PubMed Health⌕ Search

Biomedical subjects

P R Davies

Publications and source records attributed to P R Davies.

At least 19 recordsLinked to original sources
PubMed2005

Comparison of fecal culture and Danish Mix-ELISA for determination of Salmonella enterica subsp. enterica prevalence in growing swine.

In the USA, control of food-borne salmonellosis associated with meat consumption has been predominantly focused at slaughter and processing. It is expected that standards at slaughter and processing will become more stringent, creating pressure to reduce prevalence of Salmonella-positive food animals through on-farm interventions. The aim of this study was to compare traditional fecal culture and the Danish Mix-ELISA (DME) for determination of Salmonella prevalence pre-harvest in swine. In Trial 1, five cohorts of individually identified pigs were longitudinally sampled during the growing period to compare the kinetics of prevalence as estimated by fecal culture and the DME. In Trial 2, the correlation between fecal prevalence and seroprevalence was estimated pre-marketing in 49 groups of pigs. In Trial 1, fecal prevalence and seroprevalence showed similar kinetics, with a tendency of a higher OD% cut-off to more closely approximate fecal prevalence. In Trial 2, correlations between fecal culture and the DME were 0.40, 0.36, 0.43, and 0.43 (p<0.001) for OD% cut-offs > or =10, 20, 30, and 40, respectively. Based on these results, a higher OD% cut-off would be recommended if more approximate estimation of fecal prevalence is desired and longitudinal sampling would be suggested for evaluating the impact of on-farm interventions for Salmonella reduction whether utilizing fecal culture or the DME. Further evaluation of the impact of Salmonella serovar present on farms on seroprevalence and the relationship of on-farm seroprevalence with food safety risk are needed prior to utilizing the DME for pre-harvest Salmonella diagnostics in the US swine herd.

Age Factors↗
PubMed2005

Activation of oxygen at metal surfaces.

Oxygen chemisorption at metal surfaces has been shown through a combination of scanning tunnelling microscopy and photoelectron spectroscopy to involve transient states that provide low energy pathways for a wide range of surface reactions including the catalytic oxidation of ammonia and hydrocarbons. The kinetically 'hot' transients are disordered and mobile, become unreactive when they form ordered structures, and are characterized by non-classical kinetic behaviour. The role of surface additives (caesium) in controlling oxygen structures and the implications of oxygen transients for theory and reaction mechanisms in applied catalysis are considered.

Adsorption↗
PubMed2005

Detection of antibody to the foot-and-mouth disease virus (FMDV) non-structural polyprotein 3ABC in sheep by ELISA.

The specificity and sensitivity of an ELISA for detecting IgG to the 3ABC non-structural protein of foot-and-mouth disease (FMD) virus was evaluated in FMD naive, aerosol-infected, aerosol plus direct contact infected and field-exposed sheep. All 12 sheep that were experimentally infected without prior vaccination seroconverted in the test, although fewer field sera from FMD-exposed sheep were scored seropositive compared to test results for structural protein antibodies. The 3ABC test specificity was 98 or 100% according to whether sera reacting in the doubtful range were scored as positive or negative. The test was then used to investigate the antibody response of sheep vaccinated against FMD and exposed to the virus by an aerosol challenge 4-14 days later. The response of individual animals varied. Whether immunised with high or low doses of vaccine, the development of 3ABC antibody was most likely in sheep from which live virus was recovered at or beyond 9 days post-challenge. Non-structural responses were also more frequent in animals from which multiple incidences of live FMD virus isolation (perhaps more indicative of true virus replication) were demonstrated.

Animals↗
PubMed2005

Exposure of rabbits to ultraviolet light-inactivated rabbit haemorrhagic disease virus (RHDV) and subsequent challenge with virulent virus.

This study investigated whether exposure to inactivated rabbit haemorrhagic disease virus (RHDV) can produce an antigenic response in rabbits and protect them from a subsequent challenge with virulent virus. The aim was to determine if the spreading of baits containing RHDV, which is a common management practice in New Zealand to reduce rabbit numbers, could result in protective immunity in wild rabbits. RHDV was inactivated by ultraviolet (UV) light using an electronic UV crosslinker with a UV dose of 168.48 W-s/cm2 and a UV intensity of 0.0078 W/cm2. Two groups of four rabbits were then inoculated with inactivated virus via oral and intramuscular routes. Rabbits were monitored for 30 days post-inoculation and then challenged orally with virulent virus. No rabbit exposed to inactivated RHDV developed clinical signs of RHD or had antibodies at day 30 post-infection and all animals died within 82 h after challenge with virulent virus. No antibodies were detected at the time of death. These findings suggest that exposure to virus completely inactivated by UV light in the field or on baits will not protect rabbits against challenge with virulent virus.

Animals↗
PubMed2005

Survival of rabbit haemorrhagic disease virus (RHDV) in the environment.

A study was conducted to investigate the persistence of rabbit haemorrhagic disease virus (RHDV) in the environment. Virus was impregnated onto two carrier materials (cotton tape and bovine liver) and exposed to environmental conditions on pasture during autumn in New Zealand. Samples were collected after 1, 10, 44 and 91 days and the viability of the virus was determined by oral inoculation of susceptible 11- to 14-week-old New Zealand White rabbits. Evidence of RHDV infection was based on clinical and pathological signs and/or seroconversion to RHDV. Virus impregnated on cotton tape was viable at 10 days of exposure but not at 44 days, while in bovine liver it was still viable at 91 days. The results of this study suggest that RHDV in animal tissues such as rabbit carcasses can survive for at least 3 months in the field, while virus exposed directly to environmental conditions, such as dried excreted virus, is viable for a period of less than 1 month. Survival of RHDV in the tissues of dead animals could, therefore, provide a persistent reservoir of virus, which could initiate new outbreaks of disease after extended delays.

Animals↗
PubMed2004

Attitudes of New Zealand farmers to methods used to control wild rabbits.

Four years after the release of Rabbit haemorrhagic disease virus (RHDV) in New Zealand, we conducted a mail survey of farmers to ascertain their attitudes and practices about rabbit control. A multistage sampling frame (stratified by rabbit-proneness and farm type) was used to select 828 farms in eight geographical regions. The useable response proportion of the survey was 69.3%, and 21% of respondents considered rabbits to be a problem on their farms. Although practices for rabbit control had changed from 1995 to 2001, shooting (practised by 85% of respondents) remained the predominant method used (albeit less frequently than in 1995). Ten percent of farmers used RHDV baiting; of those, 90% released the virus relatively infrequently. Farmers perceived shooting to be the most-humane and environmentally safe method, while RHDV was perceived to be the most effective. Perception of the level of competition for grazing between rabbits and livestock was the factor most-strongly associated with the use of shooting and RHDV. Most (60%) respondents considered the introduction of RHDV to have been beneficial.

Animal Husbandry↗
PubMed2004

Salmonella Brandenburg - emergence of a new strain affecting stock and humans in the South Island of New Zealand.

AIMS: To report information on the spread of a new strain of Salmonella Brandenburg, which affected livestock and humans in the South Island of New Zealand, and a series of small case studies designed to investigate potential transmission of infection. METHODS: Information on the occurrence and spread of S. Brandenburg in livestock was gathered from laboratory diagnostic submissions, from case studies on the faecal excretion rate in ewes, carrier status of black-backed gulls (Larus dominicanus), spread of S. Brandenburg organisms in sheep yards, infection in lambs going to meat plants, and from post-abortion pathological changes in the reproductive tract of ewes. RESULTS: A newly recognised strain of S. Brandenburg was first diagnosed in aborting sheep from a flock in mid Canterbury in the South Island in 1996. Subsequently, the disease spread to other farms in mid and south Canterbury in 1997 and to Southland and Otago in the lower half of the South Island in 1998-2003. In 1999, the same strain was responsible for abortions in cattle and gastroenteritis in calves and adult cattle. The same strain of bacterium also caused disease in horses, goats, deer, pigs and humans. Spread of the disease on farms was strongly associated with aborting ewes, which resulted in considerable environmental contamination. During the abortion season, black-backed gulls appeared to spread the disease to other farms. Other potential sources of infection were carrier sheep, contaminated water sources and contaminated sheepyard dust. Damage to the reproductive tract may affect the ability of surviving ewes to conceive. CONCLUSION: Important features of this disease are its high morbidity and mortality within a flock or herd, rapid local spread and its role as an occupational, health and safety risk to farm workers and their families.

Journal Article↗
PubMed2004

Pneumonic lesions in lambs in New Zealand: patterns of prevalence and effects on production.

AIM: To describe temporal and spatial patterns of the prevalence of pneumonia in lambs in three regions of New Zealand, and determine effects on liveweight gain. METHODS: A longitudinal study was conducted in 1999- 2000 on 14 commercial sheep farms, five from the Southland region of the South Island, and five from the King Country and four from the Northland regions of the North Island. Pneumonia was known to be a problem in lambs on all farms selected. On each farm, 400 lambs were randomly selected at weaning and allocated at random to one of two groups (Groups I and II). Lambs in both groups were weighed at 4-weekly intervals. The extent of pneumonic lesions in lungs was scored visually at slaughter in 40 randomly selected lambs after each weighing (Group I). Lambs in Group II were selected for slaughter by the farm manager on a commercial basis of liveweight and body condition, then assessed for pneumonic lesions. RESULTS: Prevalence of extensive pneumonic lesions (>/=10% lung surface area affected) increased from December to March from 1.4 to 10.1% lambs in Southland (n=1,917), 1.2 to 25.7% in the King Country (n=1,831), and 4.7 to 21.4% in Northland (n=1,485). Overall, 42.3% of lambs in both groups had pneumonic lesions (n=5,233) and in 15.1% of these, >/=5% of the lung surface area was affected. Daily weight gain in the month prior to slaughter was reduced in lambs for which >/=20% lung surface area was affected in Group I (p<0.05) but not in Group II. CONCLUSIONS: The association between pneumonic lesions and reduced weight gain was highly significant in lambs from Group I, but not from Group II. Thus, pneumonia had a negative impact on weight gain, and selection by farmers of lambs for slaughter counteracted this association in lambs from Group II. CLINICAL RELEVANCE: Pneumonia occurs commonly as a subclinical disease in lambs in New Zealand. It has no public health significance and is not recorded at slaughter plants nor reported to farmer clients. Effects of the disease on daily weight gain of lambs is considerable and costly for lamb producers.

Journal Article↗
PubMed2004

Prevalence and clonal diversity of Campylobacter jejuni from dairy farms and urban sources.

AIM: To investigate the role of free-living animals such as sparrows, rodents and flies as potential reservoirs of Campylobacter spp on a dairy farm, and to assess the genetic diversity among Campylobacter isolates from the farm and an urban source. METHODS: A total of 290 samples (bovine, passerine and rodent faeces, and whole flies) were collected from a large commercial dairy farm in the Manawatu district in New Zealand, and from faeces from urban sparrows in a nearby city. Other samples collected from the dairy farm included five from silage, two from aprons worn by workers during milking, two from workers' boots and two from water in troughs in a paddock. Isolates of thermophilic Campylobacter spp were identified morphologically and phenotypically and further characterised molecularly using pulsed-field gel electrophoresis (PFGE) and the restriction enzyme SmaI. RESULTS: Campylobacter jejuni was the only Campylobacter species isolated from all samples. The highest prevalence was found in faeces from dairy cows (54%), followed by faeces from sparrows from the urban area (40%) and the farm (38%), and from rodents (11%) and whole flies (9%). Other samples from the farm environment such as silage, trough water, and workers' aprons and boots were also positive for C. jejuni. Of the 22 restriction patterns obtained, seven were common to more than one source. CONCLUSIONS: Cattle, sparrows, rodents and flies are potential reservoirs of C. jejuni on dairy farms. Identical clones of C. jejuni carried by cattle, sparrows, flies and rodents probably indicate a common source of infection. The high level of asymptomatic carriage of C. jejuni by healthy dairy cows could be sufficient to maintain infections within the dairy farm surroundings via environmental contamination.

Journal Article↗
PubMed2003

Free available chlorine in commercial broiler chicken drinking water in New Zealand.

Free available chlorine (FAC) concentrations in drinking water supplied to broiler chickens grown commercially in New Zealand were monitored for 11 farms in two companies. Different sites within a growout house were examined at different times of the day to determine spatial and temporal differences in FAC concentrations. Taps provided water with significantly higher FAC concentrations than did drinkers. There were no significant differences between the concentrations of FAC taken from various drinkers around the growout house. There were differences in the variations of measurements taken from the same drinker within a growout house at different times of the day, with variations increasing in the afternoon. No growout houses provided an average FAC content of 2 ppm, the suggested standard in one company. Three growout houses consistently met the chlorine concentration of 0.2 ppm suggested by the New Zealand Drinking Water Standards.

Animal Husbandry↗
PubMed2001

Longitudinal study of Salmonella enterica in growing pigs reared in multiple-site swine production systems.

Intensive longitudinal investigations of breeding and growing pig populations in two multiple-site swine production systems were conducted in NC, USA. Five cohorts of sows and individually identified growing pigs from their litters were serially sampled in order to determine the prevalence and serotypes of Salmonella enterica in each stage of production based on fecal culture. In addition to fecal samples, feed and environmental samples were obtained. Fifteen different serotypes were isolated from the two systems, the most frequently isolated serotypes were S. typhimurium var Mbandaka and S. typhimurium var Copenhagen. Pig prevalence estimates ranged from 0 to 48.1%. Environmental contamination was frequently encountered despite cleaning and disinfection. Feed was rarely (2/800, 0.25%) identified as S. enterica positive. We observed highly variable patterns of S. enterica prevalence and serotype profiles within cohorts over time and among cohorts within systems. These observations indicate that point estimates of S. enterica prevalence and serotypes cannot be considered as reliable indicators of the S. enterica status of farms, and that uncontrolled studies of interventions to control S. enterica may yield misleading results. These findings are critical to the design of epidemiological studies of S. enterica on swine farms and may suggest that cohort level, as opposed to farm or company level events or management practices, may be important as potential risk factors for S. enterica fecal shedding in market age pigs.

Animal Feed↗
PubMed2001

Emergence in Asia of foot-and-mouth disease viruses with altered host range: characterization of alterations in the 3A protein.

In 1997, an epizootic in Taiwan, Province of China, was caused by a type O foot-and-mouth disease virus which infected pigs but not cattle. The virus had an altered 3A protein, which harbored a 10-amino-acid deletion and a series of substitutions. Here we show that this deletion is present in the earliest type O virus examined from the region (from 1970), whereas substitutions surrounding the deletion accumulated over the last 29 years. Analyses of the growth of these viruses in bovine cells suggest that changes in the genome in addition to the deletion, per se, are responsible for the porcinophilic properties of current Asian viruses in this lineage.

Amino Acid Sequence↗
PubMed2000

Comparison of methods for isolating Salmonella bacteria from faeces of naturally infected pigs.

A series of experiments was conducted using faecal samples collected from commercial swine farms to evaluate the effects of variation in methods used for the detection of Salmonella bacteria. The primary objective of the studies was to compare the protocols routinely used in two laboratories in the USA. The studies included five experiments comparing the enrichment protocols used routinely in the respective laboratories (Method 1: 10 g faeces--buffered peptone water (BPW) pre-enrichment--selective enrichment in Rappaport/Vassiliadis (RV) broth; Method 2: approximately 1g faeces--primary enrichments in tetrathionate and Hajna GN broths--secondary enrichment in RV broth). The effects of enrichment temperatures (37 vs 42 degrees C) using RV broth (two experiments) and delayed secondary enrichment (four experiments) were also evaluated. Direct comparison of Method 1 and Method 2 indicated comparable results. However, when compared using faecal samples of equal weight, the Method 2 enrichment protocol was more sensitive for detecting Salmonella bacteria than the Method 1 protocol. Enrichment in RV at 42 degrees C was superior to 37 degrees C, particularly for samples that were pre-enriched in BPW. Delayed secondary enrichment increased detection of Salmonella bacteria in swine faeces. These results highlight the imperfect sensitivity of culture methods, and the need for researchers to consider the sensitivity of bacteriological methods in the design and interpretation of the results of epidemiologic studies based on faecal culture.

Animals↗
PubMed2000

Antimicrobial resistance of Salmonella isolates from swine.

We examined the antimicrobial resistance of 1,257 isolates of 30 serovars of Salmonella enterica subsp. enterica isolated from swine. Serovars Typhimurium and Typhimurium var. Copenhagen were widespread and were frequently multidrug resistant, with distinct resistance to ampicillin, kanamycin, streptomycin, sulfamethoxazole, and tetracycline and to ampicillin, chloramphenicol, streptomycin, sulfamethoxazole, and tetracycline, respectively.

Animals↗
PubMed2000

The effect of fecal sample weight on detection of Salmonella enterica in swine feces.

The effect of different fecal sample weights on the detection of Salmonella enterica in swine feces was examined. Sample weights evaluated were rectal swabs and fecal samples weighing 1 g, 10 g, and 25 g. Comparisons were made on matched fecal samples obtained from individual pigs housed on 2 commercial swine farms in North Carolina. Relative sensitivity (number of positive pigs per fecal weight category/number positive in all weight categories) increased (P < 0.001) with fecal sample weight, and ranged from 9% for rectal swabs to 78% for 25-g samples. Stomaching of fecal samples did not affect detection of S. enterica. These observations demonstrate that fecal sample weight can markedly influence estimates of prevalence of S. enterica in epidemiologic studies. Failure to consider the imperfect sensitivity of bacterial culture in the design and interpretation of epidemiologic studies will lead to underestimation of prevalence and reduced power to detect the presence of S. enterica-infected herds.

Animals↗
PubMed1999

Effects of sample storage and delayed secondary enrichment on detection of Salmonella spp in swine feces.

OBJECTIVE: To determine effects of fecal sample storage and delayed secondary enrichment (DSE) on detection of Salmonella spp in swine feces. Sample Population-Fecal samples obtained from 84 pigs in a commercial herd. PROCEDURE: Each fecal sample underwent 3 storage treatments: no storage (ie, processed on the day of collection), storage at 4 C for 6 days, and storage at -15 C for 14 days. After assigned storage treatments, all samples were enriched in Rappaport-Vassiladias (RV) broth (single enrichment) and plated on XLT4 agar. Delayed secondary enrichment was performed, using single enrichment broths that were stored for 4 days at room temperature. RESULTS: Of 504 cultures, 186 (36.9%) were Salmonella positive. A difference in proportions of samples with positive results was not found between same-day processing and storage at 4 C for 6 days. Compared with use of single enrichment for 24 hours (34% positive), use of DSE resulted in a greater proportion (40%; P < 0.001) of samples with positive results. Estimated relative sensitivities for the storage methods were 0.90, 0.85, and 0.71 for same-day processing, storage at 4 C for 6 days, and storage at -15 C for 14 days, respectively. CONCLUSIONS: Where practical, processing of fecal samples on the day of collection is recommended, although storage at 4 C for several days does not result in marked loss of sensitivity. Improved detection associated with DSE warrants further investigation and optimization.

Animals↗