Customized Open Patch Allergen Testing in a Rhesus Macaque (Macaca mulatta)

Abstract

An adult rhesus macaque (Macaca mulatta) presented with chronic, progressive dermatitis and alopecia refractory to dietary modification, environmental enrichment, and medical management. A comprehensive dermatologic workup was performed, including the application of a customized open patch allergen testing protocol to evaluate suspected environmental exposures. Patch testing identified a commercial dish soap used in routine sanitation as the likely causative contact allergen. Discontinued use of the product resulted in complete and sustained resolution of clinical signs, with recurrence only following accidental reintroduction of the soap to the facility. To our knowledge, this is the first report describing the use of customized open patch allergen testing to identify a specific contact allergen in a nonhuman primate, highlighting its potential utility as a diagnostic tool in laboratory animal medicine.

Introduction

Dermatologic disease and alopecia are common clinical findings in captive nonhuman primates and can arise from a wide range of behavioral, infectious, inflammatory, nutritional, and age-related causes.^1–4 In the laboratory setting, alopecia is often initially attributed to psychogenic causes such as overgrooming or hair pulling; however, this assumption may neglect primary dermatologic disease. Surveys and diagnostic studies in rhesus macaques, for example, have shown that coat damage and alopecia are frequent findings in captive colonies and that affected animals may have histopathologic changes consistent with chronic inflammatory or hypersensitivity dermatitis rather than purely behavioral disease.^1,3,5

While a variety of dermatoses including psoriatic, exudative, and seborrheic dermatitis have been reported in nonhuman primates, allergic dermatologic disease may be overlooked during evaluation of indoor-housed laboratory animals, where standardized environmental conditions and husbandry practices may obscure the role of repeated allergen exposure.² This stability may cause clinicians to assume that a new environmental allergy is an unlikely contributor to dermatologic disease and ignore the potential for sensitization to develop over time with repeated exposure to contact allergens. However, allergic dermatitis should be considered in cases of chronic or progressive skin disease that do not respond to standard management strategies. Standard treatment includes elimination of potential environmental exposures, dietary modification, treatment of secondary infections, and symptomatic control with antiinflammatory or antipruritic medications.^6,7 In humans, allergic contact dermatitis is known to substantially affect patient quality of life, underscoring the importance of accurate allergen identification and management.⁶

Alopecia in nonhuman primates can therefore be multifactorial and should not be presumed to solely be behavioral in origin without appropriate investigation. Behavioral abnormalities such as overgrooming may themselves arise from complex environmental and physiologic factors and should be evaluated alongside potential medical causes.⁸ When dermatologic disease persists or worsens despite behavioral or environmental interventions, primary dermatologic etiologies should be considered and investigated through a comprehensive diagnostic evaluation.^1,3

To date, only a single case of allergic contact dermatitis has been reported in a nonhuman primate—a latex sensitivity in an adult male rhesus macaque.⁹ Herein, we describe a case of chronic hypersensitivity dermatitis in a rhesus macaque diagnosed using a customized open patch allergen testing protocol modified from the human medical literature.^10,11 This report demonstrates the potential diagnostic utility for this technique for identifying contact allergens in laboratory animals and highlights the importance of considering iatrogenic environmental exposures during dermatologic evaluation.

Case Report

An experimentally naive, Indian origin adult female rhesus macaque negative for simian retrovirus type D, simian T cell leukemia virus, simian immunodeficiency virus, herpes B virus, and measles virus initially presented with mild, patchy alopecia on her hindlimbs. Small excoriations were noted, suggesting that the alopecia was likely self-induced. In order to manage a possible behavioral cause, she was provided with extra enrichment 3 times per week to target foraging behavior. However, over a period of 2 years, alopecia progressed to include all 4 limbs, her shoulders, abdomen, and caudal dorsum. This was despite increasing foraging and social enrichment opportunities including pair-housing with conspecifics. Alopecia was accompanied by intense pruritus and marked erythema and diffuse scale, most severe on her face, head, and neck. Multifocal pinpoint crusts and minor superficial excoriations were also frequently observed on her limbs, chest, abdomen, and face. The patient’s diet was transitioned from standard chow (5038 Monkey Diet; LabDiet, Richmond, IN) to a higher-fiber formulation (5049 Fiber-Plus Monkey Diet; LabDiet, Richmond, IN), as well as to a higher-protein formulation (5045 High Protein Monkey Diet; LabDiet, Richmond, IN). These transitions were implemented to introduce a novel dietary formulation in the event of a diet-related hypersensitivity and provide nutritional support aimed at potentially modulating inflammation and supporting skin barrier function. Unfortunately, several weeks on these diets did not resolve clinical signs. The patient’s condition was concurrently managed with a 3-week course of generic prednisone 0.5-1 mg/kg PO once to twice daily and diphenhydramine (Benadryl; Kenvue, Skillman, NJ) 2 mg/kg PO twice daily, with only partial resolution of signs. Clinical signs recurred following tapering and discontinuation of prednisone ∼5 months later. Treatment with oclacitinib (Apoquel; Zoetis, Parsippany, NJ) at 0.5 mg/kg PO twice daily was then initiated for ∼6 weeks, during which the patient continued to experience mild pruritus and diffuse scaling, but without erythema. Oclacitinib was discontinued 1 week before her full dermatological workup.

The patient was sedated, and the following was observed on physical examination: hypotrichosis, erythema, and mild scale of the face; alopecia of both forelimbs with a healed, focal, 1-cm, superficial excoriation on the caudal aspect of the proximal right antebrachium; mild hyperkeratosis and scale of the left shoulder; multifocal papules in both axillae; patchy alopecia and hyperkeratosis on the craniolateral thighs and distal hindlimbs, with multifocal pinpoint crusts and mild scale on the right thigh; and alopecia and mild scale of the right flank. Blood was taken for a CBC, serum chemistry, and thyroid panel, all of which were unremarkable. Cytology of all affected areas through direct impression smear and tape preparation demonstrated rare cocci, rare acantholytic cells, and rare epithelial cells with keratohyalin granules, indicating samples of the deeper layers of the epidermis. Hair at the margins of affected areas easily epilated and was collected for trichography; the trichogram was negative for fungal and parasitic organisms, although broken hair shafts indicating self-trauma were observed. Superficial and deep skin scrapes were negative for parasites. Four 6-mm punch biopsies of skin (right chest; medial proximal left forelimb; right abdomen; medial right thigh) were also submitted for evaluation. Histologic evaluation revealed mild, chronic, lymphocytic, superficial perivascular dermatitis with moderate epidermal hyperplasia and mild orthokeratotic hyperkeratosis, compared with other biopsy sites that were histologically normal (Figure 1A and B). There was no evidence of bacterial, fungi, or ectoparasites, confirmed with Gram and periodic acid–Schiff stains. Fungal culture results were negative. Based on the diagnostic findings during this workup, we presumed chronic dermatitis with secondary pyoderma.

Figure 1.

Photomicrographs of Skin Biopsies from the Affected Animal. (A) Haired skin, medial proximal left forelimb. There is moderate epidermal hyperplasia (asterisks) and mild, lymphocytic, superficial perivascular dermatitis (arrowheads). Original magnification, 20×; hematoxylin and eosin. (B) Haired skin, right lateral thigh. Histologically normal skin. Original magnification, 20×; hematoxylin and eosin.

A modified, custom open patch testing panel was created to test for 5 possible environmental allergens.⁴ These included the patient’s rubber toy and metal collar as well as a commercial liquid concentrate dish soap (Joy Professional; Procter & Gamble, Cincinnati, OH), a quaternary ammonium disinfectant (Quatricide PV; Pharmacal Research Laboratories, Waterbury, CT), and nitrile gloves used in the housing room. Small shavings were taken from each of the samples and were individually macerated in a mortar and pestle with 2 mL of 70% ethanol. While the exact mass of each sample was not quantified, comparable amounts of material were used across all test substances to ensure consistency between applications. Each sample was then mixed with 0.25 ounces of petroleum jelly and then applied in a small circle on the caudal dorsum of the patient, in addition to a circle of petroleum jelly to serve as a negative control. A transparent film dressing was placed to cover these areas, and the patient’s lower abdomen and waist were wrapped in a bandage to protect the test sites. Forty-eight hours later, the patient was sedated again to remove the bandage and evaluate the allergy test sites; multifocal pinpoint crusts were observed at the edge of the previously bandaged area. Faint erythema was seen at the dish soap site, but reddened sexual skin at the caudal dorsum made interpretation difficult. No vesiculation or ulceration were present. For follow-up testing, an area on her cranial dorsum was shaved, and 1 mL of the Joy dish soap was applied directly to the skin at this site; the same volume of a comparable commercial dish soap (Dawn Professional; Procter & Gamble, Cincinnati, OH) was applied to the inguinal regions. Forty-eight hours later, the cranial dorsum was erythematous (Figure 2); the inguinal skin appeared normal with no observable changes. The patient was diagnosed with chronic hypersensitivity dermatitis, likely exacerbated by the commercial dish soap, so we discontinued its use in our facility for daily sanitation of floors, cages, and toys. The patient’s skin remained unaffected and clinically normal for an additional 2 weeks without the oclacitinib. She experienced an acute flare of her dermatitis with facial erythema following inadvertent reintroduction of the offending allergen to the facility; this was well managed with prompt removal of the dish soap as well as oclacitinib once per day, which was eventually decreased to 3 times per week and then discontinued altogether. The animal has no longer had any alopecia or dermatitis and has not experienced any additional flare-ups in over a year.

Figure 2.

Follow-up Testing of Joy Dish Soap Directly on the Caudal Dorsum. The region within the dotted line indicates mild, focally extensive erythema at the center of the application area.

Discussion

The clinical findings and response to treatment in this case were consistent with chronic dermatitis with an allergic contact component, associated with exposure to a commercial dish soap that was used in routine sanitation. This patient had regularly been exposed for several years and likely sensitized to objects and surfaces cleaned with this product. This timeline is consistent with the pathogenesis of allergic contact dermatitis, in which sensitization develops following repeated exposure to a hapten or environmental allergen, and clinical disease is elicited upon subsequent contact.^6,7

The diagnostic approach in this case focused on systematically excluding other potential causes of chronic dermatologic disease. Infectious etiologies were considered unlikely based on negative cytology, skin scrapings, fungal culture, and special staining of histopathology. Hematologic and biochemical testing were also unremarkable; although eosinophilia may be associated with certain hypersensitivity or parasitic conditions, its absence does not exclude allergic disease, particularly in cases of contact hypersensitivity.⁷

Patch testing is considered the gold standard diagnostic method in human dermatology for identifying contact allergens and remains central to the diagnosis and management of allergic contact dermatitis.^6,10,11 The technique involves application of suspected allergens to intact skin with evaluation of localized inflammatory reactions ∼48 hours later and at delayed intervals. Variations of this approach, including open and semi-open patch testing, allow testing of products in their native form when irritant reactions are suspected.^6,10,11 In this case, the result of initial patch testing was mild, consisting of localized erythema without more severe inflammatory changes; however, reproducible clinical signs following direct reexposure and subsequent resolution with allergen removal strongly supported the Joy dish soap as a contact allergen. Patch test reactions can be subtle, with only erythema often indicating potential allergen exposure; therefore, follow-up testing may be warranted to establish a stronger causal relationship.

Although widely used in human medicine, patch testing is less commonly applied in veterinary dermatology. In dogs, it has been used to identify hypersensitivity reactions to environmental materials such as plants, shampoos, medicaments, and household products.⁷ For example, patch testing implicated a commercial shampoo as the causative agent in a case of superficial suppurative necrolytic dermatitis in a miniature schnauzer.¹² Veterinary dermatology literature also emphasizes testing materials from the animal’s environment, as locally relevant exposures may not be captured by standardized allergen panels.⁷ Reports describing contact allergen identification in nonhuman primates remain extremely limited. To our knowledge, the only previously reported case of allergic contact dermatitis in a rhesus macaque involved latex sensitivity.⁹ The present case therefore expands the limited literature on allergic contact dermatitis in laboratory primates and demonstrates the diagnostic utility of customized patch testing protocols adapted from human and veterinary dermatology.

Histopathologic evaluation in this case revealed a mild, chronic lymphocytic superficial perivascular dermatitis with epidermal hyperplasia and orthokeratotic hyperkeratosis. These findings represent a nonspecific inflammatory reaction pattern rather than a definitive diagnosis. Superficial perivascular dermatitis is commonly associated with a variety of dermatologic insults, particularly hypersensitivity disorders and ectoparasitism, but may also be observed in other infectious or inflammatory conditions.^2,9 Consequently, histologic findings must be interpreted in conjunction with clinical history and results of additional diagnostic testing when establishing an etiologic diagnosis. In this case, the absence of identifiable infectious agents supported further evaluation for a hypersensitivity-mediated process.

Laboratory animals are routinely exposed to numerous materials in their environments associated with housing, sanitation, enrichment, and research procedures. Although generally well tolerated, repeated exposure may allow sensitization to develop in susceptible individuals. In this case, removal of the suspected allergen resulted in sustained resolution of dermatologic disease, supporting a causal relationship between the exposure and clinical signs. Customized open patch testing has not been indicated in other colony animals, and no additional cases have been identified following removal of the product, suggesting this represented an individual hypersensitivity rather than a colony-wide issue.

Contact allergies should therefore be considered in laboratory settings, where animals are chronically exposed to chemicals and other materials that may promote sensitization. Dermatologic disease and chronic pruritus can significantly affect an animal’s well-being and behavior, making timely identification of underlying causes essential for effective clinical management and the maintenance of animal welfare and quality of life. This report highlights the importance of a comprehensive dermatologic workup, including consideration of allergy testing when supported by histologic findings and after other potential causes have been excluded.

Conflict of Interest

The authors have no conflicts of interest to declare.

Funding

This work was internally funded.