Opportunistic Mycoses: Mucormycosis & Aspergillosis

• Opportunistic mycoses target individuals with weakened immune systems.

Mucormycosis

• Primarily caused by Mucor and Rhizopus species, and sometimes by Apophysomyces and Rhizomucor species.
• These species are saprophytic, non-dimorphic, and possess aseptate hyphae.
• Risk factors include diabetes (especially ketoacidosis), burn injuries, bone marrow transplants, and leukemia.
• Rhinocerebral mucormycosis is a rapidly fatal form common in diabetic patients, where mold spores invade blood vessels supplying the brain.
• Infection starts in the nasal mucosa or sinuses, then progresses to the orbits, palate, and brain.
• Treatment involves high-dose amphotericin B, surgical removal of necrotic tissue, and correction of predisposing conditions.

Aspergillosis

• Primarily caused by Aspergillus fumigatus, among other Aspergillus species.
• Aspergillus species are filamentous molds, not dimorphic, and produce conidiospores.
• Can cause infections of the skin, sinuses, eyes, and ears, as well as fungus balls in the lungs and allergic bronchopulmonary aspergillosis.
• Fungal sinusitis is commonly caused by Aspergillus.
• Acute invasive aspergillosis is a severe form originating in the lungs, potentially disseminating to the brain and gastrointestinal tract.
• Aspergilloma is a non-invasive lung infection forming a mass of hyphal tissue in pre-existing lung cavities, visible on chest X-rays.
• Allergic bronchopulmonary aspergillosis (ABPA) is a hypersensitivity reaction to Aspergillus in the bronchi.
• Diagnosis involves detecting hyphae in tissue and isolating the organism from clinical samples.
• Aspergillus hyphae are septate and branch at 45-degree angles.
• Colonies display radiating chains of conidia.
• ABPA patients show elevated IgE levels specific for Aspergillus antigens and eosinophilia.
• Treatment involves amphotericin B and surgical removal of fungal masses.
• Transmission occurs via airborne asexual sporangiospores.
• These organisms are found in dust, soil, and decomposing organic matter.
• Hospital outbreaks can be linked to dust from construction work.
• Risk factors include immunocompromised and neutropenic states.
• CT scans can reveal involvement of the paranasal sinuses and periorbital soft tissue.
• Staining (PAS) shows irregular, broad hyphae with right-angle branching.
• Rhizopus species' rhizoids are visible on blood vessel staining.

Cryptococcosis

• Cryptococcus neoformans, a yeast, causes cryptococcal meningitis.
• It is the most common life-threatening basidiomycete fungal disease worldwide.
• Not dimorphic, it is an oval budding yeast with a wide polysaccharide capsule.
• Forms a narrow-based bud.
• It is abundant in soil with bird droppings, especially pigeon droppings.
• Disease primarily affects 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.
• Human infection results from inhalation.
• No human-to-human transmission occurs.
• The most common form is a mild, subclinical lung infection.
• In immunocompromised patients, it often disseminates to the brain, causing cryptococcal meningitis.
• It can cause immune reconstitution inflammatory syndrome (IRIS) upon antiretroviral therapy due to increased CD4 count.
• Diagnosis involves microscopic examination of spinal fluid mixed with India ink to visualize the capsule.
• Mucicarmine, Periodic acid-Schiff (PAS), and Methenamine silver stains are useful in lung tissue.
• Treatment involves antifungal drugs such as amphotericin B and flucytosine.
• Treatment depends on the disease stage, infection site, and patient's immune status.

Pneumocystis Pneumonia (PCP)

• Pneumocystis jirovecii causes pneumonia and is a disc-shaped yeast-like fungus.
• Previously known as Pneumocystis carinii.
• Classified as a yeast based on molecular analysis, but has protozoan characteristics.
• Acquired by inhalation, it is ubiquitous in nature.
• Not transmitted person to person.
• Disease in immunodeficient patients results from reactivation of dormant cells in the lungs.
• Most immunocompetent individuals have asymptomatic infections.
• Encysted forms induce alveolar inflammation, leading to exudate production that blocks gas exchange.
• Symptoms includes fever, nonproductive cough, and dyspnea.
• If untreated, mortality approaches 100%.
• Diagnosis is based on microscopic examination of cysts in lung tissue.
• Elevated lactic acid dehydrogenase (LDH) levels (>220 U/L) are common in PCP patients.
• Infection is generally confined to the lungs.
• Chest X-ray shows a patchy or ground-glass appearance, sparing the lower lobes.
• Bilateral rales are heard on auscultation.
• Trimethoprim-sulfamethoxazole is the first-line treatment and prophylaxis, as ergosterol is absent in the cell wall, other antifungals are ineffective.
• One of the most common opportunistic diseases in individuals infected with HIV.
• The most common AIDS-defining opportunistic infection.