Opportunistic Mycoses & Mucormycosis

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Questions and Answers

Invasive aspergillosis can manifest in several forms. Which of the following is the MOST severe and rapidly progressive?

  • Aspergilloma formation within a pre-existing lung cavity.
  • Allergic bronchopulmonary aspergillosis (ABPA) in individuals with asthma.
  • Fungal sinusitis caused by Aspergillus species.
  • Acute invasive aspergillosis originating in the lungs with potential dissemination. (correct)

A patient presents with suspected rhinocerebral mucormycosis. Microscopic examination of a tissue sample is performed. Which finding would be MOST indicative of this infection?

  • Numerous conidia forming radiating chains.
  • Septate hyphae with V-shaped branching at 45-degree angles.
  • Small, encapsulated yeast cells.
  • Aseptate, broad hyphae with right-angle branching. (correct)

A patient with poorly controlled diabetes mellitus presents with signs of rhinocerebral mucormycosis. What is the INITIAL step in managing this life-threatening infection?

  • Initiating broad-spectrum antibiotics to cover any potential bacterial co-infection.
  • Immediately performing extensive surgical debridement of all affected tissues.
  • Administering high-dose amphotericin B while simultaneously addressing the underlying diabetic ketoacidosis. (correct)
  • Ordering a chest X-ray to rule out pulmonary involvement.

A researcher is investigating the pathogenesis of Pneumocystis jirovecii pneumonia (PCP). Which of the following mechanisms is MOST directly responsible for the impaired gas exchange observed in patients with PCP?

<p>The induction of alveolar inflammation by <em>P. jirovecii</em> cysts, resulting in exudate formation that blocks gas exchange. (A)</p> Signup and view all the answers

Cryptococcus neoformans is a significant opportunistic fungal pathogen. Which of the following characteristics is MOST crucial for its virulence and ability to cause disseminated disease?

<p>Its thick polysaccharide capsule that inhibits phagocytosis. (C)</p> Signup and view all the answers

A researcher is evaluating the efficacy of different diagnostic methods for cryptococcal meningitis. Which of the following tests offers the MOST rapid and specific identification of Cryptococcus neoformans in cerebrospinal fluid?

<p>PCR assay targeting <em>Cryptococcus neoformans</em> DNA in the CSF. (A)</p> Signup and view all the answers

Several opportunistic fungal infections are associated with specific patient populations and underlying conditions. Which of the following pairs is MOST strongly linked?

<p>Invasive aspergillosis and chronic granulomatous disease. (B)</p> Signup and view all the answers

Following a lung transplant, a patient develops a pulmonary infection. Bronchoscopy with bronchoalveolar lavage (BAL) is performed, and the sample is sent for analysis. Which of the following microscopic findings in the BAL fluid would be MOST suggestive of Pneumocystis jirovecii pneumonia (PCP)?

<p>Cysts that stain with silver stain, often appearing disc-shaped. (D)</p> Signup and view all the answers

A researcher is investigating the mechanism of action of various antifungal drugs. Which of the following BEST explains why ergosterol-targeting antifungal drugs are ineffective against Pneumocystis jirovecii?

<p><em>P. jirovecii</em> lacks ergosterol in its cell membrane, making it inherently resistant to these drugs. (C)</p> Signup and view all the answers

A patient with a history of tuberculosis presents with a cavitary lesion in the upper lobe of the lung. A chest X-ray reveals a radiodense mass within the cavity that shifts position with changes in patient orientation. Which of the following opportunistic fungal infections is the MOST likely cause?

<p>Aspergilloma (fungus ball). (B)</p> Signup and view all the answers

Flashcards

Mucormycosis

Caused by Mucor or Rhizopus, restricted to those with diabetes, burns, or leukemia. Spores invade blood vessels, especially in the brain.

Acute invasive aspergillosis

Most severe and often fatal form of aspergillosis, originating in the lungs and disseminating to other organs.

Aspergilloma (fungus ball)

A non-invasive lung infection caused by Aspergillus, forming a mass of hyphal tissue in pre-existing lung cavities.

Allergic bronchopulmonary aspergillosis (ABPA)

Hypersensitivity reaction to Aspergillus in the bronchi, leading to high IgE levels and eosinophilia.

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Cryptococcus neoformans

Oval budding yeast with a wide polysaccharide capsule, causing meningitis, especially in AIDS patients.

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Cryptococcosis

Fungal infection from inhaling Cryptococcus neoformans, often starting as a lung infection and disseminating to the brain.

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Pneumocystis jirovecii

Yeast-like fungus causing pneumonia, especially in HIV/AIDS patients; induces alveolar inflammation and dyspnea.

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Pneumocystis Pneumonia (PCP)

A pneumonia with fever, nonproductive cough, and dyspnea caused by Pneumocystis jirovecii. Chest X-ray shows a 'ground-glass' pattern.

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Pneumocystis jirovecii Pneumonia (PCP)

A fungus/yeast previously known as Pneumocystis carinii, major cause of pneumonia in AIDS patients. Transmitted via airborne droplets and not person to person.

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Cryptococcal Meningitis

Serious infection of the brain caused by Cryptococcus neoformans, an AIDS-defining condition. Diagnosed via India ink stain on spinal fluid.

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Study Notes

Opportunistic Mycoses

  • Fungi that infect immunocompromised individuals cause opportunistic mycoses.

Mucormycosis

  • Mucormycosis is most often caused by Rhizopus species, and less often by Apophysomyces and Rhizomucor species.
  • These species are saprophytic and non-dimorphic, possessing aseptate hyphae. They are transmitted via airborne asexual spores.
  • Spores are abundant in rotten fruit and old bread.

Risk Factors for Mucormycosis

  • Mucormycosis is primarily found in individuals with:
    • Diabetes, especially with ketoacidosis
    • Burn injuries
    • Bone marrow transplants
    • Leukemia

Pathogenesis and Clinical Symptoms of Mucormycosis

  • Rhinocerebral mucormycosis is a common and potentially fatal form, with death possible within a week.
  • Diabetic patients are particularly susceptible to rhinocerebral mucormycosis.
  • Mold spores germinate in the sinuses, forming hyphae and invade blood vessels that supply the brain.
  • The infection begins in the nasal mucosa or sinuses and can progress to the orbits, palate, and brain.
  • Diagnosis is often made post-mortem due to the aggressive nature of the disease.

Diagnosis and Treatment of Mucormycosis

  • Treatment involves high-dose amphotericin B, surgical removal of necrotic tissue, and correction of predisposing conditions.
  • CT scans of the head reveal involvement of the paranasal sinuses and periorbital soft tissue.
  • Periodic acid-Schiff (PAS) stain of periorbital tissue demonstrates typical irregular, broad hyphae with right-angle branching.
  • Staining of blood vessels shows rhizoids of Rhizopus species.

Aspergillosis

  • Aspergillosis is primarily caused by Aspergillus fumigatus, among several Aspergillus species.
  • Aspergillus species are filamentous molds and produce numerous conidia (spores).
  • They reside in dust, soil, and decomposing organic matter, also found in dust from construction work.

Pathogenesis and Clinical Symptoms of Aspergillosis

  • Aspergillus fumigatus can infect:
    • Sinuses
    • Eyes
    • Ears
    • Lungs

Forms of Aspergillosis

  • Fungal sinusitis is commonly caused by Aspergillus.
  • Acute invasive aspergillosis is a severe and often fatal form originating in the lungs, which can spread to the brain, gastrointestinal tract, and other organs.
  • Aspergilloma is a non-invasive lung infection where a mass of hyphal tissue forms in pre-existing lung cavities.
    • Seen on chest X-rays, shifting with patient movement.
  • Allergic bronchopulmonary aspergillosis (ABPA) is a hypersensitivity reaction to Aspergillus in the bronchi.

Diagnosis and Treatment of Aspergillosis

  • Definitive diagnosis is achieved through detection of hyphae in tissue and isolation of the organism via clinical samples.
  • Aspergillus hyphae are septate and form V-shaped branches at 45-degree angles.
  • Colonies show radiating chains of conidia.
  • ABPA patients will have elevated IgE levels specific for Aspergillus antigens and prominent eosinophilia.
  • Treatment includes amphotericin B and surgical removal of fungal masses or infected tissues.

Cryptococcus neoformans

  • The yeast Cryptococcus neoformans causes cryptococcal meningitis.
  • This is the most common life-threatening basidiomycete fungal disease worldwide. Cryptococcus neoformans is not dimorphic.
  • Cryptococcus neoformans is an oval budding yeast surrounded by a wide polysaccharide capsule.
  • It forms a narrow-based bud, unlike Blastomyces, which forms a broad-based bud.
  • This yeast is abundant in soil containing pigeon droppings.

Pathogenesis and Clinical Symptoms of Cryptococcus neoformans

  • Disease caused by Cryptococcus neoformans mainly occurs in patients with reduced cell-mediated immunity, especially those with AIDS.
  • HIV-related cryptococcosis is the second most common fungal infection after candidiasis.
  • Cryptococcal meningitis is an AIDS-defining condition.

Transmission of Cryptococcus neoformans

  • Human infection results from inhalation of the organism.
  • There is no human-to-human transmission.

Clinical Features of Cryptococcus neoformans

  • The most common form of cryptococcosis is a mild, subclinical lung infection.
  • In immunocompromised patients, infection often spreads to the brain, causing meningitis with fatal consequences.

Diagnosis of Cryptococcus neoformans

  • In spinal fluid mixed with India ink, the yeast cell is seen microscopically surrounded by a wide unstained capsule.
  • Mucicarmine stain can be used for Cryptococcus neoformans in lung tissue.
  • Useful stains include periodic acid-Schiff (PAS) stain and methenamine silver stain.

Treatment of Cryptococcus neoformans

  • Antifungal drugs used include amphotericin B and flucytosine.
  • The treatment regimen depends on the stage of the disease, site of infection, and the patient’s immune status.

Pneumocystis jirovecii

  • Pneumocystis jirovecii pneumonia is caused by a yeast-like fungus.
  • It was previously called Pneumocystis carinii.
  • It is classified as a yeast based on molecular analysis, but shares protozoan characteristics.
  • This is one of the most common opportunistic diseases in individuals infected with HIV.

Transmission of Pneumocystis jirovecii

  • This fungus is ubiquitous in nature.
  • It is acquired via inhalation of airborne organisms into the lungs.
  • There is no person-to-person transmission.
  • Disease in immunodeficient patients results from reactivation of pre-existing dormant cells in the lungs.
  • Infections are mostly asymptomatic in immunocompetent individuals.

Pathogenesis of Pneumocystis jirovecii

  • The ascus forms of Pneumocystis jirovecii induce alveolar inflammation.
  • This leads to the production of an exudate that blocks gas exchange, causing dyspnea.

Clinical Symptoms of Pneumocystis jirovecii

  • Pneumocystis pneumonia (PCP) includes:
    • Fever
    • Nonproductive cough
    • Dyspnea
  • Untreated, mortality is approximately 100%.

Diagnosis of Pneumocystis jirovecii

  • Diagnosis is based on microscopic examination of lung tissue biopsy or washings.
  • Bilateral rales are heard on auscultation.
  • Chest X-ray shows a ground-glass pattern.

Treatment of Pneumocystis jirovecii

  • Most effective therapy is sulfamethoxazole and trimethoprim.
  • This can also be used for prophylaxis.
  • Other antifungal drugs are ineffective due to the absence of ergosterol in the cell wall.

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