Exam #4: Fungal Infections of the Respiratory Tract Flashcards Preview

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Flashcards in Exam #4: Fungal Infections of the Respiratory Tract Deck (60):

What is Zygomycosis (Mucromycosis)?

A class of diseases caused by infection of fungi belonging to the class, "Zygomycetes"
- Found in: soil, decaying vegetation, and food


What species of Zygomycetes cause Zygomycosis?

1) Rhizopus
2) Absidia
3) Mucor


What are the predisposing factors to zygomyces infection?

- Immunosuppression
- DM
- Burns

*Infection in a normal, healthy individual is rare


What are the characteristics of the zygomycetes?

- Non-septate hyphae
- Reproduce sexually to produce spores


Describe the common clinical presentation & pathogenesis of rhinocerebral zygomycosis.

- Primarily occurs in Diabetic patients
- Infection originates in sinuses, following inhalation of spores
- Spreads to neighboring tissues

Essentially, infection begins as a typical sinus infection but then progresses to facial/ periorbital edema, visual disturbances, altered mental status, coma, & death as the infection spread to tissues surrounding the sinuses.


Aside from the sinuses, where else can there be zygomycotic infections?

- Skin via traumatic inoculation
- GI (neonates & premature infants)


How is zygomycosis diagnosed? Morphologically what is the key feature that you're looking for?

- Observation of hyphal elements
- Culture confirmation

*Broad aseptate hyphae in blood vessels frequently branching at 90 degree angles*


How is zygomycosis treated?

Amphotericin B


What species of candidia causes most candidiasis infections?

C. albicans

Note that this is considered to be part of the normal flora


Candidia is dimorphic. Which form is present in the normal flora & which form is typically pathogenic?

Normal= yeast

Pathogenic= mold/ hyphae


What is Thrush? What are the symptoms/ presentation?

- Oral Candidiasis infection
- Diffuse erythema with white patches (cheesy) on the surface of the buccal mucosa, throat, tongue, & gums


What patient populations are susceptible to Thrush?

- Infants
- Adults undergoing treatment with: steroids, antineoplastic drugs, antibiotics
- AIDS patients


How is oral candidiasis diagnosed?

Direct observation of candidia in clinical material

*Note that culture is typically not necessary; candidia is part of the normal flora (yeast); therefore, it is difficult to distinguish between colonization & infection.


How is oral candidiasis treated?

Oral formulations of nystatin & azole compounds i.e. mouthwash or lozenges


What patient populations most frequently get an esophagitis?


*Extension of thrush/ oral candidiasis into the esophagus


What are systemic mycoses?

- Diverse group of fungal infections that initally infect the lungs & then lead to systemic infection
- All originate as an inhaled pathogen
- Occur in BOTH healthy and immunosuppressed individuals


What five fungi are considered "systemic mycoses?"

1) Histoplasma capsulatum
2) Blastomyces dermatitidis
3) Paracoccidioides brasiliensis
4) Coccidioides immits
5) Crytococcus neoformans


Which of the systemic mycoses are dimorphic? What forms are they in in the enviornment & in human?

1) Histoplasma capsulatum
2) Blastomyces dermatitidis
3) Paracoccidioides brasiliensis
4) Coccidioides immits

*Exist as MOLD in environment, & YEAST in human infection, which is opposite of candidia


What is cryptococcus neoformans?

Crytococcus neoformans is an encapsulated yeast


Where is histoplasma capsulatum geographically most prevalent?

- North & Central America
- In the U.S, specifically in the Mississippi & Ohio River Valley


What causes histoplasmosis?

Histoplasma capsulatum

Note that this disease is also known as "Darling's Disease, Cave Dweller's Disease, & Spelunker's Disease"


What form of histoplasma capsulatum is present in the environment? What causes infection?

- Mold that is commonly found in soil containing bird & bat droppings
- Infection is acquired by inhalation of micro or macroconidia

*95% of exposed individuals are asymptomatic


Describe the pathogenesis of histoplasmosis.

- Inhaled fungal spores are phagocytosed by pulmonary macrophages & convert into the YEAST form
- Organism survives and replicates within macrophages causing "pulmonary histoplasmosis."
- Progression from that state can be to chronic pulmonary histoplasmosis or disseminated histoplasmosis, both of which are more common in immunosuppressed individuals


What are the symptoms of pulmonary histoplasmosis?

Dry cough


How is pulmonary histoplasmosis treated?

- Most infections resolve without any intervention
- Calcification of pulmonary lesions due to cell mediated immunity & macrophage activation


What are the symptoms of disseminated histoplasmosis?

- Fever
- Night sweats
- Anorexia
- Weight loss
- Fatigue

+ Respiratory symptoms


How is histoplasmosis diagnosed?

1) Direct observation of organisms in tissues or clinical samples
2) Cultivation of organisms from clinical samples
3) Serological testing

*A combination of these approaches is commonly employed


How is histoplasmosis treated?

Amphotericin B

*AIDS patients and other immunosuppresssed individuals often require lifelong suppressive therapy to prevent relapse (with azoles)


What organism causes Blastomycosis

Blastomyces Dermatitidis


Where is Blastomyces Dermatitidis geographically most prevalent?

1) Ohio & Mississippi River Valley (like histoplasma capsulatum)
2) AND, to a lesser extend, the Arkansas River Basin


How is Blastomyces dermatitidis differentiated from Histoplasma?

Larger size & very thick cell wall present in Blastomyces


How does pulmonary blastomycosis present?

Like Histoplasmosis with a mild flu-like illness, as bacterial pneumoni, or as TB:
- Cough, BUT with frank sputum production
- Fever
- Fatigue


How does disseminated Blastomycosis present?

Ulcerative lesions of the skin, bone, and urogenital tract
- Skin lesions are ulcerative & disfiguring (painless)
- Bone necrosis & granuloma formation
- Prostate involvement


How is blastomycosis diagnosed?

Observation of distinct yeast form in sputum or biopsy


How is blastomycosis treated?

Amphotericin B is the gold standard

Note that Fluconazole & other azole compounds have shown promise in uncomplicated pulmonary disease


What organism causes Paracoccidioidomycosis?

Paracoccidioides barasiliensis


Where is paracoccidioides barasiliensis geographically most prevalent? Is it more common in men or women?

- Most prevalent in South America
- 90% of the disease occurs in men; appears estrogen may inhibit growth


How does paracoccidiodomycosis present?

- Most infections as asymptomatic
- Primary pulmonary infection is similar to histoplasmosis & blastomycosis
- Disseminated disease typically presents as chronic cutaneous & mucocutaneous ulcers


How is paracoccidiodomycosis diagnosed?

- Direct observation of morphology
- Large yeast covered with multiple buds
- Takes on a "ship's wheel" or "Mickey mouse ears" appearance


What is the most common systemic fungal infection seen in the US? Where is it most geographically prevalent?

- Coccidiodomycosis
- San Joaquin Valley

*Must be reported & typically
follows a drought-rain-drought cycle that results in large numbers of fungal elements in blowing dust


What are the distinguishing features of coccidiodomycosis?

Spherule, which is a multinucleated structure that undergoes several internal divisions to produce hundreds of single nucleated spores


What are the symptoms of coccidiodomycosis?

- Most infected individuals are asymptomatic
- Remainder develop flu-like symptoms
- A small number of those will later develop progressive chronic pulmonary disease with cavity formation


What is the presentation of disseminated coccidioiomycosis?

- Desert rheumatism, which is a triad of symptoms including: fever, skin nodules, & joint pain
- Coccidial meningitis (lesser of the two causes of fungal meningitis)


What is the leading cause of fungal meningitis?

Cryptococcus neoformans


How is crytococcus neoformans different from the other systemic fungi?

NOT Dimorphic; rather, it is an encapsulated yeast


Where is cryptococcus present?

Bird droppings (mostly pigeon)


How does fungal meningitis differ from bacterial meningitis?

Fungal= slow onset vs. bacterial fast onset


How is cryptococcus diagnosed?

India Ink


How is cryptococcus meningitis treated?

- Long term Amphotericin B & 5-Fluorcytosine (6-10 weeks)
- AIDS patients may require suppressive therapy


What is pneumocystis carinii pneumonia (PCP)?

The causative agent of a highly lethal form of pneumonia that develops in immunocompromised patients (AIDS)


Describe the pathogenesis of PCP.

- Single celled eukaryotic organism with simlarities to protozoa
- Exists in a cyst and trophozoites form
- Infection is initiated by inhalation of the cyst form


What is the clinical presentation of PCP?

- Dyspnea
- Nonproductive cough
- Fever


How is PCP diagnosed?

Identification of organisms in clinical material through specialized staining techniques


How is PCP treated?

Trimethoprim-sulfamethoxazole compounds that interfere with folate synthesis


What species of aspergillus are most commonly associated with disease?

A. fumigatus & A. flavus


Describe the pathogenesis of aspergillus.

- Aspergillus exists in the environment as a mold that releases conidia that are aerosolized
- Conidia are inhaled and infect existing lung lesions
- Hyphal growth in tissue causes disease pathology


What is an aspergilloma?

- Fungus ball that infections a pre-existing lung lesion


How do aspergillomas present on CXR?

Space-occupying lesions that move as the patient changes position


How is aspergillus diagnosed?

- Hyphae observed in clinical sample
- Appear as V-shaped branches at a 45 degree angle in blood vessels


How is aspergillosis treated?

- Newer classes of azoles
- Echinocandin
- Amphotericin B

*Surgical removal of aspergillomas is common

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