Diamond burr debridement of calcific band keratopathy in 24 eyes of 22 horses.

PURPOSE: To evaluate the safety and effectiveness of diamond burr debridement (DBD) for the treatment of calcific band keratopathy (CBK) in horses. METHODS: Medical records from horses with CBK were reviewed over a period of 4 years. Diagnosis of CBK was based on slit-lamp examination findings, and DBD was performed on standing sedated horses. Follow-up was obtained by clinical reevaluation of the treated eyes or a telephone survey with the referring veterinarian. RESULTS: Twenty-two horses of different ages (median: 11 years; range: 5-23) representing 24 CBK-affected eyes (14 left eyes and 10 right eyes) were included in the study. The patients had a medical history of chronic and recurrent uveitis, which required repeated long-term treatments with various combinations of ophthalmic corticosteroids. DBD alone cleared the cornea in 22 affected eyes (92%), but it was combined with blade scraping in two cases with thick calcium plaques. The postoperative medication included a topical antibiotic, atropine drops, and oral flunixin meglumine. Corneal healing was achieved in 21 eyes (87%), 5-21 days (median time 13 days) postoperatively. The three remaining horses were lost to follow-up. Recurrence occurred in 5 of the 21 (24%) reexamined eyes, 3-12.5 weeks (median 8 weeks) postoperatively, and required a second DBD. Four of the 21 eyes ended up being enucleated due to sequelae of uveitis. The main limitations of the study include those inherent to all retrospective clinical data collections. CONCLUSION: Mechanical DBD can readily and safely clear the cornea in horses with CBK, but recurrence of calcium deposition is possible.

Detection of classical BSE prions in asymptomatic cows after inoculation with atypical/Nor98 scrapie.

The emergence of bovine spongiform encephalopathy (BSE) prions from atypical scrapie has been recently observed upon experimental transmission to rodent and swine models. This study aimed to assess whether the inoculation of atypical scrapie could induce BSE-like disease in cattle. Four calves were intracerebrally challenged with atypical scrapie. Animals were euthanized without clinical signs of prion disease and tested negative for PrPSc accumulation by immunohistochemistry and western blotting. However, an emergence of BSE-like prion seeding activity was detected during in vitro propagation of brain samples from the inoculated animals. These findings suggest that atypical scrapie may represent a potential source of BSE infection in cattle.

Treatment of canine spontaneous chronic corneal epithelial defects (SCCEDs) with corneal thermal cautery: A retrospective study of 89 cases.

PURPOSE: To evaluate the clinical course and outcome of canine spontaneous chronic corneal epithelial defects (SCCEDs) treated with a combination of cotton-tip epithelial debridement (ED) and corneal thermal cautery (CTC), with or without diamond burr debridement (DBD). METHODS: Retrospective medical record review was used to identify dogs treated for SCCEDs at the Veterinary School of Toulouse between 2001 and 2021. The variables identified included signalment, history, clinical findings, previous treatments, and outcomes. Surgery was performed under manual restraint after topical anesthesia of the cornea. The outcome endpoints included healing, clearing of the cornea and complications. RESULTS: Seventy-seven dogs (89 eyes) from 28 different breeds fulfilled the inclusion criteria. The mean age was 8.78 years. The overall success rate after one procedure was 65.1% with a mean healing time of 15.4 days, but 21 eyes lost to follow-up after the initial treatment, were not included in calculations. There was no significant effect of age, eye, brachycephalic conformation and previous treatments. No significant differences in healing rates were found between groups that received DBD or not. Fifteen eyes (22.7%) underwent a second procedure. Complications (corneal pigmentation, uveitis, corneal bullae, and corneal infection) were observed in 15 cases (22%), with only two cases of complicating melting ulcer. CONCLUSIONS: CTC is a safe and effective treatment for SCCEDs in dogs and can be performed without general anesthesia. Additional DBD does not bring any significant value to CTC in SCCEDs. CTC could be interesting in cases where other procedures are less desirable.

Pyogenic granuloma of the cornea in a pony: Uncommon complication of corneal wound healing.

A 6-year-old miniature Shetland pony mare was referred for evaluation of a left corneal mass, which developed from the healing tissue of a corneal traumatic ulceration that had occurred 4 weeks previously. On gross examination, a spherical, smooth-surfaced, and pink-colored lesion of about 1 cm in diameter was protruding from the left palpebral fissure. Ophthalmic examination revealed that it was attached to the scar tissue of the cornea, and that one corpora nigra was adherent to the posterior face of corneal wounded area, without sign of uveitis. The remainder of the ophthalmic examination was unremarkable. The mass was excised, and cryotherapy was used as an adjunctive therapy. Histopathology of the resected mass was consistent with a pyogenic granuloma on the basis of radially oriented proliferating capillaries, embedded in immature granulation tissue containing an infiltrate of neutrophils, plasma cells and eosinophils. There were no histological features of malignancy. 2 months after surgery, the ventral part of the fibrotic corneal scar was slightly raised by a pink tissue, suggesting possible recurrence of the initial lesion. A second cryotherapy was performed over the leukoma area. No recurrence has been noted for a follow-up period of more than 25 months. Pyogenic granuloma is a benign proliferative fibrovascular response that typically develops after trauma or surgery. Corneal involvement is rare in humans, and to the authors' knowledge has never been documented in veterinary ophthalmology.

The emergence of classical BSE from atypical/Nor98 scrapie.

Atypical/Nor98 scrapie (AS) is a prion disease of small ruminants. Currently there are no efficient measures to control this form of prion disease, and, importantly, the zoonotic potential and the risk that AS might represent for other farmed animal species remains largely unknown. In this study, we investigated the capacity of AS to propagate in bovine PrP transgenic mice. Unexpectedly, the transmission of AS isolates originating from 5 different European countries to bovine PrP mice resulted in the propagation of the classical BSE (c-BSE) agent. Detection of prion seeding activity in vitro by protein misfolding cyclic amplification (PMCA) demonstrated that low levels of the c-BSE agent were present in the original AS isolates. C-BSE prion seeding activity was also detected in brain tissue of ovine PrP mice inoculated with limiting dilutions (endpoint titration) of ovine AS isolates. These results are consistent with the emergence and replication of c-BSE prions during the in vivo propagation of AS isolates in the natural host. These data also indicate that c-BSE prions, a known zonotic agent in humans, can emerge as a dominant prion strain during passage of AS between different species. These findings provide an unprecedented insight into the evolution of mammalian prion strain properties triggered by intra- and interspecies passage. From a public health perspective, the presence of c-BSE in AS isolates suggest that cattle exposure to small ruminant tissues and products could lead to new occurrences of c-BSE.

Ectopic cilia in 112 dogs: A multicenter retrospective study.

OBJECTIVE: The aim of this retrospective study was to review the clinical data and outcomes of patients that suffered ectopic cilium (EC). ANIMALS STUDIED: One hundred and twelve dogs from multiple private practices in France, with a clinical diagnosis of EC were included in the study. RESULTS: The mean age of affected dogs was 2.3 years. There were 64 females and 48 males. The most represented breeds were the Shi Tzu, the French Bulldog, the English Bulldog and the Chihuahua. Eleven dogs were affected bilaterally. The upper eyelid was implicated in 93.5% of the cases, with the median portion being the most affected. No statistical difference was observed between the right and the left eye. EC were associated with distichiasis in 50% of the cases. Pigmentation of the conjunctiva at the point of exit of the EC was present in 58% of the cases. EC were short in 75% and long in 25% of the cases. Corneal complications were statistically associated with short EC. The corneal lesions associated with EC were keratitis (94%), corneal granuloma (0.8%), corneal fibrosis (2.7%), corneal degeneration (0.8%), superficial corneal ulcer (68.7%), deep corneal ulcer (8%) and perforating corneal ulcer (0.8%). The surgeries which consisted of the removal of the hair follicle was successful in 88.4% of the cases. CONCLUSION: EC is a rare condition which can be treated successfully by the removal of the hair follicles. It must be suspected in cases of corneal lesions unresponsive to medical treatment.

Wide distribution of prion infectivity in the peripheral tissues of vCJD and sCJD patients.

Sporadic Creutzfeldt-Jakob disease (sCJD) is the commonest human prion disease, occurring most likely as the consequence of spontaneous formation of abnormal prion protein in the central nervous system (CNS). Variant Creutzfeldt-Jakob disease (vCJD) is an acquired prion disease that was first identified in 1996. In marked contrast to vCJD, previous investigations in sCJD revealed either inconsistent levels or an absence of PrPSc in peripheral tissues. These findings contributed to the consensus that risks of transmitting sCJD as a consequence of non-CNS invasive clinical procedures were low. In this study, we systematically measured prion infectivity levels in CNS and peripheral tissues collected from vCJD and sCJD patients. Unexpectedly, prion infectivity was detected in a wide variety of peripheral tissues in sCJD cases. Although the sCJD infectivity levels varied unpredictably in the tissues sampled and between patients, these findings could impact on our perception of the possible transmission risks associated with sCJD.

Autologous lamellar keratoplasty for the treatment of feline corneal sequestrum: A retrospective study of 35 eyes (2012-2020).

OBJECTIVE: To evaluate the use of autologous lamellar keratoplasty for the treatment of feline corneal sequestrum (FCS). PROCEDURE: The medical records of cats diagnosed with FCS that underwent autologous lamellar keratoplasty between 2012 and 2020 with a minimum of 2 months of follow-up were reviewed. After keratectomy of FCS, a button adjacent to the corneal limbus was harvested on the same eye and sutured to the recipient bed. A nictitating membrane flap was left in place until the first recheck except for one patient. Postoperative treatment with topical and systemic antibiotics and systemic nonsteroidal anti-inflammatory medications was prescribed. Follow-up examinations were carried out 2 weeks, 1 month and 2 months post-operatively and consisted of a complete ophthalmic examination. RESULTS: A total of 35 cats (35 eyes) were included. The median follow-up time was 3.2 months (range, 2-59 months). Brachycephalic cats were overrepresented (85.7%). The mean graft size was 6.5 mm (range, 6-9 mm). Minor complications consisting of melting and partial integration of the graft occurred in 2/35 eyes (5.7%). Recurrence was observed in 1/35 eyes (2.9%) and was managed by a superficial keratectomy. A good visual outcome was achieved in all eyes, and a faint or mild corneal opacification occurred in 15/35 (42.9%). CONCLUSIONS: Autologous lamellar keratoplasty is an effective treatment for FCS, providing good tectonic support to the affected cornea and resulting in good visual and cosmetic outcomes. These results should be verified in future prospective studies that include a larger number of cases and longer-term follow-up.

Conjunctival calcinosis circumscripta in a dog: Treatment combining surgical resection and amniotic membrane grafting.

This report describes the clinical features, histopathology, and surgical treatment of a case of conjunctival calcification in a 5-month-old female English Setter, referred with a history of recurrent conjunctivitis in the right eye (OD). The ophthalmic findings were limited to multifocal white plaques embedded in a markedly inflamed conjunctiva of the eyelids and the anterior nictitating membrane OD. Calcification was suspected. The blood cell count, blood chemical profile, and urinalysis were within normal limits, and long-bone radiographs appeared normal. After removal of the affected area by means of a large conjunctivectomy, cryopreserved canine amniotic membrane (AM) was transplanted to fill in the defect. Multifocal ectopic calcium deposits in the conjunctival lamina propria were confirmed histopathologically. The postoperative healing was uneventful, and no recurrence was observed during a follow-up period of five years. Conjunctival mineralization is uncommon in canine ophthalmology, and the cause remained undetermined in the present case, for which AM transplantation was able to promote conjunctival healing after a large surgical excision.

Survey of cytokines on ocular surfaces of atopic dogs by multiplex analysis using two sampling methods - a pilot study.

BACKGROUND: Conjunctivitis in atopic dogs has already been described yet is rarely observed, and likely underdiagnosed in practice. OBJECTIVES: To assay various cytokines in tears and conjunctivae from atopic and normal dogs, and to compare canine atopic dermatitis-associated conjunctivitis with controls. ANIMALS: Ten atopic and ten normal client-owned dogs. METHODS AND MATERIALS: Ocular surfaces were sampled bilaterally in a prospective study, using two different methods. Tear samples were obtained with a sterile swab previously moistened with saline solution (method A). Conjunctival impressions were obtained with a conjunctival impression device (method B). For each sample, the concentrations of a panel of 13 cytokines were measured by multiplex analyses. CADESI-4, pruritus (PS) and conjunctival (CS) scores were determined. RESULTS: Among the measured cytokines, only granulocyte-macrophage colony-stimulating factor (GM-CSF), keratinocyte-derived chemokine (KC)-like and interleukin (IL)-8 were above the limit of quantification in most samples. Absolute amounts of each cytokine were always higher in samples obtained with method A than with method B. GM-CSF amounts were lower in atopic dogs (method A, P=0.02; method B, P=0.0005). KC levels were higher in atopic dogs, yet the differences were not significant. IL-8 amounts were higher in atopic dogs (method A, P=0.0003; method B, P=0.006). CONCLUSIONS AND CLINICAL RELEVANCE: Regardless of the method, these preliminary results suggest an overexpression of IL-8 in conjunctivae and tears of atopic dogs despite subtle conjunctival symptoms. As IL-8 is commonly found in many inflammatory conditions, further studies are needed to determine its specificity in atopic conjunctivitis.

Radical Change in Zoonotic Abilities of Atypical BSE Prion Strains as Evidenced by Crossing of Sheep Species Barrier in Transgenic Mice.

Classical bovine spongiform encephalopathy (BSE) is the only zoonotic prion disease described to date. Although the zoonotic potential of atypical BSE prions have been partially studied, an extensive analysis is still needed. We conducted a systematic study by inoculating atypical BSE isolates from different countries in Europe into transgenic mice overexpressing human prion protein (PrP): TgMet129, TgMet/Val129, and TgVal129. L-type BSE showed a higher zoonotic potential in TgMet129 mice than classical BSE, whereas Val129-PrP variant was a strong molecular protector against L-type BSE prions, even in heterozygosis. H-type BSE could not be transmitted to any of the mice. We also adapted 1 H- and 1 L-type BSE isolate to sheep-PrP transgenic mice and inoculated them into human-PrP transgenic mice. Atypical BSE prions showed a modification in their zoonotic ability after adaptation to sheep-PrP producing agents able to infect TgMet129 and TgVal129, bearing features that make them indistinguishable of sporadic Creutzfeldt-Jakob disease prions.

Corneal anesthesia associated with topical application of 2% lidocaine nonophthalmic gel to healthy canine eyes.

OBJECTIVE: To assess the degree and duration of corneal anesthesia induced by topical application of 2% lidocaine gel to the healthy canine eye. ANIMALS: Nineteen adult Beagles free of ocular abnormalities. PROCEDURES: Baseline corneal touch threshold (CTT) was measured bilaterally with a Cochet-Bonnet aesthesiometer. The 2% lidocaine gel (0.1 mL) was applied to one eye, randomly assigned, and the same volume of a lubricant gel was applied to the opposite eye. The CTT measurements were repeated bilaterally within 1 minute, after drug application, and every 5 minutes, until the baseline corneal sensitivity was restored. The potential for local adverse effects was evaluated. RESULTS: Complete desensitization of the cornea (CTT = 0) was achieved one minute after lidocaine gel application and was maintained during 25.3 ± 12.5 minutes. Overall, the corneal sensitivity was significantly decreased for 58.4 ± 16.6 minutes compared with baseline level. Minor and reversible punctate epithelial erosions of the cornea were observed in the two treatment groups and were attributed to the anesthetic effect and the aesthesiometry procedure. CONCLUSIONS: In the current study, the 2% lidocaine gel provided a sustained, deep and well-tolerated corneal anesthesia in ophthalmically normal dogs.

Subconjunctival nodule due to Setaria equina erratic migration in a horse: First case report.

An 18-month-old Arabian-English filly resident in southwest France was referred for evaluation of a conjunctival mass in the right eye (OD). A pink, solid, and mobile nodular formation, measuring approximately 1.2 × 0.8 cm was found under the superior nasal bulbar conjunctiva during an ophthalmic examination that was otherwise normal. The mass was surgically removed using a standing procedure. Cytological examination of fine-needle aspirates from the mass revealed a mixed eosinophilic-lymphocytic inflammation. Histological examination confirmed the dense and diffuse eosinophilic-lymphocytic infiltrate of the mass, and it revealed several cross sections of a parasitic nematode. The morphometric diagnosis identified an immature form of a filarial worm, and molecular analysis of the mitochondrial cytochrome c oxydase subunit 1 (cox1) and 12S rRNA gene sequences led to further identification of the specimen as Setaria equina. Microfilaremia was not observed on fresh blood smears. There have been no signs of local recurrence after 18 months, nor any evidence of intraocular involvement. To the authors' knowledge, this is the first documented case of subconjunctival setariasis due to S equina in a horse.

Congenital lacrimal fistula in two prim'Holstein calves.

Two 4- and 8-month-old prim'Holstein calves were presented for chronic epiphora. Examination of the affected eyes revealed an abnormal duct opening inferonasal to the medial canthus. A diagnosis of congenital lacrimal fistula was made based on conventional and computed tomographic-dacryocystography findings. These revealed an ectopic channel connecting the nasolacrimal duct to the skin opening near the medial canthus. Both of the calves were surgically treated with resection and closure of the ectopic duct and placement of a nasolacrimal stent.

Phenotype of macular corneal dystrophy in Labrador Retrievers: A multicenter study.

OBJECTIVE: To describe the phenotype of canine macular corneal dystrophy (MCD) including the clinical presentation, multimodal ocular imaging, histopathology, and ultrastructural analysis in ten Labrador Retrievers. PROCEDURE: Multicentered data collection. RESULTS: Labrador Retrievers affected by MCD were presented between the age of 4.5 and 6 years of age with a history of cloudy eyes and/or visual impairment. Findings on ophthalmic examination included a diffuse haze of the corneal stroma and multiple, well-demarcated, off-white to yellow-brown, punctate corneal opacities heterogeneous in size. Corneal vascularization developed in most dogs as the disease progressed. Disease progression was associated with increased density of the corneal haze as well as increased number and size of the focal opacities and dogs developed significant visual impairment. Spectral domain-optical coherence tomography revealed multifocal hyper-reflective regions within the stroma. In vivo confocal microscopy revealed marked alterations in reflectivity throughout the entire stroma. Normal keratocytes could not be identified in affected areas. Histopathology showed stromal collagen fibers separated by acidophilic granular material on hematoxylin and eosin stain. The material stained with periodic acid-Schiff and colloidal iron stain but not with Masson trichrome stain, confirming the accumulation of glycosaminoglycans. On electron microscopic ultrastructural examination, keratocytes presented with vacuolated rough endoplasmic reticulum and multiple electron dense cytoplasmic inclusions. In areas keratocytes appeared ruptured, with cell organelles and proteinaceous material grouped together between collagen fibers. CONCLUSION: MCD in Labrador Retrievers has similarities with the human counterpart of the condition and is an important differential diagnosis in dogs with corneal disease.

Submicroscopic deletions at 13q32.1 cause congenital microcoria.

Congenital microcoria (MCOR) is a rare autosomal-dominant disorder characterized by inability of the iris to dilate owing to absence of dilator pupillae muscle. So far, a dozen MCOR-affected families have been reported worldwide. By using whole-genome oligonucleotide array CGH, we have identified deletions at 13q32.1 segregating with MCOR in six families originating from France, Japan, and Mexico. Breakpoint sequence analyses showed nonrecurrent deletions in 5/6 families. The deletions varied from 35 kbp to 80 kbp in size, but invariably encompassed or interrupted only two genes: TGDS encoding the TDP-glucose 4,6-dehydratase and GPR180 encoding the G protein-coupled receptor 180, also known as intimal thickness-related receptor (ITR). Unlike TGDS which has no known function in muscle cells, GPR180 is involved in the regulation of smooth muscle cell growth. The identification of a null GPR180 mutation segregating over two generations with iridocorneal angle dysgenesis, which can be regarded as a MCOR endophenotype, is consistent with the view that deletions of this gene, with or without the loss of elements regulating the expression of neighboring genes, are the cause of MCOR.

Infectivity in bone marrow from sporadic CJD patients.

Prion infectivity was recently identified in the blood of both sporadic and variant Creutzfeldt-Jakob disease (CJD) patients. In variant CJD (vCJD), the widespread distribution of prions in peripheral tissues of both asymptomatic and symptomatic patients is likely to explain the occurrence of the observed prionaemia. However, in sporadic CJD (sCJD), prion infectivity is described to be located principally in the central nervous system. In this study, we investigated the presence of prion infectivity in bone marrow collected after death in patients affected with different sCJD agents. Bioassays in transgenic mice expressing the human prion protein revealed the presence of unexpectedly high levels of infectivity in the bone marrow from seven out of eight sCJD cases. These findings may explain the presence of blood-borne infectivity in sCJD patients. They also suggest that the distribution of prion infectivity in peripheral tissues in sCJD patients could be wider than currently believed, with potential implications for the iatrogenic transmission risk of this disease. Copyright © 2017 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Effect of sedation with butorphanol on variables pertaining to the ophthalmic examination in dogs.

OBJECTIVE: To evaluate whether sedation with intramuscular butorphanol can interfere with different variables of the ocular examination in dogs. ANIMALS: Twenty-two beagles without ophthalmic abnormalities. PROCEDURES: Each dog was examined 20 min prior to and again just before administration of butorphanol to establish baseline data. The globe and nictitating membrane position was evaluated, and the following were recorded: menace response, dazzle reflex, corneal blink reflex, phenol red thread tear test (PRT), Schirmer tear test-1 (STT-1), pupil size (PS) measurement, and rebound tonometry. Then, butorphanol was injected intramuscularly at a dose of 0.2 mg/kg and these procedures were repeated 10, 20, 30, and 45 min postadministration. A sedation score graded 0 to 3 was also established at these time points. Statistical analyses were performed on quantitative data using ANOVA. RESULTS: The sedative effect was not associated with any changes in globe and nictitating membrane position; did not affect the results of the menace response, dazzle reflex, and corneal blink reflex; and had no significant effect on PRT values. However, butorphanol administration was associated with a statistically significant decrease in STT-1 and PS values (P < 0.005), and a statistically significant increase in IOP (P < 0.05). All these variations remained in the range of normal values. CONCLUSIONS AND CLINICAL RELEVANCE: Butorphanol administered intramuscularly at 0.2 mg/kg provided a degree of sedation allowing eye examination, but was found to interfere with STT-1, PS, and IOP values among the diagnostic tests studied. However, these values remained within normal limits.

Effect of topical application of 2% lidocaine gel on corneal sensitivity of clinically normal equine eyes.

OBJECTIVE: To assess the degree and duration of corneal anaesthesia provided by topical application of a non-ophthalmic 2% lidocaine gel in horses. STUDY DESIGN: Experimental, 'blinded', randomized prospective study. ANIMALS: Twelve adult horses without relevant ocular abnormalities. METHODS: Baseline corneal touch threshold (CTT) measurements were obtained bilaterally by use of a Cochet-Bonnet aesthesiometer just prior to topical treatment. A volume of 0.2mL of 2% lidocaine gel was administered in one randomly selected eye and the same volume of a viscous lubricant in the other eye to serve as control. The CTT value was measured on both eyes 5, 10, 20, 30, 45, 60, 75 and 90 minutes after drug application. The potential for local adverse effects following lidocaine gel application was also evaluated. RESULTS: Mean CTT baseline measurements were not significantly different (p>0.05) between the control eyes (3.41±0.56cm) and those subsequently treated with the lidocaine gel (3.50±0.64cm). In control eyes, no significant changes in corneal sensitivity (p>0.05) occurred over time during the study period. By contrast, a marked reduction in corneal sensitivity was observed after lidocaine application, with mean CTT values significantly lower (p<0.001) than those of the control eyes from 5 to 75 minutes. A steady-state maximal corneal anaesthesia was present from 10 to 45 minutes after lidocaine gel application with mean CTT values ranging from 0.21 to 0.45cm. Corneal epithelial irregularities were detected in three lidocaine-treated eyes, but spontaneous resolution occurred within 24hours. CONCLUSIONS AND CLINICAL RELEVANCE: Deep and sustained corneal anaesthesia is achieved after application of 2% lidocaine gel to the equine eye, with minimal changes in the corneal epithelium. It might be useful for minor ophthalmic surgeries performed in the standing sedated horse.

Mononucleated Blood Cell Populations Display Different Abilities To Transmit Prion Disease by the Transfusion Route.

UNLABELLED: Previous experiments carried out in a sheep scrapie model demonstrated that the transfusion of 200 µl of prion-infected whole blood has an apparent 100% efficacy for disease transmission. These experiments also indicated that, despite the apparent low infectious titer, the intravenous administration of white blood cells (WBC) resulted in efficient disease transmission. In the study presented here, using the same transmissible spongiform encephalopathy (TSE) animal model, our aim was to determine the minimal number of white blood cells and the specific abilities of mononucleated cell populations to transmit scrapie by the transfusion route. Our results confirmed that the transfusion of 100 µl, but not 10 µl, of fresh whole blood collected in asymptomatic scrapie-infected donor sheep can transmit the disease. The data also show that the intravenous administration of 10(5) WBCs is sufficient to cause scrapie in recipient sheep. Cell-sorted CD45R(+) (predominantly B lymphocytes), CD4(+)/CD8(+) (T lymphocytes), and CD14(+) (monocytes/macrophages) blood cell subpopulations all were shown to contain prion infectivity by bioassays in ovine PrP transgenic mice. However, while the intravenous administration of 10(6) CD45(+) or CD4(+)/8(+) living cells was able to transmit the disease, similar numbers of CD14(+) cells failed to infect the recipients. These data support the contention that mononucleated blood cell populations display different abilities to transmit TSE by the transfusion route. They also represent an important input for the risk assessment of blood-borne prion disease transmission and for refining the target performance of leukoreduction processes that currently are applied to mitigate the transmission risk in transfusion medicine. IMPORTANCE: Interindividual variant Creutzfeldt-Jakob disease (vCJD) transmission through blood and blood-derived products is considered a major public health issue in transfusion medicine. Over the last decade, TSE in sheep has emerged as a relevant model for assessing the blood-borne vCJD transmission risk. In this study, using a sheep TSE model, we characterized the ability of different peripheral blood mononucleated cell populations to infect TSE-free recipients by the transfusion route. Our results indicate that as little as 10(5) WBC and 100 µl of blood collected from asymptomatic scrapie infected animals can transmit the disease. They also demonstrate unambiguously that peripheral blood mononuclear cell subpopulations display dramatically different abilities to transmit the disease. These data represent an important input for the risk assessment of blood-borne prion disease transmission and for refining the target performance of leukoreduction processes that currently are applied to mitigate the transmission risk in transfusion medicine.