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R A Moxley

Publications and source records attributed to R A Moxley.

At least 19 recordsLinked to original sources
PubMed2005

Use of rope devices to describe and explain the feedlot ecology of Escherichia coli O157:H7 by time and place.

Escherichia coli O157:H7 is an important pathogen of humans, and cattle populations serve as an important reservoir for human exposure. The organism is ubiquitous to feedlot cattle populations, although the nature of its occurrence is quite dynamic. Why E. coli O157:H7 varies by time and place in fed cattle is poorly understood. This study was designed to describe and explain the occurrence of E. coli O157:H7 by pen-level factors of time and place. From each pen, we cultured seven ropes placed within pens for cattle to rub and chew (ROPES), in order to classify the pens as high or low prevalence in longitudinal studies conducted during the summer and winter feeding periods of 2 full years. We observed differences in occurrence of ROPES-positive pens by season, weeks within season, and feedyard. ROPES-positive pens clustered temporally. Factors associated with ROPES-positive pen-weeks during both the summer and winter feeding periods were feedyard, prior 7-day mean air temperature, recovery of E. coli O157:H7 from the composite fecal sample, and recovery of E. coli O157:H7 from the water tank. Pens of summer-fed cattle were less likely to be ROPES-positive for E. coli O157:H7 if the ROPES were positive for Salmonella spp. The condition of the pen surface was associated with the likelihood for winter-fed pens of cattle to be ROPES-positive. We were able to monitor these pens of cattle using ROPES at minimal cost and without disturbing individual cattle. These observations improve our understanding of the ecology of E. coli O157:H7 in fed cattle, and also illustrate the importance of designing and analyzing observational studies and clinical trials to account for time- and place-dependent variables that affect the probability of detecting E. coli O157:H7.

Animal Husbandry↗
PubMed2005

Use of rope devices to describe and explain the feedlot ecology of Salmonella by time and place.

Salmonella spp. are important zoonotic pathogens, and cattle can serve as an important source of this organism for human exposure through food. This study was designed to describe and explain the occurrence of Salmonella spp. by pen-level factors of time and place using a pen-level test-method previously validated for E. coli O157:H7. From each pen, we cultured seven ropes placed within the pen for cattle to rub and chew (ROPES), in order to classify the pens as ROPES-positive or ROPES-negative each week in longitudinal studies conducted during the summer and winter feeding periods of 2 full years. We observed differences in occurrence of ROPES-positive pens by week within each season such that, at times, a high proportion of pens were of the same ROPES-status even though feedyards were separated by 50-200 km. Factors associated with ROPES-positive pen-weeks during both the summer and winter feeding periods were the condition of the pen surface and recovery of Salmonella spp. from the water tank. The probability for pens of summer-fed cattle to be ROPES-positive for Salmonella spp. increased as the number of cattle in the pen increased and decreased when the pen was ROPES-positive for E. coli O157:H7. Pens of winter-fed cattle differed by feedyard in the probability of their being ROPES-positive for Salmonella spp. We were able to monitor these pens using ROPES at minimal expense, without disturbing individual cattle, and observe important time and place relationships of Salmonella spp. in fed cattle. These observations illustrate the importance of accounting for time- and place-dependent variables that affect the probability of detecting Salmonella spp. when designing and analyzing observational studies and clinical trials.

Animal Husbandry↗
PubMed2004

A diagnostic strategy to determine the Shiga toxin-producing Escherichia coli O157 status of pens of feedlot cattle.

Although cattle are reservoirs, no validated method exists to monitor Shiga toxin-producing Escherichia coli O157 (STEC O157) on farms. In 29 Midwestern United States feedlot pens we compared culturing faeces from the individual cattle to: (1) culturing rope devices that cattle rub or chew; and (2) culturing a composite of faecal pats. Eighty-six per cent (68-96%) of pens were classified correctly using rope devices to detect pens with at least 16% of the cattle shedding STEC O157 [sensitivity=82% (57-96%); specificity=92% (62-100%)]. Ninety per cent of pens (73-98%) were classified correctly using composite faeces to detect pens with at least 37% of the cattle shedding STEC O157 [sensitivity=86% (42-100%); specificity=91% (71-99%)]. Ranking pens into three risk levels based on parallel interpretation of the pen-test results correlated (Spearman's r=0.76, P<0.0001) with the pen's prevalence. This strategy could identify pens of cattle posing a higher risk to food safety.

Animals↗
PubMed2003

Incidence, duration, and prevalence of Escherichia coli O157:H7 fecal shedding by feedlot cattle during the finishing period.

The objective was to describe variability in prevalence, incidence, and duration of fecal shedding of naturally occurring E. coli O157:H7 by a group of feedlot cattle over time. One hundred steers, randomly assigned to 10 pens, were fed a high-concentrate finishing diet for 136 days (19 weeks). Rectal feces from each animal were tested for E. coli O157:H7 every week for 19 weeks. E. coli O157:H7 was recovered from each animal that completed the study and was detected from at least one animal every week. Average pen prevalence of cattle shedding E. coli O157:H7 varied significantly over time (P < 0.0001) and across pens (P < 0.0001), ranging from 1 to 80%. Pairwise comparisons of mean pen prevalence of E. coli O157:H7 between weeks and estimation of the predicted probability of an incident case of E. coli O157:H7 over time allowed the definition of three distinct phases--namely, the preepidemic, epidemic, and postepidemic periods. Average pen prevalence varied significantly over time (P < 0.01) and across pens (P < 0.001) for all time periods. The odds of an incident case were significantly greater during epidemic and postepidemic periods relative to the preepidemic period (P = 0.0002 and P = 0.03, respectively). Duration of infection was significantly longer for first or second infections that began during epidemic or postepidemic periods relative to the preepidemic period (P < 0.001). Both incidence and duration of shedding peaked during the epidemic period. Pen-level prevalence of cattle shedding E. coli O157:H7 was affected by both incidence and duration of shedding and could be explained by time- or pen-dependent risk factors, or both.

Animal Husbandry↗
PubMed2000

Escherichia coli O157:H7 induces attaching-effacing lesions in large intestinal mucosal explants from adult cattle.

Attaching-effacing (A/E) lesions following natural and experimental infection with Escherichia coli O157:H7 have been seen in neonatal and 3-4-month-old weanling but not older cattle. To test the hypothesis that the adult bovine large intestinal epithelium is resistant to the development of A/E lesions, colonic and rectal mucosal tissue explants from 18-month-old steers were inoculated with E. coli O157:H7 and examined. Epithelial cells of inoculated explants developed A/E lesions at the bacterial attachment sites, providing evidence that the large intestinal mucosal epithelium may be a site of infection that contributes to carriage of E. coli O157:H7 in adult cattle.

Animals↗
PubMed2000

Edema disease.

Edema disease is a common cause of illness and death loss in pigs during the first 2 weeks after weaning. The disease is an enterotoxemia caused by strains of E. coli that colonize the small intestine and produce Stx2e. Bacterial colonization is mediated by F18ab fimbriae. Susceptibility to disease is determined by presence of receptors for these fimbriae on small intestinal epithelial cells and is inherited as a dominant trait. Clinical signs and lesions are largely the result of Stx2e, which causes necrosis of endothelial and smooth muscle cells in small arteries and arterioles. Vascular damage in the brain stem with resultant infarction and malacia is the main cause of death in affected pigs. Studies conducted by veterinary researchers in the 1950s and 1960s identified the cause of the disease and provided future scientists with hypotheses to test regarding the pathogenesis. In the last two decades, studies using molecular-based techniques have allowed for the definitive identification of bacterial virulence factors that mediate intestinal colonization and vascular damage, that is, F18ab fimbriae and Stx2e. Identification of these virulence factors has provided a basis for current and future development of effective preventative measures, for example, vaccines.

Animals↗
PubMed1999

Comparative pathology of bacterial enteric diseases of swine.

Enteric bacterial infections are among the most common and economically significant diseases affecting swine production worldwide. Clinical signs of these infections include diarrhea, reduced growth rate, weight loss, and death of preweaned, weanling, grower-finisher, young and adult age breeding animals. The most common etiological agents include Escherichia coli, Clostridium perfringens, Lawsonia intracellularis, Salmonella enterica, and Brachyspira (Serpulina) spp. With the exception of Brachyspira (Serpulina) hyodysenteriae, the cause of swine dysentery, and Lawsonia intracellularis, the cause of proliferative enteropathy, the pathological changes seen with these agents closely resemble the diseases occurring in human beings. Histological changes in the intestines of swine with enteric bacterial infections include bacterial colonization without significant damage (e.g., certain enterotoxigenic E. coli and C. perfringens type A), attaching and effacing lesions with enteropathogenic E. coli and Brachyspira pilosicoli, the cause of colonic spirochetosis, inflammation with S. enterica, and necrotizing and hemorrhagic lesions with certain C. perfringens. Extraintestinal spread of bacteria and/or toxins occurs with some serotypes of E. coli and most serotypes of S. enterica. Enteric bacterial diseases of swine have been used as models to study the pathogenesis of similar diseases of human beings. Several of these pathogens are also important causes of food-borne disease in humans.

Animals↗
PubMed1998

Regulation of the Escherichia coli sheA gene and characterization of its encoded hemolytic activity.

Escherichia coli K-12 carries the cryptic hemolysin gene sheA which is under the control of positive and negative transcriptional regulators. The objectives of the present study were to further analyze the regulation of the sheA gene in E. coli, to compare the sheA genes from E. coli K-12 and a pathogenic E. coli strain, and to characterize the SheA hemolytic activity. Northern blot analysis demonstrated that the transcriptional regulator SlyA activates the E. coli K-12 sheA gene. The main transcriptional start site of the sheA gene was 56 nucleotides upstream from the start codon as determined by primer extension analysis. The sheA genes from E. coli K-12 and a pathogenic E. coli strain were identical. SheA hemolytic activity was cell associated and Ca2+ independent.

Animals↗
PubMed1998

Pathogenicity of an enterotoxigenic Escherichia coli hemolysin (hlyA) mutant in gnotobiotic piglets.

Pigs infected with hemolytic F4(+) strains of enterotoxigenic Escherichia coli often develop septicemia secondary to intestinal infection. We tested the hypothesis that inactivation of hemolysin would reduce the ability of F4(+) enterotoxigenic E. coli to cause septicemia in swine following oral inoculation. Inactivation of the hemolysin structural gene (hlyA) did not decrease the incidence of septicemia in the gnotobiotic piglet model.

Animals↗
PubMed1997

Effect of booster vaccination with a multivalent clostridial bacterin-toxoid on sudden death syndrome mortality rate among feedlot cattle.

OBJECTIVE: To determine whether booster vaccination with a multivalent clostridial bacterin-toxoid would affect the sudden death syndrome (SDS) mortality rate among feedlot cattle. DESIGN: Field trial. ANIMALS: 83, 115 cattle at a Nebraska feedlot. PROCEDURE: Cattle arriving at the feedlot underwent routine processing according to established protocol. All cattle received a sequentially numbered ear tag and a 2-ml dose of a multivalent bacterin-toxoid designed to protect cattle against Clostridium chauvoei, C speticum, C novyi, C sordellii, and C perfringens types C and D. Approximately 90 days prior to slaughter, growth promotants were implanted in all cattle, and cattle were allocated to a treatment or control group on the basis of the last digits of their ear tag numbers. Cattle in the treatment group received a second 2-ml dose of clostridial bacterintoxoid; control cattle did not. RESULTS: Significant differences between groups in regard to crude, feeding pen, or SDS mortality rates were not detected. Sudden death syndrome mortality rate across both groups was 0.24%. If the SDS mortality rate in midwestern feedlot cattle was reduced > or = 40% by booster vaccination with a multivalent clostridial bacterin-toxoid, this experiment included enough animals to have a 90% probability of detecting that difference. CLINICAL IMPLICATIONS: Booster vaccination with a multivalent clostridial bacterin-toxoid does not affect SDS mortality rate among feedlot cattle.

Animals↗
PubMed1997

Variation in virulence in the gnotobiotic pig model of O157:H7 Escherichia coli strains of bovine and human origin.

Escherichia coli strains of serotype O157:H7 have been incriminated in outbreaks and sporadic cases of food-borne illness, including diarrhea, hemorrhagic colitis, hemolytic uremic syndrome and thrombotic thrombocytopenic purpura. Food-producing animals, particularly cattle, are believed to be reservoirs of the organism. Whether all strains of bovine origin pose human health risk is unknown and was the impetus for this investigation. We compared the virulence of ten SLT-I, SLT-II, and eae DNA probe-positive O157:H7 strains from cattle to 10 like strains associated with human diarrheal disease outbreaks for virulence in one day-old gnotobiotic pigs. All strains caused diarrhea, and only four pigs inoculated with either of two bovine strains failed to develop that condition. Signs of central nervous system disease, death, debilitation requiring euthanasia before the end of an eight day observation period, and/or encephalomalacia occurred in 32/42 pigs inoculated with the strains isolated from human beings, 13/39 pigs inoculated with strains from cattle, and 7/7 pigs inoculated with a positive control strain. More strains of human origin (9/10) than bovine origin (5/10) caused these effects. The results of this study indicate considerable variability in virulence of O157:H7 strains possessing the same known virulence determinants, and suggest that disease outbreaks tend to be caused by the more virulent of these strains.

Adhesins, Bacterial↗
PubMed1997

beta-Carotene and alpha-tocopherol inhibit the development of atherosclerotic lesions in hypercholesterolemic rabbits.

Male New Zealand White rabbits were made hypercholesterolemic by feeding an atherogenic diet (0.5% cholesterol, 3% peanut oil, and 3% coconut oil) with or without (control) antioxidants for 8 weeks. The antioxidant treatments were intravenous injection of beta-carotene (25 mg/kg/BW, twice weekly), dietary supplementation of alpha-tocopherol (0.5%), and a combination of both. Antioxidant treatments significantly increased plasma and LDL antioxidant levels in the above three groups. Intravenous injection of beta-carotene significantly decreased total and LDL cholesterol concentrations, thoracic atherosclerotic lesion area, and intimal thickness, but had no effects on LDL oxidation ex vivo as compared to control. Added dietary alpha-tocopherol significantly decreased the susceptibility of LDL to oxidation ex vivo, aortic atherosclerotic lesion area and intimal thickness, but had no effects on plasma cholesterol levels as compared to control. Combination of both antioxidants significantly decreased total and LDL cholesterol concentrations, susceptibility of LDL to oxidation ex vivo, as well as atherosclerotic lesion area and intimal thickness at aortic arch and thoracic aorta as compared to control, but not beta-carotene or alpha-tocopherol groups. These data suggest that the antihypercholesterolemic effects of beta-carotene and antioxidant effects of alpha-tocopherol may benefit rabbits fed an atherogenic diet by inhibiting the development of atherosclerotic lesions.

Animals↗
PubMed1996

Distribution of virus and viral antigen in specific pathogen-free calves following inoculation with noncytopathic bovine viral diarrhea virus.

Gross and microscopic lesions and distribution of virus were studied in specific pathogen-free calves (SPF) 10 days post-inoculation (PI) with bovine viral diarrhea virus (BVDV). To investigate possible differences in tissue tropism between BCDV isolates, two clinically and antigenically different noncytopathic (ncp) isolates of BVDV were compared in the study. Four calves were exposed to noncytopathic (ncp) BVDV 7937, and four to ncp-BVDV 126. Two additional calves that were not exposed to virus served as controls. Both ncp-BVDV 7937 and ncp-BVDV 126 induced mild disease characterized by variable fever and anorexia. Lymphoid depletion was evident in Peyer's patch of four calves and the thymus of two calves exposed to BVDV. Differences between these isolates in the distribution of BVDV or BVDV antigen in tissues of inoculated calves were not found. High concentrations of BVDV and BVDV-specific antigen were detected in the thymus, Peyer's patch, and mesenteric lymph node of all exposed calves. BVDV was shown to infect cells of the bone marrow without causing microscopic lesions. High concentrations of BVDV were recovered from the bone marrow of all calves exposed to BVDV and BVDV-specific antigen was demonstrated at this location in six of these calves. Platelet counts of calves exposed to BVDV were significantly reduced during infection, which resulted in thrombocytopenia in one calf. Focal areas of necrosis were observed in squamous epithelial cells of the tonsil and ruminal mucosa. BVDV-specific antigen was found in and adjacent to these foci. Calves exposed to ncp-BVDV 7937 had slightly more severe clinical signs than those exposed to ncp-BVDV 126.

Animals↗
PubMed1996

Intestinal spirochetosis and giardiasis in a beagle pup with diarrhea.

This report describes the light microscopic and ultrastructural changes in a 3-month-old dog with naturally acquired intestinal spirochetosis and giardiasis. It was concluded that the pathogenetic characteristics of weakly beta-hemolytic spirochetes associated with colitis in this pup were similar to those associated with human and porcine spirochetal diarrhea.

Animals↗
PubMed1995

Enterohemorrhagic Escherichia coli O157:H7 requires intimin to colonize the gnotobiotic pig intestine and to adhere to HEp-2 cells.

In a previous study, enterohemorrhagic Escherichia coli (EHEC) O157:H7 with a deletion and insertion in the eaeA gene encoding intimin was used to establish that intimin is required for the organism to attach to and efface microvilli in the piglet intestine (M. S. Donnenberg, S. Tzipori, M. L. McKee, A. D. O'Brien, J. Alroy, and J. B. Kaper, J. Clin. Invest. 92:1418-1424, 1993). However, in the same investigation, a role for intimin in EHEC adherence to HEp-2 cells could not be definitively demonstrated. To analyze the basis for this discrepancy, we constructed an in-frame deletion of eaeA and compared the adherence capacity of this mutant with that of the wild-type strain in vitro and in vivo. We observed a direct correlation between the requisite for intimin in EHEC O157:H7 colonization of the gnotobiotic piglet intestine and adherence of the bacterium to HEp-2 cells. The in vitro-in vivo correlation lends credence to the use of the HEp-2 cell adherence model for further study of the intimin protein.

Adhesins, Bacterial↗
PubMed1993

Experience with a planned exposure program for the control of enzootic transmissible gastroenteritis in swine.

Oral inoculation of pregnant sows and gilts with a homogenate of pig intestines containing live, virulent transmissible gastroenteritis (TGE) virus was associated with significant (P < 0.01) reduction of mortality in nursery pigs in a herd affected with enzootic TGE. The mortality of weaned pigs from April through June 1981, when sows were not vaccinated or inoculated, was 9.3%. Mortality of weanling pigs from July through December 1981 was 5.7% (P < 0.01), and stayed consistently between 2.6 and 4.8% from 1982 through 1990. After beginning the exposure program, there were no clinical signs attributable to TGE in the farrowing house or nursery until 1986, when recrudescence of TGE was evident in the nursery. Although the source of the virus could not be substantiated, recrudescence suggested that TGE virus would not be eradicated as long as exposure was continued. The most plausible explanation for the decrease in the incidence of diarrhea and mortality in the nursery pigs after initiation of the planned exposure program is that a higher, longer lasting amount of lactogenic immunity was provided to suckling pigs. Presumably over time, this resulted in less TGE virus carryover into the nursery by weanling pigs, thereby reducing and confining the environmental challenge to the nursery. Strict all-in, all-out pig movement in the nursery with thorough cleaning and disinfecting presumably further reduced the environmental challenge.

Administration, Oral↗