Pythium insidiosum is an aquatic oomycete that causes invasive, progressive granulomatous lesions of the skin in dogs, horses, and cats and of the gastrointestinal tract in dogs. Although pythiosis has historically been observed most often in tropical and subtropical climates, over the past 2 decades it has been recognized in a broader area, including California1 and Wisconsin2 in the United States. Obtaining a definitive diagnosis may be challenging because histologic findings are insufficiently unique to differentiate pythiosis from lagenidiosis, paralagenidiosis, and zygomycosis. Methods that have been used to confirm a diagnosis include IgG antibody serologic testing3 and microbial culture followed by molecular confirmation of isolate identity by use of species-specific PCR assay or ribosomal RNA gene sequencing.4
In addition to use as a tool for initial diagnosis, IgG antibody serologic testing has also been used to monitor response to treatment in dogs, with maintenance of high antibody concentrations after surgery suggesting incomplete excision or early relapse.5 Conversely, decreasing anti–P insidiosum IgG concentrations have been detected in patients that are cured.6
The most effective treatment for pythiosis is wide surgical excision, which is sometimes followed by antifungal chemotherapeutics. Unfortunately, complete surgical resection is often not possible because of lesion location, and the effectiveness of medical treatment alone is limited by the fact that ergosterol is not a major component of the oomycete cell membrane. As a result, alternative modes of treatment have been evaluated, including an immunotherapeutic product originally developed for use in horses that subsequently has been recommended for use in dogs and humans. Although there is evidence indicating some efficacy of that product in horses,7,8 efficacy in dogs has not been well evaluated and anecdotally appears to be poor.9 In addition, although a mechanism of action for the product has been proposed,10 there have been no studies conducted to evaluate the effect of the immunotherapeutic product on the immune response in any species.
In addition to a lack of information about the mechanism of action of the immunotherapeutic product, information regarding its potential effect on posttreatment monitoring of anti–P insidiosum IgG concentrations is limited. As a result, some clinicians avoid use of immunotherapeutics because of concerns that they may interfere with subsequent serologic monitoring. Although 4 dogs have been described in which anti–P insidiosum IgG concentrations were monitored after treatment that included immunotherapeutics, administration protocols (frequency of administration, number of administrations, and route of administration) and sampling intervals after product administration differed widely.2,6,11,12
Therefore, the objectives of the study reported here were to evaluate the effect of administration of an immuotherapeutic product on anti–P insidiosum IgG concentrations in healthy dogs to better characterize the effect of product administration on the canine humoral immune response and to provide initial information about the potential effect of product administration on posttreatment serologic monitoring. We hypothesized that administration of the immunotherapeutic product would result in significant increases in anti–P insidiosum IgG concentrations.
Supported by a CORP grant from the Louisiana State University School of Veterinary Medicine Department of Veterinary Clinical Sciences.
The authors declare that there were no conflicts of interest.
The authors thank Michael Kearney for assistance with the statistical analysis and Chin-Chi Liu and Laure Molitor for assistance with sample collection and analysis.
Bovine serum albumin
PBS solution and 0.05% Tween
Pan American Veterinary Laboratories, Hutto, Tex.
Immulon 2HB, Thermo Scientific, Rochester, NY.
Peroxidase-conjugated affinity-purified anti-dog IgG, Rock-land Antibodies and Assays, Limerick, Pa.
TMB 2-component microwell peroxidase substrate kit, Sera-Care, Milford, Mass.
Epoch Microplate spectrophotometer, BioTek instruments Inc, Winooski, Vt.
PROC MIX, SAS, version 9.4, SAS Institute Inc, Cary, NC.
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