Mycology IV- Dimorphic Systemic Fungal Pathogens

Question 1

1. Discuss the ecologic niches, geographic distribution and distinctive environmental and pathogenic tissue forms of Histoplasma

Answer 1

convert to budding yeast in host

found in moist, rich soil in temperate climates esp with guano of birds and bats, endemic of the Miss. and Ohio River valleys and other places world wide (the most common fugal infection in the world

large epidemics in endemic areas, small outbreaks linked to specific environmental exposure and sporadic individual cases

Question 2

1. Describe the routes of infection, clinical syndromes, diagnosis and treatment for Histoplasma.

Answer 2

long-term infection may be present, infection is very common, likely by microconidia, however in the general population, clinically significant or sever disease is relatively rare

contained by CD4+ mediated activation of macrophages achieving a fungistatic state (not fungicidal)

syndromes: pulmonary, disseminated (migratory macrophages), mucocutaneous, ocular
tx. amphotericin B (IV) effective and toxic or itraconazole IV (less severe disease)

Question 3

1. Discuss the ecologic niches, geographic distribution and distinctive environmental and pathogenic tissue forms of Blastomyces.

Answer 3

decaying vegetation or soil rich in organic matter with low pH near rivers

approximates the dist. of Hc and more WI, MN

hyphae in environment convert to budding yeast in host

Question 4

1. Describe the routes of infection, clinical syndromes, diagnosis and treatment for Blastomyces.

Answer 4

most common clinical presentation are chronic cutaneous and osseous disseminated disease

most common sites of dissemination: skin, bone and UG tract

less evidence in immunocompromised populations

tx. with amphotericin B or itraconazole

Question 5

1. Discuss the ecologic niches, geographic distribution and distinctive environmental and pathogenic tissue forms of Coccidioides.

Answer 5

septate hyphae with development of arthroconidia divided by vacillated cells in environment

converts to endosporulating spherule in the host (large spherules containing endospores

most virulent fungal pathogen (only few conidida) found in the soil rich in organic material, calcium sulfate and borates in hot, semiarid climates in N and S America particularly endemic in Southwest

Question 6

1. Describe the routes of infection, clinical syndromes, diagnosis and treatment for Coccidioides.

Answer 6

most outbreaks after soil disruption, primary infections (40%) are symptomatic

syndromes from mild flu-like to severe pneumonia with cough, fever, and chest pain, night sweats and joint pains

disseminated can occur and result in sever localized or systemic signs and symptoms, frequently fatal (meninges, bone and skin)

lower incidence than Histo., common among those with AIDs (25%, third most common)

tx. with amphotericin B, fluconazole and itraconazole can be quite recalcitrant to anti fungal therapy

Question 7

2. Name the primary site of infection for the three systemic fungal pathogens.

Answer 7

dimorphic
exist as molds in the environment
infection via respiratory route

Question 8

2. Name the site of dissemination shared and commonly displayed by all three fungi

Answer 8

dissemination to the skin or other sites, with dermatologic manifestations as a consequence

Question 9

3. Explain the phenomena of persistent, clinically inactive infection and reactivation disease for Histoplasma capsulatum.

Answer 9

most people in endemic areas are infected although they may show no active signs of infection

long-term infection may be present, infection is very common, likely by microconidia, however in the general population, clinically significant or sever disease is relatively rare

Question 10

4. Recall immunocompetent people may be infected by the systemic fungal pathogens, but immunocompromised people are more at risk for severe disease.

Answer 10

all three fungi can infect and cause disease in apparently immunocompetent individuals, however there is a greater incidence and severity of infection in immunocompromised individuals

Question 11

What is the methods for diagnosis of infection by systemic dimorphic fungal pathogens?

Answer 11

gold standard: laboratory culture (low sensitivity)

histopathological visualization together with clinical features and sometimes failure to respond to anti bacterial antibiotics

specific antigen detection method for acute disseminated histoplasmosis (esp. with AIDs) of urine or serum or CSF- high sensitivity and specificity

blastomycosis antigen test very high cross-reactivity with histo and other systemic infections

serological tests for all three available, antigen response not seen in acute or immunocompromised patients

skin testing only in histoplasmosis (converters for life- used as an epidemiological tool)