16 - Fungal respiratory disease

Summary

Introduction

This chapter describes the major fungal respiratory tract infections which are usually acquired in hospital or in individuals who are substantially immunocompromised.

Aspergillosis

Aspergillus moulds are highly ubiquitous, being found in soil, dust and water, often present in food stuffs, flowers and tobacco and commonly in decaying organic material. Therefore, the scene for human infection is easily set. Yet of the 300 or so species only approximately 20 are pathogenic to man of which Aspergillus fumigatus is the most frequently encountered. Aspergillus niger, Aspergillus flavus, and Aspergillus clavatus are seen less often. Appropriate settings of exposure, virulence factors and host response interact to produce several disease entities often distinctive but occasionally overlapping. This section will describe the pulmonary manifestations both in the normal host, namely, those due to colonisation phenomena, hypersensitivity reactions, chronic invasive pulmonary aspergillosis and in the immunocompromised host – acute invasive disease.

Microbiology

Aspergillus spp. grow well on organic substrates and best at 37 °C though they will grow at temperatures up to 45 °C. On laboratory media and in tissue fluffy powdery (Fig. 16.1) or velvety colonies of different colours are produced, which darken with sporulation. Mycelia are composed of the asexual reproductive conidiophores which bear conidia (Fig. 16.2). Specimens from the airways reflecting colonisation are characterised by the presence of these conidiophores. Hyphae are thick (not always uniformly) septate approximately 4 μ in diameter and branching at 45° angles.