Animal Models of Aspergillosis

Abstract

Aspergillosis is an airborne fungal disease caused by Aspergillus spp., a group of ubiquitous molds. This disease causes high morbidity and mortality in both humans and animals. The growing importance of this infection over recent decades has created a need for practical and reproducible models of aspergillosis. The use of laboratory animals provides a platform to understand fungal virulence and pathophysiology, assess diagnostic tools, and evaluate new antifungal drugs. In this review, we describe the fungus, various Aspergillus-related diseases in humans and animals and various experimental animal models. Overall, we highlight the advantages and limitations of the animal models, the experimental variables that can affect the course of the disease and the reproducibility of infection, and the critical need for standardization of the species, immunosuppressive drugs, route of infection, and diagnostic criteria to use.

Figure 1.

Selected articles addressing important topics regarding animal models of aspergillosis

Figure 2.

General protocol for Aspergillus experimental infection in animal models.^, This flowchart indicates the estimated timing for major events, based on a model involving neutropenic rats challenged by intratracheal nebulization of A. fumigatus conidia. The duration of a protocol depends on the experimental design but lasts 15 to 30 d on average. In most invasive models, immunosuppression is needed to make the animals susceptible to experimental infection. Unique or repeated administration of alkylating drugs or steroids has been mostly described in the published literature. The regimen starts a few days to 2 wk before the Aspergillus challenge. Animals are then inoculated with Aspergillus conidia (day 0). Several routes of infection have been reported, including intravenous injection, nebulization, and intranasal or intratracheal deposition. Generally, the onset of clinical signs occurs 48 to 72 h after experimental inoculation (days 2 to 3). After that time, the animals become moribund from aspergillosis. At the end of protocol, surviving animals and controls are euthanized and examined through necropsy, histopathology, and mycologic culture, among other methods.

Figure 3.

Examples of different routes for experimental infection. (A) Hermetically sealed inhalational chamber in which the Aspergillus spp. spore suspension is nebulized. Contact of the animals (here, rats) with the spore ‘cloud’ must be prolonged, and the amount of inoculum is variable. (B) Intranasal deposition of Aspergillus spp. conidia suspension into mouse nares. (C) Instillation of the Aspergillus spp. spore suspension directly into the rat trachea by using a tuberculin syringe. This protocol requires that animals are anesthetized and tracheotomized. (D) Instillation of Aspergillus spp. spore suspension directly into the trachea by using the Microsprayer Aerosolizer (PennCentury) device. The Microsprayer Aerosolizer is composed of a metal elbow with a screw-on syringe adaptor; the device sprays a liquid solute in fine droplets due to a prism placed at its end. The anesthetized animal is positioned on a work stand, which is then tilted at 45° to allow for intubation. An otoscope is used as a laryngoscope. Spores are deposited directly at the bottom of the trachea, without surgery, because the device has the same curvature as the airways of the animal. Reprinted with permission from Guillaume Desoubeaux and Centre d'Etude des Pathologies Respiratoires, Tours, France.