Novel canine anti-Coccidioides immunoglobulin G enzyme immunoassay aids in diagnosis of coccidioidomycosis in dogs

The dog as a sentinel and animal model for coccidioidomycosis

Coccidioidomycosis is a potentially fatal fungal disease of humans and animals that follows inhalation of Coccidioides spp. arthroconidia in the environment. The disease in dogs resembles that in people, and because dogs may be at increased risk of exposure due to their proximity to the ground and digging behavior, they are valuable models for the disease in humans. Dogs have been sentinels for identification of new regions of endemicity in Washington and Texas. Canine serosurveillance has also been used to predict variables associated with environmental presence of Coccidioides spp. Expansion of the endemic region of coccidioidomycosis with climate change-along with predicted population increases and increased development in the southwest United States-may result in 45.4 million additional people at risk of infection by 2090. Here we provide an overview of the value of dogs as sentinels for the disease and encourage the routine reporting of coccidioidomycosis cases in dogs to public health agencies. We also highlight the value of dogs as naturally occurring models for studying novel treatment options and preventatives, such as a novel live avirulent coccidioidomycosis vaccine.

Diagnostic Contribution of Bronchoalveolar Lavage Sampling and Fungal Culture in a Dog With Pulmonary Coccidioidomycosis

A 7-year-old, male neutered, Miniature Australian Shepherd from Arizona was presented for evaluation of a 3-month history of progressive cough. Thoracic radiographs revealed a focal alveolar pulmonary pattern and suspected tracheobronchial lymph node enlargement. Serum anti-Coccidioides spp. IgM/IgG antibodies were not detected by agar gel immunodiffusion performed by 2 different reference commercial veterinary laboratories approximately 3.5 and 3.75 months after respiratory tract signs were first noted. The dog failed to respond to empiric therapy with a cough suppressant and various antibiotics. Tracheobronchoscopy and bronchoalveolar lavage (BAL) were subsequently performed and cytological examination of the BAL fluid identified marked neutrophilic inflammation characterized by mildly degenerate neutrophils and no infectious organisms. Bacterial cultures were negative but fungal cultures revealed growth of Coccidioides spp. Clinical signs improved shortly after initiation of fluconazole administration and the dog achieved long-term sustained clinical remission. Here, we provide a description of a dog with pulmonary coccidioidomycosis diagnosed with fungal culture of BAL fluid. Airway sampling with cytological examination and fungal culture should be considered in dogs with persistent respiratory related clinical signs, negative antibody serology, and that have lived in or traveled to endemic areas.

Comparison of Immunodiagnostic Assays for the Rapid Diagnosis of Coccidioidomycosis in Dogs

Coccidioidomycosis is a disease caused by the dimorphic fungi Coccidioides spp., which affects humans and a variety of animal species, including domestic dogs. In dogs, accurate diagnosis could provide a substantial improvement on the quality of canine life, as well as an advancement in the mapping of regions endemic for coccidioidomycosis. The purpose of this study was to compare immunodiagnostic assays for anti-Coccidioides antibody (Ab) detection in dogs’ serum. Three commercially available immunodiagnostic assays (IMMY^®; Norman, OK, USA) were evaluated, including the sōna Coccidioides Ab Lateral Flow Assay (LFA), Coccidioides IDCF immunodiffusion assay (IDCF), and the Clarus Coccidioides Ab Enzyme Immunoassay (EIA). Assays were evaluated using 98 dog serum samples: 29 from dogs with coccidioidomycosis, 15 from dogs diagnosed with histoplasmosis, 10 from dogs diagnosed with blastomycosis, and 44 from dogs without a fungal disease. Using specimens from dogs with coccidioidomycosis, the IDCF had an accuracy of 92% (95% confidence interval [95% CI] = 85–96%), the EIA had an accuracy of 91% (95% CI = 83–96%), and the LFA displayed an accuracy of 82% (95% CI = 73–89%). Using Kappa analysis, the agreement between LFA and EIA was 0.59 (95% CI = 0.42–0.75), that between LFA and IDCF was 0.64 (95% CI = 0.48–0.79), and that between EIA and IDCF was 0.79 (95% CI = 0.64–0.90). Most cross-reactions were observed in dogs with histoplasmosis. Compared with EIA and IDCF, the LFA requires substantially less laboratory equipment and infrastructure and rapidly produces results, offering a substantial improvement for the initial screening of coccidioidomycosis in dogs.

The utility of Coccidioides antigen and antibody detection in cerebrospinal fluid in the diagnosis of canine central nervous system coccidioidomycosis

OBJECTIVE

To evaluate the utility of enzyme immunoassays (EIAs) for the detection of Coccidioides antigen and antibody in CSF in the diagnosis of CNS coccidioidomycosis in dogs.

ANIMALS

51 dogs evaluated for CNS disease in a single specialty center in Tucson in 2016.

PROCEDURES

Excess CSF after routine analysis was banked after collection from dogs presented to the neurology service. Samples were tested by EIA for presence of Coccidioides antigen and antibody. Clinical data were collected from medical records retrospectively.

RESULTS

22 dogs were diagnosed with CNS coccidioidomycosis (CCM) or another neurologic disease (non-CCM). These groups of dogs overlapped in the presenting complaints, MRI results, and routine CSF analysis results. Four dogs, all with CCM, had positive antigen EIA results. With clinical diagnosis used as the reference standard, CSF antigen testing had low sensitivity (20%) but high specificity (100%) for diagnosis of CCM. Ten dogs with CCM and 4 dogs with other diagnoses had antibody detected in CSF by EIA. Sensitivity of CSF antibody testing was 46%, specificity was 86%, and positive and negative predictive values for the study population were 71% and 68%, respectively.

Clinical Relevance

Diagnosis of CNS coccidioidomycosis in dogs in an endemic region was hampered by overlap of clinical signs with other neurologic disorders and the low sensitivity of confirmatory diagnostics. The evaluated Coccidioides-specific EIAs performed on CSF can aid in the diagnosis. A prospective study is warranted to corroborate and refine these preliminary findings.

Δcps1 vaccine protects dogs against experimentally induced coccidioidomycosis

Coccidioidomycosis is a significant health problem of dogs and humans in endemic regions, especially California and Arizona in the U.S. Both species would greatly benefit from a vaccine to prevent this disease. A live avirulent vaccine candidate, Δcps1, was tested for tolerability and efficacy to prevent pulmonary coccidioidomycosis in a canine challenge model. Vaccine injection-site reactions were transient and there were no systemic effects observed. Six of seven vaccine sites tested and all draining lymph nodes were sterile post-vaccination. Following infection with Coccidioides posadasii, strain Silveira, arthroconidia into the lungs, dogs given primary and booster vaccinations had significantly reduced lung fungal burdens (P = 0.0003) and composite disease scores (P = 0.0002) compared to unvaccinated dogs. Dogs vaccinated once had fungal burdens intermediate between those given two doses or none, but disease scores were not significantly different from unvaccinated (P = 0.675). Δcps1 was well-tolerated in the dogs and it afforded a high level of protection when given as prime and boost. These results drive the Δcps1 vaccine toward a licensed veterinary vaccine and support continued development of this vaccine to prevent coccidioidomycosis in humans.

Clinical performance of a point-of-care Coccidioides antibody test in dogs

Background

Point‐of‐care (POC) Coccidioides antibody assays may provide veterinarians with rapid and accurate diagnostic information.

Objectives

To determine the agreement of a POC lateral flow assay (LFA), sona Coccidioides (IMMY, Norman, Oklahoma) with the current diagnostic standard, the immunodiffusion assay (agar gel immunodiffusion [AGID]; Coccidioidomycosis Serology Laboratory, University of California, Davis, California).

Animals

Forty‐eight sera specimens from 48 dogs.

Methods

Sera specimens were collected from client‐owned dogs that had a clinical suspicion for coccidioidomycosis. Animals were classified as Coccidioides antibody‐positive (n = 36) based on a positive AGID or Coccidioides antibody‐negative (n = 12) based on a negative AGID. The performance of the LFA assay was determined by comparing results to AGID results.

Results

The LFA assay demonstrated agreement in 32 of 36 Coccidioides antibody‐positive specimens and 12 of 12 Coccidioides antibody‐negative specimens, resulting in a positive percentage agreement of 88.9% (95% confidence interval [CI], 74.7‐95.6%) and negative percentage agreement of 100% (95% CI, 75.8‐100%) as compared to AGID. A receiver operator characteristic curve was constructed, and the area under the curve was 0.944 (CI, 0.880‐1.000).

Conclusion and Clinical importance

This LFA is a rapid alternative to the traditional AGID. The LFA provides excellent predictive value for positive results. Positive agreement was lower in dogs with low AGID titers; therefore, confirmatory testing is recommended if a high index of suspicion exists.

Evaluation of a commercially available, point-of-care Coccidioides antibody lateral flow assay to aid in rapid diagnosis of coccidioidomycosis in dogs

Coccidioidomycosis in dogs can range from mild respiratory disease or vague, chronic malaise to acute, severe life-threatening illness. The diagnosis of coccidioidomycosis in dogs is based on clinical presentation and serology. Spherule identification is not typical because of low numbers of organisms in specimens, and the invasive nature of sampling tissues and lungs. Conventional serological assays require samples to be submitted to a reference laboratory and results take several days to one week. The sōna Coccidioides Antibody Lateral Flow Assay (LFA) (IMMY Diagnostics) is a rapid, bench-side test used for detection of Coccidioides antibodies that is available and FDA-cleared for use in humans but has not been evaluated in dogs. The goal of this study was to compare the LFA to conventional agar gel immunodiffusion (AGID). Paired serum samples were collected for screening by the LFA and submitted to a commercial reference laboratory for AGID screen and titer. Of 56 paired serum samples analyzed, 30 were positive and 26 were negative on the sōna Coccidioides antibody LFA. The overall percentage agreement plus 95% confidence interval (CI) was 87.5% (76.20-93.99). Positive percent agreement was 89.7% (73.38-96.65) and negative percent agreement was 85.2% (67.25-94.36). The kappa coefficient to assess agreement was 0.749 (95% CI, 0.576-0.923), which is interpreted as good agreement between the tests (>70%). The sōna Coccidioides antibody LFA provided rapid, point-of-care results with a high level of agreement to standard AGID serology in dogs clinically suspected to have coccidioidomycosis, and may aid in diagnosis of coccidioidomycosis in dogs.