Risk of tuberculosis cattle herd breakdowns in Ireland: effects of badger culling effort, density and historic large-scale interventions.

Bovine tuberculosis (bTB) continues to be a problem in cattle herds in Ireland and Britain. It has been suggested that failure to eradicate this disease is related to the presence of a wildlife reservoir (the badger). A large-scale project was undertaken in the Republic of Ireland during 1997-2002 to assess whether badger removal could contribute to reducing risk of cattle herd breakdowns in four areas. During the period of that "four area" study, there was a significant decrease in risk in intensively culled (removal) areas relative to reference areas. In the present study, we revisit these areas to assess if there were any residual area effects of this former intervention a decade on (2007-2012). Over the study period there was an overall declining trend in bTB breakdown risk to cattle herds. Cattle herds within former removal areas experienced significantly reduced risk of breakdown relative to herds within former reference areas or herds within non-treatment areas (OR: 0.53; P < 0.001). Increased herd breakdown risk was associated with increasing herd size (OR: 1.92-2.03; P < 0.001) and herd bTB history (OR: 2.25-2.40; P < 0.001). There was increased risk of herd breakdowns in areas with higher badger densities, but this association was only significant early in the study (PD*YEAR interaction; P < 0.001). Badgers were culled in areas with higher cattle bTB risk (targeted culling). Risk tended to decline with cumulative culling effort only in three counties, but increased in the fourth (Donegal). Culling badgers is not seen as a viable long-term strategy. However, mixed policy options with biosecurity and badger vaccination, may help in managing cattle breakdown risk.

Large-scale movements in European badgers: has the tail of the movement kernel been underestimated?

Characterizing patterns of animal movement is a major aim in population ecology, and yet doing so at an appropriate spatial scale remains a major challenge. Estimating the frequency and distances of movements is of particular importance when species are implicated in the transmission of zoonotic diseases. European badgers (Meles meles) are classically viewed as exhibiting limited dispersal, and yet their movements bring them into conflict with farmers due to their potential to spread bovine tuberculosis in parts of their range. Considerable uncertainty surrounds the movement potential of badgers, and this may be related to the spatial scale of previous empirical studies. We conducted a large-scale mark-recapture study (755 km(2); 2008-2012; 1935 capture events; 963 badgers) to investigate movement patterns in badgers, and undertook a comparative meta-analysis using published data from 15 European populations. The dispersal movement (>1 km) kernel followed an inverse power-law function, with a substantial 'tail' indicating the occurrence of rare long-distance dispersal attempts during the study period. The mean recorded distance from this distribution was 2.6 km, the 95 percentile was 7.3 km and the longest recorded was 22.1 km. Dispersal frequency distributions were significantly different between genders; males dispersed more frequently than females, but females made proportionally more long-distance dispersal attempts than males. We used a subsampling approach to demonstrate that the appropriate minimum spatial scale to characterize badger movements in our study population was 80 km(2), substantially larger than many previous badger studies. Furthermore, the meta-analysis indicated a significant association between maximum movement distance and study area size, while controlling for population density. Maximum long-distance movements were often only recorded by chance beyond the boundaries of study areas. These findings suggest that the tail of the badger movement distribution is currently underestimated. The implications of this for understanding the spatial ecology of badger populations and for the design of disease intervention strategies are potentially significant.

Risk factors associated with increased mortality of farmed Pacific oysters in Ireland during 2011.

The Pacific oyster, Crassostrea gigas, plays a significant role in the aquaculture industry in Ireland. Episodes of increased mortality in C. gigas have been described in many countries, and in Ireland since 2008. The cause of mortality events in C. gigas spat and larvae is suspected to be multifactorial, with ostreid herpesvirus 1 (OsHV-1, in particular OsHV-1µvar) considered a necessary, but not sufficient, cause. The objectives of the current study were to describe mortality events that occurred in C. gigas in Ireland during the summer of 2011 and to identify any associated environmental, husbandry and oyster endogenous factors. A prospective cohort study was conducted during 2010-2012, involving 80 study batches, located at 24 sites within 17 bays. All 17 bays had previously tested positive for OsHV-1µvar. All study farmers were initially surveyed to gather relevant data on each study batch, which was then tracked from placement in the bay to first grading. The outcome of interest was cumulative batch-level mortality (%). Environmental data at high and low mortality sites were compared, and a risk factor analysis, using a multiple linear regression mixed effects model, was conducted. Cumulative batch mortality ranged from 2% to 100% (median=16%, interquartile range: 10-34%). The final multivariable risk factor model indicated that batches imported from French hatcheries had significantly lower mortalities than non-French hatcheries; sites which tested negative for OsHV-1µvar during the study had significantly lower mortalities than sites which tested positive and mortalities increased with temperature until a peak was reached. There were several differences between the seed stocks from French and non-French hatcheries, including prior OsHV-1µvar exposure and ploidy. A range of risk factors relating to farm management were also considered, but were not found significant. The relative importance of prior OsHV-1µvar infection and ploidy will become clearer with ongoing selection towards OsHV-1µvar resistant oysters. Work is currently underway in Ireland to investigate these factors further, by tracking seed from various hatchery sources which were put to sea in 2012 under similar husbandry and environmental conditions.

The importance of 'neighbourhood' in the persistence of bovine tuberculosis in Irish cattle herds.

Local persistence of infection is a key feature of bovine tuberculosis (bTB) among cattle herds in the Republic of Ireland. The aim of this study was to determine the relative importance of 'neighbourhood', specifically farm-to-farm spread and spread from wildlife, in the persistence of bTB by investigating herds having a bTB episode in 2006. A case-control study was conducted on the association between the occurrence of a bTB episode in 2006 and the occurrence of bTB in previous years among neighbouring herd(s) within 1 km, while controlling for each herd's bTB history and other risk factors. Neighbouring herds were grouped into three zones, based on distance, and bTB incidence measures summarised within each zone and by calendar year (2001-2005). The incidence of bTB was associated with an increased animal incidence in two subsets of neighbouring herds: (i) herds directly contiguous during the previous 2 years (attributable fraction=0.20), and (ii) herds at a distance of >25 m in the previous year (attributable fraction=0.19). Other predictors of bTB in a herd in 2006 included the occurrence of a bTB episode within that herd in any of the previous 5 years, herd size, and the number of animals purchased at age greater than 12 months. An infected wildlife source best explains the existence of a "neighbouring herd risk" for bTB at distances greater than 25 m. Further studies will be necessary to determine to what extent neighbouring herd risk within 25 m may be confounded by the same wildlife (badger) source.

Factors affecting European badger (Meles meles) capture numbers in one county in Ireland.

Understanding factors affecting the number of badgers captured at and around badger setts (burrows) is of considerable applied importance. These factors could be used to estimate probable badger densities for bovine tuberculosis (bTB) control and also for monitoring badger populations from a conservation perspective. Furthermore, badger management and vaccination programs would benefit by increasing the probability of efficiently capturing the target badger populations. Within this context, it was investigated whether badger capture numbers can be estimated from field signs and previous capture histories. Badger capture records (initial and repeated capture numbers at a sett) from a large-scale removal program (405 km(2), 643 setts) were used. Univariable count models indicated that there were a number of significant potential predictors of badger numbers, during initial capture attempts. Using a multivariable zero-inflated Poisson (ZIP) model of initial captures we found that badger capture numbers were significantly affected by sett type, season, year, and the number of sett entrances in active use. Badger capture numbers were also affected by the total previous catch during repeated capture events and by the number of previous capture attempts. There was a significant negative trend in badger captures across events. Measures of the ability of these models to estimate badger captures suggested that the models might be useful in estimating badger numbers across a population; however the confidence intervals associated with these predictions were large.

Population estimation and trappability of the European badger (Meles meles): implications for tuberculosis management.

Estimates of population size and trappability inform vaccine efficacy modelling and are required for adaptive management during prolonged wildlife vaccination campaigns. We present an analysis of mark-recapture data from a badger vaccine (Bacille Calmette-Guérin) study in Ireland. This study is the largest scale (755 km(2)) mark-recapture study ever undertaken with this species. The study area was divided into three approximately equal-sized zones, each with similar survey and capture effort. A mean badger population size of 671 (SD: 76) was estimated using a closed-subpopulation model (CSpM) based on data from capturing sessions of the entire area and was consistent with a separate multiplicative model. Minimum number alive estimates calculated from the same data were on average 49-51% smaller than the CSpM estimates, but these are considered severely negatively biased when trappability is low. Population densities derived from the CSpM estimates were 0.82-1.06 badgers km(-2), and broadly consistent with previous reports for an adjacent area. Mean trappability was estimated to be 34-35% per session across the population. By the fifth capture session, 79% of the adult badgers caught had been marked previously. Multivariable modelling suggested significant differences in badger trappability depending on zone, season and age-class. There were more putatively trap-wary badgers identified in the population than trap-happy badgers, but wariness was not related to individual's sex, zone or season of capture. Live-trapping efficacy can vary significantly amongst sites, seasons, age, or personality, hence monitoring of trappability is recommended as part of an adaptive management regime during large-scale wildlife vaccination programs to counter biases and to improve efficiencies.

Field efficacy of an inactivated bivalent influenza vaccine in a multi-site swine production system during an outbreak of systemic porcine circovirus associated disease.

Swine influenza (SI) is a disease of significance for the swine industry, and vaccination is often recommended as a way to reduce its impact on production. The efficacy of SI vaccines is well established under experimental conditions, but information about field efficacy is scarce. The objective of this study was to evaluate the efficacy of a commercial inactivated bivalent (H1N1/H3N2) vaccine under conditions of natural exposure to a field SI variant. To accomplish our goal we used a randomized, blinded, field trial in 2 cohorts of finisher pigs in a multi-site swine production system located in southern Ontario. During the trial, this herd experienced an outbreak of porcine circovirus associated disease (PCVAD). The efficacy of the SI vaccine was assessed through its effect on average daily weight gain, and serological responses to SI over time. The effect of vaccination on pig growth was different in the 2 cohorts. Weight gain was higher in vaccinated pigs than in control pigs in Cohort 1, but was numerically higher for control pigs than for vaccinated pigs in Cohort 2. Vaccination against swine influenza, in a herd experiencing an outbreak of PCVAD, was of questionable value.

From explanation to prediction: a model for recurrent bovine tuberculosis in Irish cattle herds.

There is a good understanding of factors associated with bovine tuberculosis (BTB) risk in Irish herds. As yet, however, this knowledge has not been incorporated into predictive models with the potential for improved, risk-based surveillance. The goal of the study was to enhance the national herd scoring system for BTB risk, thus leading to improved identification of cattle herds at high risk of recurrent BTB episodes. A retrospective cohort study was conducted to develop a statistical model predictive of recurrent bovine tuberculosis episodes in cattle herds in the Republic of Ireland. Herd-level disease history data for the previous 12 years, the previous 3 years, the previous episode, and the current-episode were used in survival analyses to determine the aspects of disease history that were predictive of a recurrent breakdown within 3 years of a cleared BTB episode. Relative to herds with 0-1 standard reactors in the current BTB episode, hazard ratios increased to 1.3 and 1.6 for herds with 2-5 and >5 standard reactors, respectively. Compared to herds with <30 animals, hazard ratios increased from 1.8 to 2.5 and then to 3.1 for herds with 30-79, 80-173, and >174 animals respectively. Relative to herds with <4 herd-level tests in the previous 3 years, herds with 4-5 and >5 tests had 1.1 and 1.4 times greater hazard of a BTB breakdown. Herds that did not have a BTB episode in the 5 years prior to their 2001 episode were 0.8 times less likely to breakdown in the next 3 years than herds that did. Herds breaking down in the spring or summer were 0.8 times less likely to suffer a recurrent breakdown than herds breaking down in autumn or winter (this was likely due to seasonality in testing regimes). The presence of a confirmed BTB lesion was not predictive of increased risk of recurrent BTB. Despite the availability of detailed disease history, the predictive ability of the model was poor. One explanation for this was that herds suffering a recurrence of BTB on their first test after clearing a BTB episode were different from herds that broke down later in the period at risk. Future research might need to include additional variables to identify which subsets of herd BTB episodes, if any, have identifiable features that are predictive of recurrent breakdowns.

An assessment of injury to European badgers (meles meles) due to capture in stopped restraints.

As part of ongoing culling operations, European badgers (Meles meles) were captured using stopped restraints in winter (October to December 2005) and summer (May to June 2006) in the Republic of Ireland. A subset of these badgers, those caught during four consecutive nights, was examined postmortem to determine the frequency and severity of physical injuries resulting from capture in the restraints. The skin and the tissues underlying the restraint of 343 badgers were assessed for injury by visual examination. There was an absence of skin damage or only minor skin abrasions in 88% of badgers; an absence of subcutaneous tissue injury or only localized subcutaneous tissue injury in 69%; and an absence of muscle injury or only slight muscle bruising in 99% of badgers. Only 2% of badgers had cuts to the skin and 5.5% had extensive subcutaneous edema, whereas 1.2% had areas of hemorrhage and tearing of the underlying muscle. Our results show that the majority of badgers examined sustained minimal injuries attributable to capture in stopped restraints.

Pig and herd level prevalence of Toxoplasma gondii in Ontario finisher pigs in 2001, 2003, and 2004.

The objective of this study was to estimate the apparent and true prevalence of exposure to Toxoplasma gondii in Ontario finisher pigs. During the study period (2001 to 2004), sera from 6048 pigs were tested with a commercial enzyme-linked immunosorbent assay (ELISA); 103 farms were included 1 to 3 times in the study. True prevalence was estimated using a Bayesian approach. Apparent prevalence at the pig level was 1.59% [95% confidence interval (CI): 0.45, 2.99] in 2001, 0.06% (95% CI: 0.00, 0.46) in 2003, and 0.26% (95% CI: 0.00, 0.82) in 2004. Apparent prevalence at the herd-level was 13.7% (95% CI: 7.5, 22.3) in 2001; 1.25% (95% CI: 0.03, 6.77) in 2003, and 3.75% (95% CI: 0.78, 10.6) in 2004. Similarly, posterior Bayesian estimates of true prevalence at the pig level were 1.7% [95% probability interval (PI): 1.2, 2.2] in 2001, 0.2% (95% PI: 0.04, 0.4) in 2003, and 0.3% (95% PI: 0.1, 0.7) in 2004. At the herd level, posterior estimates of prevalence were 11.6% (95% PI: 7.4, 16.8) in 2001, 0% (95% PI: 0.0, 2.5) in 2003, and 1.2% (95% PI: 0.0, 5.0) in 2004 when a herd cut-point > or = 1 was used. Exposure to T. gondii in finishing pig farms in Ontario appears to be infrequent.

Occurrence of Anoplocephala perfoliata infection in horses in Ontario, Canada and associations with colic and management practices.

Infection with the tapeworm Anoplocephala perfoliata has been found to be associated with equine colic in horses in the United Kingdom. Using a matched case-control study design, data collected from 117 pairs of horses in Ontario were examined for evidence of associations between risk of colic and A. perfoliata infection, and between seropositivity to infection and management practices. Cases were horses in southern Ontario diagnosed with colic by local veterinarians, and control horses were from the same stables as cases and were matched by age, breed and gender where possible. Infection status was defined on the basis of positive results upon coprological examination, and/or seropositivity to a 12/13 kDa A. perfoliata secretory protein. Fifty-six percent of the 234 horses were seropositive for A. perfoliata, but eggs were found in samples from only 6% of horses. Horses dependent on pasture for a large part of their diet were significantly more likely to have ELISA optical density levels above 0.600 compared to other horses (odds ratio [OR]=6.38; p=0.029). This finding identified exposure to pasture as an important source of A. perfoliata infection in the horses used in the study. In a subset of 46 pairs of horses for which control horses had no known history of colic, a statistically significant negative association was found between the risk of colic and optical density (OD) levels >0.200-0.600, relative to OD levels < or = 0.090 (OR=0.08; p=0.017). There was no other statistical evidence of an association between the risk of colic and A. perfoliata infection.

Prevalence of and risk factors for influenza in southern Ontario swine herds in 2001 and 2003.

This research included 2 prevalence studies and a risk-factor investigation conducted in 2001 at 93 sites with sows only, finishers only, or both. In 2001, 1300 serum samples from sows in 65 herds and 720 serum samples from finisher pigs in 72 herds were tested for antibodies to swine influenzavirus (SIV) of H1N1 subtype with an enzyme-linked immunosorbent assay (ELISA). In 2003, 1140 serum samples from sows in 76 herds were tested for antibodies to SIV of H3N2 subtype with a hemagglutination-inhibition assay based on A/Swine/Colorado/1/77 and A/Swine/Texas/4199-2/98 isolates. The apparent pig-level H1N1 seroprevalence in 2001 was 61.1% and 24.3% in sows and finishers, respectively. The apparent pig-level seroprevalence in 2003 for H3N2 A/Sw/CO/1/77 and A/Sw/TX/4199-2/98 in sows was 0.6% and 0.7%, respectively. The factors associated with sow-herd H1N1 positivity included pig or farm density at different geographic levels, an external source of breeding pigs, number of animals on site, and decreasing proximity to other barns. Higher-parity sows had higher odds of seropositivity, but there was significant random variability in this association among herds. The odds of finisher-herd SIV positivity were higher with large herd size, high pig farm density, and farrow-to-finish type of farm. Finisher herds were SIV-positive only if source sow herds were positive. Simultaneously, 45% of finisher herds were SIV-negative although sow source herds were positive.

Association between management practices and within-herd prevalence of Cryptosporidium parvum shedding on dairy farms in southern Ontario.

To identify management practices associated with an increased within-herd prevalence of Cryptosporidium parvum shedding on dairy farms in southern Ontario, fecal samples were taken from 1089 calves aged 7-28 days, from 119 herds. Information on management practices was obtained by administering a questionnaire compiled using a modified Delphi technique. Data were analyzed using univariable and multivariable negative binomial regression. Overall, 30% of the calves in the study were shedding C. parvum oocysts, with at least one positive calf detected in 77% of herds. Within-herd prevalence ranged from 0 to 80%. Predictors significantly associated with an increased prevalence of shedding in multivariable modelling were the use of calf scour prophylaxis in cows (risk ratio [RR] 1.70, P<0.01) and calves (RR 1.38, P=0.02) and the feeding of milk replacer in the first week of life (RR 1.40, P=0.02). In contrast, the presence of concrete flooring in calf housing areas (RR 0.59, P<0.01) and the use of soap or detergent when washing calf feeding utensils (RR 0.61, P<0.01) appeared to be protective.

Epidemiologic characteristics of catastrophic musculoskeletal injuries in Thoroughbred racehorses.

OBJECTIVE: To determine characteristics, incidence rate, and possible associations with selected demographic characteristics of catastrophic musculoskeletal injuries (CMIs) in Thoroughbred racehorses. ANIMALS: 76 Thoroughbreds with CMIs. PROCEDURES: Incidence rates of CMIs during racing or training were calculated with number of CMIs as the numerator and overall numbers of races or training events during 2004 and 2005 as the denominators. Exact 95% confidence intervals were calculated. Associations between incidence and dichotomous exposure factors, nominal factors, and ordinal factors were determined. Only univariable associations were examined. RESULTS: 76 horses were euthanized because of CMI and represented 2.36 and 1.69 deaths/1,000 racing starts in 2004 and 2005, respectively. Of these, 57 were euthanized within 60 days before or after a race, which yielded a point incidence of 1.05/1,000 racing starts and 0.39/1,000 training starts. CONCLUSIONS AND CLINICAL RELEVANCE: Incidence rate of CMIs at 2 Ontario racetracks was similar to that at other North American racetracks. A cumulative death rate of 1 to 2 deaths/wk should be considered typical when designing prevention strategies and offers a baseline value for measuring improvement.

Spatial clustering of swine influenza in Ontario on the basis of herd-level disease status with different misclassification errors.

This approach maximizes sensitivity of serology-based monitoring systems by considering spatial clustering of herds classified as false positive by herd testing, allowing outbreaks to be detected in an early phase. The primary objective of this study was to determine whether swine herds infected with influenza viruses cluster in space, and if so, where they cluster. The secondary objective was to investigate the combining of a multivariate spatial scan statistic with herd test results to maximize the sensitivity of the surveillance system for swine influenza. We tested for spatial clustering of swine influenza using the Cuzick-Edwards test as a global test. The location of the most likely spatial clusters of cases for each subtype and strain in a sample of 65 sow and 72 finisher herds in 2001 (Ontario, Canada), and 76 sow herds in 2003 (Ontario, Canada) was determined by a spatial scan statistic in a purely spatial Bernoulli model based on single and multiple datasets. A case herd was defined by true herd-disease status for sow or finisher herds tested for H1N1, and by apparent herd-disease status for sow herds tested for two H3N2 strains (A/Swine/Colorado/1/77 (Sw/Col/77) and A/Swine/Texas/4199-2/98 (Sw/Tex/98)). In sow herds, there was no statistically significant clustering of H1N1 influenza after adjustment for pig-farm density. Similarly, spatial clustering was not found in finisher herds. In contrast, clustering of H3N2 Sw/Col/77 (prevalence ratio=12.5) and H3N2 Sw/Tex/98 (prevalence ratio=15) was identified in an area close to a region with documented isolation of avian influenza isolates from pigs. For the H1N1 subtype tested by ELISA, we used an approach that minimized overall misclassification at the herd level. This could be more applicable for detecting clusters of positive farms when herd prevalence is moderate to high than when herd prevalence is low. For the H3N2 strains we used an approach that maximized herd-level sensitivity by minimizing the herd cut-off. This is useful in situations where prevalence of the pathogen is low. The results of applying a multivariate spatial scan statistic approach, led us to generate the hypothesis that an unknown variant of influenza of avian origin was circulating in swine herds close to an area where avian strains had previously been isolated from swine. Maximizing herd sensitivity and linking it with the spatial information can be of use for monitoring of pathogens that exhibit the potential for rapid antigenic change, which, consequently, might then lead to diminished cross-reactivity of routinely used assays and lower test sensitivity for the newly emerged variants. Veterinary authorities might incorporate this approach into animal disease surveillance programs that either substantiate freedom from disease, or are aimed at detecting early incursion of a pathogen, such as influenza virus, or both.

Neospora caninum and Leptospira serovar serostatus in dairy cattle in Ontario.

No significant association existed between Neospora caninum titer and serostatus to Leptospira serovar hardjo, icterohaemorrhagiae, or pomona in cattle on 78 dairy herds in Ontario. Leptospira titer increased with parity. Amongst herds not vaccinated against Leptospira, the proportions of herds with > or = 1 animal seropositive to serovar hardjo, icterohaemorrhagiae, or pomona were 45%, 42%, and 58%, respectively.

Syndromic Surveillance of Norovirus using Over-the-counter Sales of Medications Related to Gastrointestinal Illness.

OBJECTIVE: To assess whether over-the-counter (OTC) sales of gastrointestinal illness (GI)-related medications are associated with temporal trends of reportable community viral, bacterial and parasitic infections. METHODS: The temporal patterns in weekly and seasonal sales of nonprescription products related to GI were compared with those of reportable viral, bacterial and parasitic infections in a Canadian province. RESULTS: Temporal patterns of OTC product sales and Norovirus activity were similar, both having highest activity in the winter months. In contrast, GI cases from both bacterial and parasitic agents were highest from late spring through to early fall. CONCLUSIONS: Nonprescription sales of antidiarrheal and antinauseant products are a good predictor of community Norovirus activity. Syndromic surveillance through monitoring of OTC product sales could be useful as an early indicator of the Norovirus season, allowing for appropriate interventions to reduce the number of infections.

Ten years of bovine virus diarrhoea virus (BVDV) control in Norway: a cost-benefit analysis.

A retrospective cost-benefit analysis was carried out on the Norwegian bovine virus diarrhoea (BVD) control and eradication strategy, for the years 1993-2003. Information regarding the control cost input parameters was gathered from the cattle industry (TINE Norwegian Dairies, GENO Breeding and AI association, and GILDE Norwegian Meat), The National Animal Health Authorities and The Veterinary Institute. We accounted for variable costs (both direct costs associated with the control, and those costs carried by the farmers as a consequence of the control program). The benefit was estimated as the difference between the assumed losses without control - represented overall as 10% increase of the observed 1993 BVD virus infection level - and the observed losses during the control period. An estimate of the financial losses associated with the BVD virus (BVDV) infection was based on studies of the herd level effects on health, reproduction, and production in dairy herds with evidence of recent BVDV infection. We used a stochastic simulation model to account for the total uncertainty in both the control cost and financial loss estimates. The annual net benefits over the 10 years of BVD control were discounted to a 1993 net present value (NPV). The median NPV of the BVD control, nationally, was estimated at 130 million NOK with a distribution of the NPV ranging from +51 to +201 million NOK (5th and 95th percentiles, respectively). Out of the total control costs the farmers and the farmer-owned industries (the co-operatives) had carried about 62% of these costs; however, the farmers were also the main beneficiaries. The Norwegian experience shows a robust cost-efficiency for a BVDV eradication strategy; this stands in sharp contrast to earlier studies where the results were not supportive. Even though every cattle population and country is unique, the Norwegian findings and experiences should have wider implications.

Temporal clusters of Salmonella serovars in humans in Alberta, 1990-2001.

BACKGROUND: Temporal clusters of salmonellosis are believed to occur but have not been quantitatively explored, thus, our objectives were to describe trends, seasonal patterns, and clusters of salmonellosis in humans in Alberta by examining isolates reported through passive surveillance systems. METHODS: Cases of salmonellosis reported through Notifiable Disease Records between January 1990 and December 2001 were obtained from Alberta Health and Wellness. Least squares regression was used to characterize the distribution (long-term trends and seasonal patterns) of isolates. A cluster detection test was used to determine if and when isolates of specific serovars aggregated in time, over and above the background distribution. Comparisons were made to temporal patterns in Alberta livestock and to known outbreaks in humans. RESULTS: S. Typhimurium, Enteritidis, Hadar, Heidelberg, and Thompson were the five most common serovars of the 9,188 isolates reported. The annual number of isolates was relatively stable over time, with a distinct summertime seasonal pattern. Clusters were observed in 23 of 32 serovars examined. More clusters occurred in September and October than in other months, and in 1998 through 2001 than in the early to mid-1990s. Also, more clusters were of short duration than long. INTERPRETATION: Short-duration clusters likely indicate a point source of infection, while long-duration clusters may indicate exposure to a persistent common source or the occurrence of secondary infections. A sharp increasing trend and a large cluster of S. Heidelberg may have public health implications. Surveillance activities focussed on similarities between common serovars, trends, and temporal clusters in humans and animals, and studies on factors associated with autumn clusters may be useful in preventing outbreaks in humans.