Oppurtunistic infection Flashcards
What is the definitive host for Toxoplasma gondii?
Cats
Sexual rep. occurs in cats
What are the main ways humans are infected with Toxoplasma gondii?
Ingestion of oocysts (from cat feces)
ingestion of tissue cysts (from undercooked meat)
congenital infection.
What are the three most serious clinical manifestations of toxoplasmosis?
Ocular toxoplasmosis, encephalitis, congenital toxoplasmosis.
How is toxoplasmosis diagnosed?
Definitive diagnosis through demonstration of the organism in histological section or PCR. Serologic tests (IgG and IgM) can also be used. In pregnancy, TORCHES testing may be performed.
What is the treatment for toxoplasmosis?
Pyrimethamine and sulfadiazine are the drugs of choice.
What are the main virulence factors of Candida albicans?
Surface adhesins
acid proteases
phospholipases
phenotypic switching (ability to switch between yeast and hyphal forms).
Name three common clinical manifestations of Candida albicans infection.
Cutaneous candidiasis (including intertrigo and paronychia), oropharyngeal candidiasis (thrush), vulvovaginal candidiasis.
How is Candida albicans diagnosed?
KOH prep of mucocutaneous lesions to reveal yeast, pseudohyphae, or hyphae. Blood cultures (for candidemia), germ tube test, carbohydrate assimilation tests, PCR, API 20C, CHROMagar tests, or (1,3)-β-D-glucan assay.
What is the most common species of Aspergillus causing infections?
Aspergillus fumigatus
Name four major pulmonary syndromes caused by Aspergillus
Allergic bronchopulmonary aspergillosis (ABPA)
chronic necrotizing pulmonary aspergillosis (CNPA)
aspergilloma
invasive aspergillosis.
How is invasive aspergillosis typically diagnosed?
Clinical specimens (sputum, bronchial wash, lung biopsy)
culture
galactomannan test
microscopy (KOH prep, silver stain).
What type of organism is Pneumocystis jiroveci?
Fungus (originally misclassified as a protozoan).
Seen primarily in immunocompromised individuals, especially those with HIV infection.
How is Pneumocystis jiroveci pneumonia dx’d?
Histopathological examination of lung tissue (Giemsa or GMS stain) showing foamy eosinophilic material containing masses of organisms.
Describe the pathogenesis of M. tuberculosis infection
Inhalation of aerosolized droplets containing M. tuberculosis.
Phagocytosis by alveolar macrophages
Prevention of phagolysosome fusion
escape into cytosol
Immune response leads to granuloma formation.
What are the main diagnostic methods for M. tuberculosis?
Acid-fast stain of sputum
culture (Lowenstein-Jensen agar),
nucleic acid amplification tests (NAATs)
Mantoux tuberculin skin test (TST),
interferon-gamma release assay (IGRA).
What is the most common non-tuberculous mycobacteria species?
Mycobacterium avium complex (MAC)
Disease presentation: Pulmonary disease (resembling TB), lymphadenitis, skin and soft tissue infections, disseminated disease.
Describe the clinical presentation of allergic bronchopulmonary aspergillosis (ABPA)
Asthma, recurrent pulmonary infiltrates, fever, cough,
production of mucus plugs (bronchial casts)
elevated IgE levels
What is the characteristic histological appearance of Pneumocystis jiroveci pneumonia?
Foamy eosinophilic material containing masses of the organism, alveolar macrophages, epithelial cells, neutrophils, and surfactant. Best visualized with Giemsa or Gomori’s methenamine silver (GMS) stain.
What is the treatment for Pneumocystis jiroveci pneumonia (PCP)?
Trimethoprim-sulfamethoxazole (TMP-SMX)
What is a Ghon complex?
The primary lesion of tuberculosis, consisting of the initial parenchymal infection (Ghon focus) and associated hilar lymph node involvement.
What is the Lady Windermere syndrome?
Suppression of the cough reflex in elderly women, increasing susceptibility to Mycobacterium avium complex (MAC) lung infections.
What antifungal drug classes are commonly used to treat invasive aspergillosis?
Echinocandins (e.g., caspofungin), triazoles (e.g., voriconazole, itraconazole), amphotericin B (often as a liposomal formulation).
How does Mycobacterium tuberculosis evade the host immune system?
M. tuberculosis prevents phagolysosome fusion, preventing destruction within macrophages.
It also utilizes various virulence factors, such as LAM and cord factor, to inhibit immune responses and promote intracellular survival. It can establish a latent state within granulomas.
Eplain the role of granulomas in M. tuberculosis infection
Granulomas are a hallmark of M. tuberculosis infection.
They create a niche for bacterial persistence during latent infection, leading to reactivation later on.
Caseous necrosis within the granuloma indicates severe tissue damage and active infection.
What is the purpose of the germ tube test?
From oppurtunistic infection lecture
To rapidly identify Candida albicans. A positive test shows the formation of germ tubes (elongated hyphal structures) when yeast cells are incubated in serum.
Compare the sensitivity and specificity of the TST (tuberculin skin test) and IGRA (interferon-gamma release assay) for tuberculosis.
TST: High sensitivity, but lower specificity (can yield false positives due to BCG vaccination or prior exposure to environmental mycobacteria).
IGRA: Higher specificity, but potentially lower sensitivity than TST, particularly in recently infected individuals or those with weak immune responses.
What is the galactomannan test used for?
Detection of Aspergillus antigens in serum or bronchoalveolar lavage fluid.
Useful in diagnosing invasive aspergillosis especially in immunocompromised patients where culture may be negative.
What are the potential complications of untreated or inadequately treated Candida albicans infections?
Dissemination (candidemia), endocarditis, meningitis, other organ system involvement, potentially fatal outcomes.
What is the significance of detecting “peripheral fringe” in a Candida albicans culture?
Suggests the presence of pseudohyphae, indicating the potential for more invasive disease.
Describe Extrapulmonary Tuberculosis
TB infection outside the lungs, commonly affecting:
lymph nodes (scrofula)
bones (Pott’s disease)
meninges (tuberculous meningitis),
genitourinary tract, and other organs. Often associated with disseminated TB.
What is the significance of a positive galactomannan test in a patient with suspected aspergillosis who is also HIV-positive?
While a positive galactomannan test suggests invasive aspergillosis, interpretation in immunocompromised patients, such as those with HIV, requires caution. The test can show false positives.
Corroboration with other diagnostic modalities like imaging and microscopy is crucial.
What are some unusual presentations of candidiasis?
Endocarditis, osteomyelitis, peritonitis, and disseminated candidiasis (candidemia) are less frequent but severe forms.
Chronic mucocutaneous candidiasis (CMC) is a rare condition characterized by persistent and recurrent infections of the skin, hair, nails, and mucous membranes.
What are some of the challenges associated with diagnosing and treating NTM infections?
Slower growth rates compared to M. tuberculosis, leading to longer turnaround time for cultures.
Wide range of species with varied susceptibility profiles, necessitating species-specific treatment.
Overlapping clinical presentations with other respiratory illnesses.
Ring lesions associated with Toxoplasmic encephalitis
Congenital toxoplasmosis
Pneumocystis jiroveci
Cup shaped cysts from bronchiolar lavage
Mycobacteria tuberculosis: General Characteristics
Acid fast aerobic rods
Allergic Bronchopulmonary Aspergillosis (ABPA)
Chronic Necrotizing Pulmonary Aspergillosis (CNPA)
Aspergilloma “Fungus Ball”
Invasive Aspergillus
-Typically acquired in those with profound neutropenia or immunocompromised
-Tx w/ IV voriconazole or Amphoterricin B
Aspergillus “fungus balls” = Aspergilloma
Which diagnostic method is most commonly used to confirm a suspected case of Pneumocystis jirovecii pneumonia?
Bronchoalveolar lavage (BAL) w/ silver staining
A 35-year-old woman with HIV and a CD4 count of less than 100 cell/mm3 (normal is 500-1200 cells/mm3) complains of difficulty and pain with swallowing. A white patch on the buccal cavity is scraped and a KOH prep is performed. Which of the following would the prep most likely reveal?
E. Budding yeast and pseudohyphae
A 60-year-old female is beginning to have issues with headaches and remembering simple things. She is an animal lover and has many pets. A CT scan is performed of her head to rule out tumors. Multiple ring-shaped anomalies are identified in the scan. What infectious agent is most likely the cause of this woman’s illness?
Toxoplasma gondii
Pneumocystis jiroveci
A 53-year-old female is under immune ablation therapy for a stem cell transplant, and she is severely immune-suppressed. A cough she has is getting progressively worse and now sputum has become bloody. The antibiotic therapy she began at the start of the cough is not helping. She is hospitalized and a biopsy of the lung is taken and stained for analysis. Septate hyphae with sub-acute branching are identified. Which of the following is most likely the cause of this woman’s illness?
E. Aspergillus fumigatus
A. First semester (although less likely)
C. Aerosolized droplets from humans (Pneumocystis jiroveci)
B. 10%
A. It is an obligate intracellular aerobe that can be inhibited by the hypoxic environment in granulomas
What do macrophages secrete to recruite neutrophils?
IL-12 (induces secretion of IFN-gamma in NK and T cells initiating cascade to recruit)
and TNFalpha (unregulated adhesins on endothelial wall)
B. Aspergillus fumigatus
Galactomannan - tests specifically for Aspergillus (but is not very sensitive ~50-80%)
