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.

OBJECTIVE: 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. SAMPLE POPULATION: Proximal sesamoid bones obtained from both forelimbs of cadavers of 328 racing Thoroughbreds. PROCEDURE: 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. RESULTS: 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. CONCLUSIONS AND CLINICAL RELEVANCE: 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.

Environmental air sampling to detect exotic Newcastle disease virus in two California commercial poultry flocks.

The 2002--2003 Exotic Newcastle Disease (END) outbreak in Southern California poultry provided an opportunity to evaluate environmental air sampling as an efficient and cost-effective means of sampling flocks for detection of a circulating virus. Exotic Newcastle Disease virus was detected by real-time reverse transcriptase PCR from air samples collected using a wetted-wall cyclone-style air sampler placed within 2 m of birds in 2 commercial flocks suspected of being naturally exposed to END virus during the outbreak. Exotic Newcastle Disease virus was detected after 2 hours of air sampling the poultry-house environments of the 2 naturally infected flocks.

High-throughput real-time RT-PCR assay to detect the exotic Newcastle Disease Virus during the California 2002--2003 outbreak.

During the 2002--2003 Exotic Newcastle Disease (END) outbreak in Southern California, a high-throughput real-time reverse transcriptase-polymerase chain reaction (RRT-PCR) system was developed to respond to the large diagnostic and surveillance sample workload. A 96-well RNA extraction method, using magnetic bead technology, combined with a 96-well RRT-PCR assay, allowed 1 technician to process and test more than 400 samples per day. A 3-technician team could complete testing on approximately 1,900 samples per day. The diagnostic sensitivity of the high-throughput RRT-PCR assay was 0.9967 (95% CI 0.9937-0.9997) based on 926 virus isolation confirmed positive samples. Diagnostic specificity using an initial 434 virus isolation confirmed negative samples was 100%. A diagnostic specificity of 0.9999 (95% CI 0.9999, >0.9999) was subsequently calculated on the basis of 2 false-positive results among 65,343 surveillance samples collected after the final END-positive case was confirmed in May 2003. Assay performance over 500 replicates, including reproducibility of the combined extraction and RRT-PCR amplification steps yielded a standard deviation of 0.70 RRT-PCR cycle thresholds (Ct) and a standard deviation of 0.59 Ct for the RRT-PCR steps alone. The high-throughput RRT-PCR developed for END contributed significantly to the 2002--2003 END control effort, reducing the predicted timeline for eradication from 3 years to just 11 months, primarily because of the large number of samples that could be rapidly tested. The 96-well approach described for high-throughput END RRT-PCR could be adapted to other rapid, high-volume testing needs, as required for potential foreign animal disease responses or intensive surveillance efforts.

Determination of the median toxic dose of type C botulinum toxin in lactating dairy cows.

Because of the difficulty in identifying botulinum toxin in cattle, it is hypothesized that cattle are sensitive to levels of toxin below the detection limits of current diagnostic techniques (the mouse protection bioassay and the immunostick enzyme-linked immunosorbent assay [ELISA] for type C botulinum toxin). Using an up-down method for toxicologic testing, the median toxic dose (MTD50) for cattle was determined. Four lactating Holstein cows were dosed at 0.125 or 0.25 ng/kg with Clostridium botulinum type C toxin and failed to develop clinical signs of botulism during the 7-day observation period. Three cows given 0.50 ng/kg of toxin developed clinical signs of botulism. From these results, the MTD50 was calculated at 0.388 ng/kg (3.88 mouse lethal doses/kg) using the trim-logit method. These results suggest that cattle are 12.88 times more sensitive to type C botulinum toxin than a mouse on a per kilogram weight basis. The mouse protection bioassay and the immunostick ELISA for type C botulinum toxin failed to identify the presence of the toxin in the serum, blood, and milk samples taken from all 7 animals.

Molecular weapons against agricultural vulnerability and the war on terror.

The multiple reports in this issue of the Journal from the Agenda for Action conference, coupled with the analysis by the National Academy of Sciences, the National Research Council, and the Auditor General (UK) on bioterror preparedness and homeland security, highlight the immediate need for rapid disease detection and advanced diagnostic capabilities to protect the public health, animal agriculture, and the numerous associated economies in the United States. In response to the potentially devastating consequences that could arise, there is an acute need for rapid detection of a variety of the lethal foreign animal diseases, such as foot-and-mouth disease virus (FMDV), highly pathogenic strains of avian influenza, classical swine fever, rinderpest, exotic Newcastle disease virus (END), and domestic, vesicular look-alike diseases that include bluetongue, epizootic hemorrhagic disease, vesicular stomatitis, bovine herpes IBR, contagious ecthyma, bovine herpes mammilitis virus, vesicular exanthema, malignant catarrhal fever, and papular stomatitis. Some striking advances are occurring in the creation of rapid technology, including microfluidics, robotics, miniaturization, and biostabilization that are quickly being applied to the development of rapid microbial detection assays. These are now providing important weapons to combat this agricultural vulnerability.