Internal Medicine_Infectious Diseases_16 Flashcards
Fungal infections
What is Sporothrix schenckii and what disease does it cause?
Sporothrix schenckii is a dimorphic fungus that causes sporotrichosis, also known as rose gardener’s disease.
Mold in the cold (25 - 30 C)
Yeast in the heat (35 - 37 C)
Where is Sporothrix schenckii commonly found?
Found in soil, plant debris, tree bark, and bushes.
Associated with rose thorns and other contaminated plant materials.
How does Sporothrix schenckii enter the body?
Through physical trauma, such as a puncture wound from a thorn or contaminated material. Infection often occurs after handling plants contaminated with Sporothrix schenckii, such as being pricked by rose thorns.
What are the characteristic microscopic features of Sporothrix schenckii in its yeast form?
Cigar-shaped cells are seen microscopically in its yeast form.
Can be visualized with methanemine silver.
What is the pattern of lesion spread in lymphocutaneous sporotrichosis?
Lesions spread in an ascending pattern along the lymphatic channels.
Start as local pustules or ulcers, progressing to subcutaneous nodules.
What is the gold standard for diagnosing sporotrichosis?
Culture of the organism.
Biopsy showing granulomas with histiocytes, multinucleated giant cells, and yeast cells is also diagnostic.
What is the preferred treatment for sporotrichosis?
Itraconazole is the first-line treatment for cutaneous and lymphocutaneous sporotrichosis.
What historical treatment is sometimes used for sporotrichosis?
Saturated solution of potassium iodide (SSKI), though modern antifungal medications are preferred.
Where is Histoplasma capsulatum geographically endemic?
The Midwestern and Central United States, particularly along the Mississippi and Ohio River Valleys.
How is Histoplasma capsulatum transmitted?
Inhalation of airborne fungal spores from soil or mold.
Often associated with bird droppings and bat guano.
What type of individuals are at increased risk of histoplasmosis?
Most are asymptomatic.
Immunocompromised patients, such as those with HIV/AIDS or undergoing chemotherapy, are the people most at risk, as are individuals exposed to bird or bat droppings.
What are the key clinical features of histoplasmosis?
Constitutional symptoms:
Fever, Fatigue, Malaise, weight loss
Pulmonary symptoms:
Cough, lung cavitations (resembles tuberculosis), patchy/nodular infiltrates, Hilar lymphadenopathy.
Disseminated disease:
Arthalgias, Hepatosplenomegaly, skin nodules, ulcers and other skin manifestations like erythema nodosum.
What dermatologic finding is associated with histoplasmosis?
Erythema nodosum, characterized by painful red nodules on the shins.
What is the role of lung calcifications in histoplasmosis?
Chronic histoplasmosis can lead to calcified mediastinal and hilar lymph nodes, as part of the healing process.
What would pertinent lab findings show in a patient with histoplasmosis?
Pancytopenia
Elevated AST/ALT
Elevated LDH
What is the histological hallmark of Histoplasma capsulatum on microscopy?
Small intracellular oval yeast bodies within macrophages.
These yeast cells are smaller than red blood cells.
What diagnostic tests are available for histoplasmosis?
Antigen testing of serum or urine (SAg, UAg).
Tissue biopsy or respiratory specimen staining.
Culture is the gold standard.
What is the treatment for mild histoplasmosis?
Itraconazole (an azole antifungal).
What is the treatment for severe or disseminated histoplasmosis?
Amphotericin B is the drug of choice for severe cases, followed by itraconazole as step-down therapy.
Where is Blastomyces dermatitidis geographically endemic?
Eastern and Central United States
Near the Ohio and Mississippi River Valleys
The Great Lakes region
What is Blastomyces dermatitidis and what disease does it cause?
Blastomyces dermatitidis is a dimorphic fungus that causes blastomycosis, a systemic fungal infection.
Which populations are at higher risk for disseminated blastomycosis?
Immunocompromised individuals, such as those with HIV/AIDS or undergoing chemotherapy.
Can disseminate even if immunocompetent.
How is Blastomyces dermatitidis transmitted?
Through inhalation of mold spores.
The spores convert to yeast form upon entering the lungs.
What are the common pulmonary manifestations of blastomycosis?
Known to cause acute and chronic pneumonia
Patchy alveolar infiltrates or “haziness” on chest X-rays (CXR).
May include mass-like lesions or cavitations.
Granulomatous infection, with the lungs being the most commonly affected organ.
What systemic organs are affected in disseminated blastomycosis?
Lungs (most common), skin, and bones.
Skin lesions: Papules, pustules, ulcers, or verrucous growths.
Bone involvement: Painful lytic lesions, osteomyelitis.
What is the characteristic morphology of Blastomyces dermatitidis in its yeast form?
Yeast form exhibits broad-based budding with a double refractile cell wall.
Similar in size to a red blood cell (RBC).
What diagnostic methods are used for blastomycosis?
Urine antigen test.
Microscopy, culture, or histopathology (gold standard).
What is the treatment for mild to moderate blastomycosis?
Itraconazole or fluconazole.
What is the treatment for severe or disseminated blastomycosis?
Amphotericin B is the drug of choice.
Followed by Itraconazole.
What is Coccidioides immitis, and what disease does it cause?
Coccidioides immitis is a dimorphic fungus that causes coccidioidomycosis, also known as San Joaquin Valley fever.
Where is Coccidioides immitis geographically endemic?
Southwestern United States (e.g., California, Arizona)
Northern Mexico
Found in desert soils.
How is Coccidioides immitis transmitted?
Through inhalation of airborne arthroconidia (mold spores).
Spores become airborne when soil is disturbed (e.g., farming, construction, earthquakes, or dust storms).
What is the characteristic morphology of Coccidioides immitis in tissue samples?
Appears as large yeast-like spherules containing endospores.
These spherules are larger than red blood cells (RBCs).
Which patients are at risk for disseminated coccidioidomycosis?
Immunocompromised patients, such as those with HIV/AIDS or undergoing immunosuppressive therapy.
What are the common clinical features of coccidioidomycosis?
Acute pneumonia: Cough, fever, chest pain, and arthralgia.
Erythema nodosum: Painful red nodules on the lower extremities.
In some cases, hilar lymphadenopathy and lung nodules or cavities.
What are the manifestations of disseminated coccidioidomycosis?
Systemic symptoms: fever, night sweats, weight loss.
Skin lesions: Papules, pustules, ulcers, verrucous growths.
Osteolytic bone lesions.
CNS involvement, such as meningitis.
What imaging findings are associated with primary coccidioidomycosis?
Unilateral infiltrates.
Hilar lymphadenopathy.
Nodules or cavities (though imaging may be normal in some cases).
How does Coccidioides immitis exhibit dimorphism?
Grows as mold in cooler environments (25–30°C).
Converts to yeast at human body temperature (35–37°C).
How is coccidioidomycosis diagnosed?
Serology using IgM
Cultures
What are the treatments for coccidioidomycosis?
Mild to moderate disease: Itraconazole or fluconazole.
Severe or disseminated disease: Amphotericin B, followed by Itraconazole.
What is Paracoccidioides brasiliensis, and what disease does it cause?
Paracoccidioides brasiliensis is a dimorphic fungus that causes paracoccidioidomycosis, a systemic fungal infection.
Where is Paracoccidioides brasiliensis geographically endemic?
Central and South America, particularly in Brazil.
What is the characteristic morphology of Paracoccidioides brasiliensis in its yeast form?
Multipolar budding radiating from a central cell, resembling a captain’s wheel.
The yeast is larger than red blood cells (RBCs).
How is Paracoccidioides brasiliensis transmitted?
Through inhalation of mold spores.
What are the common clinical features of paracoccidioidomycosis?
Coughing and lymphadenopathy affecting cervical, axillary, and inguinal lymph nodes.
Granulomas in the lungs.
Mucosal ulcers in the upper respiratory tract.
Which organs are commonly affected in disseminated paracoccidioidomycosis?
Lungs, oral mucosa, and lymph nodes.
In severe cases, other organs may also be involved.
What are the treatments for paracoccidioidomycosis?
Mild to moderate disease: Azoles (e.g., itraconazole).
Severe disease: Amphotericin B.
What is Malassezia furfur, and what conditions does it cause?
Malassezia furfur is a fungus that is part of the normal skin flora.
Thrives in hot and humid conditions.
It causes pityriasis versicolor and seborrheic dermatitis.
How does Paracoccidioides brasiliensis exhibit dimorphism?
Grows as mold in cooler environments (25–30°C).
Converts to yeast at human body temperature (35–37°C).
How does Malassezia furfur appear on a KOH prep?
It has a characteristic “spaghetti and meatballs” appearance due to its yeast and hyphae forms.
What are the typical clinical features of pityriasis versicolor?
Hypopigmented or hyperpigmented macules or patches, often with fine scaling.
Commonly affects the back and chest.
Patches can merge into larger areas.
What environmental conditions favor the pathogenic form of Malassezia furfur?
Hot and humid conditions.
What layer of the skin does Malassezia furfur primarily infect?
The stratum corneum, the most superficial layer of the epidermis.
What systemic complication is associated with Malassezia furfur in neonates?
Malassezia fungemia, particularly in neonates receiving total parenteral nutrition (TPN) through central venous catheters.
What is the pathogenesis of the skin lesions in pityriasis versicolor?
Lipid degradation by the fungus produces acid, which damages melanocytes, leading to pigmentation changes (inhibiting tyrosinase).
How is pityriasis versicolor treated?
Topical selenium sulfide (e.g., Selsun Blue).
Promotes the shedding of the stratum corneum where the fungus resides.
Oral ketoconazole.
Terbinafine.
What can be used to determine the extent of the disease caused by Malassezia spp.?
Use of a Woods Lamp.
What are common clinical features of tinea capitis?
Scaly patches with alopecia (hair loss).
Often fluoresces under Wood’s lamp in cases caused by Microsporum.
Black dots with hair shaft.
How is Candida albicans tested in a laboratory?
Candida albicans can produce germ tubes when incubated in serum at 37°C.
What are the characteristics of Aspergillus spp.?
Catalase-positive fungi. Catalase allows them to neutralize reactive oxygen species, enhancing survival.
Aspergillus spp. is considered to be opportunistic.
Aspergillus spp. exhibit characteristic septate hyphae with acute branching angles, often around 45 degrees.
Bronchiectasis is associated with ________, which is a hypersensitivity reaction to Aspergillus
Allergic bronchopulmonary aspergillosis (ABPA)
Note: Bronchiectasis is the permanent dilation of airways.
What are the hallmark radiological features of invasive aspergillosis?
Nodular infiltrates with halo sign (ground-glass opacity)
Air crescent sign in later stages.
Gravity-dependent lesion that moves with changes in position.
What is Cryptococcus neoformans?
An opportunistic fungus that is urease-positive and heavily encapsulated.
What staining technique is used to visualize Cryptococcus neoformans?
India ink stain, revealing encapsulated cells with clear halos against a dark background.
This is largely replaced by the latex agglutination test or ELISA with CSF
What imaging finding is associated with Cryptococcal meningitis?
“Soap bubble” lesions in the brain’s gray matter on MRI.
What is used to diagnose pneumonia secondary to Cryptococcus?
Bronchoalveolar lavage samples can be prepared with mucicarmine (red) or methenamine (silver) stain for diagnosis of pulmonary
cryptococcosis.
Histologic appearance of Mucor and Rhizopus
Non-septate hyphae with wide-angle (90°) branching, often seen in tissue samples.
Clinical hallmark of rhinocerebral mucormycosis
Black eschar visible in the nasal cavity or on the palate/turbinates, indicative of necrosis.
