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.     

Microbiological differences between cull cattle slaughtered at an abattoir and cull cattle slaughtered on farms

Tissue samples from 27 casualty adult dairy cattle slaughtered on farms and 32 'normal' cull dairy cattle were analysed microbiologically for total viable counts (tvc), Enterobacteriaceae, Escherichia coli o157, Salmonella enterica and Campylobacter species. Overall the counts of Enterobacteriaceae and tvc were higher in the animals slaughtered on farms, particularly in the spleen. One 'normal' animal yielded E coli O157, and one yielded Campylobacter jejuni, and eight of the cattle slaughtered on farms yielded C jejuni and five yielded S enterica.     

A descriptive survey of lesions from cull sows harvested at two Midwestern U.S. facilities

Physical and reproductive conditions of cull sows (3158) from two U.S. Midwestern harvest plants were assessed. Body condition, feet, shoulders, teeth, lungs, and reproductive tracts were visually evaluated for gross lesions on harvested sows. PROC FREQ (SAS, Cary, NC) was used to calculate the frequency of each binary trait event. Pearson chi-square tests were used to test the alternative hypothesis that a linear association existed between binary traits and body condition score (BCS). The most common foot lesions observed were rear (n = 2064, 67.5%) and front (n = 1024, 32.9%) heel lesions. Cracked hooves were found on the front feet of 703 (22.6%) and rear feet of 552 (18.1%) sows. Rear digital overgrowth was observed in 644 (21.1%) sows. The most common reproductive gross lesion observed among harvested cull sows was acyclic ovaries (n = 277, 9.0%). Presence of acyclic ovaries increased (p < 0.01) as BCS decreased. Cystic ovaries were found in 192 (6.3%) sows, which increased (p < 0.01) as BCS increased. Pneumonia was observed in 298 (9.7%) sows, and increased in frequency as BCS decreased (p < 0.01). The most frequently observed shoulder lesion among harvested cull sows was shoulder abrasions (n = 394, 12.5%). The presence of shoulder abrasions increased (p < 0.01) as BCS decreased. The prevalence of reproductive lesions detected in the present study was less than the reported percentage of sows culled for reproductive failure from previous studies based on record keeping summaries.     

Application of nucleotide sequence of RNA polymerase beta-subunit gene (rpoB) to molecular differentiation of serovars of Salmonella enterica subsp. enterica.

To establish a molecular differentiation method for Salmonella enterica subsp. enterica, a hyper-variable region of RNA polymerase beta-subunit (rpoB) of S. enterica subsp. enterica (I), serotype Typhimurium, and Escherichia coli were investigated through comparison of nucleotide sequence of the region. The hyper-variable region was identified at 612-937 of the gene. After PCR amplification of the region in the 17 serotypes and two biotypes of serotype Gallinarum of S. enterica subsp. enterica (I), the nucleotide sequences of the region were determined and compared. All serotypes were distantly related to E. coli with 82.8-84.7% identities in nucleotide sequence while showing 96.6-100% identities with each other. According to the phylogenetic analysis based on the sequenced region with the neighbor-joining method, relatedness of biotype Gallinarum to serotype Enteritidis and biotype Pullorum was determined. Biotype Gallinarum was more closely related to serotype Enteritidis than biotype Pullorum. These results suggested that the 612-937 variable region of rpoB might be useful for molecular evolutionary analysis of serotypes of S. enterica subsp. enterica (I).     

Diversity of Salmonella serotypes in cull (market) dairy cows at slaughter.

OBJECTIVE: To determine the diversity of Salmonella serotypes isolated from a large population of cull (market) dairy cows at slaughter. DESIGN: Cross-sectional study. SAMPLE POPULATION: Salmonella organisms isolated from the cecal-colon contents of 5,087 market dairy cows. PROCEDURE: During winter and summer 1996, cecal-colon contents of cull dairy cows at slaughter were obtained from 5 US slaughter establishments. Specimens were subjected to microbiologic culturing for Salmonella spp at 1 laboratory. Identified isolates were compared with Salmonella isolation lists published by the Centers for Disease Control and Prevention (CDC) and the National Veterinary Services Laboratory (NVSL) for approximately the same period. The Simpson diversity index was used to calculate the likelihood that Salmonella isolates selected randomly by establishment were different. RESULTS: Of 58 Salmonella serotypes identified, Salmonella ser. Montevideo was the most prevalent. Two of the top 10 CDC serotypes identified from in 1996, Salmonella ser. Typhimurium and S Montevideo, appeared on our top 10 list; 8 of the top 10 were found on NVSL listings. Thirty-one of 59 S. Typhimurium isolates were identified as DT104 and found at a west slaughter establishment, 30 during the winter and 1 during the summer. The greatest diversity of serotypes was at a southeast establishment during the summer; the least diversity was at a central establishment in the winter. CONCLUSIONS AND CLINICAL RELEVANCE: 58 Salmonella serotypes were isolated from market dairy cows at slaughter and could pose a threat for food-borne illness. Salmonella Montevideo was the most frequently isolated serotype and may contribute substantially to salmonellosis in dairy cattle.     

Environmental surveillance for Salmonella enterica in a veterinary teaching hospital

OBJECTIVE: To evaluate the extent of environmental contamination with Salmonella enterica in a veterinary teaching hospital. DESIGN: Longitudinal study. SAMPLES: Environmental samples obtained from 69 representative locations within a veterinary teaching hospital by use of a commercially available electrostatic wipe. PROCEDURE: Environmental samples were obtained for bacteriologic culture, and antimicrobial susceptibility testing was performed on each environmental isolate. Environmental isolates were compared with isolates obtained from animals during the same period to investigate potential sources of environmental contamination. RESULTS: 54 S. enterica isolates were recovered from 452 (11.9%) cultured environmental samples. Five different serotypes were recovered; the most common serotypes were S. Newport and S. Agona. Within the 5 serotypes recovered, 10 distinguishable phenotypes were identified by use of serotype and antimicrobial susceptibility patterns. Of the environmental isolates, 41 of 54 (75.9%) could be matched to phenotypes of isolates obtained from animal submissions in the month prior to collection of environmental samples. CONCLUSIONS AND CLINICAL RELEVANCE: Results indicated that environments in veterinary hospitals can be frequently contaminated with S. enterica near where infected animals are managed and fecal specimens containing S. enterica are processed for culture in a diagnostic laboratory. Bacteriologic culture of environmental samples collected with electrostatic wipes is an effective means of detecting contamination in a veterinary hospital environment and may be beneficial as part of surveillance activities for other veterinary and animal-rearing facilities.     

Special problems of long-distance road transports of cattle

Physiological and behavioural field studies on long distance road transport of 116 heifers, 135 bulls and 64 steers in 10 goose-necked double decked semitrailers from northern Germany to mediteranean ports showed different impacts of handling during pre-transport (i.e. collection of animals, weighing, loading), transport journey itself and post transport handling (i.e. lairage time) on coping strategies of the different categories of cattle. It was found loss of body weight in steers (-6.65%) coming from pasture was higher compared to bulls (-4.6%) during transport, but they recovered during lairage time in a better way. All categories of cattle showed catabolic energy metabolism during transport, but only in bulls and to a farer extent in heifers this leads to a tendency of a ketotic metabolism during second parts of transport and lairage time. During whole transport time no more than 20% of bulls and steers were laying down, and less than 5% were feeding during driving intervals. In all parts of transport general stress parameters like heart rate (with exception to steers) and cortisol were elevated as a part of adaptation to the transport environment, but indicating high physical and emotional loads on the animals with no resting possibilities. In this context animals have to be prepared carefully to be transported, i.e. in reference to energy and fluid balance, and to be feed in sufficient time intervals (breaks) and lengths to maintain fundamental behavioural and physiological needs of the animals during transport. The lairage facilities are very important for the bulls and in the case of heifers the feeding regime during lairage time must be improved to ensure the possibility for a real resting and recovery of the animals after transport.     

Salmonella in sows: a longitudinal study in farrow-to-finish pig herds

Besides finishing pigs, sows are also believed to be important in the epidemiology of Salmonella. The study objective was to investigate the prevalence of Salmonella excretion in sows during an entire reproductive cycle. In 3 farrow-to-finish herds, groups of 34, 40 and 32 sows, respectively, were sampled serially. Faecal samples, environmental swabs and feed samples were taken and submitted to a qualitative Salmonella isolation. All isolates were characterised using RAPD and a representative number of isolates was serotyped. The prevalence of Salmonella excretion was < 10% during gestation, around farrowing and during lactation, but a significant increase in the number of Salmonella excreting sows was found in herds A (p < 0.01) and C (p = 0.02) after weaning. S. Infantis was the most prevalent serotype in herd A, S. Derby in herds B and C. Except for the S. Infantis group in herd A, all isolates within each group of the RAPD analysis belonged to the same serotype. Three sows in herd A and 1 sow in herd C shed different serotypes at different time points. The present results indicate that sows can maintain Salmonella infections in farrow-to-finish herds and that culled sows, leaving the herd after weaning, may constitute a substantial risk for contamination of their carcasses with Salmonella.     

Culture methods differ on the isolation of Salmonella enterica serotypes from naturally contaminated swine fecal samples.

Four culture methods (A, B, C, and D) were comparatively evaluated for their ability to isolate Salmonella enterica from pooled swine fecal samples (n = 100). None of the methods was able to isolate Salmonella from all positive samples. The relative sensitivity of the culture methods evaluated was 82%, 94%, 95%, and 78% for methods A, B, C, and D, respectively. The comparison of sensitivities showed that methods B and C performed significantly better (P < 0.05) than methods A and D. Although relative sensitivities of methods B and C were equal, from the 89 positive samples concomitantly detected by both, 35 (39.3%) had different serotypes (no match) isolated by each method. On the basis of the results of this study, it was concluded that culture methods differ on the isolation of S. enterica serotypes from naturally contaminated swine fecal samples. Depending on the objective(s) of investigations on the ecology and epidemiology of S. enterica in swine populations, a method or a combination of methods should be considered for more reliable results.     

Negative effects of stress immediately before slaughter on pork quality are aggravated by suboptimal transport and lairage conditions

The objectives of the present experiment were 1) to study the effects of transport conditions and lairage duration on stress level, muscle glycolytic potential, and pork quality; and 2) to investigate whether the negative effects of high stress immediately preslaughter are affected by preceding handling factors (transport and lairage). In a 2 x 2 x 2 factorial design, halothane-free pigs (n = 384) were assigned to either short (50 min) and smooth or long (3 h) and rough transport; long (3 h) or short (<45 min) lairage; and minimal or high preslaughter stress. Pigs were processed in eight groups (48 pigs per group) on various days at a commercial plant. Blood samples were taken at exsanguination to measure plasma cortisol and lactate concentrations. Muscle pH and temperature were measured at 30 and 40 min, respectively, and both were measured at 3 h, postmortem. A LM sample was taken 135 min postmortem to estimate glycogen content and rate of glycolysis. Pork quality attributes were assessed 23 h postmortem. Short transport increased cortisol when followed by short lairage (transport x lairage; P < 0.01). Long transport, but not lairage (P > 0.30), tended to increase (P = 0.06) muscle glycolytic potential. Long transport tended to increase (P = 0.08) electrical conductivity, and decreased a* (P < 0.01) and b* (P < 0.02) values. Decreasing lairage from 3 h to <45 min decreased (P < 0.05) the L* value, but it did not (P > 0.10) affect other pork quality traits. High stress decreased (P < 0.001) muscle glycolytic potential, and increased (P < 0.001) plasma lactate, cortisol, muscle temperature, rate of pH decline, and ultimate pH. Except for decreased (P < 0.001) b* values, pork color was not (P > 0.40) affected by high stress, but water-holding properties (measured by electrical conductivity, filter paper moisture, and drip loss) were impaired (P < 0.001) by high stress. Fiber optic-measured light scattering and Warner-Bratzler shear force were not (P > 0.12) affected by any treatment. Comparisons with the "optimal" handling (short transport, long lairage, and minimal stress) revealed that, with regard to water-holding properties, the negative effects of high stress were aggravated by suboptimal transport and lairage conditions. High stress alone increased electrical conductivity by 56%, whereas high stress in combination with short lairage led to an 88% increase. However, high preslaughter stress contributed most and was the major factor responsible for reductions in pork quality.     

Impact of energy intake and pregnancy status on rate and efficiency of gain and backfat changes of sows postweaning

A collaborative study was conducted to evaluate factors related to determining optimal feeding and management programs for increasing net returns from marketing cull sows. A total of 269 multiparous sows averaging 192 kg of body weight were weaned, moved to individual gestation crates, and assigned to one of eight treatment combinations in a 2 x 2 x 2 factorial arrangement for a 42-d postweaning feeding experiment. Factors included limited (L) (1.8 kg/sow/d) or ad libitum (AL) access to feed during wk 1 postweaning, a corn-soybean meal (corn) or barley-sunflower meal (barley) diet, and pregnant or nonpregnant status. All sows were provided ad libitum access to feed from wk 2 to 6 postweaning. Gain and feed intake (FI) data were collected weekly for each sow and used to calculate gain:feed (G/F). Ultrasonic backfat (BF) data were collected on d 0, 21, and 42 postweaning. Sows on the AL treatment had greater FI (P < 0.05) but similar gain (P = 0.80) for the 42-d postweaning period compared to sows on the L treatment. Most of this response was due to lower sow body weight loss during wk 1 postweaning (P < 0.01) when sows were provided AL (-7.2 kg) vs L (-13.2 kg) access to feed. Sows fed the corn diet had higher gain (P < 0.01), improved G/F (P < 0.01), and increased BF (P < 0.01) over the 42-d feeding period than sows fed barley. The corn diet resulted in less sow BW loss (P < 0.01) during wk 1 (-8.8 kg) than the barley diet (-11.6 kg). Pregnant sows had higher gain, FI, G/ F, and BF (P < 0.01) than nonpregnant sows over the 42-d feeding period. Most of this advantage occurred during wk 4 postweaning when FI and gain of nonpregnant sows was lower (P < 0.01) than for pregnant sows. An economic analysis indicated that, when cull sow prices are relatively high and feed prices are moderate to low, maintaining and managing cull sows for an additional 6 wk postweaning may be economically advantageous compared to 0 or 3 wk. Pregnant sows fed the corn diet produced the greatest economic return. These results suggest that mating sows as they return to estrus postweaning and providing ad libitum access to a corn-soybean meal diet improves growth performance and feed efficiency, and may thereby provide increased returns when marketing cull sows.     

An investigation on the effect of transport and lairage on the faecal shedding prevalence of Escherichia coli O157 in cattle

The aim of the study was to investigate the effect of transport and lairage on the prevalence of Escherichia coli O157 faecal shedding and the subsequent contamination of beef carcasses. Individual rectal faecal samples were taken from two cohorts of cattle (109 and 59) at the farm before transport and at the abattoir post-transport and lairage. The entire outer and inner surfaces of the carcass of each animal were swabbed immediately following slaughter and dressing. The prevalence of E. coli O157 shedding in cattle sampled at farm, post-transport and lairage was 18% (20), 13% (14) and 12% (13) for cohort A and 1.7% (1), 1.7% (1) and 0 for cohort B, respectively. No E. coli O157 was recovered from the 168 dressed carcasses. In total, 98% (46 of 47) of the E. coli O157 isolates from cohort A were potentially pathogenic to man. Transport and lairage do not cause an increase in the prevalence of E. coli O157 faecal shedding in cattle. This study demonstrates that even positive cohorts of cattle may be slaughtered and processed to produce clean carcasses by following good hygienic practices.     

Effects of transport and lairage time on some blood constituents of Friesian-cross steers in Chile

The objective of this study was to determine the effect of two transport journeys (3 and 16 h) and four lairage times at the abattoir (3, 6, 12 and 24 h) on some stress indicators in steers to validate the current Chilean legislation of a minimum lairage period of 12 h for cattle arriving at abattoirs.The study was carried out twice, 80 steers in the winter and 80 in the summer of 1999. Forty steers were transported for 3 h and 40 for 16 h. At arrival in the slaughterhouse, the 40 transported steers were randomly divided in four lairage groups. Blood samples were collected before loading at arrival at the slaughterhouse and at slaughter during exsanguination.Mixed models were used to determine the associations between the stress indicators and the independent variables while correcting for the repeated observations on animals. Lairage increased plasma cortisol and PCV values independent of the transport duration. Glucose concentrations in steers transported for 16 h further increased after 3 and 6 h of lairage but decreased after 12 and 24 h of lairage. In steers transported for 3 h, glucose concentrations only increased after 24 h of lairage. After 24 h of lairage, the steers transported for 16 h had increased βHB concentrations compared with those transported for 3 h. Plasma CK activity was increased in steers after transport but was not affected by lairage. The study shows that there is no beneficial effect on the welfare of the animals by a long lairage time at the abattoir.     

Investigation of the effects of transport and lairage on hydration state and resting behaviour of calves for export.

Plasma sodium concentrations, packed cell volume, total plasma protein concentration and dermal skinfold thickness were used to assess the state of hydration of 113 transported calves before and after lairage and in 30 control calves on the farm of origin. Skin thickness increased significantly (P less than 0.05) and total protein increased slightly during transport and decreased during lairage. These changes suggest that transport may cause dehydration and lairage may help in recovery. Plasma potassium concentration decreased during transport, but the effect was inversely related to the distance travelled, and the concentration increased during lairage. These changes are consistent with recovery from initially high cortisol levels at loading. The resting behaviour of 150 transported calves was recorded hourly for six hours. More time was spent resting and sleeping by the transported calves than has been reported for non-transported calves and more still by small transported calves, suggesting that transport is exhausting, that lairage helps recovery and that small calves are more adversely affected. During lairage the numbers of calves asleep decreased to values reported for normal calves, suggesting that 10 hours lairage was adequate. However, small calves did not return to their normal rest patterns within the observation period.     

Prevalence of Salmonella spp in cull (market) dairy cows at slaughter.

OBJECTIVE: To determine the prevalence of Salmonella spp in the cecal-colon contents of cull (market) dairy cows at slaughter because of potential public health ramifications. DESIGN: Survey study. SAMPLE POPULATION: Cecal-colon contents collected from 5,087 cull (market) dairy cows at slaughter at 5 slaughter establishments across the United States. PROCEDURE: During 2 periods of the year, winter (January and February) and summer (July through September), 5 cull (market) cow slaughter establishments in the United States--west (WE), southeast (SEE), central (CE), north central (NCE), and south central (SCE)--establishments were visited, and cecal-colon contents of cull dairy cows were obtained at the time of slaughter. Samples were examined by microbiologic culture at a single laboratory for Salmonella spp. RESULTS: Salmonella spp were detected in 23.1% of cecal-colon content samples from cull dairy cows across the 5 slaughter establishments. The highest site prevalence (54.5%) was detected at the WE during the summer period, whereas the lowest was found at the CE during the summer (4.3%) and at the NCE during the winter (4.5%). Considerable variation in the daily prevalence of Salmonella spp was found, particularly at the WE and the SCE. Salmonella spp were isolated from 93% of cecal-colon contents collected on a summer day at the WE. CONCLUSIONS AND CLINICAL RELEVANCE: Results strongly suggest that there is a high prevalence of Salmonella spp in cull dairy cows at slaughter, which could burden Hazard Analysis Critical Control Point programs implemented in slaughter establishments. Procedures to reduce Salmonella load at the dairy farm and during transport to slaughter could reduce the risk of spread during the slaughter process.     

Salmonella enterica isolates from faeces of domestic reptiles and a study of their antimicrobial in vitro sensitivity

From October 2001 to February 2002, the faecal samples of 305 reptiles (165 saurians, 99 ophidians and 41 chelonians) were bacteriologically examined to detect Salmonella enterica. S. enterica was isolated from 73 (23.93%) faecal samples including 44 (60.27%) samples collected from saurians, 15 (20.55%) from chelonians and 14 (19.18%) from ophidians; considering the number of samples taken for each reptile group, S. enterica was isolated from the 36.58% of chelonians, 26.66% of saurians and 14.14% of ophidians. The isolates were distributed among 38 serotypes. Sixty-nine (94.52%) isolates were resistant to erythromycin. About one-third of the isolates was resistant to sulfisoxazole (35.61%), gentamycin (32.88%), amoxycillin (31.51%) and ampicillin (27.40%). All but one of the isolates were sensitive to chloramphenicol. A high percentages of isolates were sensitive to enrofloxacin (84.93%), nitrofurantoin (80.82%), trimethoprim (76.71%) and tetracycline (75.34%).     

Effect of separate transport, lairage, and slaughter on occurrence of Salmonella typhimurium on slaughter carcasses

The study aimed to reduce cross-contamination between finishers from Salmonella-positive and Salmonella-negative herds during transport, lairage, and slaughter, thereby reducing the prevalence of Salmonella Typhimurium on slaughter carcasses. In Phase 1 of the study, pigs from Salmonella-negative herds were kept in lairage for 2-4 hours either in clean pens (intervention group) or pens contaminated with Salmonella-infected faeces (control group). All pigs were slaughtered on the same slaughterline, and carcass swabs 24 hours after slaughter revealed a low degree of cross-contamination in the pens: there was no difference in Salmonella-positive carcasses between intervention (1.7%) and control groups (0.8%). In Phase 2, control pigs from Salmonella-negative herds were mixed with pigs from Salmonella-positive herds during lairage for 2-4 hours, while the intervention group still consisted of pigs from Salmonella-negative herds. All pigs were slaughtered on the same line: first intervention, then control. Carcass swabs taken 24 hours after slaughter failed to show a reduction in Salmonella-positive carcasses in the intervention group (4.5%) compared with the originally Salmonella-negative pigs in the control group (3.6%). In pigs from Salmonella-positive herds the occurrence of Salmonella was substantially higher at 10.4%. When the results were corrected for 6 carcass samples found positive with S. Heidelberg on the same day, which was attributed to a transient hygiene failure, only 2.2% of the carcasses in the intervention group were Salmonella-positive. We conclude that even though cross-contamination occurs in the abattoir pens, its importance on the slaughter line may be greater. However, the final results of this study should be awaited to conclude whether separate slaughter of pigs from Salmonella-positive and Salmonella-negative herds should be recommended.     

Time in lairage needed by pigs to recover from the stress of transport.

Two experiments were carried out in which a total of 602 pigs were slaughtered after being held in lairage for periods ranging from less than one hour to 21 hours. In the first experiment the pigs were handled under ideal conditions and slaughtered at the University of Bristol slaughterhouse; in the second the pigs were killed at a commercial plant. Blood samples collected at exsanguination were analysed for indices of stress. There were no consistent effects of time in lairage on the levels of lactate and creatine phosphokinase. Plasma cortisol and beta-endorphin levels were reduced by lairage for three hours or more in the first experiment and cortisol was reduced by lairage for two hours or more in the second; beta-endorphin was not measured in the second experiment. A period of rest in lairage allowed the pigs to recover from transport and the associated handling and the recovery appeared to be complete within two to three hours.     

沙门菌肠毒素基因克隆及序列分析

研究常见的不同血清型沙门菌肠毒素(stn)基因核苷酸序列之间的差异及其分布情况。根据沙门菌的stn核苷酸序列设计一对引物,应用PCR技术,分别对肠炎沙门菌、鼠伤寒沙门菌和鸡白痢沙门菌进行PCR扩增,对扩增产物进行克隆及序列分析,并用所设计的引物检测7种血清型沙门菌(42株)。结果显示,3种沙门菌经PCR均扩增出749 bp的特异条带,DNA序列分析证实,沙门菌的stn核苷酸序列比较保守,42株沙门菌stn的检出率为100%。本试验成功克隆出沙门菌的stn,调查其在不同血清型沙门菌中的分布及序列分析,为进一步研究stn致病机理及研制减毒沙门菌活菌疫苗奠定了基础。     

Clinical and laboratory investigations of five outbreaks of foot-and-mouth disease during the 2001 epidemic in the United Kingdom

Clinical and laboratory investigations of five outbreaks of foot-and-mouth disease (FMD) were made during the early stages of the 2001 epidemic in the UK. The first outbreak, confirmed on February 20, was at an abattoir in Essex which specialised in the processing of culled sows and boars. On February 23, the disease was confirmed at a pig farm in Northumberland which held cull sows and boars fed on waste food; the findings indicated that it was the first of the five premises to be infected. The disease had probably been present since early February, and it was the most likely origin of the epidemic. The other premises investigated were a waste food-fed cull sow/boar pig unit in Essex, approximately 30 km from the abattoir, which was probably infected at the same time or before the abattoir, a sheep and cattle farm approximately 6 km from the Northumberland pig farm, which was probably infected by airborne virus from it in the period immediately before February 13, and a sheep and cattle farm in Devon which had clinical disease from February 20 and was probably infected by sheep transported from Northumberland on February 13 which arrived on February 15.