibodies in serum.  Laboratory diagnosis of Histoplasmosis Skin test detects a delayed-type hypersensitivity to histoplasmal antigens that occurs 3–6 weeks after exposure. A positive skin test indicates a past or present infection. DNA probes and polymerase chain reaction (PCR) are also used for diagnosis of the condition. Systemic Mycoses 4) Blastomycosis (a granulomatous fungal infection) Properties: B. dermatitidis is a dimorphic fungus, which occurs in two stages: as mold in soil and as yeast Saprobic Phase Parasitic Phase in tissue. the yeast is a round structure with a double refractile wall. How infections occurs?  Clinical feature of Blastomycosis Pulmonary infection is the major clinical manifestation. A flu-like illness with fever, chills, myalgia, headache, and a non- productive cough may occur, which resolves within days. Extrapulmonary dissemination to other organs, more often, occurs in patients with chronic pulmonary illness and in those who are immunocompromised. The skin is the most common site of extrapulmonary blastomycosis.  Laboratory diagnosis of Blastomycosis Sputum microscopy is a very useful test for demonstration yeasts of B. dermatitidis. KOH wet mount of pus aspirated from skin microabscesses, fistulae, or subcutaneous abscesses is useful to demonstrate the yeast. Sputum culture on SDA medium confirms diagnosis of the condition. it may take as early as 5 days or as late as 30 days for colony formation. ELISA is a useful test to detect antibodies of B. dermatitidis in the patient’s serum. Radioimmunoassays (RIAs) and Western blot techniques are the newer tests that use more specific cell wall antigens of B. dermatitidis for detection of antibodies in the serum. Skin test is not reliable for diagnosis. Systemic Mycoses 5) Cryptococcus neoformans Disease: Cryptococcus neoformans (causing a severe form of meningitis in people with HIV Saprobic Phase Parasitic Phase infection and AIDS). Properties: Monomorphic with yeast phase only. This is the only pathogenic yeast with a capsule. The capsule is extremely large. Laboratory diagnosis of cryptococcal infection Demonstration of the yeast in CSF, sputum, pus, and brain biopsy tissue by smear and culture. Methenamine silver or periodic acid-Schiff stains are used to stain the tissue specimens for demonstration of the capsule of C. neoformans. Fixed tissue may also be stained with mucicarmine. India ink Latex agglutination test (LAT) is a frequently used serological test to detect cryptococcal polysaccharide antigen in the serum.