Detection of invasive aspergillosis

Abstract

Invasive aspergillosis (IA) caused by the fungus Aspergillus fumigatus is a frequent and life-threatening complication of chemotherapy and bone marrow transplantation with high rates of mortality and morbidity. Diagnosis of IA is complex and can only be confirmed by identification of the fungus in biopsy samples. Capturing tissue for diagnosis is in itself hazardous, and because of this many patients receive empirical antifungal treatment rather than undergo biopsy. However, the treatment carries with it significant side effects and is prohibitively expensive. Because of this, attempts have been made to develop specific and sensitive diagnostic tests that can be used to track the early onset of infection and permit rational administration of antifungal drugs. Early attempts at nonculture-based diagnosis using human immune serum to detect circulating Aspergillus antigens proved unreliable, and so focus turned to hybridoma technology and the use of monoclonal antibodies (MAbs) to detect signature molecules of infection. Detection of one such signature molecule, galactomannan (and associated galactomannoprotein molecules), forms the basis of the commercial Platelia enzyme immunoassay (EIA), an assay that has found widespread use in IA diagnosis. Nevertheless, concerns surrounding its accuracy mean that alternative strategies to diagnosis have been sought including detection of the fungal cell wall component (1-->3)-beta-d-glucan and polymerase chain reaction (PCR). The poor specificity of "panfungal" (1-->3)-beta-d-glucan tests and current lack of standardization of PCR assays have led to the recent development of next-generation MAb-based assays that detect surrogate markers of infection and that have been incorporated into "point-of-care" diagnostic devices. This chapter examines the development of antibody-antigen, (1-->3)-beta-d-glucan, and nucleic acid-based approaches to IA detection, current concerns surrounding accurate disease diagnosis, and how animal models of infection can be used to inform assay development and validation.