RHS21 - Respiratory Tract Infections 8 Flashcards
List the primary and opportunistic fungal pathogens we need to know that cause RTIs
- Primary
- Histoplasma capsulatum
- Blastomyces dermatidis
- Coccidioides immitis
- Opportunistic
- Cryptococcus neoformans
- Aspergillus spp
- Pneumocystis jiroveci
What are the shared features amongst the primary fungal pathogens?
- Acquired via inhalation of spores in the environment
- Each fugus is endemic to a specific area
- H. capsulatum and B. dermatitidis are usually found in the mississippi river and ohio river valleys
- C. immitis is usually found in the western united states
- All are dimorphic
- in the environment as moulds that release spores
- Once they hit the warm LRTI they switch to a yeast form
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What are the clinical features commonly seen in fungal pneumonias?
- Asymptomatic with very gradual onset of Sx
- Association with an endemic region
- Mild fever and dry cough
- Progressive dyspnea
- Weight loss
What lab diagnostics are usually used to diagnose fungal RTIs?
- Acid-Fast Bacilli (AFB) test to rule out TB
- Direct microscopy of sputum, lavage, or aspirate since fungi are big enough to see without stains
- Can be grown on sabouraud’s agar but it takes weeks
- Hypersensitivity skin tests can be done as well
Where do Histoplasmosis outbreaks usually occur and why?
- Areas where birds or bats roost and areas where buildings are undergoing demoltion/reconstruction
This is because reservoir for histoplasma capsulatum is soil with high nitrogen content (from bird/bat droppings)
What are the clinical features seen with histoplasmosis?
It depends upon the level of exposure and the immunological status of the person.
- Low intensity exposure is almost always asymptomatic
- High intensity exposure in a healthy individual could lead to mild fever, dry cough, and chest pain
- High intensity exposure in an immunocompromised individual could lead to the above and other organ involvement (dissemination)
Describe the histological appearance of histoplasmosis
Non encapsulated, thick walled and budding yeasts in alveolar macrophages
Facts to know about blastomyces dermatitidis
- Infection is called Blastomycosis
- Similar to that of histoplasmosis except:
- Clinical presentation typically invovles a skin lesion (see image left) in addition to pulmonary symptoms
- On histology the yeast appears with a single broad base bud (see image right) instead of the narrower bud seen with histoplasmosis (see image middle)
Facts to know about coccidioides immitis
- Infection is called coccidioidomycosis, aka - Valley Fever
- Endemic to western America, particularly the deserts
- On fluorescent stain, it appears as a spherule (small sphere) with spores inside (see image)
- Most virulent of mycotic pathogens because it only takes inhalation of a few spores to develop coccidioidomycosis which is asymptomatic 60% of the time and presents with flu-like symptoms 40% of the time
What are the shared characteristics amongst the opportunistic fungal pathogens?
- Usually seen in immunocompromised patients
- Usually monomorphic
What are the primary opportunistic fungal pathogen infections seen in these conditions:
- Organ transplant
- HIV/AIDS
- Neutropenia
- Organ Transplant and HIV/ADIS - pneumocystis or C. neoformans
- Neutropenia - aspergillus spp.
What is a Cryptococcus neoformans infection called? Describe the morphological features of C. neoformans
Cryptococcosis
It is an encapsulated, narrow base budding yeast (refer to image)
Describe where C. neoformans is usually found and how it is usually transmitted.
Usually found in soil enriched with bird droppings
Transmission is via inhalation of the yeasts
List the virulence factors of C. neoformans
- A GXM capsule that is produced upon inhalation. It helps avoid phagocytosis and it down regulates the immune response
Describe the morphology of aspergillus spp.
There is a septal hyphae with a conidiophore coming off at an acute angle and conidia being released from the tip of the conidiophore (see image)
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