Spatiotemporal patterns and risks of herd breakdowns in pigs with postweaning multisystemic wasting syndrome

A retrospective cohort study of 116 British pig farms was undertaken to investigate the epidemiological risk factors associated with herd breakdowns with postweaning multisystemic wasting syndrome (PMWS). Farmers reported the PMWS status of their herd (case definition 1) and, where applicable, when the disease was first suspected and what they observed; they described a prolonged increase in mortality in six to 16-week-old pigs that was not attributable to any disease known to be on their farm. There was over 90 per cent agreement on the farmers' PMWS status between the farmers and their veterinarians. Approximately 70 per cent of the breakdowns were confirmed at the laboratory (case definition 2) except during the outbreak of foot-and-mouth disease (FMD) in 2001 when it was reduced to 30 per cent. Porcine circovirus type 2 antigen was detected in pigs examined postmortem (case definition 3) in approximately 90 per cent of the farms with increased mortality. The breakdowns occurred initially in the south of England and spread west and north, as well as locally in a radial pattern from the affected farms, and there was strong statistical evidence that there was non-random space-time clustering. The risk of herd breakdowns with PMWS was not constant; therefore, for each case definition, three survival models were developed with outcome variable time to breakdown of between January 2000 and January 2001, February 2001 to September 2001 (during FMD) or October 2001 to December 2003. Exposures with a bivariable significance of P<0.20 were tested in three multivariable Cox proportional hazard models. From January 2000 to January 2001 the risk of a herd breakdown with PMWS for definitions 1, 2 and 3 was greater for farms with 600 or more breeding sows, and for definitions 1 and 3 there was an increased risk associated with the purchase of replacement gilts rather than using homebred replacements. For definitions 1 and 3 the farms where the nearest pig farm had no breeding pigs were at greater risk of a breakdown than those where the nearest farm had breeding stock, as were the farms where visitors were not requested to avoid pigs for more than three days before visiting the farm during the FMD outbreak. From October 2001, the associated risks were identical for all three case definitions; farms were at greater risk when they had 600 or more breeding sows, if visitors had not avoided contact with pigs for more than three days before visiting the farm, and when there was a farm with PMWS less than five miles away. The affected farms were more likely to have disease associated with porcine parvovirus, porcine reproduction and respiratory syndrome virus, erysipelas, Escherichia coli and salmonella. These exposures were positively associated with large herds and the farm being close to other pig farms, but did not remain in the final models for breakdown with PMWS, indicating that such farms may be at greater risk of many infectious diseases.     

Risk factors for local spread of foot-and-mouth disease, 2010 epidemic in Japan

To provide a basis for effective foot-and-mouth disease (FMD) prevention measures, factors associated with local spread were investigated in this study using data of the 2010 FMD epidemic in Japan. Thirty-eight local clusters within a 500-m radius from source farms were selected. In the clusters with pig source farms, more neighboring farms were infected in a short time compared with the clusters with cattle source farms. The influence of distance and wind upon local spread did not show a significant difference between infected and noninfected neighboring farms. Large-size pig farms posed a greater risk of inducing local spread; the odds ratio with reference to small-size cattle farms was 16.73. Middle-size and large-size cattle farms had a greater risk of infection; odds ratios with reference to small-size cattle farms were 15.65 and 25.52, respectively. The present results are useful for understanding features of local spread and prioritizing farms for control measures.     

How do resources influence control measures during a simulated outbreak of foot and mouth disease in Australia?

An outbreak of foot and mouth disease (FMD) could seriously impact Australia's livestock sector and economy. As an FMD-free country, an outbreak would trigger a major disease control and eradication program that would include the culling of infected and at risk animals (‘stamping out’), movement restrictions and zoo-sanitary measures. Additional control measures may also include pre-emptive culling or vaccination. However, it is unclear what disease strategy would be most effective under Australian conditions and different resource levels. Using a stochastic simulation model that describes FMD transmission between farms in a livestock dense region of Australia, our results suggest that using current estimates of human resource capacity for surveillance, infected premises operations and vaccination, outbreaks were effectively controlled under a stamping out strategy. However, under more constrained resource allocations, ring vaccination was more likely to achieve eradication faster than stamping out or pre-emptive culling strategies.     

The foot-and-mouth disease epidemic in The Netherlands in 2001

An outbreak of foot-and-mouth disease (FMD) in Great Britain was reported on 21 February 2001, followed by an outbreak of FMD in The Netherlands a month later. This Dutch index outbreak occurred on a mixed, veal-calf/dairy-goat farm in Oene, in the central part of The Netherlands. The most-likely route of infection was the import of Irish veal-calves to this Dutch herd via an FMD-contaminated staging point in France. With hindsight, more herds seemed to be infected by the time the index outbreak was confirmed. The regular EU control measures were implemented, in combination with pre-emptive culling of herds within 1km of each outbreak. Nevertheless, more outbreaks of FMD occurred. Most of the virus infections on those farms were "neighborhood infections". Because the situation seemed out of control locally and the destruction capacity became insufficient, it was decided to implement an emergency vaccination strategy for all biungulates in a large area around Oene to stop further spread of the virus. All susceptible animals on approximately 1800 farms in this area were vaccinated. All farms subsequently were depopulated, starting from 2 weeks after vaccination. In total, 26 outbreaks were detected (the last outbreak on 22 April 2001). In total, approximately 260,000 animals were killed.     

Factors associated with the early detection of foot-and-mouth disease during the 2001 epidemic in the United Kingdom

An essential objective of an effective foot-and-mouth disease (FMD) eradication campaign is to shorten the infectious period by rapidly detecting and destroying cases of disease. The purpose of our investigation was to identify factors associated with the early detection of clinical FMD during the 2001 outbreak in the United Kingdom. We performed a logistic regression analysis, using early versus late detection of disease as the outcome of interest.During the 2001 FMD outbreak in the United Kingdom, infected premises were more likely to be detected early under the following circumstances: 1) cattle (particularly dairy) were infected rather than sheep; 2) a recently confirmed infected premises was within 3 km of the new case; and 3) the case was initially reported by the farmer, rather than a Local Disease Control Centre-initiated surveillance activity (patrol, tracing, pre-emptive cull). Our findings suggest that reporting by farmers and initiatives that increase farmer education and awareness should be encouraged.     

Infectious laryngotracheitis in the niagara peninsula: a case control study

The method(s) of spread of infectious laryngotracheitis in poultry flocks is uncertain. Based on an outbreak of the disease in the Niagara Peninsula in the summer of 1982, managers of infected (case) flocks and noninfected (control) flocks were interviewed to compare their management practices. The data were statistically analyzed; however, the results are not conclusive since only thirteen farms were involved in the outbreak. The results do suggest the following: farms with previous infectious laryngotracheitis infected flocks are more likely to have future outbreaks than are infectious laryngotracheitis-free farms, sanitation procedures of people entering the barns (changing boots and coveralls) appears to be related to infection status and air inlet location on the barn may be associated with infection. These items should be examined more thoroughly in future outbreaks.     

Evaluation of the transmission risk of foot-and-mouth disease in Japan

The transmission risk of foot-and-mouth disease (FMD) in Japan was evaluated using a mathematical FMD transmission model. The distance-based transmission rate between farms, which was parameterized using the FMD epidemic data in 2010 in Japan, was used to calculate the local-level reproduction numbers—expected numbers of secondary infections caused by one infected farm—for all cattle and pig farms in the country, which were then visualized as a risk map. The risk map demonstrated the spatial heterogeneity of transmission risk in the country and identified risk areas with higher possibility of disease spread. This result suggests that, particularly in high-risk areas, it is important to prepare for the smooth and efficient implementation of control measures against FMD outbreaks.     

Effectiveness of movement-prevention regulations to reduce the spread of foot-and-mouth disease in The Netherlands

After the foot-and-mouth disease (FMD) outbreak in 2001 the Dutch government implemented movement-prevention regulations to reduce the number of contacts between farms and consequently the risk of spread of highly contagious animal infections in the future. We studied the efficacy of these regulations by comparing registered cattle-movement data from 2000 to those from 2002. We also used the spatial and stochastic simulation model InterFMD to evaluate the consequences of the observed alterations in cattle-contact structure on the spread and control of a FMD epidemic.

There was a significant decrease in the number of cattle movements “for live use”, no difference in the number of group movements “for live use” and a distinct change in the overall contact structure. The most important structure changes were a decrease in the number of group movements from dairy farms to cattle-collection centres (−44%), and an increase in the number of group movements from dairy farms to beef farms (111%).

Our simulations demonstrated that the implemented regulations result in a concentration of the FMD-affected area and therefore in a reduction in size of the epidemics. Based on the intended Dutch strategy to control future FMD outbreaks, the decrease in extreme epidemics (95th percentiles) went from 31 infected farms in an epidemic-length of 65 days to 8 infected farms in an epidemic-length of 53 days in sparsely populated areas. In densely populated areas this decrease went from 135 infected farms to 103, while the duration reduced from 88 days to 81.     

Descriptive epidemiology of the 2001 foot-and-mouth disease epidemic in Great Britain: the first five months.

In February 2001, foot-and-mouth disease (FMD) was confirmed in Great Britain. A major epidemic developed, which peaked around 50 cases a day in late March, declining to under 10 a day by May. By mid-July, 1849 cases had been detected. The main control measures employed were livestock movement restrictions and the rapid slaughter of infected and exposed livestock. The first detected case was in south-east England; infection was traced to a farm in north-east England to which all other cases were linked. The epidemic was large as a result of a combination of events, including a delay in the diagnosis of the index case, the movement of infected sheep to market before FMD was first diagnosed, and the time of year. Virus was introduced at a time when there were many sheep movements around the country and weather conditions supported survival of the virus. The consequence was multiple, effectively primary, introductions of FMD virus into major sheep-keeping areas. Subsequent local spread from these introductions accounted for the majority of cases. The largest local epidemics were in areas with dense sheep populations and livestock dealers who were active during the key period. Most affected farms kept both sheep and cattle. At the time of writing the epidemic was still ongoing; however, this paper provides a basis for scientific discussion of the first five months.     

Risk factors for clinical Salmonella enterica subsp. enterica serovar Typhimurium infection on Dutch dairy farms

Risk factors for outbreaks in 1999 of clinical Salmonella enterica subsp. enterica serovar Typhimurium infection on dairy farms were studied in a matched case-control study with 47 case farms and 47 control farms. All 47 case farms experienced a clinical outbreak of salmonellosis which was confirmed with a positive bacteriologic culture for serovar Typhimurium in one or more samples. Serovar Typhimurium phage type 401 and 506 (definitive type 104, DT104) were the most frequently isolated phage types (13 isolates). On most farms (66%), clinical signs were seen only among adult cows. The most frequently reported clinical signs were diarrhoea (in 92% of the farms) and depression (in 79% of the farms).Control farms were matched on region and had no history of salmonellosis. A questionnaire was used to collect data on case and control farms. The relationship between serovar Typhimurium status of the farm and possible risk factors was tested using conditional logistic regression. Significant factors in the final model were presence of cats on the farm (OR=0.06), purchase of manure (OR=21.5), feeding colostrum only from own dam (OR=0.08), a non-seasonal calving pattern (OR=25), unrestricted grazing of lactating cows (OR=0.07), and a high mean mowing percentage of pasture (OR=1.02).     

Herd and individual animal risks associated with bovine tuberculosis skin test positivity in cattle in herds in south west England

The aim of this study was to investigate the cattle—exposure factors associated with the risk of a bovine animal reacting to a bovine tuberculosis (bTB) skin test at a whole herd test. There were 148 study farms enrolled. These were located in six counties of the south west of England in an area considered endemic for bovine tuberculosis (bTB): 24% were restocked after foot and mouth disease (FMD) in 2001; all farms were located within the Randomised Badger Culling Trial (RBCT) area. Data on cattle on these farms were sourced from the bTB Vetnet database from 1996 to 2004 and from the British Cattle Movement Scheme database. Individual animal records were created that included data on whether or not an animal became a reactor at a full-herd bTB test between 1 June 2001 and 19 August 2004, their prior exposure to cattle with bTB (defined by presence at a bTB test where at least one reactor was detected), whether the animal was homebred, the farm history of bTB and the farm restocking status. Data from 144 farms were used, 4 farms had no data.Cattle were more likely to react to the bTB skin test when they had been present at a previous bTB herd test (or tests) where other cattle had reacted to the skin test. This positively correlated with age and the number of bTB tests an animal had had. Cattle on restocked farms were less likely to react to the skin test compared with cattle on continuously stocked farms. These results highlight the likely importance of exposure to infected cattle at a previous test as a source of infection to cattle that subsequently became reactors and suggest that there was a lower risk of exposure to bTB to cattle in newly formed herds.     

Case-control study investigating an anthrax outbreak in Saskatchewan, Canada--Summer 2006

In 2006, an outbreak of anthrax in Saskatchewan affected several species but most of the losses occurred in cattle. Potential risk factors contributing to this outbreak were investigated through questionnaires involving 117 case farms and 259 control farms geographically representative of the Saskatchewan beef herd. The occurrence of flooding [odds ratio (OR) = 3.4; 95% confidence interval (CI): 1.8 to 6.4], wetter pastures (Good: OR = 3.5; 95% CI: 1.4 to 8.5; Wet: OR = 7.2; 95% CI: 2.9 to 18.1), shorter pasture grass length (OR = 3.0; 95% CI: 1.4 to 6.4), and higher density of the animals on pasture (OR = 3.0; 95% CI: 1.6 to 5.7) were more likely to have been reported for case herds than for control herds. Case farms were more likely than control farms to have vaccinated more than 1 week after the first reported case in the rural municipality (OR = 6.3; 95% CI: 2.6 to 15.3). Timing of vaccination in case herds was also significantly associated with the occurrence of subsequent deaths on these farms (P = 0.001).     

Factors related to the incidence of clinical encephalomyocarditis virus (EMCV) infection on Belgian pig farms

We set up a matched case-control study of potential risk factors for clinical encephalomyocarditis virus (EMCV) in 58 pig farms in West Flanders (Belgium). In total, 29 farms experienced a clinical outbreak of EMCV confirmed by EMC virus isolation. Mortality was seen only among suckling piglets (18 case farms), in piglets and other age-groups (4 case farms), or only among fattening pigs (7 case farms). Five farms had reproductive problems among the sows. Control farms were matched geographically on farm size and farm type and were selected on the absence of clinical signs. A questionnaire on potential risk factors for EMCV was developed to collect data at both case and control farms. The exploration of the data used clusters of factors associated with clinical EMCV infection: (a) rodents, (b) general farm set up and (c) general hygiene. The multivariable relationships between clinical appearance of EMCV and potential risk factors were tested with conditional logistic regression. The final model on all farms contained presence of mice (OR=8.3) as a risk factor for clinical EMCV infection while the flow of manure up through the slatted floor (OR=0.11) and movement of manure between manure pits in the pig stable (OR=0.14) were protective.     

Control of foot-and-mouth disease through vaccination and the isolation of infected animals

Foot-and-mouth disease (FMD) within Saudi Arabian dairy herds has been controlled for the past decade through vaccination. Data from 19 outbreaks on Saudi farms has suggested that the durability of these vaccines extended for 2.5 months, providing an 81–98% level of protection. Vaccination has nevertheless failed to prevent the establishment and sometimes persistence of the disease. This is probably because the highly contagious nature of FMD creates increasing levels of viral excretion during an outbreak, and the co-habitation in Saudi farms of affected/susceptible animals following diagnosis, predisposes the herds to re-infection. Pre-clinical excretion of the virus leads to the infection of additional in-contact susceptible animals prior to diagnosis, so the isolation of clinically infected animals does not guarantee a removal of infection. Saudi Arabian farms are subdivided into managed farm pens and isolation (away from the farm) of all animals in infected pens not only removes the infectious individuals showing clinical signs, but also those that are sub-clinical and excreting virus. Simulations suggest that removing all infectious animals from the herd significantly reduces the per cent infected in the herd.     

Immune responses to foot-and-mouth disease virus in pig farms after the 1997 outbreak in Taiwan

This paper reports on a retrospective study of the antibody responses to structural and non-structural proteins of FMD virus O Taiwan 97 in six pig herds in Taiwan in the year after the 1997 Taiwanese FMD outbreak. All herds were vaccinated against FMD after the outbreak as part of the countrywide control program. Three of the herds had confirmed FMD infections (herds N, O and P) and three herds remained non-infected (herds K, L and M). The serum neutralizing antibody titers and the non-structural protein ELISA (NSP) antibody responses in sows and 1-month-old pigs in the infected herds were higher than in the non-infected herds, but over time a number of positive NSP reactors were detected. From the serological studies and the herd monitoring and investigations it was considered that the FMD NSP positive reactors may not have constituted a true reservoir of FMD virus infection especially in herds where susceptible pigs were no longer present post-exposure or post-vaccination. Pigs vaccinated with an unpurified FMD type O vaccines being used at that time also showed false positive responses for NSP antibodies.     

Foot-and-mouth disease eradication efforts in the Republic of Korea

On March 20, 2000, a suspected vesicular disease in cattle was reported to the National Veterinary Research and Quarantine Service (NVRQS) of the Republic of Korea. This represented the index case of a foot-and-mouth disease (FMD) outbreak, which spread through several provinces. The Republic of Korea had been free of FMD for 66 years prior to the reintroduction of the virus and had recently suspended imports of pork and pork products from neighboring Japan owing to a reported FMD outbreak in that country. The Korean outbreak was ultimately controlled through the combination of preemptive slaughter, animal movement restrictions, and a strategy of ring vaccination. The purpose of this paper is to review the current FMD situation in Korea in the aftermath of its 2000 epizootic and how it may affect future efforts to eradicate or reduce risk of reintroduction of the disease into Korea.     

Risk factors for porcine reproductive and respiratory syndrome outbreaks in Vietnamese small stock farms

AIM: To examine risk factors that could have played a role in the 2010 porcine reproductive and respiratory syndrome (PRRS) outbreak in Yenhung district, Quangninh province, North-Vietnam, with the purpose of establishing why existing control measures implemented after previous outbreaks had failed to prevent further outbreaks.

METHODS: A case-control study was carried out in Yenhung district. Data were obtained by an interview-based questionnaire survey. The sampling unit was households, which equated to small-scale pig farms. A total of 150 case and 150 control households were selected at communes affected by the 2010 PRRS epidemic during April to June. Risk factors were analysed using binary logistic regression and unconditional multiple logistic regression.

RESULTS: Households infected with PRRS were significantly associated with multiple variables belonging to three main groups: (1) location of the farms: i.e. farms positioned <1,000?m from a pig abattoir or within 500?m of local markets or 100?m of main roads; (2) farm management: i.e. where there was non-application of weekly farm disinfection, feeding uncooked swill, new introduction of purchased pigs without isolation, or usage of water from irrigation systems for raising pigs; (3) people and animal contact: i.e. where households kept animals with either no confinement or partial confinement, had visits by family members to other affected farms or had frequent visits by neighbours. The use of water from irrigation systems was found to be the risk factor most strongly associated with infected households in the 2010 outbreak (OR=22; 95% CI=12–42).

CONCLUSIONS: The results show that the epidemiology of PRRS in Quangninh province was linked to sociological and cultural practices, and that effective PRRS control needs an integrated approach coupled with behavioural changes in the pig raising practices of the general public. Failure to recognise this could explain why further outbreaks have occurred.     

A decision-tree to optimise control measures during the early stage of a foot-and-mouth disease epidemic

A decision-tree was developed to support decision making on control measures during the first days after the declaration of an outbreak of foot-and-mouth disease (FMD). The objective of the tree was to minimise direct costs and export losses of FMD epidemics under several scenarios based on livestock and herd density in the outbreak region, the possibility of airborne spread, and the time between first infection and first detection. The starting point of the tree was an epidemiological model based on a deterministic susceptible–infectious–recovered approach. The effect of four control strategies on FMD dynamics was modelled. In addition to the standard control strategy of stamping out and culling of high-risk contact herds, strategies involving ring culling within 1 km of an infected herd, ring-vaccination within 1 km of an infected herd, and ring-vaccination within 3 km of an infected herd were assessed. An economic model converted outbreak and control effects of farming and processing operations into estimates of direct costs and export losses. Ring-vaccination is the economically optimal control strategy for densely populated livestock areas whereas ring culling is the economically optimal control strategy for sparsely populated livestock areas.     

Risk factors for highly pathogenic H7N1 avian influenza virus infection in poultry during the 1999-2000 epidemic in Italy

In 1999-2000, Italian poultry production was disrupted by an H7N1 virus subtype epidemic of highly pathogenic avian influenza (HPAI). The objectives of the present study were to identify risk factors for infection on poultry farms located in regions that had the highest number of outbreaks (Veneto and Lombardia) and the impact of pre-emptive culling as a complementary measure for eradicating infection. A Cox regression model that included spatial factors, such as the G index, was used. The results confirmed the relationship between risk of infection and poultry species, production type and size of farms. The effectiveness of pre-emptive culling was confirmed. An increased risk of infection was observed for poultry farms located near an infected farm and those at altitudes less than 150m above sea level. The measures for the control and eradication of AI virus infection need to consider species differences in susceptibility, the types of production and the density of poultry farms in the affected areas.