Whole blood and tissue fungal DNA quantification in the diagnosis of canine sino-nasal aspergillosis

Utility of fungal polymerase chain reaction on nasal swab samples in the diagnosis and monitoring of sinonasal aspergillosis in dogs

Background

In dogs with sinonasal aspergillosis (SNA) the utility of PCR in the diagnosis and monitoring of the disease after treatment has not been assessed.

Objectives

To evaluate the presence of fungal DNA using quantitative PCR targeting Aspergillus fumigatus (Aspfum) and Aspergillus spp. (PanAsp), and PCR targeting multiple fungal species (PanFun), in samples obtained from nasal cavities of dogs with SNA, other nasal diseases and healthy dogs.

Animals

Sixty‐two dogs including 20 with SNA, 12 with cured SNA (of which 10 are from the SNA group), 20 dogs with Non‐SNA nasal disease, and 20 healthy dogs.

Methods

Prospective cross‐sectional study. Aspfum, PanAsp, and PanFun were performed on blindly collected nasal swabs obtained in anesthetized dogs.

Results

In SNA dogs, Aspfum and PanAsp were positive in 13/20 and 14/20 dogs. In all dogs in the 3 other groups, A. fumigatus DNA was not detected using Aspfum. PanAsp was positive in 3 non‐SNA dogs: 1 with cured SNA and 2 with Non‐SNA nasal disease. A Ct cut‐off value of 33.3 for Aspfum demonstrated 65% sensitivity and 100% specificity. A Ct cut‐off value of 34.5 for PanAsp demonstrated 70% sensitivity and 96.2% specificity. PanFun was positive in 16/20, 12/12, 19/20, and 7/20 dogs in the SNA, cured SNA, Non‐SNA, and healthy groups, respectively.

Conclusion and Clinical Importance

Aspfum and PanAsp on blindly collected nasal swabs can be useful for the detection of SNA at diagnosis and at cure, especially when more invasive methods are not available.

Fungal Rhinosinusitis and Disseminated Invasive Aspergillosis in Cats

Fungal rhinosinusitis, including sinonasal aspergillosis (SNA) and sino-orbital aspergillosis (SOA), is the most common type of aspergillosis encountered in cats. Other focal forms of aspergillosis including disseminated invasive aspergillosis occur less frequently. SOA is an invasive mycosis that is increasingly recognized and is most commonly caused by Aspergillus felis, a close relative of Aspergillus fumigatus. SNA can be invasive or noninvasive and is most commonly caused by A fumigatus and Aspergillus niger. Molecular methods are required to correctly identify the fungi that cause SNA and SOA. SNA has a favorable prognosis with treatment, whereas the prognosis for SOA remains poor.

What causes canine sino-nasal aspergillosis? A molecular approach to species identification

On the basis of phenotypic identification methods, Aspergillus fumigatus is reported as the most commonly identified aetiological agent of canine sino-nasal aspergillosis (SNA). However, definitive identification of Aspergillus spp. using phenotypic features alone is unreliable. The aim of this study was to determine the molecular identities of fungal species causing SNA in dogs. Genomic DNA was extracted from 91 fungal isolates from 90 dogs diagnosed with SNA in Australia, the USA and Belgium, and the ITS1-5.8S-ITS2 ribosomal DNA and partial β-tubulin regions were sequenced. Eighty-eight of 91 (96.7%) isolates were identified as A. fumigatus and 3/91 (3.3%) belonged to Aspergillus section Nigri spp. (Aspergillus tubingensis: 2/91; Aspergillus uvarum: 1/91). These findings confirm that A. fumigatus is the most common aetiological agent of canine SNA. This is the first report to document a pathogenic role for A. tubingensis and A. uvarum in dogs.

Potential role of Alternaria and Cladosporium species in canine lymphoplasmacytic rhinitis

OBJECTIVES

To evaluate the possible role of Alternaria and Cladosporium species in the pathogenesis of canine lymphoplasmacytic rhinitis by comparing the amount of specific fungal DNA in nasal mucosal biopsies between dogs without nasal neoplasia and those with lymphoplasmacytic rhinitis or nasal neoplasia.

METHODS

Quantitative real-time polymerase chain reaction (qPCR) assays detecting DNA from Alternaria and Cladosporium fungi were applied to nasal mucosal biopsies collected from dogs with lymphoplasmacytic rhinitis (n = 8), dogs with nasal neoplasia (n = 10) and control animals (n = 10). A copy number for each sample was calculated using a standard curve of known copy number and differences amongst groups were assessed using Kruskal-Wallis tests.

RESULTS

No significant difference was found between the groups. Low levels of Alternaria DNA (10-100 copies/PCR) were detected in one sample; very low levels of DNA (<10 copies/qPCR) were detected in 6 samples, and 21 samples were negative. Low levels of Cladosporium DNA were detected in 2 samples; very low levels of DNA in 18; and 8 were negative.

CLINICAL SIGNIFICANCE

Results of this study reveal that Alternaria and Cladosporium species are part of the canine nasal flora, and that these fungi are probably not involved in the pathogenesis of lymphoplasmacytic rhinitis.

Sinonasal aspergillosis in dogs: a review

Sinonasal aspergillosis is an uncommon, yet debilitating and often frustrating condition to treat in dogs despite years of research evaluating pathogenesis, diagnosis and treatment. The disease is most commonly caused by non-invasive fungal infection, thought to be secondary to altered innate and/or adaptive immune responses. Attempts to confirm this have however failed. A variety of conflicting opinions regarding the diagnosis and treatment of sinonasal aspergillosis exist. Often the use of a particular treatment protocol is based upon personal or regional preference. Evaluation of the veterinary literature demonstrates that the evidence base in support of individual treatment recommendations is weak. A number of recent publications have helped to expand the current knowledge base and therefore our understanding of important practicalities for both diagnostic options and treatment protocols. The following review examines the current evidence for the pathogenesis of sinonasal aspergillosis in dogs, as well as the various diagnostic options. The available evidence for frequently utilised -therapeutic options and their likely outcomes is also explored.

Aspergillus fumigatus Bronchopneumonia in a Hellenic Shepherd Dog

A 3 yr old intact female Hellenic shepherd dog was referred due to depression, partial anorexia, fever, and a mild productive cough of 2 mo duration. Thoracic radiographs showed increased opacity of all of the left lung lobes. Upon bronchoscopy, a sanguineous, purulent discharge was detected in the tracheal lumen with hyperplastic tissue narrowing the left main stem bronchus. Cultures were positive for bacteria (Bacillus spp. and Clostridium spp.) but negative for fungi. Due to the severity of the lesions, a complete left lung pneumonectomy was performed. Histopathological examination of the excised lung tissues revealed a severe granulomatous bronchopneumonia with numerous alveolar macrophages laden with structures stained positively by periodic acid-Schiff and Grocott stain that had morphology consistent with fungi. PCR and sequencing of internal transcribed spacer regions 1 and 2 from genetic material extracted from paraffin-embedded pulmonary tissue confirmed the presence of Aspergillus fumigatus. Itraconazole was administrated for 5.5 mo and the dog was clinically normal 26 mo after surgery.

Effect of sampling method and incubation temperature on fungal culture in canine sinonasal aspergillosis

OBJECTIVES

To evaluate the most appropriate sampling procedure and the effect of incubation temperature on fungal culture in the diagnosis of canine sinonasal aspergillosis (SNA).

METHODS

Sixteen dogs with SNA and 20 dogs with non-fungal nasal disease entered a prospective study. Nasal secretions and mucosal biopsies were collected in all dogs. Fungal plaques were also sampled in dogs with SNA. Each specimen was taken in duplicate from each dog and incubated at room temperature and 37 degrees C.

RESULTS

In dogs with SNA, nasal secretions, mucosal biopsies and fungal plaques yielded fungal growth at room temperature in one, one and seven dogs, respectively, whereas fungal growth was obtained at 37 degrees C in three, 12 and 14 dogs, respectively. No specimen collected from any dog with non-fungal nasal disease yielded fungal growth at room temperature or at 37 degrees C.

CLINICAL SIGNIFICANCE

The diagnosis of canine SNA is more likely to be confirmed following culture of mucosal biopsies or fungal plaques than nasal secretions sampled blindly with swabs. Incubating cultures at 37 degrees C is more likely to provide a diagnostic outcome than when samples are cultured at room temperature. Fungal culture of nasal specimens has good specificity for the diagnosis of SNA in dogs.

Comparison of the value of measurement of serum galactomannan and Aspergillus-specific antibodies in the diagnosis of canine sino-nasal aspergillosis

Serology is currently used for the diagnosis of canine sino-nasal aspergillosis (SNA). However, the accuracy of serological testing using commercially available, standardized purified antigen preparations of Aspergillus (CAPurAspAg) has only been poorly documented. The aim of the present study was to assess the diagnostic value of an agar-gel double immunodiffusion (AGDD) test and an anti-Aspergillus IgG ELISA, using CAPurAspAg and the commercially available Platelia test for the detection of serum galactomannan. Sera from 17 dogs with SNA, 18 dogs with a nasal tumour (NT), 11 dogs with lymphoplasmacytic rhinitis (LPR) and 33 control dogs were tested with the 3 methods. AGDD result was positive in 76.5% of dogs with SNA, whereas all sera from dogs with non-fungal nasal disease and control dogs were negative. A positive IgG ELISA result was obtained in 88% of dogs with SNA and in 18% of dogs with LPR. All patients with NT and control dogs had a negative IgG ELISA result. The Platelia test was positive in 24% of dogs with SNA, 11% of dogs with NT, 9% of dogs with LPR and 24% of control dogs. The results of this study suggest that (1) the detection of serum Aspergillus-specific antibodies with AGDD or ELISA, using CAPurAspAg, provides excellent specificity and good sensitivity, (2) the specificity is higher for AGDD (100%) than for ELISA (96.8%) while sensitivity is higher for ELISA (88.2%) than for AGDD (76.5%) and (3) serum galactomannan quantification with the Plateliat test is unreliable for the diagnosis of canine SNA.