Equine neuroborreliosis in Scandinavia: cerebrospinal fluid PCR confirmation and successful treatment in a mare

Equine neuroborreliosis in Scandinavia: cerebrospinal fluid PCR confirmation and successful treatment in a mare | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Case Report Equine neuroborreliosis in Scandinavia: cerebrospinal fluid PCR confirmation and successful treatment in a mare Sofia Valencia Ruiz, Marianne Øverlie, Amanda Bergren, Ingunn Risnes Hellings This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-9209934/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Background Lyme borreliosis (LB), caused by Borrelia burgdorferi , is an emerging concern in human medicine, and is a controversial topic in equine medicine. Neuroborreliosis (NB), a neurologic manifestation of LB, remains challenging to diagnose due to nonspecific clinical signs and the lack of definitive diagnostic methods. This report describes the first documented case of equine NB in Scandinavia. Case presentation: An 11-year-old mare presented with progressive weight loss, ataxia, muscle atrophy, and hyperesthesia. Cerebrospinal fluid (CSF) analysis revealed neutrophilic pleocytosis, elevated protein and a positive PCR result for Borrelia spp . The mare showed clinical improvement and long-term recovery following prolonged doxycycline therapy. Conclusions: This case is the first reported case of neuroborreliosis in a horse in Scandinavia and supports the diagnostic relevance of CSF PCR in conjunction with clinical and cytological findings. It also underscores the potential for recovery in equine NB when early antimicrobial treatment is initiated. Borrelia cerebrospinal fluid doxycycline equine neuroinfection Background Lyme borreliosis (LB), caused by Borrelia burgdorferi , is a zoonotic tick-borne disease with growing relevance in both veterinary and human medicine. In the past few decades, climate change and shifting land use have contributed to a gradual expansion in tick habitats, particularly Ixodes ricinus in Europe and I. scapularis in North America [ 1 , 2 ]. As a result, LB has become the most commonly reported human tick-borne disease in both regions[ 3 , 2 ]. However, despite high seroprevalence of B. burgdorferi in horses, there are few cases of documented equine LB [ 4 – 14 ]. While horses can be exposed frequently to B. burgdorferi in endemic areas, which is reflected in the high numbers of seropositive healthy horses [ 15 , 16 , 10 , 17 ], clinical disease remains rare, particularly in Europe [ 4 , 8 ]. Among the various clinical forms, neuroborreliosis (NB) is one of the best documented clinical syndromes attributed to B. burgdorferi infection in horses [ 4 , 6 , 7 , 9 , 11 , 13 ], with additional documented manifestations which may include cardiac arrhythmias, uveitis, and cutaneous lesions [ 10 , 18 ]. Clinical signs of NB are frequently non-specific, and resemble those seen in other musculoskeletal or neurological conditions [ 10 ] and may include synovitis, muscle atrophy, progressive weight loss, cranial nerve deficits, laryngeal dysfunction, spinal ataxia, hyperesthesia, fasciculations, cervical and back stiffness [ 4 , 6 , 5 , 9 , 7 , 10 , 11 , 13 ]. The diagnosis of equine NB remains controversial due to the lack of a definitive diagnostic standard, the aforementioned high seroprevalence observed in clinically healthy horses, and the variability in the disease's clinical manifestations. Serological tests are commonly used but cannot distinguish between past and active infection, nor confirm causality of clinical signs [ 18 , 10 , 19 ]. Antigen detection tests on affected tissues may be attempted but are considered low yield, while culture remains technically challenging. Consequently, the sensitivity and specificity of these approaches still require further evaluation [ 7 , 10 , 19 , 13 ]. In suspected equine NB cases, uncertainty is compounded by limited data on antimicrobial penetration across a presumed disrupted blood-brain barrier [ 10 ]. These factors contribute to delays in diagnosis and treatment, likely impacting clinical outcomes, with a reported median duration of neurologic dysfunction preceding death of approximately 120 days [ 9 , 10 ]. Here, we describe the first reported case of equine NB in Scandinavia, where positive identification of Borrelia spp . by PCR in cerebrospinal (CSF) fluid samples led to a diagnosis, positive response to treatment and long-term survival. Case presentation An 11-year-old Norwegian Warmblood mare was initially examined by a field veterinarian in September 2022 for urticaria and progressive weight loss. Over the following week, the mare became increasingly dull, painful on muscle palpation, reluctant to move, and continued to lose weight. She was subsequently referred to Bjerke Dyrehospital (Oslo, Norway). On admission, the mare was quiet but alert and responsive, with vital parameters within reference limits. She showed marked, bilateral epaxial and cervical muscle atrophy, had a body condition score of 3/9 (Henneke Horse Body Condition Scoring Scale), generalized hyperesthesia, marked cervical pain with reduced range of motion, and lumbar back pain. Neurologic examination revealed grade 1/5 symmetrical ataxia [ 20 ] affecting all four limbs, accentuated by head elevation and walking downhill. Both hind limbs displayed mild circumduction, and tail-pull testing indicated right-sided weakness. Reduced distal limb nociception was noted in all four limbs, consistent with diffuse spinal cord involvement. No cranial nerve deficits were detected. Hematologic findings were consistent with a systemic inflammatory response, characterized by moderate anemia (RBC 5.06 × 10^12/L [6.4–10.4], HCT 22% [30–47], hemoglobin 8.0 g/dL [10.7–16.5]), mild leukopenia (3.97 × 10^9/L [4.9–11.1]) and markedly increased serum amyloid A (SAA) (651 mmol/L [< 20]). Serum biochemistry only showed mild hyperglobulinemia (48 g/L [24–47]). Vitamin E levels were within normal limits. Gastroscopy and an oral glucose absorption test were unremarkable. Survey radiographs of the cervical and thoracolumbar spine showed no osseous abnormalities. CSF collected from the lumbosacral space was slightly cloudy. Laboratory analysis was performed at LABOKLIN GmbH & Co.KG (Bad Kissingen, Germany). Analysis of the CSF revealed a marked increased white blood cell count (2,644 cells/µL [0–6]) with neutrophilic pleocytosis and elevated total protein concentration (100 mg/dL [5–100]), consistent with marked neutrophilic meningoencephalomyelitis. Bacterial culture of the CSF yielded moderate growth of Staphylococcus capitis . Polymerase chain reaction testing of CSF was positive for Borrelia spp . [ 21 ], while PCR for EHV-1, Streptococcu equi equi as well as S. equi zooepidemicus were all negative. ELISA testing for antibodies against tick-borne encephalitis virus was negative. Based on the compatible clinical presentation, exclusion of alternative infectious etiologies, and CSF cytologic and molecular findings, a diagnosis of neuroborreliosis was made. Treatment was initiated with doxycycline (10mg/kg PO q12h (Karidox 100mg/ml, Alivira, Barcelona, Spain) and flunixin meglumine (1.1 mg/kg IV q24h (Flunixin Biovet Vet 50mg/ml, ScanVet, Fredensborg, Denmark). Within 7 days of initiating treatment, the mare showed marked improvement in mentation and comfort, accompanied by normalization of hematologic parameters and SAA (381 mmol/L). NSAIDs were discontinued after 10 days, but clinical deterioration followed. Meloxicam (0.6 mg/kg PO q24h (Metacam 15mg/ml, Boehringer Ingelheim Vetmedica GmbH, Ingelheim, Germany) was then introduced for an additional five days, leading to clinical stabilization. Inflammatory markers, including SAA, returned to within reference limits at 13 days after treatment initiation, and the mare was discharged after 19 days of hospitalization with continued doxycycline. At re-examination 10 days post-discharge, the mare was brighter, had gained 18 kg, but showed mild residual neurologic deficits (grade 1 ataxia, hind limb toe dragging, and right-sided weakness). SAA was normal (4mmol/L); hematology showed mild anemia (RBC 6,15 x 10^12/L [6.4–10.4], HCT 26,7% [30–47] and HGB 9,7 g /dl [10.7–16.5]) and leukopenia (4,71x10^9/L [4.9–11.1])). CSF was clear, with near-normal cytologic findings (3 cells/µL [0–6]), protein 107 mg/dL [5–100]), negative bacterial culture, and negative PCR for Borrelia spp. , supporting treatment efficacy. Antimicrobial therapy was continued for a total of 7 weeks. The mare continued to improve, with progressive weight gain and normalization of behavior. After two months of rest, ridden exercise was reintroduced without recurrence of neurologic or musculoskeletal abnormalities. At the time of writing, the mare remains clinically healthy and is in amateur dressage training. Discussion and Conclusions This the first case of neuroborreliosis reported from a horse in Norway and from Scandinavia. The case had many of the typical clinical signs previously reported in horses with neuroborreliosis, but none of these signs are pathognomonic. In human medicine, criteria suggested for making a diagnosis of LD include known or presumed tick exposure, compatible clinical signs, exclusion of other conditions, and supportive laboratory findings. The mare in this report had a relevant exposure history, having been pastured in southeastern Norway, where the prevalence of I. ricinus and Borrelia spp . is well documented [ 1 , 22 ]. Supporting the likelihood of exposure, studies investigating the presence of antibodies against B. burgdorferi in Scandinavian equine populations reported an apparent seroprevalence of 16.8% in Sweden [ 15 ], 29.0% in Denmark [ 16 ] and 47% in Norway [ 17 ]. This case presented with signs commonly associated with neuroborreliosis, including weight loss, muscle atrophy, proprioceptive and spinal ataxia, hyperesthesia and cervical stiffness. Although other signs such as cranial nerve deficits, laryngeal dysfunction, synovitis and fasciculations were not observed, previous reports emphasize that equine Lyme disease presents variably and lacks a pathognomonic pattern [ 9 , 10 ]. Laboratory support included a CSF cytological evaluation showing xanthochromia, neutrophilic pleocytosis, and elevated total protein – findings consistent with previous equine neuroborreliosis cases [ 7 , 9 , 13 ]. The presence of S. capitis in the bacterial culture of the fluid, a commensal organism often found in human skin, was deemed the result of inadvertent sample contamination. Although it has been rarely associated with central nervous system infections, such as meningitis in immunocompromised adult human patients[ 23 ], its role as primary pathogen in equine neurology remains undocumented to the author’s knowledge. Lastly, the PCR analysis of the CSF sample for Borrelia spp . DNA yielded a positive result, further supporting the diagnosis of neuroborreliosis in this horse. While PCR of CSF is considered a low-yield procedure due to limited organism presence in fluid [ 5 ], positive results are regarded as clinically meaningful, particularly in the absence of findings suggesting involvement of other pathogens and when serology is unavailable, as in this case. Notably, antemortem diagnoses of equine neuroborreliosis have previously been reported based on a combination of supportive findings, including a positive CSF PCR [ 7 , 13 ]. However, as previously reported by Divers et al. (2022), the conventionally available PCR methods may not always be sufficient, and newer techniques such as the genomic hybrid capture may have improved sensitivity for detecting B. burgdorferi DNA in CSF samples. While the lack of antibody testing in this case limits full diagnostic certainty, its absence should be considered in light of growing evidence suggesting that serology in these cases has limited diagnostic utility, with several reported equine neuroborreliosis cases having equivocal or negative results in serum and/or CSF samples [ 5 – 7 , 9 , 13 , 19 ]. Consequently, serology remains a supportive rather than definitive tool, and its omission in this case does not preclude a justified diagnosis. Another consideration in the diagnostic process involved the possibility of viral encephalitis, including EHV-1, borna disease and flaviviral infections such as West Nile virus (WNV), Usutu virus (USUV), tick-born encephalitis (TBE) and Louping ill virus (LIV), as part of the differentials in horses with neurologic signs such as the one presented in this case. While TBEV was specifically tested for and ruled out in this case, WNV, USUV and LIV were not assessed. At the time (2022), WNV had only been reported in equine cases in central and southern Europe, and the majority of infections are either subclinical or result in mild clinical signs [ 24 ]. Furthermore, the mare had no history of travelling outside Norway and WNV has so far not been reported in horses in Norway. Equine USUV- related clinical signs have not been described up to date. LIV, an extremely rare cause of encephalitis in horses, shares I. ricinus as a vector with both TBEV and Borrelia, but reported cases are mostly confined to enzootic areas of the British Isles [ 24 ]. Importantly, the clinical improvement observed following antimicrobial therapy, normalization of inflammatory markers, and PCR confirmation of Borrelia spp . in the CSF sample strongly support bacterial etiology rather than a viral one. In addition, CSF in viral encephalomyelitis typically reveals a mononuclear pleocytosis rather than a neutrophilic pleocytosis as seen in this mare, which further supports a bacterial aetiology in this case. The horse responded well to oral doxycycline in combination with NSAIDS treatment, with gradual clinical improvement and long-term recovery, which is an infrequently reported outcome based on previous cases of equine neuroborreliosis, many of which deteriorated despite treatment [ 4 , 5 , 8 , 9 ]. Although doxycycline is seen to have low CSF penetration in healthy horses [ 25 ], its efficacy in this case may reflect improved access during inflammatory stages and early therapeutic intervention. Moreover, the successful antibiotic efficacy seen was later supported by the lack of pathogen detection in the control CSF sample, which aligns to the favorable outcome reported by Wagner et al. (2011) when treating a comparable equine NB case using doxycycline as the sole antimicrobial agent. In conclusion, this case expands the documented geographic range of equine neuroborreliosis by presenting the first report from Scandinavia. It also provides molecular confirmation of Borrelia spp. DNA in cerebrospinal fluid and adds to the limited number of cases with documented treatment success and sustained long-term recovery. This highlights the potential for horses to recover from NB when appropriate and timely antimicrobial therapy is initiated. Consequently, research on diagnostic and therapeutic methods, as well as further epidemiological evaluations and insights made on a case-by-case report basis, may allow progress in the management of neuroborreliosis in the living horse. Abbreviations AAEP American Association of Equine Practitioners BCS Body condition score CSF Cerebrospinal fluid IACUC Institutional Animal Care and Use Committee LB Lyme borreliosis NB Neuroborreliosis PCR Polymerase chain reaction SAA Serum amyloid A Declarations Authors’ contributions SVR: Writing – Original Draft. MØ: Conceptualization, Writing – Review & Editing. AB: Writing – Review & Editing. IRH: Supervision. All authors have read and approved the final version of the manuscript. Acknowledgements The authors thank the staff at Bjerke Dyrehospital for their assistance with clinical management of the case and sample collection. The authors also acknowledge the diagnostic laboratory personnel involved in the cerebrospinal fluid analyses. Competing interests The authors declare that they have no competing interests. Availability of data and materials Data sharing is not applicable to this article as no datasets were generated or analysed in the case report. Consent for publication The owner of the horse has given approval for publication of this case. Ethics approval This case report did not require official or institutional ethical approval. The animal was handled according to high ethical standards and national legislation. Prior publication Data have not been published previously. Funding This case report was based on internal funding. References Jore S, Viljugrein H, Hofshagen M, Brun-Hansen H, Kristoffersen A, nygård K, et al. Multi-source analysis reveals latitudinal and altitudinal shifts in range of Ixodes ricinus at its northern distribution limit. Parasit Vectors. 2011;4:84. https://doi.org/10.1186/1756-3305-4-84 . Marques AR, Strle F, Wormser GP. Comparison of Lyme Disease in the United States and Europe. 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Borrelia burgdorferi infection and Lyme disease guidelines. AAEP Infectious Disease Guidelines. Available at: https://aaep.org/wp-content/uploads/2020/02/Borrelia-Burgdorferi-Infection-and-Lyme-Disease-Guidelines.pdf [Internet]. [cited 2026 Jan 9]. https://aaep.org/wp-content/uploads/2020/02/Borrelia-Burgdorferi-Infection-and-Lyme-Disease-Guidelines.pdf. Accessed 9 Jan 2026. Johnson AL, Johnstone LK, Stefanovski D. Cerebrospinal fluid Lyme multiplex assay results are not diagnostic in horses with neuroborreliosis. J Vet Intern Med. 2018;32:832–8. https://doi.org/10.1111/jvim.15067 . Mayhew IG, deLahunta A, Whitlock RH, Krook L, Tasker JB. Spinal cord disease in the horse. Cornell Vet. 1978;68(Suppl 6):1–207. Rijpkema S, Molkenboer M, Schouls L, Jongejan F, Schellekens J. Simultaneous detection and genotyping of three genomic groups of Borrelia burgdorferi sensu lato in Dutch Ixodes ricinus ticks by characterization of the amplified intergenic spacer region between 5S and 23S rRNA genes. J Clin Microbiol [Internet]. J Clin Microbiol; 1995 [cited 2026 Jan 16];33. https://doi.org/10.1128/jcm.33.12.3091-3095.1995 Kjelland V, Stuen S, Skarpaas T, Slettan A. Prevalence and genotypes of Borrelia burgdorferi sensu lato infection in Ixodes ricinus ticks in southern Norway. Scand J Infect Dis. 2010;42:579–85. https://doi.org/10.3109/00365541003716526 . Oud L. Community-acquired meningitis due to Staphylococcus capitis in the absence of neurologic trauma, surgery, or implants. Heart Lung. 2011;40:467–71. https://doi.org/10.1016/j.hrtlng.2010.09.002 . Cavalleri J-MV, Korbacska-Kutasi O, Leblond A, Paillot R, Pusterla N, Steinmann E, et al. European College of Equine Internal Medicine consensus statement on equine flaviviridae infections in Europe. J Vet Intern Med. 2022;36:1858–71. https://doi.org/10.1111/jvim.16581 . Bryant JE, Brown MP, Gronwall RR, Merritt KA. Study of intragastric administration of doxycycline: pharmacokinetics including body fluid, endometrial and minimum inhibitory concentrations. Equine Vet J. 2000;32:233–8. https://doi.org/10.2746/042516400776563608 . Additional Declarations No competing interests reported. Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-9209934","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Case Report","associatedPublications":[],"authors":[{"id":626332392,"identity":"fdccf7e4-8c06-4a65-ad09-fd89e1677916","order_by":0,"name":"Sofia Valencia Ruiz","email":"data:image/png;base64,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","orcid":"","institution":"Sankt Mikaels Veg 285","correspondingAuthor":true,"prefix":"","firstName":"Sofia","middleName":"Valencia","lastName":"Ruiz","suffix":""},{"id":626332393,"identity":"6e6da648-d254-4e57-ba4a-c9f6be0d3810","order_by":1,"name":"Marianne Øverlie","email":"","orcid":"","institution":"Bjerke Dyrehospital","correspondingAuthor":false,"prefix":"","firstName":"Marianne","middleName":"","lastName":"Øverlie","suffix":""},{"id":626332394,"identity":"085a453e-8c3e-4093-9ee6-8ad95988a49f","order_by":2,"name":"Amanda Bergren","email":"","orcid":"","institution":"Bjerke Dyrehospital","correspondingAuthor":false,"prefix":"","firstName":"Amanda","middleName":"","lastName":"Bergren","suffix":""},{"id":626332395,"identity":"08fea75e-2ec4-41e3-abe7-f67c9dffe159","order_by":3,"name":"Ingunn Risnes Hellings","email":"","orcid":"","institution":"Norwegian University of Life Sciences","correspondingAuthor":false,"prefix":"","firstName":"Ingunn","middleName":"Risnes","lastName":"Hellings","suffix":""}],"badges":[],"createdAt":"2026-03-24 09:40:29","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-9209934/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-9209934/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":107520226,"identity":"a5aecfc9-e421-4277-92c1-f0f97c0a401b","added_by":"auto","created_at":"2026-04-22 08:59:29","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":192807,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-9209934/v1/c1f218a1-33ef-42ef-8e72-17ca63fe2e2d.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Equine neuroborreliosis in Scandinavia: cerebrospinal fluid PCR confirmation and successful treatment in a mare","fulltext":[{"header":"Background","content":"\u003cp\u003eLyme borreliosis (LB), caused by \u003cem\u003eBorrelia burgdorferi\u003c/em\u003e, is a zoonotic tick-borne disease with growing relevance in both veterinary and human medicine. In the past few decades, climate change and shifting land use have contributed to a gradual expansion in tick habitats, particularly \u003cem\u003eIxodes ricinus\u003c/em\u003e in Europe and \u003cem\u003eI. scapularis\u003c/em\u003e in North America [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. As a result, LB has become the most commonly reported human tick-borne disease in both regions[\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. However, despite high seroprevalence of \u003cem\u003eB. burgdorferi\u003c/em\u003e in horses, there are few cases of documented equine LB [\u003cspan additionalcitationids=\"CR5 CR6 CR7 CR8 CR9 CR10 CR11 CR12 CR13\" citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eWhile horses can be exposed frequently to \u003cem\u003eB. burgdorferi\u003c/em\u003e in endemic areas, which is reflected in the high numbers of seropositive healthy horses [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e, \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e, \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e, \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e], clinical disease remains rare, particularly in Europe [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. Among the various clinical forms, neuroborreliosis (NB) is one of the best documented clinical syndromes attributed to \u003cem\u003eB. burgdorferi\u003c/em\u003e infection in horses [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e, \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e, \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e, \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e, \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e, \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e], with additional documented manifestations which may include cardiac arrhythmias, uveitis, and cutaneous lesions [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e, \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]. Clinical signs of NB are frequently non-specific, and resemble those seen in other musculoskeletal or neurological conditions [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e] and may include synovitis, muscle atrophy, progressive weight loss, cranial nerve deficits, laryngeal dysfunction, spinal ataxia, hyperesthesia, fasciculations, cervical and back stiffness [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e, \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e, \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e, \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e, \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e, \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e, \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e, \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThe diagnosis of equine NB remains controversial due to the lack of a definitive diagnostic standard, the aforementioned high seroprevalence observed in clinically healthy horses, and the variability in the disease's clinical manifestations. Serological tests are commonly used but cannot distinguish between past and active infection, nor confirm causality of clinical signs [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e, \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e, \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e]. Antigen detection tests on affected tissues may be attempted but are considered\u003c/p\u003e \u003cp\u003elow yield, while culture remains technically challenging. Consequently, the sensitivity and specificity of these approaches still require further evaluation [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e, \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e, \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e, \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]. In suspected equine NB cases, uncertainty is compounded by limited data on antimicrobial penetration across a presumed disrupted blood-brain barrier [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]. These factors contribute to delays in diagnosis and treatment, likely impacting clinical outcomes, with a reported median duration of neurologic dysfunction preceding death of approximately 120 days [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e, \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eHere, we describe the first reported case of equine NB in Scandinavia, where positive identification of \u003cem\u003eBorrelia spp\u003c/em\u003e. by PCR in cerebrospinal (CSF) fluid samples led to a diagnosis, positive response to treatment and long-term survival.\u003c/p\u003e"},{"header":"Case presentation","content":"\u003cp\u003eAn 11-year-old Norwegian Warmblood mare was initially examined by a field veterinarian in September 2022 for urticaria and progressive weight loss. Over the following week, the mare became increasingly dull, painful on muscle palpation, reluctant to move, and continued to lose weight. She was subsequently referred to Bjerke Dyrehospital (Oslo, Norway).\u003c/p\u003e \u003cp\u003eOn admission, the mare was quiet but alert and responsive, with vital parameters within reference limits. She showed marked, bilateral epaxial and cervical muscle atrophy, had a body condition score of 3/9 (Henneke Horse Body Condition Scoring Scale), generalized hyperesthesia, marked cervical pain with reduced range of motion, and lumbar back pain. Neurologic examination revealed grade 1/5 symmetrical ataxia [\u003cspan class=\"CitationRef\"\u003e20\u003c/span\u003e] affecting all four limbs, accentuated by head elevation and walking downhill. Both hind limbs displayed mild circumduction, and tail-pull testing indicated right-sided weakness. Reduced distal limb nociception was noted in all four limbs, consistent with diffuse spinal cord involvement. No cranial nerve deficits were detected.\u003c/p\u003e \u003cp\u003eHematologic findings were consistent with a systemic inflammatory response, characterized by moderate anemia (RBC 5.06 × 10^12/L [6.4–10.4], HCT 22% [30–47], hemoglobin 8.0 g/dL [10.7–16.5]), mild leukopenia (3.97 × 10^9/L [4.9–11.1]) and markedly increased serum amyloid A (SAA) (651 mmol/L [\u0026lt; 20]). Serum biochemistry only showed mild hyperglobulinemia (48 g/L [24–47]). Vitamin E levels were within normal limits. Gastroscopy and an oral glucose absorption test were unremarkable. Survey radiographs of the cervical and thoracolumbar spine showed no osseous abnormalities.\u003c/p\u003e \u003cp\u003eCSF collected from the lumbosacral space was slightly cloudy. Laboratory analysis was performed at LABOKLIN GmbH \u0026amp; Co.KG (Bad Kissingen, Germany). Analysis of the CSF revealed a marked increased white blood cell count (2,644 cells/µL [0–6]) with neutrophilic pleocytosis and elevated total protein concentration (100 mg/dL [5–100]), consistent with marked neutrophilic meningoencephalomyelitis. Bacterial culture of the CSF yielded moderate growth of \u003cem\u003eStaphylococcus capitis\u003c/em\u003e. Polymerase chain reaction testing of CSF was positive for \u003cem\u003eBorrelia spp\u003c/em\u003e. [\u003cspan class=\"CitationRef\"\u003e21\u003c/span\u003e], while PCR for EHV-1, \u003cem\u003eStreptococcu equi equi\u003c/em\u003e as well as \u003cem\u003eS. equi zooepidemicus\u003c/em\u003e were all negative. ELISA testing for antibodies against tick-borne encephalitis virus was negative.\u003c/p\u003e \u003cp\u003eBased on the compatible clinical presentation, exclusion of alternative infectious etiologies, and CSF cytologic and molecular findings, a diagnosis of neuroborreliosis was made. Treatment was initiated with doxycycline (10mg/kg PO q12h (Karidox 100mg/ml, Alivira, Barcelona, Spain) and flunixin meglumine (1.1 mg/kg IV q24h (Flunixin Biovet Vet 50mg/ml, ScanVet, Fredensborg, Denmark).\u003c/p\u003e \u003cp\u003eWithin 7 days of initiating treatment, the mare showed marked improvement in mentation and comfort, accompanied by normalization of hematologic parameters and SAA (381 mmol/L). NSAIDs were discontinued after 10 days, but clinical deterioration followed. Meloxicam (0.6 mg/kg PO q24h (Metacam 15mg/ml, Boehringer Ingelheim Vetmedica GmbH, Ingelheim, Germany) was then introduced for an additional five days, leading to clinical stabilization. Inflammatory markers, including SAA, returned to within reference limits at 13 days after treatment initiation, and the mare was discharged after 19 days of hospitalization with continued doxycycline.\u003c/p\u003e \u003cp\u003eAt re-examination 10 days post-discharge, the mare was brighter, had gained 18 kg, but showed mild residual neurologic deficits (grade 1 ataxia, hind limb toe dragging, and right-sided weakness). SAA was normal (4mmol/L); hematology showed mild anemia (RBC 6,15 x 10^12/L [6.4–10.4], HCT 26,7% [30–47] and HGB 9,7 g /dl [10.7–16.5]) and leukopenia (4,71x10^9/L [4.9–11.1])). CSF was clear, with near-normal cytologic findings (3 cells/µL [0–6]), protein 107 mg/dL [5–100]), negative bacterial culture, and negative PCR for \u003cem\u003eBorrelia spp.\u003c/em\u003e, supporting treatment efficacy. Antimicrobial therapy was continued for a total of 7 weeks.\u003c/p\u003e \u003cp\u003eThe mare continued to improve, with progressive weight gain and normalization of behavior. After two months of rest, ridden exercise was reintroduced without recurrence of neurologic or musculoskeletal abnormalities. At the time of writing, the mare remains clinically healthy and is in amateur dressage training.\u003c/p\u003e "},{"header":"Discussion and Conclusions","content":"\u003cp\u003eThis the first case of neuroborreliosis reported from a horse in Norway and from Scandinavia. The case had many of the typical clinical signs previously reported in horses with neuroborreliosis, but none of these signs are pathognomonic. In human medicine, criteria suggested for making a diagnosis of LD include known or presumed tick exposure, compatible clinical signs, exclusion of other conditions, and supportive laboratory findings.\u003c/p\u003e\u003cp\u003eThe mare in this report had a relevant exposure history, having been pastured in southeastern Norway, where the prevalence of \u003cem\u003eI. ricinus\u003c/em\u003e and \u003cem\u003eBorrelia spp\u003c/em\u003e. is well documented [\u003cspan class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e22\u003c/span\u003e]. Supporting the likelihood of exposure, studies investigating the presence of antibodies against \u003cem\u003eB. burgdorferi\u003c/em\u003e in Scandinavian equine populations reported an apparent seroprevalence of 16.8% in Sweden [\u003cspan class=\"CitationRef\"\u003e15\u003c/span\u003e], 29.0% in Denmark [\u003cspan class=\"CitationRef\"\u003e16\u003c/span\u003e] and 47% in Norway [\u003cspan class=\"CitationRef\"\u003e17\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eThis case presented with signs commonly associated with neuroborreliosis, including weight loss, muscle atrophy, proprioceptive and spinal ataxia, hyperesthesia and cervical stiffness. Although other signs such as cranial nerve deficits, laryngeal dysfunction, synovitis and fasciculations were not observed, previous reports emphasize that equine Lyme disease presents variably and lacks a pathognomonic pattern [\u003cspan class=\"CitationRef\"\u003e9\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e10\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eLaboratory support included a CSF cytological evaluation showing xanthochromia, neutrophilic pleocytosis, and elevated total protein – findings consistent with previous equine neuroborreliosis cases [\u003cspan class=\"CitationRef\"\u003e7\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e9\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e13\u003c/span\u003e]. The presence of \u003cem\u003eS. capitis\u003c/em\u003e in the bacterial culture of the fluid, a commensal organism often found in human skin, was deemed the result of inadvertent sample contamination. Although it has been rarely associated with central nervous system infections, such as meningitis in immunocompromised adult human patients[\u003cspan class=\"CitationRef\"\u003e23\u003c/span\u003e], its role as primary pathogen in equine neurology remains undocumented to the author’s knowledge. Lastly, the PCR analysis of the CSF sample for \u003cem\u003eBorrelia spp\u003c/em\u003e. DNA yielded a positive result, further supporting the diagnosis of neuroborreliosis in this horse. While PCR of CSF is considered a low-yield procedure due to limited organism presence in fluid [\u003cspan class=\"CitationRef\"\u003e5\u003c/span\u003e], positive results are regarded as clinically meaningful, particularly in the absence of findings suggesting involvement of other pathogens and when serology is unavailable, as in this case. Notably, antemortem diagnoses of equine neuroborreliosis have previously been reported based on a combination of supportive findings, including a positive CSF PCR [\u003cspan class=\"CitationRef\"\u003e7\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e13\u003c/span\u003e]. However, as previously reported by Divers et al. (2022), the conventionally available PCR methods may not always be sufficient, and newer techniques such as the genomic hybrid capture may have improved sensitivity for detecting \u003cem\u003eB. burgdorferi\u003c/em\u003e DNA in CSF samples.\u003c/p\u003e\u003cp\u003eWhile the lack of antibody testing in this case limits full diagnostic certainty, its absence should be considered in light of growing evidence suggesting that serology in these cases has limited diagnostic utility, with several reported equine neuroborreliosis cases having equivocal or negative results in serum and/or CSF samples [\u003cspan class=\"CitationRef\"\u003e5\u003c/span\u003e–\u003cspan class=\"CitationRef\"\u003e7\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e9\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e13\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e19\u003c/span\u003e]. Consequently, serology remains a supportive rather than definitive tool, and its omission in this case does not preclude a justified diagnosis.\u003c/p\u003e\u003cp\u003eAnother consideration in the diagnostic process involved the possibility of viral encephalitis, including EHV-1, borna disease and flaviviral infections such as West Nile virus (WNV), Usutu virus (USUV), tick-born encephalitis (TBE) and Louping ill virus (LIV), as part of the differentials in horses with neurologic signs such as the one presented in this case. While TBEV was specifically tested for and ruled out in this case, WNV, USUV and LIV were not assessed. At the time (2022), WNV had only been reported in equine cases in central and southern Europe, and the majority of infections are either subclinical or result in mild clinical signs [\u003cspan class=\"CitationRef\"\u003e24\u003c/span\u003e]. Furthermore, the mare had no history of travelling outside Norway and WNV has so far not been reported in horses in Norway. Equine USUV- related clinical signs have not been described up to date. LIV, an extremely rare cause of encephalitis in horses, shares \u003cem\u003eI. ricinus\u003c/em\u003e as a vector with both TBEV and Borrelia, but reported cases are mostly confined to enzootic areas of the British Isles [\u003cspan class=\"CitationRef\"\u003e24\u003c/span\u003e]. Importantly, the clinical improvement observed following antimicrobial therapy, normalization of inflammatory markers, and PCR confirmation of \u003cem\u003eBorrelia spp\u003c/em\u003e. in the CSF sample strongly support bacterial etiology rather than a viral one. In addition, CSF in viral encephalomyelitis typically reveals a mononuclear pleocytosis rather than a neutrophilic pleocytosis as seen in this mare, which further supports a bacterial aetiology in this case.\u003c/p\u003e\u003cp\u003eThe horse responded well to oral doxycycline in combination with NSAIDS treatment, with gradual clinical improvement and long-term recovery, which is an infrequently reported outcome based on previous cases of equine neuroborreliosis, many of which deteriorated despite treatment [\u003cspan class=\"CitationRef\"\u003e4\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e5\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e8\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e9\u003c/span\u003e]. Although doxycycline is seen to have low CSF penetration in healthy horses [\u003cspan class=\"CitationRef\"\u003e25\u003c/span\u003e], its efficacy in this case may reflect improved access during inflammatory stages and early therapeutic intervention. Moreover, the successful antibiotic efficacy seen was later supported by the lack of pathogen detection in the control CSF sample, which aligns to the favorable outcome reported by Wagner et al. (2011) when treating a comparable equine NB case using doxycycline as the sole antimicrobial agent.\u003c/p\u003e\u003cp\u003eIn conclusion, this case expands the documented geographic range of equine neuroborreliosis by presenting the first report from Scandinavia. It also provides molecular confirmation of \u003cem\u003eBorrelia spp.\u003c/em\u003e DNA in cerebrospinal fluid and adds to the limited number of cases with documented treatment success and sustained long-term recovery. This highlights the potential for horses to recover from NB when appropriate and timely antimicrobial therapy is initiated. Consequently, research on diagnostic and therapeutic methods, as well as further epidemiological evaluations and insights made on a case-by-case report basis, may allow progress in the management of neuroborreliosis in the living horse.\u003c/p\u003e"},{"header":"Abbreviations","content":"\u003cdiv class=\"DefinitionList\"\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eAAEP\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eAmerican Association of Equine Practitioners\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eBCS\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eBody condition score\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eCSF\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eCerebrospinal fluid\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eIACUC\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eInstitutional Animal Care and Use Committee\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eLB\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eLyme borreliosis\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eNB\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eNeuroborreliosis\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003ePCR\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003ePolymerase chain reaction\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eSAA\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eSerum amyloid A\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003c/div\u003e"},{"header":"Declarations","content":"\u003ch3\u003eAuthors\u0026rsquo; contributions\u0026nbsp;\u003c/h3\u003e\n\u003cp\u003eSVR: Writing \u0026ndash; Original Draft. M\u0026Oslash;: Conceptualization, Writing \u0026ndash; Review \u0026amp; Editing. AB: Writing \u0026ndash; Review \u0026amp; Editing. IRH: Supervision. All authors have read and approved the final version of the manuscript. \u003c/p\u003e\n\u003ch3\u003eAcknowledgements\u0026nbsp;\u003c/h3\u003e\n\u003cp\u003eThe authors thank the staff at Bjerke Dyrehospital for their assistance with clinical management of the case and sample collection. The authors also acknowledge the diagnostic laboratory personnel involved in the cerebrospinal fluid analyses.\u003c/p\u003e\n\u003ch3\u003eCompeting interests\u003c/h3\u003e\n\u003cp\u003eThe authors declare that they have no competing interests. \u003c/p\u003e\n\u003ch3\u003eAvailability of data and materials\u0026nbsp;\u003c/h3\u003e\n\u003cp\u003eData sharing is not applicable to this article as no datasets were generated or analysed in the case report.\u0026nbsp;\u003c/p\u003e\n\u003ch3\u003eConsent for publication\u0026nbsp;\u003c/h3\u003e\n\u003cp\u003eThe owner of the horse has given approval for publication of this case.\u0026nbsp;\u003c/p\u003e\n\u003ch3\u003eEthics approval\u0026nbsp;\u003c/h3\u003e\n\u003cp\u003eThis case report did not require official or institutional ethical approval. The animal was handled according to high ethical standards and national legislation.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003ePrior publication\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eData have not been published previously.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThis case report was based on internal funding.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eJore S, Viljugrein H, Hofshagen M, Brun-Hansen H, Kristoffersen A, nyg\u0026aring;rd K, et al. Multi-source analysis reveals latitudinal and altitudinal shifts in range of Ixodes ricinus at its northern distribution limit. 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J Vet Intern Med. 2022;36:1858\u0026ndash;71. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1111/jvim.16581\u003c/span\u003e\u003cspan address=\"10.1111/jvim.16581\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBryant JE, Brown MP, Gronwall RR, Merritt KA. Study of intragastric administration of doxycycline: pharmacokinetics including body fluid, endometrial and minimum inhibitory concentrations. Equine Vet J. 2000;32:233\u0026ndash;8. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.2746/042516400776563608\u003c/span\u003e\u003cspan address=\"10.2746/042516400776563608\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Borrelia, cerebrospinal fluid, doxycycline, equine, neuroinfection","lastPublishedDoi":"10.21203/rs.3.rs-9209934/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-9209934/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003ch2\u003eBackground\u003c/h2\u003e \u003cp\u003eLyme borreliosis (LB), caused by \u003cem\u003eBorrelia burgdorferi\u003c/em\u003e, is an emerging concern in human medicine, and is a controversial topic in equine medicine. Neuroborreliosis (NB), a neurologic manifestation of LB, remains challenging to diagnose due to nonspecific clinical signs and the lack of definitive diagnostic methods. This report describes the first documented case of equine NB in Scandinavia.\u003c/p\u003e\u003ch2\u003eCase presentation:\u003c/h2\u003e \u003cp\u003eAn 11-year-old mare presented with progressive weight loss, ataxia, muscle atrophy, and hyperesthesia. Cerebrospinal fluid (CSF) analysis revealed neutrophilic pleocytosis, elevated protein and a positive PCR result for \u003cem\u003eBorrelia spp\u003c/em\u003e. The mare showed clinical improvement and long-term recovery following prolonged doxycycline therapy.\u003c/p\u003e\u003ch2\u003eConclusions:\u003c/h2\u003e \u003cp\u003eThis case is the first reported case of neuroborreliosis in a horse in Scandinavia and supports the diagnostic relevance of CSF PCR in conjunction with clinical and cytological findings. It also underscores the potential for recovery in equine NB when early antimicrobial treatment is initiated.\u003c/p\u003e","manuscriptTitle":"Equine neuroborreliosis in Scandinavia: cerebrospinal fluid PCR confirmation and successful treatment in a mare","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-04-22 08:57:19","doi":"10.21203/rs.3.rs-9209934/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"55de5b5d-b77d-486e-9538-5ad0f40fb5fe","owner":[],"postedDate":"April 22nd, 2026","published":true,"recentEditorialEvents":[{"type":"reviewerAgreed","content":"23815905495575646485236875397126231712","date":"2026-05-04T17:29:50+00:00","index":20,"fulltext":""}],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2026-04-22T08:57:19+00:00","versionOfRecord":[],"versionCreatedAt":"2026-04-22 08:57:19","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-9209934","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-9209934","identity":"rs-9209934","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}