Etiological distribution of isolated oculomotor nerve palsy: analysis of 633 patients and literature review.

BACKGROUND AND PURPOSE: The etiological distribution of oculomotor nerve palsy has varied amongst the studies. This study aimed to define the clinical features and underlying etiologies of isolated oculomotor nerve palsy by recruiting patients from all departments in a referral-based university hospital. METHODS: The medical records of 672 patients who had a confirmed diagnosis of isolated oculomotor nerve palsy at all departments of Seoul National University Bundang Hospital, Seongnam, South Korea, from 2003 to 2020 were reviewed. A proportion of the etiology of isolated oculomotor nerve palsy was also compared with that of patients pooled from the previous studies that were searched on PubMed in May 2022. RESULTS: The most common etiology was microvascular (n = 168, 26.5%), followed by vascular anomalies (n = 110, 17.4%), neoplastic (n = 86, 13.6%), inflammatory (n = 79, 12.5%), idiopathic (n = 60, 9.5%) and traumatic (n = 53, 8.4%). Neurologists were mainly involved in the management of microvascular and inflammatory oculomotor nerve palsies whilst ophthalmologists mainly participated in the care of idiopathic, neoplastic and traumatic palsies. Neurosurgeons mostly took care of oculomotor nerve palsy due to vascular anomalies. CONCLUSIONS: The proportion of etiologies of isolated oculomotor nerve palsy may differ according to the specialties involved in the management. The results of previous studies on the etiological distribution of isolated oculomotor nerve palsy should be interpreted with this consideration.

Risk of central nervous system demyelinating attack or optic neuritis recurrence after pediatric optic neuritis in Korea.

PURPOSE: To investigate the rate of development of symptomatic central nervous system (CNS) demyelinating attacks or recurrent optic neuritis (ON) after the first episode of ON and its risk factors for Korean pediatric patients. METHODS: This multicenter retrospective cohort study included the patients under 18 years of age (n=132) diagnosed with ON without previous or simultaneous CNS demyelinating diseases. We obtained the clinical data including the results of neuro-ophthalmological examinations, magnetic resonance images (MRIs), antibody assays, and laboratory tests. We investigated the chronological course of demyelinating disease with respect to the occurrence of neurological symptoms and/or signs, and calculated the 5-year cumulative probability of CNS demyelinating disease or ON recurrence.  RESULTS: During the follow-up period (63.1±46.7 months), 18 patients had experienced other CNS demyelinating attacks, and the 5-year cumulative probability was 14.0±3.6%. Involvement of the extraorbital optic nerve or optic chiasm and asymptomatic lesions on the brain or spinal MRI at initial presentation were significant predictors for CNS demyelinating attack after the first ON. The 5-year cumulative probability of CNS demyelinating attack was 44.4 ± 24.8% in the AQP4-IgG group, 26.2±11.4% in the MOG-IgG group, and 8.7±5.9% in the double-negative group (P=0.416). Thirty-two patients had experienced a recurrence of ON, and the 5-year cumulative probability was 24.6±4.0%. In the AQP4-IgG group, the 5-year cumulative probability was 83.3±15.2%, which was significantly higher than in the other groups (P<0.001). CONCLUSIONS: A careful and multidisciplinary approach including brain/spinal imaging and antibody assay can help predict further demyelinating attacks in pediatric ON patients.

Etiologic distribution of isolated abducens nerve palsy: Analysis of 807 patients and literature review.

BACKGROUND AND PURPOSE: The etiologies of abducens nerve palsy have shown a large variability among studies. This study aimed to establish the clinical features and underlying etiologies of isolated abducens nerve palsy by recruiting patients from all departments in a referral-based university hospital. METHODS: We reviewed the medical records of 807 patients with a confirmed diagnosis of isolated abducens nerve palsy at all departments of Seoul National University Bundang Hospital, Seongnam, Republic of Korea, from 2003 to 2020. We also compared the proportion of etiology with that of the patients pooled from the previous studies. RESULTS: The most common etiology was microvascular (n = 296, 36.7%), followed by idiopathic (n = 143, 17.7%), neoplastic (n = 115, 14.3%), vascular anomalies (n = 82, 10.2%), inflammatory (n = 76, 9.4%), and traumatic (n = 35, 4.3%). Patients were mostly managed by ophthalmologists (n = 576, 71.4%), followed by neurologists (n = 479, 59.4%), emergency physicians (n = 278, 34.4%), neurosurgeons (n = 191, 23.7%), and others (n = 72, 8.9%). The proportion of etiology significantly differed according to the age and sex of the patients and the specialties involved in the management (p < 0.001). Compared to the pooled data from the previous reports, the current study showed a higher prevalence of microvascular cause but a lower occurrence of traumatic and neoplastic causes. CONCLUSIONS: The results of previous studies on etiologic distribution of isolated abducens nerve palsy should be interpreted with consideration of the demographic features of patients recruited and the specialties involved.

Deep Learning System Outperforms Clinicians in Identifying Optic Disc Abnormalities.

BACKGROUND: The examination of the optic nerve head (optic disc) is mandatory in patients with headache, hypertension, or any neurological symptoms, yet it is rarely or poorly performed in general clinics. We recently developed a brain and optic nerve study with artificial intelligence-deep learning system (BONSAI-DLS) capable of accurately detecting optic disc abnormalities including papilledema (swelling due to elevated intracranial pressure) on digital fundus photographs with a comparable classification performance to expert neuro-ophthalmologists, but its performance compared to first-line clinicians remains unknown. METHODS: In this international, cross-sectional multicenter study, the DLS, trained on 14,341 fundus photographs, was tested on a retrospectively collected convenience sample of 800 photographs (400 normal optic discs, 201 papilledema and 199 other abnormalities) from 454 patients with a robust ground truth diagnosis provided by the referring expert neuro-ophthalmologists. The areas under the receiver-operating-characteristic curves were calculated for the BONSAI-DLS. Error rates, accuracy, sensitivity, and specificity of the algorithm were compared with those of 30 clinicians with or without ophthalmic training (6 general ophthalmologists, 6 optometrists, 6 neurologists, 6 internists, 6 emergency department [ED] physicians) who graded the same testing set of images. RESULTS: With an error rate of 15.3%, the DLS outperformed all clinicians (average error rates 24.4%, 24.8%, 38.2%, 44.8%, 47.9% for general ophthalmologists, optometrists, neurologists, internists and ED physicians, respectively) in the overall classification of optic disc appearance. The DLS displayed significantly higher accuracies than 100%, 86.7% and 93.3% of clinicians (n = 30) for the classification of papilledema, normal, and other disc abnormalities, respectively. CONCLUSIONS: The performance of the BONSAI-DLS to classify optic discs on fundus photographs was superior to that of clinicians with or without ophthalmic training. A trained DLS may offer valuable diagnostic aid to clinicians from various clinical settings for the screening of optic disc abnormalities harboring potentially sight- or life-threatening neurological conditions.

Etiologic distribution of isolated trochlear palsy: Analysis of 1020 patients and literature review.

BACKGROUND AND PURPOSE: Trochlear palsy is the most common cause of vertical diplopia. The etiologies of trochlear palsy have shown a large discrepancy among studies. This study aimed to establish the clinical features and underlying etiologies of isolated trochlear palsy by recruiting the patients from all departments in a referral-based university hospital. METHODS: We reviewed the medical records of 1258 patients who had a confirmed diagnosis of isolated trochlear palsy at all departments of Seoul National University Bundang Hospital, Seongnam, South Korea, from 2003 to 2020. We also compared the proportion of etiologies with that of the patients pooled from previous studies. RESULTS: The most common etiology was congenital (n = 330, 32.4%), followed by idiopathic (n = 256, 25.1%), microvascular (n = 212, 20.8%), and traumatic (n = 145, 14.2%). These four etiologies explained 92.5% of isolated trochlear palsy. Patients were mostly managed by ophthalmologists (n = 841, 82.5%), followed by neurologists (n = 380, 37.3%), emergency physicians (n = 197, 19.3%), neurosurgeons (n = 75, 7.4%), and others (n = 18, 1.8%). The etiologic distribution of isolated trochlear palsy in the current study did not differ from that of 2664 patients pooled from the previous studies. CONCLUSIONS: The proportion of etiologies of isolated trochlear palsy differs according to the age ranges of the patients and specialties involved in the management. The etiologic distribution of isolated trochlear palsy in the current study was comparable to the pooled result of previous reports.

Factors associated with seropositivity to Aino virus among sheep and goats in South Korea.

Aino virus infection is responsible for epizootic and/or sporadic outbreaks of abortions, stillbirths and premature delivery among pregnant ruminants. The epizootiology of Aino virus infection is poorly defined in South Korea, therefore our aim was to assess its seroprevalence among sheep and goats. We also wanted to evaluate management and regional risk factors that might influence the frequency of infection. Between 2012 and 2013, 26 of 331 flocks (7.9%) and 139 of 915 heads (15.2%) were found serologically positive. In 2018, when samples were again collected in the same regions, 35 of 308 flocks (11.4%) and 89 of 735 heads (12.1%) showed serum-neutralising antibodies against Aino virus. Our results revealed that the age class and history of reproductive problems in the flocks are connected to an increased risk of being positive. The management risk factor attributes showed that preventive measures, such as the routine application of insecticide in farms, decreased the odds for seropositivity to Aino virus (OR = 0.453, P = 0.001). We observed a significant difference in the individual likelihood of being positive in the southern and western provinces with respect to that in the northern and eastern provinces, respectively (OR = 2.199, P < 0.001 and OR = 2.177, P < 0.001). The results of this study may serve as a basis for future epizootic studies on Aino virus infection in South Korea.

Optic Disc Classification by Deep Learning versus Expert Neuro-Ophthalmologists.

OBJECTIVE: To compare the diagnostic performance of an artificial intelligence deep learning system with that of expert neuro-ophthalmologists in classifying optic disc appearance. METHODS: The deep learning system was previously trained and validated on 14,341 ocular fundus photographs from 19 international centers. The performance of the system was evaluated on 800 new fundus photographs (400 normal optic discs, 201 papilledema [disc edema from elevated intracranial pressure], 199 other optic disc abnormalities) and compared with that of 2 expert neuro-ophthalmologists who independently reviewed the same randomly presented images without clinical information. Area under the receiver operating characteristic curve, accuracy, sensitivity, and specificity were calculated. RESULTS: The system correctly classified 678 of 800 (84.7%) photographs, compared with 675 of 800 (84.4%) for Expert 1 and 641 of 800 (80.1%) for Expert 2. The system yielded areas under the receiver operating characteristic curve of 0.97 (95% confidence interval [CI] = 0.96-0.98), 0.96 (95% CI = 0.94-0.97), and 0.89 (95% CI = 0.87-0.92) for the detection of normal discs, papilledema, and other disc abnormalities, respectively. The accuracy, sensitivity, and specificity of the system's classification of optic discs were similar to or better than the 2 experts. Intergrader agreement at the eye level was 0.71 (95% CI = 0.67-0.76) between Expert 1 and Expert 2, 0.72 (95% CI = 0.68-0.76) between the system and Expert 1, and 0.65 (95% CI = 0.61-0.70) between the system and Expert 2. INTERPRETATION: The performance of this deep learning system at classifying optic disc abnormalities was at least as good as 2 expert neuro-ophthalmologists. Future prospective studies are needed to validate this system as a diagnostic aid in relevant clinical settings. ANN NEUROL 2020;88:785-795.

Association of lateral rectus muscle volume and ocular motility with the abducens nerve in Duane's retraction syndrome.

PURPOSE: To investigate the relationship between ocular motility and lateral rectus (LR) muscle volume according to the presence or absence of the abducens nerve in patients with Duane's retraction syndrome (DRS) using high-resolution magnetic resonance imaging (MRI). METHODS: A total of 54 unilateral DRS patients were divided into two groups according to high-resolution MRI findings: DRS without an abducens nerve on the affected side (absent CN6 group, n = 45) and DRS with symmetric abducens nerves on both sides (present CN6 group, n = 9). Ocular motility was measured by image analysis based on nine gaze photographs. LR volume was measured on T2-weighted coronal MRI of the orbit, and the ratio of paretic/normal side (P/N) LR volume was investigated. Association of the abducens nerve with various parameters including ocular motility, LR volume, and ratios of P/N LR volume were determined. RESULTS: LR volume was smaller in the affected eye than the non-affected eye in both groups. In the present CN6 group, abducens nerve diameter and the ratio of P/N LR volume showed a positive correlation. A smaller LR volume and more limitation of abduction in the affected eye were predictive of an absent abducens nerve in DRS. CONCLUSIONS: LR muscle hypoplasia was apparent in the affected eye of DRS patients. Abducens nerve diameter positively correlated with the ratio of P/N LR volume in the present CN6 group. Graphical abstract.

Glaucoma-like Parapapillary Choroidal Microvasculature Dropout in Patients with Compressive Optic Neuropathy.

PURPOSE: To characterize peripapillary choroidal microvasculature dropout (MvD) in patients with compressive optic neuropathy (CON) as compared with those with open-angle glaucoma (OAG) using OCT angiography (OCTA). DESIGN: Cross-sectional, observational study. PARTICIPANTS: Eighty-eight eyes of 44 patients with CON; 88 eyes of 88 patients with OAG matched by age, spherical error, and OCT-determined retinal nerve fiber layer thickness (RNFLT); and 88 eyes of 44 control participants matched by age and spherical error. METHODS: Peripapillary microvasculature was evaluated, and peripapillary vessel density was measured in en face images segmented into inner-retinal and choroidal layers using swept-source OCTA. An MvD was defined as a focal sectoral capillary dropout with no visible microvascular network in the choroidal layer. MAIN OUTCOME MEASURES: Comparative characteristics of MvD in eyes with CON and OAG. RESULTS: Microvasculature dropout was observed in 30 eyes (34.1%) of 22 patients (50.0%) with CON, and in 48 eyes of 48 patients (54.5%) with OAG (P = 0.011). All MvDs in the CON group were located in the temporal parapapillary sector, whereas MvDs in the OAG group were located in the temporal-inferior (n = 36) and temporal-superior (n = 4) sectors. At their locations, MvDs in the CON group were accompanied by significant reductions in retinal vessel density and RNFLT, but this was not observed in the OAG group. The presence of MvD was associated significantly with female gender (P = 0.020) and thinner global retinal nerve fiber layer (P = 0.006) in the CON group, but not in the OAG group. CONCLUSIONS: OCT angiography of the peripapillary area showed retinal and choroidal microvasculature impairment in patients with both CON and OAG. However, the features and associated characteristics of MvD differed between these groups, suggesting that the pathogenesis of peripapillary microvascular impairment may be diverse.

Ocular coloboma combined with cleft lip and palate: a case report.

BACKGROUND: Ocular coloboma is an excavation of ocular structures that occurs due to abnormal fusion of the embryonic optic fissure. Further, cleft lip/palate (CL/P), a congenital midline abnormality, is caused by a defect in the fusion of the frontonasal, maxillary, and mandibular prominences. No study has reported the association between these two phenotypes in the absence of other systemic abnormalities. We present a case of ocular coloboma along with CL/P and without other neurological abnormalities. CASE PRESENTATION: A 5-year-old Asian boy presented with decreased visual acuity in his right eye. Physical examination revealed no abnormal findings except CL/P, which was surgically corrected at the age of 9 months. Best-corrected visual acuity was 20/60 in the right eye and 20/25 in the left eye. Anterior segment examination revealed iris coloboma in the inferior quadrant of his right eye as well as a large inferonasal optic disc and chorioretinal coloboma in the same eye. He was prescribed glasses based on his cycloplegic refractive errors and part-time occlusion of the left eye was recommended. After 3 months, best-corrected visual acuity improved to 20/30 in the right eye. CONCLUSION: The association of ocular coloboma should be kept in mind when encountering a patient with CL/P without other neurological or systemic abnormalities.

Serological evidence of bluetongue virus infection and serotype distribution in dairy cattle in South Korea.

BACKGROUND: Bluetongue is a vector-borne viral disease, and bluetongue virus (BTV) outbreaks can cause substantial economic losses. Even subclinical infection may carry significant associated costs, including a loss of condition, reduced milk yield, and infertility and abortion, and indirect costs, largely due to the export restrictions and surveillance requirements imposed to limit the spread of the virus. However, the BTV epidemiology in the Far East remains incompletely understood, especially in the cattle population in South Korea. In this study, the seroprevalence of BTV antibodies and distribution of BTV serotypes in dairy cattle in South Korea were evaluated to improve the understanding of the BTV epidemiological situation in the Asia-Pacific region. RESULTS: Between 2012 and 2013, a total of 37 out of 171 dairy cattle herds (21.6%) and 85 out of 466 dairy cattle heads (18.2%) showed antibodies against BTV. Neutralizing antibodies to BTV-1, - 2, - 3, - 4, - 7, - 15, and - 16 serotypes were identified, and the RNAs of the BTV-1, - 2, - 3, - 15, and - 16 serotypes were detected, indicating that BTV was circulating in the dairy cattle population in South Korea. CONCLUSIONS: These findings indicate that BTV is widespread and has circulated in dairy cattle in South Korea. This is the first report presenting evidence of circulating antibodies against BTV and the serotype distribution in bovine populations in South Korea.

Infrared photographs with a selective wavelength filter to diagnose small-angle esotropia in young children.

PURPOSE: To validate the effectiveness of the selective wavelength filter analysis with infrared photographs for diagnosing small-angle esotropia in children under age 4. METHODS: This is a retrospective, observational, case-control study. A total of 83 esotropes with an esodeviation of ≤ 16 prism diopters (PD) and 75 orthotropic controls under 4 years of age were included. Full-face infrared photographs were taken with a selective wavelength filter in front of either eye. The angles of esodeviation on photographs were measured with the three-dimensional Strabismus Photo Analyzer. The alternate prism and cover test or the Krimsky test were repeatedly performed to measure ocular alignment. RESULTS: The testability of infrared photographs using selective wavelength filters in children under 4 years of age was 85.6%. The mean angle of esodeviation was 11.3 ± 4.0 PD by manual measurements and 11.5 ± 4.4 PD by the infrared photograph analysis. Manual measurements and the infrared photograph analysis showed a strong positive correlation (R = 0.815, P < 0.001). The sensitivity and specificity of the infrared photograph analysis for detecting small-angle esotropia were 95.2% and 77.9%, respectively, with a cutoff value of 4.0 PD. CONCLUSIONS: The automated infrared photograph analysis was simple and effective for diagnosing small-angle esotropia in young children.

Surgical outcomes of strabismus after iatrogenic ophthalmic artery occlusion caused by cosmetic filler injections.

BACKGROUND: To investigate the surgical outcomes of strabismus related to iatrogenic occlusion of the ophthalmic artery and its branches from cosmetic facial filler injection. METHODS: A retrospective study was performed on 6 patients who underwent strabismus surgery among 23 patients who had suffered occlusion of the ophthalmic artery and its branches after cosmetic facial filler injection. Initial, preoperative and final ocular motility examinations, the type of surgery and surgical outcomes were evaluated. RESULTS: At initial presentation, visual acuity was no light perception in 5 patients and hand motion in one patient. Five out of 6 patients showed initial ophthalmoplegia. Among these 5 patients, eye motility fully recovered in 3 patients although sensory strabismus developed during follow-up, while the remaining 2 patients had persistent ocular motility limitations. Strabismus surgery was performed at 2.2 ± 1.5 years after iatrogenic ophthalmic artery occlusion. Preoperatively, 5 of the 6 patients showed exotropia, and one patient had esotropia. Vertical deviation was found in 3 out of 6 patients in addition to the horizontal deviation. Successful outcome was achieved only in the 4 patients without persistent ophthalmoplegia after 1.4 ± 1.0 years from surgery. The other two patients with persistent ocular motility limitations failed to achieve successful alignment after surgery, and one patient eventually underwent evisceration due to phthisis bulbi. CONCLUSIONS: In our study, surgical outcomes of strabismus caused by cosmetic facial filler injection were successful only in patients without persistent ophthalmoplegia at the time of surgery.

Möbius syndrome: clinico-radiologic correlation.

PURPOSE: Möbius syndrome is characterized by abducens and facial nerve palsy. However, the presence/absence of corresponding cranial nerves on MRI was not fully evaluated. The purpose of this study was to investigate the mechanism of Möbius syndrome by associating the presence of abducens and facial nerves on MR imagings with clinical features. METHODS: We retrospectively reviewed the medical records and MR imagings of nine patients with Möbius syndrome between January 2004 and October 2015. The presence/absence of abducens and facial nerves on MR imaging, as well as corresponding neuro-ophthalmologic clinical features, was investigated. RESULTS: Facial palsy was bilateral in six and unilateral in three patients. Abduction was limited bilaterally in five and unilaterally in four patients. The degrees of facial palsy and abduction limitation were variable, and asymmetric even in the bilateral cases. MR imaging documented bilateral absence of the abducens and facial nerves in six, absence of unilateral facial nerve and bilateral abducens nerves in one, and absence of facial and abducens nerves unilaterally on the same side in another. Both abducens and facial nerves were visualized bilaterally only in the one remaining patient. CONCLUSIONS: The absence of abducens and facial nerves on MR imaging was mostly correlated with the findings of facial palsy and abduction limitation in patients with Möbius syndrome. MR imaging aids in diagnosis of Möbius syndrome by documenting the absence or presence of abducens and facial nerves.

IgG4-related ophthalmic disease involving extraocular muscles: case series.

BACKGROUND: To elucidate the clinical features of strabismus associated with IgG4-related ophthalmic disease (IgG4-ROD). All of the four patients with IgG4-ROD showed marked enlargement of the extraocular muscles, however, two patients showed orthotropia with full ductions and versions. One patient showed a small angle of exotropia and hypertropia of less than 5 prism diopters. One remaining patient showed orthotropia, full ductions and versions despite marked enlargement of the extraocular muscles, then developed hypertropia up to 35 prism diopters with activation of inflammation, which promptly improved after treatment with oral steroids. CONCLUSIONS: IgG4-ROD usually shows normal ocular motility despite extraocular muscle enlargement, which is the key distinguishing feature from other orbital inflammatory diseases. Active flare-up with increased serum IgG4 levels may produce a large angle of eye deviation, but mostly respond well to steroid treatment.

Case Report: Ocular Myasthenia Gravis Associated with In Vitro Fertilization Procedures.

SIGNIFICANCE: Ocular myasthenia gravis is a localized form of myasthenia gravis, which is a postsynaptic disorder of the neuromuscular junction that causes fluctuating weakness of extraocular muscles resulting from autoimmune mechanisms. In women with myasthenia, changes in sex hormone levels and administration of corticosteroids can trigger or worsen symptoms of myasthenia gravis. PURPOSE: To describe a case of seronegative ocular myasthenia gravis whose first symptom appeared a day after in vitro fertilization procedure. CASE REPORT: A 37-year-old woman suddenly developed mild ptosis and fluctuating diplopia that worsened in the evening. Before the development of symptoms, she had undergone in vitro fertilization procedure and had taken oral steroids. Ocular motility examination revealed an intermittent exotropia in primary gaze at both distance and near. The neostigmine test confirmed her diagnosis as ocular myasthenia gravis. CONCLUSIONS: When taking a history for young women with sudden onset of binocular diplopia, steroids and sex hormones should be taken into account, which may trigger or exacerbate symptoms of ocular myasthenia gravis.

Lawsonia intracellularis in the feces of wild rodents and stray cats captured around equine farms.

BACKGROUND: Proliferative enteropathy is a global enteric disease of particular importance in pigs. The causative bacterium, Lawsonia intracellularis, has a wide range of susceptible host species. Recently, L. intracellularis has been recognized as an etiologic agent of an emerging enteric disease in foals called equine proliferative enteropathy (EPE). The presence of L. intracellularis in nonruminant wildlife has raised questions regarding the role of these species in EPE transmission. RESULTS: This study investigated exposure to L. intracellularis in wild rodents and feral cats from eight farms with confirmed EPE. Serum (42) and fecal (40) samples from resident foals and fecal samples (131), intestinal mucosa tissues (14), and mesenteric lymph nodes (14) from wild and feral animals were collected for the evaluation of the farm status and the molecular detection of L. intracellularis following the diagnosis of EPE in index cases. Fresh feces from wild rodents and feral cats were collected from the ground while walking the premises or after trapping the animals using live traps. A total of 3 brown rats, 7 house mice, 1 striped field mouse, 2 grey red-backed voles, and 3 feral cats showed evidence of prior exposure to L. intracellularis. CONCLUSIONS: Our data add to increasing evidence demonstrating the potential for L. intracellularis transmission and infection in wild rodents and feral cats and provide possible evidence of interspecies transmission. The exposure of wild rodents and feral cats provides potential evidence for the spillover of L. intracellularis to wildlife species and raises the question of spillback to horses. Additionally, these animals may represent an indicator of environmental exposure or may be actively involved in the transmission of L. intracellularis to foals by acting as potential reservoir/amplifier hosts. This study is the first to demonstrate the magnitude of L. intracellularis shedding in the feces of wild rodents and feral cats and to indicate the significant infection risk that wild rodents and feral cats pose to naïve horses in South Korea.