Journal of Exotic Pet Medicine 40 (2022) 41 44 Contents lists available at ScienceDirect Journal of Exotic Pet Medicine journal homepage: www.elsevier.com/locate/jepm Case report Cerebral thromboembolism secondary to infective endocarditis in a pet rabbit Ferran Solanes, DVM a, Tiziana Bassan, DVM a, Alex Cobos, DVM c, Maria Frau, DVM d, Jaume Martorell, DVM, PhD, Dip. ECZM a,b,* a Servei d’Exotics, Fundacio Hospital Clínic Veterinari, Campus Universitat Autonoma de Barcelona, Bellaterra, Spain b Departament de Medicina i Cirurgia Animals, Facultat de Veterinaria, Edifici V, Universitat Autonoma de Barcelona, Bellaterra, Spain c Servei de Diagnostic de Patologia Veterinaria, Departament de Sanitat i d’Anatomia Animals, Facultat de Veterinaria, Campus Universitat Autonoma de Barcelona, Bella- terra, Spain d Servei de Diagnostic per la Imatge, Fundacio Hospital Clínic Veterinari, Campus Universitat Autonoma de Barcelona, Bellaterra, Spain A R T I C L E I N F O A B S T R A C T Keywords: Central vestibular disease is one of the most common problems in pet rabbits. Encephalitozoon cuniculi infection Cerebral thromboembolism appears to be the most frequent etiology, but other causes have been described. It is known that infective endocar- Head tilt ditis can cause thromboembolic disease affecting multiple organ systems in dogs. Secondary embolism from bac- Infective endocarditis terial endocarditis commonly occurs, mainly in the spleen and kidneys; but cerebral thromboembolism disease Vestibular disease Magnetic resonance imaging secondary to infective endocarditis has rarely been reported in dogs. In this case, an 8-year-old, neutered male rabbit (Oryctolagus cuniculus) presented with mild hyperthermia, left head tilt and rolling. Radiographic examina- tion, complete blood count, serum biochemistry and abdominal ultrasound were unremarkable. Magnetic reso- nance imaging did not show any abnormalities in the central nervous system. An Encephalitozoon cuniculi serology was performed with elevated IgM and IgG titers (1:320; 1:1280 respectively), the patient was hospitalized and treated for encephalitozoonis but the rabbit died 8 days after presentation and the body was submitted for nec- ropsy. Histopathological examination revealed multifocal necrotizing and suppurative myocarditis, with multiple emboli in kidneys, lungs and central nervous system. Polymerase chain reaction, immunohistochemistry, and Ziehl-Neelsen staining of samples from the central nervous system and kidneys yielded negative results for Ence- phalitozoon cuniculi. Due to the positive predictive value of 92% of indirect fluorescent antibody technique Ence- phalitozoon cuniculi serology, in this case a false positive was suspected. Based on the results, final diagnosis of cerebral thromboembolism secondary to infective endocarditis was emitted. This is the first report of this process naturally occurring in rabbits, and it should be included in the differential diagnosis of central vestibular syn- drome in this species. Introduction Case presentation Vestibular signs are the most common presentation of neurologic dis- An 8-year-old neutered male rabbit (Oryctolagus cuniculus) presented ease in pet rabbits [1,2]. Encephalitozoon cuniculi infection appears to be with acute left head tilt and whole body rolling. The rabbit was housed the most frequent cause of central vestibular disease, but other etiologies in a large commercial cage with access to the room, and was fed a com- have been described. Bacterial otitis media/interna is the main causes of mercial pellet diet for pet rabbits, hay and carrots. No other pets were peripheral vestibular disease [4]. There are no reports of cerebral throm- housed at home. boembolisms secondary to infective endocarditis (IE) in exotic pets. On physical examination, the animal was alert and weighed 2.3 kg. Infective endocarditis is uncommon in dogs and thromboembolism Persistent mild hyperthermia (39.7°C) was also noted [8]. The neurolog- occurs in 70 80% the reported incidence of emboli involving the brain ical examination revealed left head tilt and whole body rolling, horizon- is 0.1 1% [5 7]. tal nystagmus with the fast phase away from the head tilt, although placing and postural reactions were apparently normal. Initial Abbreviations: CNS, Central nervous system; IE, Infective endocarditis; MRI, Magnetic resonance imaging; E. cuniculi, Encephalitozoon cuniculi; PCR, Polymerase chain reaction * Corresponding author. J. Martorell. E-mail address: Jaumemiquel.martorell@uab.cat (J. Martorell). https://doi.org/10.1053/j.jepm.2021.11.002 1557-5063/© 2021 The Author(s). Published by Elsevier Inc. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by- nc-nd/4.0/) F. Solanes et al. Journal of Exotic Pet Medicine 40 (2022) 41 44 differential diagnosis included E. cuniculi, bacterial infection, trauma and neoplasia. Complete blood count and serum biochemistry were per- formed to rule out inflammatory/infectious process. They were within normal ranges [9]. Imaging was performed in order to determine if medical condition, especially related to encephalitozoonosis, other infectious process such as pneumonia, neoplasia and any sign of a secondary gastrointestinal ileus were present. Total body radiographs showed increased urinary bladder opacity consistent with hypercalciuria. Urinalysis, collected by cystocentesis, revealed proteinuria (+1) and hematuria (+1); then, an abdominal ultrasound was performed, and a microbiological culture was taken. Abdominal ultrasound was unremarkable. The urine microbi- ological culture was negative. The patient was hospitalized with intravenous fluid therapy with bal- anced crystalloid fluid (Ringer Lactate Braun® 500 mL, Braun Veterina- ria, Barcelona, Spain) supplemented with 5% of dextrose at 100mL/kg/ day, and ranitidine 2mg/kg IV every 12 hours (Ranitidina Normon, Lab- oratorios Normon SA, Madrid, Spain), meloxicam 0.2mg/kg IV every 12 hours (Metacam®, Boehringer, Ingelheim, Germany). Assisted oral feeding with critical care formula diet for herbivores (Oxbow Animal Health, Murdock, NE, U.S.A) was administered at 15 20 mL/kg every Fig. 1. Histopathology of the heart of the rabbit with cerebral thromboembo- 8 hours mixing one part of the powder with two parts of warm water. lism secondary to infective endocarditis. A fibrin thrombus (arrow), and large Due to the suspicion of a central nervous system (CNS) infectious amounts of degenerated leukocytes (arrowheads) within the myocardial arterio- and/or neoplastic process, a low-field magnetic resonance imaging lar lumen were observed. The vascular wall was circumferentially and transmur- (MRI) scan of the brain (0.4 Teslas Hitachi Aperto, Tokyo, Japan) was ally effaced by fibrin (fibrinoid change) and degenerated leukocytes (vasculitis). performed the following day. The patient was premedicated with mida- zolam 0.5mg/kg IV (Midazolam Normon, Laboratorios Normon SA, and the kidneys showed multifocal embolic nephritis (Fig. 3). All these Madrid, Spain) and butorphanol 0,5mg/kg IV (Torbugesic®Vet, Zoetis lesions were accompanied by deeply basophilic bacterial colonies show- Spain SL, Madrid, Spain). General anesthesia was induced with propofol ing a coccoid morphology. Examination of the CNS revealed multifocal 5mg/kg IV (Propovet®, Zoetis Spain SL, Madrid, Spain). The patient and bilateral histological lesions. The leptomeninges, choroid plexus, was intubated with a 2.0 uncuffed endotracheal tube and maintained white and gray matter of the cerebellum and cerebrum, and to a lesser with sevoflurane 3 4% (Sevoflo® sevo- flurane 100%, Abbott) and extent, the brainstem, showed well demarcated and nonencapsulated 100% oxygen during the MRI. inflammatory infiltrates, composed of markedly degenerated heterophils MRI showed a mild presence of fluid in the right tympanic bulla com- and a few macrophages, with abundant necrotic debris and similar bac- patible with otitis media, and fluid in both external ear canals compati- terial colonies to those observed in the other organs (Figs. 4, 5 and 6A). ble with otitis externa or ceruminous debris. No intracranial lesions Vasculitis was observed in some affected areas, capillaries and arterioles were found. presented necrotic intramural leucocytes (vasculitis), and their lumen An E. cuniculi serology with indirect fluorescent antibody technique was occasionally occluded by the fibrin thrombi and/or coccoid bacte- showed a marked increase in IgM and IgG antibodies (1:320; 1:1280 ria. No foci of nonsuppurative inflammation which could be suggestive respectively) [10] and a urine E. cuniculi polymerase chain reaction (PCR) (Vetgenomics, Barcelona, Spain) was performed and yielded neg- ative results. Due to suspected encephalitozoonosis and secondary complications stemming from the hematuria, fenbendazole 20mg/kg PO every 24 hours (Panacur® 100mg/ml, MSD Animal Health, Salamanca, Spain), enro- floxacin 10mg/kg IV every 12 hours (Baytril® 50mg/ml injectable solu- tion, Bayer Hispania SL, Barcelona, Spain) were added to the initial treatment. The rabbit’s condition did not improve and it was discharged as per owner’s wishes with the same medication as described above to be given orally. It died 48 hours later and was submitted for necropsy. Gross postmortem examination showed bilateral cranioventral pul- monary consolidation, white millimetric nodules throughout the myo- cardium, and similar nodules were found in both kidneys. No remarkable lesions were identified in the mitral valve. The presence of ceruminous debris was observed in the bilateral external auditory canal, although not in the tympanic bulla. Additionally, the right kidney showed two large flat areas of pale discoloration on the renal surface, measuring 1 and 3 cm in diameter, surrounded by a red halo, which extended radially to the medulla. No changes were found in other inter- nal organs and neither on gross examination of the CNS. Tissues from all Fig. 2. Histopathology of the heart of the rabbit with cerebral thromboembo- the internal organs were formalin-fixed paraffin-embedded for 24 hours lism secondary to infective endocarditis. It showed a fibrinosuppurative mitral and processed routinely for histopathology. Fresh or frozen samples endocarditis. The mitral valve (asterisk) and the adjacent endocardium (arrows) were not collected. were replaced by abundant amounts of fibrin, degenerated heterophils and coc- Histopathological examination revealed multifocal necrotizing and coid bacterial aggregates, which further extended to the underlying myocar- suppurative myocarditis (Fig. 1), as well as fibrinosuppurative mitral dium. Septic thrombi (arrowhead) were detached and could be seen within the endocarditis (Fig. 2). The lungs showed suppurative bronchopneumonia, ventricular lumen. 42 F. Solanes et al. Journal of Exotic Pet Medicine 40 (2022) 41 44 Fig. 3. Histopathology of the kidney of the rabbit with cerebral thromboembo- Fig. 5. Histopathology of the cerebral cortex of the rabbit with cerebral throm- lism secondary to infective endocarditis. Multifocal areas of lytic necrosis with boembolism secondary to infective endocarditis. A large area of lytic necrosis degenerated heterophils (microabscesses) could be seen scattered throughout with high amounts of degenerated heterophils (microabscess) measuring renal parenchyma (arrowheads). approximately 400um in diameter was observed featuring a necrotic blood ves- sel in the center with abundant coccoid bacteria in its lumen. of E. cuniculi could be observed in any of the brain sections assessed. Gram staining of the tissue sections of the CNS confirmed the presence Discussion of Gram positive cocci (Fig. 6B). An immunohistochemistry analysis using a polyclonal antiserum In a retrospective study of rabbits with neurological disease, the most against E. cuniculi (Medicago, Quebec, Canada) and Ziehl-Neelsen stain- commonly observed clinical signs were vestibular signs [1]. Differentiat- ing were performed. Both tests yielded negative results for E. cuniculi ing peripheral from central vestibular syndrome can be challenging, as it compared to positive controls from previously diagnosed cases. Encepha- is difficult to perform an accurate neurological examination on pet rab- litozoon cuniculi was targeted in FFPE kidneys and CNS tissue samples bits, due to their prey response [11 13]. In addition, E. cuniculi central using Vetgenomics PCR, as described in urine. It yielded a negative nervous system infections cause signs resembling peripheral dysfunction result. in this species [14]. In rabbits E. cuniculi infections are commonly chronic and subclinical, with a wide range of seroprevalence percentage, from 15% to 84,7% [15]. Other reported causes of central vestibular syn- drome in rabbits include: bacterial infection; toxoplasmosis; herpes virus encephalitis; cerebrovascular accident; cerebral larva migrans; trauma; lead toxicity; neoplasia; sepsis; hepatic encephalopathy; osteomyelitis of the petrous temporal bone, rabies, hypoxia and cerebellum infarction [1,3,4,16]. On the other hand, the most frequent cause of peripheral ves- tibular disease is otitis media/interna, while traumatic rupture of the tympanic bulla, aminoglycoside-mediated ototoxicity, and idiopathic vestibular disease are other less common causes of peripheral vestibular disease [3,4]. In the case presented here, E. cuniculi infection was ruled out as a cause of neurological signs based on the absence of focal, nonsuppura- tive meningoencephalitis lesions on histopathological examination, these lesions being typical for encephalitozoonosis [3,4,17]. Although a serology resulted positive, a PCR, immunohistochemistry and Ziehl- Neelsen staining from samples of CNS and kidneys yielded negative results. Brain and kidneys were selected because they have the highest diagnostic value for detection of E. cuniculi by histology, IHC, and real- time PCR [17]. It is demonstrated that real-time PCR is the most sensi- tive method for the confirmation of E. cuniculi infection, followed by immunohistochemistry and histological spore detection. The gold stan- dard for confirmation of the pathogenic role of E. cuniculi infection would be a combination of histological investigation of predilection sites Fig. 4. Histopathology of the cerebellar cortex of the rabbit with cerebral with real-time PCR performed on the above-mentioned tissues [17]. thromboembolism secondary to infective endocarditis. A large area of lytic Cray et al. reported a positive predictive value of a serology with IgM necrosis with high amounts of degenerated heterophils (microabscess) measur- >1:64 and IgG >1:512 of 92%, so the remaining 8% could explain the ing approximately 600um in diameter is observed disrupting the molecular, Pur- false positive serologic determination resulting in the case here [10,18]. kinje and granular layers of the cerebellar cortex (arrowhead). Similar lesions of Reports of endocarditis in rabbits are limited to experimental infec- smaller caliber can be found within cerebellar white matter (arrow). tion with one exception, in which Pasteurella multocida was isolated 43 F. Solanes et al. Journal of Exotic Pet Medicine 40 (2022) 41 44 Fig. 6. Histopathology of the hippocampus of the rab- bit with cerebral thromboembolism secondary to infec- tive endocarditis. (A) A large area of lytic necrosis with high amounts of degenerated heterophils (microab- scess) measuring approximately 600um in diameter was observed disrupting the hippocampus. (B) Gram stain showed coccoid Gram-positive bacterial aggre- gates (arrowheads). [19]. In the case presented here, Pasteurella multocida was ruled out [5] Sykes JE, Kittleson MD, Chomel BB, Macdonald KA, Pesavento PA. Clinicopathologic because the histopathological examination revealed gram positive cocci findings and outcome in dogs with infective endocarditis: 71 cases (1992 2005). J Am Vet Med Assoc 2006;228(11):1735–47. doi: 10.2460/javma.228.11.1735. colonies. Clinical signs of IE may include detectable heart murmur and [6] MacDonald K. Infective endocarditis in dogs: diagnosis and therapy. Vet Clin North fever in 74% and 80 90% in dogs, respectively [7]. 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