Nor98 scrapie identified in the United States

A distinct strain of scrapie identified in sheep of Norway in 1998 has since been identified in numerous countries throughout Europe. The disease is known as Nor98 or Nor98-like scrapie, among other names. Distinctions between classic scrapie and Nor98 scrapie are made based on histopathology and immunodiagnostic results. There are also differences in the epidemiology, typical signalment, and likelihood of clinical signs being observed. In addition, sheep that have genotypes associated with resistance to classic scrapie are not spared from Nor98 disease. The various differences between classic and Nor98 scrapie have been consistently reported in the vast majority of cases described across Europe. The current study describes in detail the pathologic changes and diagnostic results of the first 6 cases of Nor98 scrapie disease diagnosed in sheep of the United States

Pathology of, and risk factors for, forelimb proximal sesamoid bone fractures in thoroughbred racehorses

Forelimb proximal sesamoid bone (PSB) fractures are the most common fatal racing and training musculoskeletal injuries in California Thoroughbred racehorses. PSB fractures are believed to be preceded by fatigue-induced structural bone damage and repetitive musculoskeletal overuse during training. The goal of this project was to determine if underlying changes in the PSBs predispose them to fracture, and if risk factors could be determined for PSB fracture. Repetitive injury, stress fractures and incomplete healing precede complete, fatal fractures of the humerus, third metacarpal bone, pelvis and vertebrae in Thoroughbred racehorses. Exercise intensity, hoof conformation, and horseshoe characteristics are known risk factors for suspensory apparatus failure, and are likely similar for PSB fractures. In our first study, we proposed that there were significant differences for types and distribution of PSB fractures between left and right limbs, medial and lateral bones, and for horses of different age and sex. We also predicted that radiographically detectable changes of osteophytes and vascular channels were positively associated with PSB fractures. Of the 328 equine cadavers, 136 (41.5%) had at least 1 fractured PSB. Few differences in fracture characteristics were apparent between left and right forelimbs. Medial bones appeared preferentially affected with complete transverse or split transverse simple fractures. Fractured medial bones tended to have indistinct fracture margins; > 1 vascular channel > 1 mm in width; and osteophytes in abaxial wing, basilar middle, or basilar abaxial locations. Oblique, partial transverse and axial fractures were detected predominantly in lateral bones. Fracture prevalence relative to horses actively training and racing increased with age up to 5 years. Osteophytes and vascular channels were common in fractured and intact proximal sesamoid bones. Odds for incurring a fracture in a PSB were lower in bones with osteophytes and vascular channels than in bones without these features. The second study evaluated whether exercise, hoof conformation, and horseshoe traction devices increased the likelihood of bone damage and thus acted as risk factors for PSB fractures. Compared with horses that died without PSB fractures, horses that died with PSB fractures were more likely to be sexually intact males, spend more time in active training and racing, complete more events, train and race longer since their last lay-up, have higher exercise intensities during the 12 months prior to death, and have greater cumulative distances for their career. Horses with PSB midbody fractures were more likely to be sexually intact males, train and race longer since their last lay-up, and have higher exercise intensities during the 12 months prior to death. Transverse fractures of the PSBs were suspected to be acute manifestations of a more chronic process. We examined PSBs from Thoroughbred racehorses with a PSB midbody fracture, the contralateral intact PSB from the same horse and intact PSBs from horses matched by age and gender to the fracture cases to find evidence of microstructural features that might predispose horses to acute PSB fractures. Compaction of trabecular bone and lower bone porosity were observed in fractured PSBs and their contralateral intact PSBs compared to intact PSBs from the age- and gender-matched horses, particularly in the medullary region of the bone. Fracture margin incongruity was evident on the palmar aspect of the fracture margins in 6 of 8 horses with PSB fracture. An additional focal defect, consistent with bone remodeling, was found in medial, fractured and contralateral intact PSBs in 2 of the 6 horses with fracture margin incongruity. Fracture appeared to initiate from sites of previous remodeling in the palmar flexor region and propagate towards the articular surface

Risk factors for proximal sesamoid bone fractures associated with exercise history and horseshoe characteristics in Thoroughbred racehorses

abstract: Objective: Animals: Procedures: Results: Conclusions and Clinical Relevance: To assess individual and combined associations of high-speed exercise and horseshoe characteristics with risk of forelimb proximal sesamoid bone fractures and proximal sesamoid bone midbody fractures in Thoroughbred racehorses.269 deceased Thoroughbred racehorses.A case-control study design was used to compare 121 horses with a fracture of at least 1 of 4 forelimb proximal sesamoid bones (75 horses had a midbody fracture) and 148 horses without a forelimb proximal sesamoid bone fracture. Univariable and multivariable logistic regression analyses were used to evaluate potential risk factors for association with proximal sesamoid bone fracture.Compared with horses that died without proximal sesamoid bone fractures, horses that died with proximal sesamoid bone fractures were more likely to be sexually intact males, spend more time in active trainingand racing, complete more events, train and race longer since their last layup, have higher exercise intensities during the 12 months prior to death, and have greater cumulative distances for their career. Horses with proximal sesamoid bone midbody fractures were more likely to be sexually intact males, train and race longer since their last layup, and have higher exercise intensities during the 12 months prior to death.Limitingexercise intensity and the continuous time spent in activity duringa horse's career may decrease the frequency of forelimb proximal sesamoid bone fractures in Thoroughbred horses

Comparison of macrostructural and microstructural bone features in Thoroughbred racehorses with and without midbody fracture of the proximal sesamoid bone

abstract: Objective: Sample Population: Procedures: Results: Conclusions and Clinical Relevance: To compare macrostructural and microstructural features of proximal sesamoid bones (PSBs) from horses with and without PSB midbody fracture to gain insight into the pathogenesis of PSB fracture.PSBs from 16 Thoroughbred racehorses (8 with and 8 without a PSB midbody fracture).Parasagittal sections of fractured and contralateral intact PSBs from horses with a PSB fracture and an intact PSB from age- and sex-matched control horses without a PSB fracture were evaluated for visual, radiographic, microradiographic, histologic, and his-tomorphometric differences in bone porosity, vascular channels, heme pigment, trabecular anisotropy, and pathological findings.Fractured PSBs and their contralateral intact PSBs had more compacted trabecular bone than did control PSBs. Focal repair or remodeling was evident in the palmar aspect of many fractured and contralateral intact PSBs. Fracture coincided with microstructural features and propagated from the flexor to the articular surface.Fractured PSBs had adapted to high loading but had focal evidence of excessive remodeling and porosity that likely predisposed the horses to complete fracture and catastrophic injury. Detection of focal injury before complete fracture provides an opportunity for prevention of catastrophic injury. Development of diagnostic imaging methods to assess porosity of PSBs may help to identify at-risk horses and allow for modifications of training and racing schedules to reduce the incidence of PSB fracture in Thoroughbred racehorses

Association between findings on palmarodorsal radiographic images and detection of a fracture in the proximal sesamoid bones of forelimbs obtained from cadavers of racing Thoroughbreds

abstract: Objective: Sample Population: Procedure: Results: Conclusions and Clinical Relevance: To determine the distribution for limbs and bones in horses with fractures of the proximal sesamoid bones and relationships with findings on palmarodorsal radiographic images.Proximal sesamoid bones obtained from both forelimbs of cadavers of 328 racing Thoroughbreds.Osteophytes; large vascular channels; and fracture location, orientation, configuration, and margin distinctness were categorized by use of high-detail contact palmarodorsal radiographs. Distributions of findings were determined. Relationships between radiographic findings and fracture characteristics were examined by use of chi2 and logistic regression techniques.Fractures were detected in 136 (41.5%) horses. Biaxial fractures were evident in 109 (80%) horses with a fracture. Osteophytes and large vascular channels were evident in 266 (81%) and 325 (99%) horses, respectively. Medial bones typically had complete transverse or split transverse simple fractures, indistinct fracture margins, > 1 vascular channel that was > 1 mm in width, and osteophytes in abaxial wing and basilar middle or basilar abaxial locations. Lateral bones typically had an oblique fracture and distinct fracture margins. Odds of proximal sesamoid bone fracture were approximately 2 to 5 times higher in bones without radiographic evidence of osteophytes or large vascular channels, respectively.Biaxial fractures of proximal sesamoid bones were common in cadavers of racing Thoroughbreds. Differences between medial and lateral bones for characteristics associated with fracture may relate to differences in fracture pathogeneses for these bones. Osteophytes and vascular channels were common findings; however, fractures were less likely to occur in bones with these features