Pruritus and Unkempt Coat in a New Zealand White Rabbit (Oryctolagus cuniculus)

History

A 3-y-old, 4.2-kg (9.3-lb), intact male, wild-type New Zealand White laboratory rabbit (Oryctolagus cuniculus) obtained from Robinson Services, Inc. (Mocksville, NC) was reported to the veterinary team at the University of Michigan for debris in the fur. This rabbit had no previously reported clinical issues and had not undergone any experimental manipulations. This rabbit was singly housed, and he was previously noted for spraying urine in his enclosure.

Upon physical examination, the rabbit had several pieces of small brown or black debris distributed over the entire dorsum, particularly the caudal dorsum. This material was attached to individual hairs on the middle of the hair shaft (Figure 1). No associated skin lesions were identified. In addition, the rabbit was hypersensitive to handling and restraint, and he scratched or rubbed his sides and dorsum several times during examination, suggesting he was pruritic. The rest of the physical examination was unremarkable.

Figure 1.

Dark debris (arrows) attached to hairs over the dorsum of the affected rabbit. The material is localized to the middle of the hair shaft.

An initial tape strip sample of the material was obtained for microscopy, which revealed several brown ovoid mites (Figure 2A). Several mites were clasped to the hair shafts with ventrally positioned legs, and some possessed a posterior appendage. A wet paper test revealed no evidence of flea excrement (or “flea dirt”).

Figure 2.

Brown mites identified on (A) tape strip and (B) fur pluck samples.

There was concern that the mites would be transmitted to other rabbits in the colony, so all rabbits in surrounding enclosures were visually examined for the presence of mites, and tape strip samples were obtained for microscopy. No mites were identified with the naked eye or microscopically, and the samples were unremarkable overall.

At our institution, we perform quarterly testing in our direct samples collected from a proportion of all rabbit colonies using the Charles River Laboratories Rabbit Surveillance Plus PRIA PCR Panel (Charles River Laboratories, Wilmington, MA). We also perform physical examinations on each individual rabbit annually after 2 y of age and semiannually after 4 y of age. No mite species had been previously identified in this colony.

Differential Diagnoses

Upon initial visual examination, this rabbit’s documented urine spraying was considered to be a cause of his unkempt coat. Additional considerations included acariasis (for example, Cheyletiella parasitovorax, Sarcoptes scabiei), flea infestation (for example, Spilopsyllus cuniculi, Ctenocephalides felis), and pediculosis (for example, Haemodipsus ventricosus). Our differential diagnoses were narrowed down to a mite infestation following microscopic examination of dermatological samples.

Treatment and Management

The affected rabbit was treated with topical selamectin (14 mg/kg; Selarid; Norbrook, Inc., Lenexa, KS) applied directly to the skin at the base of the neck. The treatment was administered 3 times, with each application 2 to 3 wk apart. Six days after ectoparasiticide treatment was initiated, the rabbit was briefly sedated with dexmedetomidine (15 µg/kg) and butorphanol tartrate (0.5 mg/kg) administered intramuscularly to perform a more thorough dermatological examination. Microscopic examination of tape strip and hair pluck samples revealed several dead or slow-moving mites (Figure 2B), whereas skin scrape samples were unremarkable. The rabbit’s pruritus improved within 2 wk of the first dose and resolved approximately 2 wk after the second dose. The presence of live or dead mites did not resolve until 2 wk after the third dose. No clinical concerns were identified in this rabbit following ectoparasiticide treatment, so no additional interventions were pursued.

Because the clinical presentation and mite morphology in this case were not consistent with any of the more common rabbit mites (for example, C. parasitovorax, Psoroptes cuniculi, S. scabiei), fur samples containing the mites were submitted to Charles River Laboratories (Wilmington, MA) for PCR analysis and DNA sequencing. PCR targeting COX1 and 28S revealed positivity for 2 fur samples, while both regions were negative on specificity testing for mouse, rat, and rabbit DNA and on colony screening (Table 1). An identified Sanger region (COX1) was found in multicopy and subsequently separated into both sequences to design a TaqMan assay (Figure 3). This revealed high similarity between these regions and 3 reference sequences for Leporacarus gibbus in GenBank (https://www.ncbi.nlm.nih.gov/genbank/).

Table 1.

Detection of Leporacarus gibbus using TaqMan polymerase chain reaction

Fluorogenic PCR Data	PCR target 1COX1	PCR target 228S	Comments
Suspected case 1: fur pluck	+	+
Suspected case 2: fur pluck	+	+
Specificity testing
Mouse fecal DNA	−	−	No reactivity for any of the listed sample types
Mouse genomic DNA	−	−
Rabbit cecal DNA	−	−
Rabbit MLN DNA	−	−
Rat fecal DNA	−	−
Rat genomic DNA	−	−
Vendor screening	−	−	All colonies tested negative

Publicly available National Center for Biotechnology Information sequences were used to develop the COX1 TaqMan assay, whereas the 28S TaqMan assay was obtained using proprietary sequences. Suspected L. gibbus cases 1 and 2 tested positive using both COX1 and 28S gene targets. The L. gibbus TaqMan assay was specific for L. gibbus and did not cross-react with mouse fecal, mouse genomic, rabbit cecal, rabbit mesenteric lymph node (MLN), rat fecal, or rat genomic DNA. Through vendor screening, all rabbit colonies tested were negative.

Figure 3.

Sanger sequencing of COX1 identifies the mite as Leporacarus gibbus. Mapping contigs by neighbor-joining tree analysis shows (A) L. gibbus Sanger 1 region closely related to GQ864335, whereas (D) L. gibbus Sanger 2 region is related to MW286180 and MW286214. The (B) percent similarity and (C) number of differences are noted for L. gibbus Sanger 1 region, and the (E) percent identity and (F) number of differences can be seen for L. gibbus Sanger 2 region. The multiple regions sequenced in L. gibbus suggest the presence of COX1 in multicopy (Geneious Prime 2024.0.3).

Discussion

Leporacarus gibbus (previously known as Listrophorus gibbus) is a fur mite that has been identified in laboratory and pet rabbits, as well as wild rabbits and hares, in several countries across the globe.¹ It is generally considered a rare mite of rabbits; however, some studies² suggest that L. gibbus is often underdiagnosed or misdiagnosed. It has a direct life cycle on the host, where it feeds on sebum and epithelial cells.¹ These mites can be found anywhere on the body but tend to concentrate over the lumbar region.² Many infestations are subclinical, but some rabbits may present with alopecia, pruritus, scaling, erythema, and/or moist dermatitis.^3,4

The rabbit in this case report had a history of urine spraying, which may have explained his unkempt coat. His pruritus, however, raised the suspicion of an ectoparasitic infestation. The mites identified via microscopy were distributed over the dorsum and attached to individual hair shafts, consistent with the most common fur mite in rabbits, Cheyletiella parasitovorax. However, infestation with this species is typically subclinical or associated with milder clinical signs like scaling or alopecia.⁵ In addition, the morphology of the mites identified on microscopy was not consistent with that of Cheyletiella. Cheyletiella mites are ovoid or saddle shaped and whitish in color (therefore, the common name “walking dandruff”) with longer legs extending out laterally, whereas L. gibbus mites are ovoid and brown with shorter, ventrally directed legs⁵ like the mites obtained from this rabbit. L. gibbus mites are also noticeably sexually dimorphic, with male mites having large adanal clasping organs,¹ which were noted in some of the mites from our samples (Figure 2A).

L. gibbus can be diagnosed via microscopic assessment of fur samples. One previous study² found that visual examination was another reliable screening method for these mites, as they may be visualized with the naked eye and have a characteristic “salt and pepper” appearance. It was easy to visualize mites on the affected rabbit, and several mites were successfully identified on microscopy of fur pluck and tape strip samples. Skin scrapes did not yield as many mites, which may be explained by previous findings that these mites occupy the distal third of the hair shaft.²

Regular health monitoring in the form of surveillance tests and physical examination of individual animals can be helpful in identifying ectoparasitic infestations. Sanger sequencing of the mites from this rabbit resulted in the development of a commercially available PCR assay for L. gibbus, which is now available as an add-on assay to the Rabbit PRIA PCR Panel from Charles River Laboratories. This screening test can be used to screen rabbit colonies for this parasite as well as confirm the diagnosis in suspected cases of L. gibbus infestation.

Therapies reported to successfully treat L. gibbus infestation include selamectin, imidacloprid plus permethrin,² moxidectin plus imidacloprid,⁶ ivermectin,⁷ and lotilaner.⁸ A previous study² comparing the efficacy of selamectin with that of imidacloprid plus permethrin in New Zealand White rabbits infested with L. gibbus found that while both treatments were effective, selamectin more efficiently eliminated infestation after just a single dose. The rabbit in this case report was successfully treated with 3 consecutive doses of selamectin administered 2 to 3 wk apart. No live mites were noted on samples obtained 1 wk after the first dose, although dead mites remained attached to the hair shafts until after the third dose. Clinically, the rabbit’s pruritus improved after the first dose was administered and completely resolved after the second dose.

Accurate diagnosis and treatment of L. gibbus are important to prevent transmission to other rabbits. Fortunately, no other rabbits housed near the rabbit in this report were found to have mite infestations. This was not surprising, as L. gibbus is generally transmitted via direct contact,¹ and this rabbit was singly housed due to being an intact male who was not part of a bonded pair. However, this raises the question of how this rabbit became infested in the first place. One possibility is that the mite was brought in by humans who interact with rabbits outside of our institution, although all staff are required to wear dedicated work uniforms and/or personal protective equipment in the vivaria. Another potential source could be contaminated hay or treats provided to the rabbits. Finally, it is possible that this rabbit arrived at our institution with these mites; this is less likely, as this rabbit’s clinical signs were not noted until 2 y after delivery. Unfortunately, the source of the mite could not ultimately be confirmed.

Previous reports of the zoonotic potential of L. gibbus further emphasize the importance of adequate identification of this mite. To our knowledge, 2 reports of L. gibbus-associated dermatitis in humans have been published in the literature. These include a 6-y-old girl in the United Kingdom with a pet rabbit housed outdoors⁹ and a 30-y-old woman in Italy with 2 indoor pet rabbits.⁶ Both individuals developed a papular dermatitis of the extremities that resolved after the rabbits’ infestations were treated.^6,9

In conclusion, L. gibbus was identified in a laboratory rabbit and confirmed using PCR analysis and Sanger sequencing. This mite species should be considered as a differential diagnosis in laboratory rabbits with clinical signs such as unkempt coat, pruritus, alopecia, and skin lesions. These mites can be identified microscopically, and the diagnosis can be confirmed via screening tests.

Conflict of Interest

The authors have no conflicts of interest to declare.

Funding

This work was internally funded.