Detection of Aspergillus-specific antibodies by agar gel double immunodiffusion and IgG ELISA in feline upper respiratory tract aspergillosis

Retrospective study of 540 cats with respiratory diseases in Japan (2003-2020)

BACKGROUND

Few epidemiological studies on respiratory medicine and the relationship between clinical signs and various respiratory diseases in cats have been reported.

OBJECTIVES

This retrospective study aimed to investigate the prevalence and breed predisposition to feline respiratory diseases in Japan and determine the association between clinical signs, duration and type of respiratory diseases.

METHODS

The medical records of cats with feline respiratory diseases were examined to obtain information on age, sex, breed, final diagnosis, clinical signs and duration. The odds ratios (ORs) and 95% confidence intervals were calculated to evaluate breed predispositions. Mann-Whitney U, Kruskal-Wallis and Dunn's tests were used to assess the duration of clinical signs.

RESULTS

This study included 540 cats with 615 respiratory diagnoses. The American Shorthair breed was predisposed to bronchopneumonia (BP; OR: 5.0) and pulmonary tumour (PT; OR: 3.6), while the Russian Blue breed exhibited a predisposition to inflammatory lower airway diseases (OR: 3.4), BP (OR: 6.1) and interstitial lung diseases (OR: 11.1). Similarly, the Scottish Fold breed displayed predisposition to PTs (OR: 5.8). The duration of clinical signs among nasal diseases, nasopharyngeal diseases and lower tracheal/bronchial and pulmonary diseases differed significantly (p = 0.001, p = 0.012, p < 0.0001, respectively).

CONCLUSIONS

The results suggest that some popular breeds in Japan are predisposed to feline respiratory diseases, especially the American Shorthair, Russian Blue and Scottish Fold breeds. The characteristics of occurrence, clinical signs and duration of each disease will aid in diagnosing, treating, preventing and elucidating the pathophysiology of feline respiratory disease.

Invasive Fungal Infections and Oomycoses in Cats: 1. Diagnostic approach

CLINICAL RELEVANCE

In contrast to superficial fungal infections, such as dermatophytosis, invasive fungal infections (IFIs) are characterised by penetration of tissues by fungal elements. Disease can spread locally within a region or can disseminate haematogenously or via the lymphatics. The environment is the most common reservoir of infection. Since fungal spores are airborne, indoor cats are also susceptible to IFIs. Some environmental fungi are ubiquitous and present globally, while others are endemic or hyperendemic within specific geographic regions. Zoonotic pathogens include Microsporum canis, Sporothrix schenckii and Sporothrix brasiliensis.

AIM

In the first of a two-part article series, the approach to the investigation of feline IFIs and oomycoses is reviewed. As well as tips for diagnosis, and information on the ecological niche and distribution of fungal pathogens, the review covers clinical presentation of the most common IFIs, including cryptococcosis, histoplasmosis, blastomycosis, coccidioidomycosis, sporotrichosis, phaeohyphomycosis, aspergillosis and dermatophytic pseudomycetoma, as well as the oomycoses pythiosis, lagenidiosis and paralagenidiosis. In Part 2, the spectrum of activity, mechanisms of action, pharmacokinetic and pharmacodynamic properties and adverse effects of antifungal drugs are reviewed, and the treatment and prognosis for specific IFIs and oomycoses are discussed.

EVIDENCE BASE

The review draws on published evidence and the authors' combined expertise in feline medicine, mycology, dermatology, clinical pathology and anatomical pathology.

Sino-orbital aspergillosis with obstructive cervical lymphadenopathy in a cat caused by Aspergillus viridinutans complex

Case summary

This report describes an indoor-only cat with a rare form of sino-orbital aspergillosis (SOA) with cervical lymphadenopathy causing local obstruction. Extensive work-up on initial presentation failed to identify the underlying etiology and the diagnosis was not determined until the disease progressed during a prolonged course of glucocorticoid therapy.

Relevance and novel information

SOA caused by Aspergillus viridinutans complex is increasingly recognized as a significant cause of mortality in cats in recent years, with most cases reported in Australia, Europe and Asia. Feline SOA carries a poor prognosis owing to its invasive nature and resistance to antifungal therapy. This case demonstrates the importance of clinical awareness of SOA as a differential for cats with chronic nasal signs and exophthalmos in the USA. Moreover, it demonstrates a rare form of presentation and potential difficulty in achieving a correct diagnosis.

Complete clinical response to combined antifungal therapy in two cats with invasive fungal rhinosinusitis caused by cryptic Aspergillus species in section Fumigati

Cryptic species in Aspergillus section Fumigati are increasingly reported to cause invasive aspergillosis in humans and animals. These infections are often refractory to treatment because of intrinsic antifungal resistance. We report two cases of invasive fungal rhinosinusitis in domestic cats caused by A. udagawae and A. felis. Clinical signs resolved after combined therapy including posaconazole, caspofungin and terbinafine. Both cases remained asymptomatic more than 2 years from initial presentation.

Invasive fungal rhinitis with adnexal involvement caused by Histoplasma capsulatum in a cat from a non-enzootic location

Case summary

This report describes a cat with a rare form of histoplasmosis: invasive rhinitis with adnexal involvement, mimicking disease more commonly caused by cryptococcosis or aspergillosis. This case is especially noteworthy as it was from an area where histoplasmosis is not enzootic.

Relevance and novel information

Invasive fungal rhinitis causes significant morbidity in cats. Diagnostic investigation of more common pathogens includes detection of fungal antigen (Cryptococcus) or antifungal antibodies (Aspergillus). This case demonstrates that histoplasmosis can present as chronic nasal disease in cats. Histoplasma antigen testing provides a non-invasive diagnostic option. Moreover, this case serves as a reminder that histoplasmosis can affect cats anywhere, even in non-enzootic areas.

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.

Genetic polymorphisms in toll-like receptors 1, 2, and 4 in feline upper respiratory tract aspergillosis

Fungal species in the genus Aspergillus are environmental saprophytes that can act as opportunistic pathogens of the nasal cavity and paranasal sinuses in humans, cats and other species. Upper respiratory tract aspergillosis (URTA) presents as non-invasive and invasive forms with the latter occurring almost exclusively in immunocompromised hosts. However, in domestic cats, invasive URTA affects apparently immunocompetent patients. A defect in innate immunity has been proposed as a predisposing factor in invasive feline URTA. Single nucleotide polymorphisms (SNPs) in pattern recognition receptor genes have been implicated in the pathogenesis of aspergillosis in humans. The aims of this study were to identify non-synonymous SNPs in the coding regions of toll-like receptors involved in the immune response to Aspergillus spp. and to compare the frequency of these SNPs between affected and control cats. The coding and flanking regions of TLR1, TLR2 and TLR4 were sequenced in 14 cats with URTA and the sequences were compared with those in 20 control cats without aspergillosis. In total, 23 non-synonymous SNPs were identified in TLR1 (n = 11), TLR2 (n = 3) and TLR4 (n = 10). Differences in allelic frequency of non-synonymous SNPs between affected and controls were not identified either within breeds or overall or between non-invasive and invasive disease phenotypes. Although allelic frequency differed between cat breeds that are overrepresented for URTA and underrepresented breeds there was no association differences identified between affected cats and underrepresented breeds. The difference in allelic frequency of an INDEL point mutation identified in intron 1 of TLR4, between cats with non-invasive versus invasive aspergillosis approached significance (p = 0.054). While results from this study do not support a role for non-synonymous SNPs in the pathogenesis of feline URTA they do provide evidence that investigation for polymorphisms in non-coding regions of these genes and in other pattern recognition receptors are warranted.

Breed-specific variations in the coding region of toll-like receptor 4 in the domestic cat

Specific point mutations in the human toll-like receptor 4 (TLR4) confer altered risk for diverse diseases including sepsis, aspergillosis and inflammatory bowel disease. Some of these TLR4 polymorphisms are racially specific. We hypothesised that feline TLR4 polymorphisms might underlie an observed increased risk to infectious and inflammatory diseases in some cat breeds. The aim of this study was to identify breed-specific variations in the coding region of feline TLR4 and to model the effect of mutations on protein structure and function in silico. The entire coding region of TLR4 was sequenced in 8 groups (7 pure-bred, 1 crossbred) of domestic cats (Felis catus) comprising 158 individuals. Twenty-two single nucleotide polymorphisms (SNPs) were identified in TLR4, with 16 located in the coding region (11 non-synonymous) and four in the 3′UTR. Comparison of breed specific allelic frequencies indicated that Burmese and British shorthairs most commonly differed from other breeds. In silico analyses to predict the impact of the 11 non-synonymous variants indicated a deleterious effect on protein structure for one SNP (c.869 G > A), which was not associated with a specific breed. Overall, findings from this study do not support a role of TLR4 dysfunction in breed-predispositions to infectious diseases in domestic cats in Australia.

Diagnostic Aspects of Veterinary and Human Aspergillosis

The genus Aspergillus is composed of more than 300 species, a fraction of which are involved in animal or human infections mostly following environmental exposure. Various risk factors (i.e., immunosuppression, tuberculosis) have been recognized for human whereas for veterinary infections, unhygienic management, trauma, anatomical conformation of the skull, or suspected immunological deficiencies have been suggested. In animals, aspergillosis is mostly sporadic but in some circumstance such as infections on poultry farms may involve the whole flock. Since the high prevalence of immunosuppression in human patients has not been mirrored in veterinary medicine, and although to the best of our knowledge, no comprehensive data on the prevalence of aspergillosis in animals has been published, their epidemiology has not changed during the last decades. The impact of these infections may be economic or if they are incurable, sentimental. The objective of the first part is to describe the diagnosis of the main clinical entities caused by Aspergillus spp. in animals. It includes disseminated canine aspergillosis, canine and feline sino-nasal and sino-orbital aspergillosis, guttural pouch mycosis in horses, mycotic abortion in cattle, mycotic keratitis in horses, and avian aspergillosis. When pathogenesis and clinical aspects are relevant for diagnosis—they will be addressed as well. The second part deals with human aspergillosis, which is a multifaceted disease, manifested in a spectrum of clinical entities affecting one or more organs. Diagnosis is based on the clinical manifestation, supported and confirmed by laboratory means, involving the classical approach of demonstrating the etiological agent in the clinical specimens and in culture. Noncultural methods, such as antigen detection and/or molecular assays to detect fungal nucleic acids or protein profiles, are used as well. The isolation and identification of the fungus allows the determination of its susceptibility to antifungal drugs. Thus, antifungal susceptibility testing maybe considered as part of the diagnostic process, which is of relevance for management of the infection. In this review article, the part dealing with diagnostic aspects of aspergillosis in humans concentrates on susceptibility testing of Aspergillus spp. to antifungal drugs and drug combinations. The technologies and methods of susceptibility testing are described and evaluated.

Evaluation of Serum Aspergillus-Specific Immunoglobulin A by Indirect ELISA for Diagnosis of Feline Upper Respiratory Tract Aspergillosis

Background

Serological tests for diagnosis of aspergillosis in immunocompetent humans and animals are based on Aspergillus‐specific IgG (As‐IgG). In humans with chronic pulmonary aspergillosis, As‐IgA may be detectable even if IgG titers are negative. Cats with upper respiratory tract aspergillosis (URTA) have detectable As‐IgG, but their ability to mount an IgA response and its diagnostic utility are unknown.

Objectives

To determine whether serum As‐IgA can be detected in cats with URTA and evaluate its diagnostic utility alone or combined with As‐IgG.

Animals

Twenty‐three cats with URTA (Group 1), 32 cats with other respiratory diseases (Group 2), and 84 nonrespiratory controls (Group 3).

Methods

Serum As‐IgA and As‐IgG was measured by indirect ELISA. Optimal cutoff values were determined by receiver‐operating curve analysis. Sensitivity (Se) and specificity (Sp) for URTA diagnosis were determined.

Results

Serum IgA was detected in 91.3% of Group 1 cats. The Se of IgA detection was 78.3% and Sp was 96.9% for Group 2, 85.7% for Group 3 and 88.8% for Group 2 and 3 combined. Assay Se for IgG was 100% and Sp was 92.2%. Using combined IgA and IgG results at cutoffs optimized for Sp for IgA and Se for IgG and combined controls (Groups 2 and 3), Se for diagnosis was 100% and Sp was 91.4%.

Conclusion and Clinical Importance

Most cats with URTA have serum As‐IgA antibodies that can be detected by ELISA. Paired measurement of serum As‐IgA and IgG shows no benefit for diagnosis of feline URTA over IgG alone.

Immunohistochemical Analysis of Leucocyte Subsets in the Sinonasal Mucosa of Cats with Upper Respiratory Tract Aspergillosis

Leucocyte populations in the sinonasal mucosa of cats with and without upper respiratory tract aspergillosis were compared using immunohistochemistry and computer-aided morphometry. Inflammation was identified in the nasal mucosa of all affected cats, comprising predominantly of lymphoplasmacytic infiltration of the lamina propria associated with epithelial proliferation and degeneration. There was intense and diffuse expression of class II antigens of the major histocompatibility complex, associated with sites of hyphal invasion with hyperplasia and ulceration of the epithelium adjacent to fungal elements. Significantly more CD79b(+) cells, total lymphocytes, immunoglobulin (Ig)-expressing cells and MAC387(+) cells infiltrated the epithelium and more IgG(+) cells and total Ig-expressing cells infiltrated the lamina propria in affected cats compared with controls. Importantly, the inflammatory profile in affected cats was not consistent with the T helper (Th)1 and Th17 cell-mediated response that confers protective acquired immunity against invasive aspergillosis in dogs and people and in murine models of the infection. This finding may help to explain the development of invasive aspergillosis in systemically immunocompetent cats.

Aspergillus and aspergilloses in wild and domestic animals: a global health concern with parallels to human disease

The importance of aspergillosis in humans and various animal species has increased over the last decades. Aspergillus species are found worldwide in humans and in almost all domestic animals and birds as well as in many wild species, causing a wide range of diseases from localized infections to fatal disseminated diseases, as well as allergic responses to inhaled conidia. Some prevalent forms of animal aspergillosis are invasive fatal infections in sea fan corals, stonebrood mummification in honey bees, pulmonary and air sac infection in birds, mycotic abortion and mammary gland infections in cattle, guttural pouch mycoses in horses, sinonasal infections in dogs and cats, and invasive pulmonary and cerebral infections in marine mammals and nonhuman primates. This article represents a comprehensive overview of the most common infections reported by Aspergillus species and the corresponding diseases in various types of animals.