Browsing by Author "Scarratt, W. Kent"

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    Comparison of Airway Response in Recurrent Airway Obstruction-Affected Horses Fed Steamed Versus Non-steamed Hay
    Blumerich, Celeste Ann (Virginia Tech, 2012-06-21)
    Recurrent Airway Obstruction (RAO)-affected horses experience bronchoconstriction and airway inflammation in response to inhalation of irritants including hay molds. Steaming hay reduces fungal content, but the effect on the antigenic potential has not been investigated. We tested the hypothesis that RAO-affected horses develop less severe clinical disease when fed steamed versus non-steamed hay and this reduction coincides with decreased hay fungal content. Six RAO-affected horses in clinical remission were divided in two groups and fed steamed or non-steamed hay for 10 days using a two-way cross-over design. Hay was steamed using a commercial hay-steamer. Clinical assessment was performed daily. Full assessment, including airway endoscopy, tracheal mucous scores and maximal change in pleural pressure, was performed on days 1, 5, and 10. Bronchial fluid sampling and cytology were performed on days 1 and 10. Hay core samples were collected pre- and post-steaming and cultured to determine fungal and bacterial concentrations. Statistical analysis was based on data distribution and quantity and performed using SAS®. P-value <0.05 was significant. Steaming significantly decreased the number of bacterial and fungal colony-forming-units in hay. Horses fed non-steamed hay experienced a significant increase in clinical score and a trend towards airway neutrophilia, while parameters were unchanged in horses fed steamed hay. Only horses fed non-steamed hay experienced a significant increase in tracheal mucous score. Horses fed steamed hay gained significantly more weight compared to horses fed non-steamed hay, even though the amount of hay consumed not greater on a dry matter basis. These results indicate that steaming reduces the RAO-affected horse's response to hay which coincides with a reduction in viable fungal content of hay.
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    Evaluation of iohexol clearance to estimate glomerular filtration rate in normal horses
    Wilson, Katherine E. (Virginia Tech, 2006-04-18)
    In adult horses and foals, renal dysfunction can occur as a secondary complication to gastrointestinal disorders, dehydration, septicemia, endotoxemia and nephrotoxic drug administration. Measurement of renal function is an important feature not only in the diagnosis, but also in the prognosis and management of renal disease. Commonly used drugs such as phenylbutazone and gentamicin can be highly nephrotoxic under certain conditions. Estimation of the glomerular filtration rate (GFR), accepted as one of the earliest and most sensitive assessments of renal function, can be determined in horses using standard techniques such as endogenous or exogenous renal creatinine clearance. These techniques can be time consuming, dangerous to perform on fractious patients, require trained personnel and are subject to errors most often associated with improper or incomplete urine collection. Recently, tests using iohexol, a radiographic contrast agent, have been developed to estimate the GFR in human beings, pigs, sheep, dogs, cats and horse foals with results that have been validated by traditional standards. Serum clearance of a substance that is freely filtered by the kidneys without tubular secretion or reabsorption, that is not protein bound, and that is not metabolized, is a measurement of glomerular filtration rate. Iohexol meets all of these requirements and thus its clearance from serum should accurately estimate GFR. Utilization of serum clearance studies for estimation of GFR provides a clinically feasible and reproducible method in order to measure GFR in horses. Other commonly used methods to assess renal function in horses are fraught with inherent and operator error. Serum clearance of iohexol does not necessitate collection of urine and has been shown to be a safe, reproducible method using collection of timed blood samples to assess renal function in humans and animals. The objectives of this project were 1) to determine a method of estimation of GFR based on serum clearance of a substance that meets the requirements of a marker for GFR, and 2) to make the method clinically applicable by developing a method using two blood samples to derive clearance and thus GFR in normal adult horses. Results of this study showed good agreement between GFR derived by exogenous creatinine clearance and serum clearance of iohexol. In addition, GFR values for all horses using either method were within published reference ranges for this species. The results of this study indicate that a single intravenous injection of iohexol at a dose of 150 mg/kg, followed by collection of 2 serum samples at 3 and 4 hours post injection can be used to estimate the GFR in healthy horses.
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    Evaluation of the Normal Equine Pituitary Gland
    McKlveen, Tori Leigh (Virginia Tech, 2003-07-21)
    Computed tomography (CT) is becoming more available as a diagnostic tool in the evaluation of the equine skull and brain. Objectives of this study were: 1) refine a CT protocol for evaluating the equine pituitary gland, 2.) define the CT anatomy of the pituitary region, 3.) determine a set of normal values for the pituitary dimensions (length, width, height, volume and weight), 4.) refine CT techniques for measuring pituitary size. Horses were scanned using 10x10mm, 10x5mm, 4x4mm and 4x2mm slice thickness and interval combinations. The pituitary glands were removed immediately after CT and gross measurements were performed. CT measurements were compared with gross pituitary measurements using analysis of variance (ANOVA) in a randomized block design. Accuracy percentages were also calculated using gross measurements as the known value. Mean dimensions of the histologically normal pituitary glands were: length 21.07mm, width 21.62mm, height 9.78mm and volume 2.66cm³. The weights ranged from 1.7g to 3.4g with a mean of 2.6g. Computed tomographic measurement analysis demonstrated that the 10mm slices were the most accurate way to estimate the length of the gland. The 4mm slices yielded the highest accuracy values for width, height and volume of the pituitary gland. The volume was underestimated by all interval and slice thickness combinations performed by CT. No evidence of an overlap effect was identified for any of the dimensions. Our findings indicated that contrast-enhanced CT is an accurate technique for estimating pituitary linear dimensions. Three-dimensional CT volumetry may not be an accurate method for estimating pituitary volume.
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    The Molecular Characterization of Phosphorylcholine (ChoP) on Histophilus somni Lipooligosaccharide: Contribution of ChoP to Bacterial Virulence and Pathogenesis
    Elswaifi, Shaadi Fouad (Virginia Tech, 2006-11-16)
    Histophilus somni virulence factors include expression and antigenic variation of lipooligosaccharide (LOS). Phosphorylcholine (ChoP) is often expressed on H. somni LOS and also undergoes antigenic variation. In this study, five genes that play a role in expression and antigenic variation of ChoP, lic1ABCD and glpQ, were identified in the genome sequence of H. somni through sequence homology with Haemophilus influenzae genes. The open reading frame (ORF) of lic1A contained a variable number of tandem repeats of the tetranucleotide unit 5'-AACC-3'. Slipped strand mispairing in the repeat region during replication leads to shifting the downstream reading frame in and out of frame with the start codon, thus controlling phase variation of lic1A expression. Removal of the repeats from lic1A, cloning the gene in E. coli, and performing a functional assay on the product indicated that lic1A encodes a choline kinase and that the repeats were not required for expression of a functional gene product. Variation in the number of repeats in lic1A correlated with the antigenic variation of ChoP expression in strain 124P, but not in strain 738. This result supported previous findings that antigenic variation of ChoP expression in strain 738 is controlled through extension/truncation of the LOS outer core. Therefore, these results indicated that the lic1ABCD and glpQ genes control expression and antigenic variation of ChoP on the LOS of H. somni and that there are two possible mechanisms for ChoP antigenic variation. The role of H. somni expression of ChoP in colonization of the host respiratory tract was also examined. Experimental infection in the natural host showed that the population of H. somni that expresses ChoP was enriched in the bacteria that colonized the respiratory tract. In addition, bacteria expressing ChoP were able to aggregate bovine platelets through binding to the platelet activating factor receptor (PAF-R), which is also present on epithelial and endothelial cells. These results indicated that ChoP may play a role in the process of colonization and subsequent systemic invasion of host tissues, which may occur through binding of ChoP to PAF-R. Bacteria that did not express ChoP were more prevalent in systemic sites, indicating that ChoP expression may be disadvantageous for the organism during systemic dissemination.
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    The role of lipooligosaccharide phosphorylcholine in colonization and pathogenesis of Histophilus somni in cattle
    Elswaifi, Shaadi F.; Scarratt, W. Kent; Inzana, Thomas J. (Biomed Central, 2012-06-07)
    Histophilus somni is a Gram-negative bacterium and member of the Pasteurellaceae that is responsible for respiratory disease and other systemic infections in cattle. One of the bacterium’s virulence factors is antigenic phase variation of its lipooligosaccharide (LOS). LOS antigenic variation may occur through variation in composition or structure of glycoses or their substitutions, such as phosphorylcholine (ChoP). However, the role of ChoP in the pathogenesis of H. somni disease has not been established. In Haemophilus influenzae ChoP on the LOS binds to platelet activating factor on epithelial cells, promoting bacterial colonization of the host upper respiratory tract. However, ChoP is not expressed in the blood as it also binds C-reactive protein, resulting in complement activation and killing of the bacteria. In order to simulate the susceptibility of calves with suppressed immunity due to stress or previous infection, calves were challenged with bovine herpes virus-1 or dexamethazone 3 days prior to challenge with H. somni. Following challenge, expression of ChoP on the LOS of 2 different H. somni strains was associated with colonization of the upper respiratory tract. In contrast, lack of ChoP expression was associated with bacteria recovered from systemic sites. Histopathology of cardiac tissue from myocarditis revealed lesions containing bacterial clusters that appeared similar to a biofilm. Furthermore, some respiratory cultures contained substantial numbers of Pasteurella multocida, which were not present on preculture screens. Subsequent biofilm experiments have shown that H. somni and P. multocida grow equally well together in a biofilm, suggesting a commensal relationship may exist between the two species. Our results also showed that ChoP contributed to, but was not required for, adhesion to respiratory epithelial cells. In conclusion, expression of ChoP on H. somni LOS contributed to colonization of the bacteria to the host upper respiratory tract, but phase variable loss of ChoP expression may help the bacteria survive systemically.