The Systemic Fungal Pathogens: Cryptococcus, Histoplasma, Blastomyces, Coccidioides, Paracoccidioides | Sherris Medical Microbiology, 7e | AccessBiomedical Science

INTRODUCTION

The fungi discussed in this chapter cause a variety of infections, each ranging in severity from subclinical to progressive, debilitating disease. Some of these species are dimorphic, growing in the infectious mold form in the environment but switching to a round, yeast-like form in infected tissues. They differ from the opportunistic fungi in their ability to cause disease in previously healthy persons. However, the most serious infections still occur in patients with compromised immune systems. With the exception of Cryptococcus neoformans, each of these fungi is restricted to geographic niches corresponding to the environmental habitats of the mold form of the species. None of these infections is transmitted from human to human. The major features of the systemic pathogens are summarized in Table 47–1.

TABLE 47–1^a^b^c^d^e^fFeatures of Systemic Fungal Pathogens

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TABLE 47–1 Features of Systemic Fungal Pathogens

GROWTH

ORGANISM

CULTURE AT 25°C

CULTURE AT 37°C

TISSUE

SOURCE

PRIMARYDISEASE

DISSEMINATED DISEASE

Cryptococcus neoformans, C gattii

Encapsulated yeast

Environment, worldwide

Pneumonia

Chronic meningitis

Histoplasma capsulatum

Mold, tuberculate macroconidia^a

Small yeast

Small intracellular yeast^b

Environment, US Midwest^d

Pneumonia, hilar adenopathy

RES enlargement

Blastomyces dermatitidis

Mold^a

Yeast

Environment, US Midwest^c

Pneumonia

Skin and bone lesions

Coccidioides immitis, C posadasii

Mold, arthroconidia

(Spherules)^e

Spherules

Environment, Sonoran desert^c,f

Valley fever

Pneumonia, meningitis, skin, and bone

Paracoccidioides brasiliensis

Mold

Yeast, multiple blastoconidia

Environment, Latin America

Pneumonia

Mucocutaneous, RES

RES, reticuloendothelial system (lymph nodes, liver, spleen, and bone marrow).

Micoconidia are formed but are not distinctive.

Typically multiple yeast within macrophages.

Ecologic “islands” are found throughout the Americas.

Ecologic islands are found worldwide.

It is difficult to grow the spherule phase in culture.

In the United States and includes parts of Arizona, California, Nevada, and western Texas.

CRYPTOCOCCUS

Overview

Cryptococci are yeasts distinguished by a surrounding capsule. The primary disease caused by cryptococci is a chronic meningitis. The clinical onset is slow, even insidious, with low-grade fever and headache progressing to altered mental state and seizures. In the cerebrospinal fluid (CSF) and in tissues, the inflammatory response is often remarkably muted. Most patients who develop this infection have some obvious form of immune compromise, although some show no demonstrable immune defect.

CRYPTOCOCCUS NEOFORMANS AND CRYPTOCOCCUS GATTII

Cryptococcus species were first isolated from environmental sources more than a century ago, and they are now recognized as important human pathogens, especially in the setting of HIV infection. The most important clinical manifestation of cryptococcal disease is a life-threatening meningitis in immunocompromised patients.

Found throughout the world, Cryptococcus species grow primarily as a budding yeast 4 to 6 μm in diameter. The most characteristic feature of these cells is a ...

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