Jennifer E. Graham

Members of the microsporidial genus Encephalitozoon have the capacity to infect both mammals and birds, and E. cuniculi is most commonly found in rabbits. With a seroprevalence ranging up to 85%, E. cuniculi can be a problem in pet rabbits as well as in food production and laboratory animal science. While most infections are likely subclinical, there are three main clinical presentations: neurological, renal, and ocular. Typical clinical signs including vestibular disease and phacoclastic uveitis may develop with initial or relapsing infection, while renal infection is usually progressive and associated with non-specific clinical signs. High-sensitivity/specificity ante mortem diagnostic options are lacking, and serological testing most often provides adjunct rather than definitive information such that physical examination and other diagnostics are used more so for ruling out other differentials and comorbidities, rather than confirming infection. In the veterinary community, treatment regimens are variable given the lack of thorough studies and a consensus. The aim of this document is to present the available literature to give a concise review of this organism and its infection of rabbits as well as to propose guidelines and protocols for diagnostics and treatment regimens. In addition, the current challenges and recommendations for further studies are discussed.

In 2022–2023, the first survey of clinicians regarding Encephalitozoon cuniculi infection of rabbits was undertaken. The purpose was to assess the current worldwide knowledge of clinicians regarding influence of breed and age, clinical presentations, use of various diagnostic tools, and treatment regimens and to explore how responses may differ by geographic location. Identifying mostly as exotic animal clinicians, 339 respondents participated, with nearly half from the United States and the remainder from 35 other countries. Neurological signs were most consistently reported as associated with Encephalitozoon cuniculi and the most recurrent clinical case presentation. Other responses showed differences by geographic location. For example, age predilection for disease varied, with 71.1% of international respondents indicating that infection was more common in young rabbits versus 28.9% who suggested it was more frequent in older rabbits. This was significantly different (p = 0.001) from the information from respondents from the United States, where 48.0% indicated that younger rabbits had an increased incidence versus 52.0% who indicated that older age increased occurrence. While some differences may be related to the practice composition and the training level of respondents, many responses were in alignment with the existing literature. Future inquiries should focus more on these discrepancies to aid in generating guidelines for the diagnosis and treatment of this infectious disease.

CASE DESCRIPTION 3 ferrets (Mustela putorius furo), aged 1 to 2 years, were referred for evaluation of a 4-day to 2-week history of gastrointestinal signs, including anorexia, regurgitation, and vomiting. CLINICAL FINDINGS All 3 ferrets had clinical signs suggestive of dysphagia or esophagitis on initial examination. Esophagoscopy, barium-contrast esophagography, or both revealed foreign bodies with mucosal inflammation in 1 patient and an esophageal foreign body with stricture in 2 patients. One of the latter ferrets had a recent history of gastrotomy to remove a foreign body. TREATMENT AND OUTCOME 1 ferret was treated with endoscopic retrieval of the foreign bodies. Esophageal stricture was treated in 2 ferrets by means of endoscopic balloon dilation accompanied by placement of an esophageal stent in 1 ferret. After resolution of clinical signs and completion of all prescribed treatments, 2 of 3 ferrets successfully transitioned to a regular hard kibble diet; 1 ferret remained on a soft diet for 2 years. All owners were satisfied with the outcome of treatment. CLINICAL RELEVANCE Ferrets are prone to foreign body ingestion. Results of this small series of cases suggested that minimally invasive techniques may be useful for the management of esophageal disease in this species.

Macropods are susceptible to trauma, and fractures of the cervical vertebrae due to collisions are relatively common. A 4-yr-old, intact male Bennett's wallaby (Macropus rufogriseus) was presented acutely nonambulatory and tetraparetic but with motor function present in all limbs. Cervical radiographs revealed a C4 vertebral fracture. Surgical stabilization was obtained through a ventral midline approach whereby the vertebral bodies were distracted and then secured with screws and polymethylmethacrylate (PMMA). Postoperative radiographs revealed restoration of the spinal canal and appropriate implant placement. The patient was discharged 4 days postoperatively and gradually recovered full neurologic function per the owner over the ensuing 10 wk. Subsequent radiographs obtained 10.5 mo postoperatively revealed a healed fracture with stable implants. The ventral spinal distraction and stabilization technique using screws and PMMA, as are used in the domestic dog, was successful in this wallaby despite its smaller vertebral size and comparable lack of soft-tissue support.

OBJECTIVE To compare effectiveness of glycerol, dimethyl sulfoxide (DMSO), and hydroxyethyl starch (HES) solutions for cryopreservation of avian RBCs. SAMPLE RBCs from 12 healthy Ameraucana hens (Gallus gallus domesticus). PROCEDURES RBCs were stored in 20% (wt/vol) glycerol, 10% (wt/vol) DMSO freezing medium, or various concentrations of HES solution (7.5%, 11.5%, and 20% [wt/vol]) and frozen for 2 months in liquid nitrogen. Cells were then thawed and evaluated by use of cell recovery and saline stability tests, cell staining (7-aminoactinomycin D and annexin V) and flow cytometry, and scanning electron microscopy. RESULTS Percentage of RBCs recovered was highest for 20% glycerol solution (mean ± SE, 99.71 ± 0.04%) and did not differ significantly from the value for 7.5% HES solution (99.57 ± 0.04%). Mean saline stability of RBCs was highest for 10% DMSO (96.11 ± 0.25%) and did not differ significantly from the value for 20% HES solution (95.74 ± 0.25%). Percentages of cells with 7-aminoactinomycin D staining but without annexin V staining (indicating necrosis or late apoptosis) were lowest for 10% DMSO freezing medium (3%) and 20% glycerol solution (1%) and highest for all HES concentrations (60% to 80%). Scanning electron microscopy revealed severe membrane changes in RBCs cryopreserved in 20% HES solution, compared with membrane appearance in freshly harvested RBCs and RBCs cryopreserved in 10% DMSO freezing medium. CONCLUSIONS AND CLINICAL RELEVANCE Cryopreservation of avian RBCs with HES solution, regardless of HES concentration, resulted in greater degrees of apoptosis and cell death than did cryopreservation with other media. Transfusion with RBCs cryopreserved in HES solution may result in posttransfusion hemolysis in birds.