Model of recurrent pulmonary aspergillosis in rats

Inhaled Antifungal Agents for Treatment and Prophylaxis of Bronchopulmonary Invasive Mold Infections

Pulmonary mold infections are life-threatening diseases with high morbi-mortalities. Treatment is based on systemic antifungal agents belonging to the families of polyenes (amphotericin B) and triazoles. Despite this treatment, mortality remains high and the doses of systemic antifungals cannot be increased as they often lead to toxicity. The pulmonary aerosolization of antifungal agents can theoretically increase their concentration at the infectious site, which could improve their efficacy while limiting their systemic exposure and toxicity. However, clinical experience is poor and thus inhaled agent utilization remains unclear in term of indications, drugs, and devices. This comprehensive literature review aims to describe the pharmacokinetic behavior and the efficacy of inhaled antifungal drugs as prophylaxes and curative treatments both in animal models and humans.

Tissue Distribution and Penetration of Isavuconazole at the Site of Infection in Experimental Invasive Aspergillosis in Mice with Underlying Chronic Granulomatous Disease

Isavuconazole, the active moiety of the prodrug isavuconazonium sulfate, has potent activity against a wide spectrum of fungal pathogens and is approved for the treatment of invasive aspergillosis, yet little is known about the tissue penetration of isavuconazole at the target sites of infection. Here, we explored the spatial and quantitative distribution of isavuconazole in tissue lesions in experimental pulmonary aspergillosis established in mice with chronic granulomatous disease (CGD) (gp91^phox-). Matrix-assisted laser desorption ionization mass spectrometry imaging (MALDI-MSI) and laser capture microdissection (LCM)-directed high-pressure liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS) were used to analyze infected lungs and brain tissues collected 1, 3, 6, and 24 h after a single oral administration of the prodrug at a dose of 256 mg/kg of body weight (corresponding to 122.9 mg/kg of isavuconazole). Drug enrichment within granulomatous lesions was observed in lung tissue at 1 h postdose, although drug levels quickly equilibrated afterwards between lesion and nonlesion areas. A prominent antifungal effect in the infected lung tissue was revealed by histopathological analysis. Isavuconazole also penetrated into the brain with high efficiency. These data further support the value of isavuconazole to treat patients with invasive aspergillosis.

Nutritional Heterogeneity Among Aspergillus fumigatus Strains Has Consequences for Virulence in a Strain- and Host-Dependent Manner

Acquisition and subsequent metabolism of different carbon and nitrogen sources have been shown to play an important role in virulence attributes of the fungal pathogen Aspergillus fumigatus, such as the secretion of host tissue-damaging proteases and fungal cell wall integrity. We examined the relationship between the metabolic processes of carbon catabolite repression (CCR), nitrogen catabolite repression (NCR) and virulence in a variety of A. fumigatus clinical isolates. A considerable amount of heterogeneity with respect to the degree of CCR and NCR was observed and a positive correlation between NCR and virulence in a neutropenic mouse model of pulmonary aspergillosis (PA) was found. Isolate Afs35 was selected for further analysis and compared to the reference strain A1163, with both strains presenting the same degree of virulence in a neutropenic mouse model of PA. Afs35 metabolome analysis in physiological-relevant carbon sources indicated an accumulation of intracellular sugars that also serve as cell wall polysaccharide precursors. Genome analysis showed an accumulation of missense substitutions in the regulator of protease secretion and in genes encoding enzymes required for cell wall sugar metabolism. Based on these results, the virulence of strains Afs35 and A1163 was assessed in a triamcinolone murine model of PA and found to be significantly different, confirming the known importance of using different mouse models to assess strain-specific pathogenicity. These results highlight the importance of nitrogen metabolism for virulence and provide a detailed example of the heterogeneity that exists between A. fumigatus isolates with consequences for virulence in a strain-specific and host-dependent manner.

Emergence of Echinocandin Resistance Due to a Point Mutation in the fks1 Gene of Aspergillus fumigatus in a Patient with Chronic Pulmonary Aspergillosis

We have identified the first case of an fks1 hot spot 1 point mutation causing echinocandin resistance in a clinical Aspergillus fumigatus isolate recovered from a chronic pulmonary aspergillosis patient with an aspergilloma who first failed azole and polyene therapy and subsequently failed micafungin treatment.

A novel fungus concentration-dependent rat model for acute invasive fungal rhinosinusitis: an experimental study

Background

Acute invasive fungal rhinosinusitis is a lethal infectious process afflicting immunocompromised individuals. Knowledge about this disease is still limited due to the scarcity of animal models designed to study the pathogenesis of this infection. Mast cells are tissue-resident immune cells that participate in a variety of allergic and inflammatory conditions. Limited attention has been given to the role of mast cells in acute invasive fungal rhinosinusitis. Therefore, the objectives of this study were to create a rat model of acute invasive fungal rhinosinusitis based on analyzing the impact of different fungal concentrations on establishing infection, and to observe the changes of mast cells in rats with this disease.

Methods

Sprague–Dawley rats were divided randomly into four groups, three of which were experimental and received different concentrations of Aspergillus fumigatus inoculations, and one was a control group (D). The inoculated Aspergillus fumigatus concentrations were 5 × 10⁷ conidia/ml in group A, 10⁷ conidia/ml in group B, and 10⁶ conidia/ml in group C. Before fungal inoculation, rats were immunosuppressed using cyclophosphamide and cortisone acetate, and had Merocel sponges inserted into the right nares. Hematology and histopathology investigations were then performed.

Results

An acute invasive fungal rhinosinusitis rat model was established successfully with an incidence rate of 90% in group A, 50% in group B and 10% in group C. Aspergillus fumigatus invasion was observed in 20% of the lungs in group A, but was not seen in the remaining groups. In addition, no fungi invaded the orbital tissue, brains, livers, spleens or kidneys of any rat. Compared with the control set, the total number of mast cells in the experimental groups was not significantly increased, but mast cell degranulation, on the other hand, was only found in infected nasal cavities.

Conclusions

This investigation illustrates that various fungal concentrations have different effects on the incidence of acute invasive fungal rhinosinusitis, and it also demonstrates the feasibility of using this model to study the process of fungal rhinosinusoidal invasion. In addition, the results suggest that mast cells may play a role in the protection of sinuses against acute Aspergillus fumigatus infection and in the clearance of established hyphal masses.

Electronic supplementary material

The online version of this article (doi:10.1186/s12879-014-0713-y) contains supplementary material, which is available to authorized users.

Aerosolized amphotericin B as prophylaxis for invasive pulmonary aspergillosis: a meta-analysis

OBJECTIVES

Invasive pulmonary aspergillosis (IPA) is associated with high mortality in high-risk (immunosuppressed) patients. Many studies have investigated whether prophylactic inhalation of amphotericin B (AMB) reduces the incidence of IPA, but no definitive conclusions have been reached. The present meta-analysis was performed to evaluate the efficacy of prophylactic inhalation of AMB for the prevention of IPA.

METHODS

MEDLINE and other databases were searched for relevant articles published until December 2013. Randomized controlled trials that compared aerosolized AMB with placebo were included. Two reviewers independently assessed and extracted the data of all trials.

RESULTS

Six animal studies and two clinical trials involving 768 high-risk patients were eligible. The animal studies showed lower overall mortality rate among animals that underwent aerosolized AMB prophylaxis (odds ratio (OR) 0.13, 95% confidence interval (CI) 0.08-0.21). Similarly, the clinical trials showed a lower incidence of IPA among patients who underwent aerosolized AMB prophylaxis (OR 0.42, 95% CI 0.22-0.79).

CONCLUSIONS

This analysis provides evidence supporting the notion that the prophylactic use of aerosolized AMB effectively reduces the incidence of IPA among high-risk patients.

The proteomic signature of Aspergillus fumigatus during early development

Aspergillus fumigatus is a saprophytic fungus that causes a range of diseases in humans including invasive aspergillosis. All forms of disease begin with the inhalation of conidia, which germinate and develop. Four stages of early development were evaluated using the gel free system of isobaric tagging for relative and absolute quantitation to determine the full proteomic profile of the pathogen. A total of 461 proteins were identified at 0, 4, 8, and 16 h and fold changes for each were established. Ten proteins including the hydrophobin rodlet protein RodA and a protein involved in melanin synthesis Abr2 were found to decrease relative to conidia. To generate a more comprehensive view of early development, a whole genome microarray analysis was performed comparing conidia to 8 and 16 h of growth. A total of 1871 genes were found to change significantly at 8 h with 1001 genes up-regulated and 870 down-regulated. At 16 h, 1235 genes changed significantly with 855 up-regulated and 380 down-regulated. When a comparison between the proteomics and microarray data was performed at 8 h, a total of 22 proteins with significant changes also had corresponding genes that changed significantly. When the same comparison was performed at 16 h, 12 protein and gene combinations were found. This study, the most comprehensive to date, provides insights into early pathways activated during growth and development of A. fumigatus. It reveals a pathogen that is gearing up for rapid growth by building translation machinery, generating ATP, and is very much committed to aerobic metabolism.

Meta-analysis of nebulized amphotericin B to prevent or treat pulmonary aspergillosis in immunosuppressed animals

OBJECTIVES

Pulmonary aspergillosis in immunosuppressed patients is associated with significant mortality and morbidity. We assessed the prophylactic and therapeutic effect of nebulized amphotericin B (AmB) on mortality of immunosuppressed animals with pulmonary aspergillosis in this meta-analysis.

METHODS

Literature search was based on MEDLINE (1966 to January 15, 2007), EMBASE, and Cochrane-Controlled Trials Register (2006 issue 4) databases. Only randomized-controlled studies comparing nebulized AmB with placebo on immunosuppressed animals were included. Two reviewers reviewed and extracted the data independently.

RESULTS

Eight studies including 839 immunosuppressed animals were considered. The overall mortality of the immunosuppressed animals with pulmonary aspergillosis treated with nebulized AmB was reduced (69.4% versus 87.7%, odds ratio [OR] 0.12, 95% confidence interval [CI]: 0.08-0.19; P < 0.0001). The effect of nebulized AmB on mortality was more significant when the drug was administered as prophylaxis before the inoculation of Aspergillus fumigatus (OR 0.07, 95% CI: 0.03-0.12, P = 0.0001; I(2) = 0) than as a therapeutic agent (OR 0.20, 95% CI: 0.11-0.36, P < 0.0001; I(2) = 0) (ratio of the 2 ORs = 2.86, 95% CI: 1.03-6.11; P = 0.04). The effectiveness of AmB desoxycholate (OR 0.16, 0.06-0.38, P < 0.0001; I(2) = 0) and lipid-associated (liposomal, or lipid complex or colloidal dispersion) amphotericin (OR 0.11, 95% CI: 0.06-0.20, P < 0.0001; I(2) = 0) was not significantly different (ratio of the 2 ORs = 1.46, 95% CI: 0.49-4.39; P = 0.50). Three studies evaluated the potential side effects of nebulized amphotericin and showed that there was no significant renal toxicity but the amphotericin desoxycholate had some detrimental effects on pulmonary surfactant function.

CONCLUSIONS

The use of nebulized amphotericin, either as a prophylactic or therapeutic agent, is effective in reducing mortality of immunosuppressed animals with pulmonary aspergillosis. A large randomized controlled trial is needed to confirm whether combining nebulized amphotericin with systemic antifungal agents will reduce mortality in immunosuppressed patients with suspected or proven pulmonary aspergillosis.

Comparative study on the efficacy of AmBisome and Fungizone in a mouse model of pulmonary aspergillosis

OBJECTIVES

The aim of this study was to evaluate the efficacy and tissue concentration of AmBisome and Fungizone in murine pulmonary aspergillosis, and to investigate the localization of AmBisome at the infection site.

METHODS

Mice were infected intratracheally with Aspergillus fumigatus. A single dose of each of the antifungals was administered intravenously 4 h after infection. The efficacy of the antifungal treatment was assessed by the pulmonary fungal burden at 20 h post-treatment and the survival time over 1 month. The pulmonary amphotericin B (AMB) concentration was measured until 48 h after administration. The distribution of AmBisome in the lung was evaluated using rhodamine-labelled AmBisome and an anti-AMB antibody.

RESULTS

AmBisome at a dose of > or =1 mg/kg significantly prolonged the survival time of infected mice compared with the control group. At the maximum tolerated dose, 10 mg/kg AmBisome exhibited greater efficacy than 1 mg/kg Fungizone in terms of increasing survival and reducing the fungal burden. The pulmonary AMB concentration of 10 mg/kg AmBisome was higher than that of 1 mg/kg Fungizone. Tissue distribution analysis showed that AmBisome was localized at the infection site in the lung, and this might explain the potent in vivo efficacy in this infection model.

CONCLUSIONS

AmBisome is localized at the infection site in the lung and consequently may fully exhibit its in vivo activity. The efficacy of AmBisome is superior to that of Fungizone against pulmonary aspergillosis.

Efficacy of high loading doses of liposomal amphotericin B in the treatment of experimental invasive pulmonary aspergillosis

This study aimed to investigate whether initial treatment of experimental pulmonary aspergillosis with high loading doses can be used as an alternative to standard therapeutic regimens. Steroid-immunosuppressed rats, infected intratracheally with Aspergillus fumigatus, received either amphotericin B deoxycholate (d-AmB) 1 mg/kg/day, liposomal amphotericin B (L-AmB) 5 mg/kg/day, or underwent a 3-day course of L-AmB 10 mg/kg, or 10 mg/kg for the first 3 or 4 days of treatment, followed by 3 mg/kg until the end of treatment. Therapy started 24 h after fungal challenge and lasted for 7 days. Compared to controls, survival was improved significantly in animals receiving any L-AmB regimen (p <or= 0.003), but not d-AmB. Compared with d-AmB, L-AmB at initial doses of 10 mg/kg followed by 3 mg/kg/day was consistently more effective, but only when measured in terms of survival, lung weight and glucosamine levels, and not log CFU. Despite the absence of significant differences between any of the L-AmB regimens, a trend towards better response rates with the higher loading dose was observed.

Pathophysiology of pulmonary aspergillosis

A description of the pathophysiology of aspergillosis is followed by a review of investigational considerations of animal models. Because a large body of invasive Aspergillus infection occurs as opportunistic infection, there is a large spectrum of the histopathological feature of lesions demonstrated at the site of infection. Histopathology of the lesions can be understood as a phenotypical representation of interaction between lowered defense mechanisms in the host and the virulence of invading fungi. Detailed observations with a consideration of previous pathological knowledge of infection and inflammation provide much important information useful in predicting the pathophysiology of the patient. Moreover, experimental studies can also provide much insight to elucidate pathogenesis of the infection that emerges from the clinical and pathological investigations. The importance of pathophysiology should be emphasized to understand the implications of radiographic images, clinical symptoms, and laboratory dates. By reviewing these, especially computed tomography (CT) images, we can see that they accurately mirror the histological features of the lesion that can be recognized as a phenotypical representation of pathophysiology of Aspergillus infection. This is also confirmed by the reports emphasizing the importance of CT scans to identify hallmark clinical signs and symptoms of the disease.

Evaluation of antimicrobial agents using an experimental pulmonary superinfection model with Aspergillus fumigatus and Pseudomonas aeruginosain leukopenic mice

The therapeutic efficacy of amphotericin B (AmB), imipenem/cilastatin (IPM/CS), pazufloxacin (PZFX) mesilate, and combinations of these, was evaluated using an experimental pulmonary superinfection model in mice caused by Pseudomonas aeruginosa and Aspergillus fumigatus. The superinfected mice died within 3 days. Although the viable cell count of P. aeruginosa increased markedly from 10(3) to 10(8) CFU/lung on day 2 after infection, that of A. fumigatus decreased from 10(3) to 10(2) CFU/lung on that day, showing that P. aeruginosa facilitated the mortality in the superinfection. Extensive necrosis in the lung parenchyma and moderate hyphae proliferation of A. fumigatus were observed on day 2 after infection. Mice treated with PZFX mesilate (50 mg/kg per day) and the combination of PZFX mesilate (50 mg/kg per day) - AmB (2.5 mg/kg per day) showed prolonged survival in comparison to untreated control mice ( P < 0.05). In the PZFX mesilate-treated group, no significant necrosis was observed, but necrosis due to the hyphae proliferation of A. fumigatus was still observed in the lung parenchyma on day 6 after infection. However, neither significant necrosis nor hyphae proliferation of A. fumigatus was observed in mice treated with the combination of PZFX mesilate - AmB. On the other hand, the survival rates of mice treated with AmB (2.5 mg/kg per day), IPM/CS (50 mg/kg per day), and the IPM/CS-AmB combination were all less than 10%. The viable cell count of P. aeruginosa decreased in PZFX mesilate-alone group and in the combination of PZFX mesilate - AmB group, but no significant decrease in this count was observed in the IPM/CS and combination of IPM/CS-AmB group. The viable count of A. fumigatus was increased in the IPM/CS, PZFX mesilate-alone, and combination of IPM/CS-AmB groups, but the count was suppressed in the AmB-alone and the combination of PZFX mesilate - AmB group. In conclusion, this superinfection model would be useful to evaluate the therapeutic potential of combinations of antibacterial and antifungal agents, and the scheduling of drug administration in terminal infections caused by P. aeruginosa and A. fumigatus.

Disseminated aspergillosis due to Aspergillus flavus in an experimental model: efficacy of azole therapy

The aim of this investigation was to create a reproducible experimental model of disseminated Aspergillus flavus aspergillosis, and to compare the relative therapeutic efficacies of itraconazole and fluconazole in this model. Temporarily immunosuppressed male Wistar rats received intravenous challenge by A. flavus conidia. Treatment was initiated 24 h later with oral itraconazole (1 mg kg-1 BW day-1), oral fluconazole (1 mg kg-1 BW day-1) or excipient only (infected-untreated rats); this was continued for 10 days. At this time, although 100% mortality had occurred among all infected-untreated rats, no mortality was noted among the control-uninfected, infected-itraconazole-treated or infected-fluconazole-treated rats. After killing, essential organs were processed for microbiological and histopathological studies. Aspergillus flavus was recovered in high colony counts from the organs of infected-untreated rats (lungs > liver > brain > kidneys), but in significantly lower colony counts, or not at all, from the organs of itraconazole-treated and fluconazole-treated rats. Histopathological alterations were pronounced in tissues of infected-untreated rats, but less so in treated rats. These data suggest that administration of itraconazole or fluconazole sufficiently early may prevent, or retard, progression of lesions in disseminated aspergillosis.

Nebulized antibiotics in cystic fibrosis

Nebulization is a useful administration route in cystic fibrosis (CF) as it delivers antibiotics directly to the endobronchial site of infection and is associated with decreased toxicity because of limited systemic absorption. It is assumed that the concentration of antibiotics in bronchial secretions should be as high as 10 times the minimum inhibiting concentration to allow penetration of antibiotics into biofilms, suppress inhibitory factors and promote bactericidal effectiveness. However, effective aerosol delivery is compromised by nebulizers with limited capacity to produce particles of a size in the respirable range. Three antibiotics are commonly used for inhalation: tobramycin, amikacin and colistin (colomycin). Placebo-controlled studies evaluating antibiotic aerosol maintenance in stable patients chronically infected with Pseudomonas aeruginosa indicate a significant improvement of lung function and a reduction of the number of hospital admissions for an acute exacerbation of CF. TOBI is a recently marketed preservative- and sulfate-free formula of tobramycin, specially designed for diffusion in the bronchioles and optimal tolerance. A wide-scope study involving 520 patients compared TOBI (300 mg twice daily; n = 258) with placebo (n = 262) for three 28-day cycles with each cycle separated by a 28-day period of no treatment. Respiratory function was significantly improved as early as in the second week and remained so for the rest of the trial even during periods without aerosol treatment. There was also a parallel decrease in the relative risk of hospitalization, the number of days of hospitalization and the number of days on intravenous antipyocyanic treatment. Toxicity studies carried out so far have shown no renal or ototoxicity with nebulized tobramycin. Introduction or selection of resistant bacteria is relatively rare but remains a matter of concern. Aerosol maintenance treatment with an appropriate antibiotic in a high enough dosage can be recommended for patients with CF who are chronically infected with P. aeruginosa.

Monitoring acute inflammatory processes in mouse muscle by MR imaging and spectroscopy: a comparison with pathological results

We have studied an animal model of acute local inflammation in muscle induced by Aspergillus fumigatus by using magnetic resonance imaging (MRI) and magnetic resonance spectroscopy (MRS). We have compared our data to those found using histopathology and segmentation maps obtained by the mathematical processing of three-dimensional T2-weighted MRI data via a neural network. The MRI patterns agreed satisfactorily with the clinical and biological evidence of the phases of acute local infection and its evolution towards chronicity. The MRS results show a statistically significant increase in inorganic phosphate and a significant decrease in phosphocreatine levels in the inflamed region. Image segmentation made with a self-organizing, neural-network map yielded a set of ordered representatives that remained constant for all animals during the inflammatory process, allowing a non-invasive, three-dimensional identification and quantification of the inflamed infected regions by MRI.

The role of murine models in the development of antifungal therapy for systemic mycoses

Animal testing is crucial to the development of new antifungal compounds. This review describes the role that murine and other animal models have played in the development of three classes of antifungal agents: the polyenes, the triazoles and the echinocandins and the ways in which these models have been either the positive link in the path from in vitro studies to the patient, or have foreclosed later clinical evaluation. Efficacy studies in particular mycoses are discussed, as well as studies designed to determine whether combinations of antifungal drugs may have value over single agents. Copyright 2000 Harcourt Publishers Ltd.

A new model of pulmonary superinfection with Aspergillus fumigatus and Pseudomonas aeruginosa in mice

We have produced a new model of pulmonary super-infection with Aspergillus fumigatus and Pseudomonas aeruginosa in immunosuppressed mice. Male ICR mice were given an intratracheal inoculation of 4 x 10(5) conidia of A. fumigatus in agar beads, and were immunosuppressed with 100 mg/kg subcutaneous injections of cortisone acetate on days 7, 9, 12, 14, and 16 after inoculation. Twelve days after inoculation, with the agar beads, the mice were challenged with the intranasal instillation of 2 x 10(6) CFU of P. aeruginosa. The survival rates of superinfected, A. fumigatus-alone, P. aeruginosa-alone, and non-infected mice were 50%, 30%, 90%, and 100% 14 days after pseudomonal infection (26 days after inoculation of A. fumigatus), respectively. In the superinfected mice, both A. fumigatus and P. aeruginosa were detected more than 10 days after pseudomonal infection (22 days after inoculation of A. fumigatus). Histopathological examination revealed peribronchial necrosis around A. fumigatus hyphae and inflammation by P. aeruginosa. This infection model in mice would be useful for studying the pathogenesis of superinfection.

Efficacy of NND-502, a novel imidazole antimycotic agent, in experimental models of Candida albicans and Aspergillus fumigatus infections

In vitro and in vivo anti-Candida albicans and anti-Aspergillus fumigatus activities of NND-502, a new imidazole-antimycotic, were compared with those of fluconazole (FCZ), itraconazole (ITZ) and/or amphotericin B (AmB). NND-502 exhibited strong in vitro antifungal activity against both fungal species; its MIC against C. albicans was 1-4 times lower than that of FCZ, and its MIC against A. fumigatus was at least 60-2000 times lower than that of ITZ and AmB. In vivo antifungal treatments with each drug were initiated 1 h after inoculation in the experimental models, so that antifungal potential reflected prophylactic activity rather than therapeutic activity. The oral regimen of NND-502 in a murine model of systemic C. albicans infection was much less effective than that of FCZ. In vivo anti-A. fumigatus activity of oral NND-502 in a murine model of systemic infection was apparently superior to that of FCZ and ITZ in terms of prolonging survival. In addition to the murine model of systemic aspergillosis, intravenous NND-502 was shown to be highly effective in a rat model of pulmonary aspergillosis compared with intravenous AmB; 90% of animals survived at a dose of 2.5 mg/kg per day of NND-502 while only 30% of animals escaped death when 5 mg/kg per day of AmB was used. This potent efficacy of NND-502 was also confirmed in a sublethal challenge study in which the administration of the agent at a dose as low as 1.25 mg/kg per day resulted in the significant reduction of organisms in the lung; no comparable effect of AmB was found.

Aspergillus fumigatus and aspergillosis

Aspergillus fumigatus is one of the most ubiquitous of the airborne saprophytic fungi. Humans and animals constantly inhale numerous conidia of this fungus. The conidia are normally eliminated in the immunocompetent host by innate immune mechanisms, and aspergilloma and allergic bronchopulmonary aspergillosis, uncommon clinical syndromes, are the only infections observed in such hosts. Thus, A. fumigatus was considered for years to be a weak pathogen. With increases in the number of immunosuppressed patients, however, there has been a dramatic increase in severe and usually fatal invasive aspergillosis, now the most common mold infection worldwide. In this review, the focus is on the biology of A. fumigatus and the diseases it causes. Included are discussions of (i) genomic and molecular characterization of the organism, (ii) clinical and laboratory methods available for the diagnosis of aspergillosis in immunocompetent and immunocompromised hosts, (iii) identification of host and fungal factors that play a role in the establishment of the fungus in vivo, and (iv) problems associated with antifungal therapy.

Rabbit as an animal model of paranasal sinus mycoses

Paranasal sinus mycoses are endemic in rural populations of northern India. To study host-parasite interactions, we developed an animal model of paranasal sinus mycoses. After failure in small animals such as mice and rats, we used New Zealand white rabbits weighing 2.5-3 kg. Inoculum sizes consisted of 0.75-1.0 x 10(8), 0.75-1.0 x 10(7), 0.75-1.0 x 10(6) conidia of a clinical isolate of Aspergillus flavus. The inoculum was injected at a spot 0.5 cm in front of the alveolar process of the maxilla and 0.5 cm below the maxillary process of frontal bone and vertically to a depth of 0.5 cm across the bone directly into the nasal sinus. Paranasal sinus mycoses proven by culture and histopathology developed in 67% of animals injected with 0.75-1.0 x 10(8) conidia and 17% of animals with 0.75 x 10(7) conidia. No lesions were found in the group injected with 0.75-1.0 x 10(6) conidia. Precipitating antibody against culture filtrate antigen was found in rabbits with paranasal sinus mycoses. Therefore, rabbits can be used as an animal model to study paranasal sinus mycoses.

Antifungal prophylaxis during neutropenia and immunodeficiency

Fungal infections represent a major source of morbidity and mortality in patients with almost all types of immunodeficiencies. These infections may be nosocomial (aspergillosis) or community acquired (cryptococcosis), or both (candidiasis). Endemic mycoses such as histoplasmosis, coccidioidomycosis, and penicilliosis may infect many immunocompromised hosts in some geographic areas and thereby create major public health problems. With the wide availability of oral azoles, antifungal prophylactic strategies have been extensively developed. However, only a few well-designed studies involving strict criteria have been performed, mostly in patients with hematological malignancies or AIDS. In these situations, the best dose and duration of administration of the antifungal drug often remain to be determined. In high-risk neutropenic or bone marrow transplant patients, fluconazole is effective for the prevention of superficial and/or systemic candidal infections but is not always able to prolong overall survival and potentially selects less susceptible or resistant Candida spp. Primary prophylaxis against aspergillosis remains investigative. At present, no standard general recommendation for primary antifungal prophylaxis can be proposed for AIDS patients or transplant recipients. However, for persistently immunocompromised patients who previously experienced a noncandidal systemic fungal infection, prolonged suppressive antifungal therapy is often indicated to prevent a relapse. Better strategies for controlling immune deficiencies should also help to avoid some potentially life-threatening deep mycoses. When prescribing antifungal prophylaxis, physicians should be aware of the potential emergence of resistant strains, drug-drug interactions, and the cost. Well-designed, randomized, multicenter clinical trials in high-risk immunocompromised hosts are urgently needed to better define how to prevent severe invasive mycoses.

Murine model of invasive pulmonary aspergillosis following an earlier stage, noninvasive Aspergillus infection

Aspergillus spp. occasionally cause invasive pulmonary aspergillosis following noninvasive infection in patients with underlying bronchopulmonary disorders regardless of their systemic immunological conditions. We developed a murine model of invasive pulmonary aspergillosis following an earlier stage, noninvasive Aspergillus infection. BALB/c mice were inoculated intratracheally with agarose beads containing Aspergillus fumigatus conidia. Two weeks after inoculation, half of the mice were immunosuppressed with cortisone acetate. During a 4-week observation period, the survival rate of infected immunosuppressed mice was significantly lower (P < 0.01) than that of infected nonimmunosuppressed mice. The number of CFU in the lungs gradually decreased in the nonimmunosuppressed mice, whereas a time-related significant increase (P < 0.05) of CFU was demonstrated in the immunosuppressed mice. In the lungs of the nonimmunosuppressed mice, there was marked accumulation of neutrophils, lymphocytes, and macrophages (in this order) around the agarose beads in the bronchi. Aspergillus hyphae were surrounded by the inflammatory cells and did not invade the lung parenchyma. In contrast, in the immunosuppressed mice, Aspergillus hyphae proliferated markedly and invaded the lung parenchyma after immunosuppression. In this model, the two-dimensional extents of the lesions were also evaluated with an image-processing system. Time-related increase of the area of peribronchial necrotic lesions was significant (P < 0.05) after immunosuppression. This model should therefore be useful for investigating the pathophysiology of noninvasive Aspergillus infection and invasive pulmonary aspergillosis and also for clarifying the mechanism of conversion to the invasive disease from the noninvasive stage.

Use of amphotericin B aerosols for the prevention of pulmonary aspergillosis

Invasive pulmonary Aspergillus infections are increasingly recognized among severely neutropenic and/or immunosuppressed individuals. As the infections are usually acquired through the inhalation of Aspergillus conidia, at present prevention of invasive pulmonary aspergillosis consists mainly of the reduction of environmental exposure to aspergillus conidia. More recently, prophylaxis with amphotericin B aerosols has been investigated. Inhalations with amphotericin B aerosols significantly delayed mortality in an animal model of invasive pulmonary aspergillosis and high pulmonary concentrations of amphotericin B could be achieved. In man, pulmonary deposition of amphotericin B could also be demonstrated using commercially available nebulizers. Inhalations were well tolerated with little systemic absorption of the drug. In order to evaluate the efficacy of aerosol amphotericin B administrations for the prevention of invasive pulmonary aspergillosis, a prospective randomized trial has been initiated.

Efficacy of intravenous itraconazole against experimental pulmonary aspergillosis

The efficacy of intravenous itraconazole solubilized in hydroxypropyl-beta-cyclodextrin was assessed in a rat model of Aspergillus fumigatus pneumonia. Immunosuppressed rats were infected by intratracheal inoculation of A. fumigatus conidia. Intravenous administration of various doses of itraconazole was started immediately after infection and continued once a day for 7 days. A 10-mg dose of intravenous itraconazole per kg was as effective on survival as 1 mg of amphotericin B per kg daily (a survival rate of 100% in 28 days), while treatment with 1 mg/kg did not increase the survival rate. The 50% lethal dose of intravenous itraconazole given to immunosuppressed and uninfected rats for 7 days was 24.5 mg/kg/day. A microbiological assay to estimate accumulation in tissue after five daily intravenous administrations of itraconazole at 10 mg/kg showed that itraconazole and its active metabolites were present in the lungs for at least 6 h, reaching the MIC as previously described (B. Dupont and E. Drouchet, Rev. Infect. Dis. 9(Suppl. 1):71-76, 1987; A. Espinel-Ingroff, S. Shadomy, and R. J. Gebhart, Antimicrob. Agents Chemother. 26:5-9, 1984). Intravenous itraconazole was considered to be worth evaluating in clinical trials of aspergillosis.