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Fig. 6.33 A-C. Hypersensitive pulmonary aspergillosis. A The chest radiograph of a teenage. Indian girl with chronic asthma. There are mucoid plugs in the right upper lobe with elongated, cigar-shaped densities. There is some air trapping within them, which must be distinguished from cavitation. These shadows were migratory and transient: chest radiographs taken at other times showed similar branching mucous plugs in other lobes. The lungs are hyperinflated because of asthma. B Another patient with chronic asthma, mucous plugs, and the constantly changing linear and round densities. C Standard tomography (8 cm) of the same patient. (B and C courtesy of Dr. Glenn Lillington)

 

 

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Aspergillosis

The history of aspergillosis is fascinating, the nomenclature is confusing, and the term "aspergillosis" has been said to "describe so many different clinical entities, that, without qualification, the term is almost meaningless" (Kwon-Chung and Bennett, 1992).

Aspergillus candidus was first isolated in 1842 from a bullfinch. Aspergillus spp. were then described in various avian species, including a great bustard. Human infection was reported by Virchow in 1856. Since then there have been an increasing number of infections by the various Aspergilli, matched by variations in the names given to them. It was not until 1938 that a pulmonary aspergilloma (fungus ball) was described, and the invasive form was only recognized in the 1950s. Worldwide, the number of invasive infections has increased and continues to grow considerably, helped by the number of patients who are immunodeficient as a result of leukemia, organ transplantation, or corticosteroids; patients with AIDS do not often suffer from aspergillosis.

Synonyms

Ger: Pulmonary aspergillosis = Schimmelpilzerkrankung. Fr: Aspergillose (pseudotuberculose aspergillaire). Sp: Aspergillosis.

Definition

Aspergillosis describes a disease complex caused by any species of the genus Aspergillus, the commonest being A. fumigatus. This, and A. oryzae, are the pathogenic species most frequently seen in tropical and subtropical regions.

Geographic Distribution

The organism occurs worldwide, with variation only in the prevalence of different species. In Sudan, for example, the most frequently found is A. flavus. Elsewhere, A. niger causes ear infections and aspergillomas. Sometimes more than one species is found in the same infection (a mixed colony infection). There are many variations on this theme.

Epidemiology and Pathology

There are over 200 species of Aspergillus. They are ubiquitous, being found everywhere in the environment. They are most common where there is decaying vegetation, such as compost, hay stacks, and, in some countries, moldy grains. They are found in the soil and in many liquids, and have even been isolated from acids and formalin. They have been identified in roofing material, leather, timber, and food products with high concentrations of salt or sugar (salted meat, jams, and jellies). They frequently cause contamination in laboratory cultures.

The histopathological findings in aspergillosis show that any organ or site can be infected. The fungus may cause:

A) Invasive aspergillosis:
Inflammatory granulomas, infarction, edema, and necrotizing lesions of the lungs and other sites, such as
the paranasal sinuses Systemic (and often fatal) disseminated fungemia and infarctions, with tissue
invasion.

B) Saprophytic aspergillosis:
Massive colonies, aspergillomas (fungal balls of entangled mycelial filaments) in preformed cavities (such as
those of tuberculosis or any other etiology).

C) Allergic aspergillosis:
Allergy to the fungus anywhere in the body, particularly in the bronchi, with toxic effects.

The underlying tissue reaction is polymorphic, with macrophages and giant cells containing the separate mycelial filaments. Invasive aspergillosis in any organ is characterized by invasion of vessels, causing septic infarction with necrosis and abscess formation. Within preexisting pulmonary cavities, colonies of Aspergillus grow, regardless of the etiology of the cavity, as long as it is dark, moist, aerated, and at least partially sequestered from the body's immune reactions.

There is little systemic reaction to the fungus, other than a moderate eosinophilia, unless there is a specific allergy. Patients with allergic reactions to Aspergillus spp. have elevated IgE antibodies but no IgG precipitins, as compared with invasive infections when there are specific antibodies.

The diagnosis of aspergillosis is confirmed by identifying the characteristic branched, septate hyphae and spores in sputum or tissue sections. Culture permits further identification, but the fungus is so ubiquitous that its growth does not necessarily mean that it is responsible for the illness: tissue invasion must be shown. Serological studies help to confirm the diagnosis of intracavitary aspergilloma and allergic bronchopulmonary aspergillosis but these, too, need clinical correlation. The fungi are more often saprophytic than parasitic.

 

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