Evaluation of environmental fecal culture for Mycobacterium avium subspecies paratuberculosis detection in dairy herds and association with apparent within-herd prevalence.

This study evaluated test characteristics of environmental culture (EC) for the detection of Mycobacterium avium subspecies paratuberculosis (MAP) in 32 herds over a 2-year period. Individual fecal samples were collected every 6 mo and environmental samples every 3 mo. Individual fecal culture was performed on samples from positive pools. Samples were cultured in broth, with confirmatory polymerase chain reaction performed on positive fecal samples. Repeated measures were accounted for using GEE logistic models. Relative to a MAP herd-status based on all pooled fecal culture results collected during the study, sensitivity of a set of 6 EC-samples collected from prescribed locations within the herd environment (EC-6) was 71% [95% confidence interval (CI): 49% to 86%] and specificity was 99% (95% CI: 95% to 100%). Sensitivity of EC increased as apparent within-herd fecal culture prevalence (aWHP) increased. The estimated aWHP increased as the proportion of positive EC-samples within an EC-6 set increased. Environmental culture is an acceptable tool for herd diagnosis of MAP in low-prevalence herds.

Évaluation de la culture fécale environnementale pour la détection deMycobacterium aviumsous-espèceparatuberculosisdans les troupeaux laitiers et l'association avec la prévalence apparente dans les troupeaux. Cette étude a évalué les caractéristiques des tests de cultures environnementales (CE) pour la détection de Mycobacterium avium sous-espèce paratuberculosis (MAP) dans 32 troupeaux pendant une période de deux ans. Des échantillons fécaux individuels ont été prélevés tous les 6 mois et des échantillons environnementaux tous les 3 mois. La culture fécale individuelle a été réalisée sur des échantillons provenant des échantillons regroupés positifs. Les échantillons ont été cultivés dans du bouillon et l'amplification en chaîne par la polymérase de confirmation a été réalisée sur des échantillons fécaux positifs. Des mesures répétées ont été enregistrées à l'aide de modèles logistiques d'équations généralisées d'estimation. En rapport avec un statut de troupeau pour MAP fondé sur tous les résultats des cultures fécales regroupées prélevées durant l'étude, la sensibilité d'un groupe de 6 échantillons-CE prélevés dans les lieux prescrits au sein de l'environnement du troupeau (CE-6) était de 71 % [intervalle de confiance (IC) de 95 %: de 49 % à 86 %] et la spécificité était de 99 % (IC de 95 %: de 95 % à 100 %). La sensibilité de CE a augmenté au fur et à mesure que la prévalence apparente de la culture fécale dans le troupeau (PaCF) montait. La PaCF estimée augmentait tandis que la proportion d'échantillons CE positifs dans le groupe CE-6 montait. La culture environnementale est un outil acceptable pour le diagnostic de MAP chez le troupeau pour les troupeaux avec une faible prévalence.(Traduit par Isabelle Vallières).

Effectiveness of emamectin benzoate for treatment of Lepeophtheirus salmonis on farmed Atlantic salmon Salmo salar in the Bay of Fundy, Canada.

Emamectin benzoate (an avermectin chemotherapeutant administered to fish as an in-feed treatment) has been used to treat infestations of sea lice Lepeophtheirus salmonis on farmed Atlantic salmon Salmo salar in the Bay of Fundy, New Brunswick, Canada, since 1999. This retrospective study examined the effectiveness of 114 emamectin benzoate treatment episodes from 2004 to 2008 across 54 farms. Study objectives were to establish whether changes in the effectiveness of emamectin benzoate were present for this period, examine factors associated with treatment outcome, and determine variables that influenced differences in L. salmonis abundance after treatment. The analysis was carried out in 2 parts: first, trends in treatment effectiveness and L. salmonis abundance were explored, and second, statistical modelling (linear and logistic regression) was used to examine the effects of multiple variables on post-treatment abundance and treatment outcome. Post-treatment sea lice abundance increased in the later years examined. Mean abundance differed between locations in the Bay of Fundy, and higher numbers were found at farms closer to the mainland and lower levels were found in the areas around Grand Manan Island. Treatment effectiveness varied by geographical region and decreased over time. There was an increased risk for unsuccessful treatments in 2008, and treatments applied during autumn months were more likely to be ineffective than those applied during summer months.

Bulk tank milk selenium and its association with milk production parameters in Canadian dairy herds.

An observational study was conducted in 63 Canadian dairy farms to evaluate the association of bulk tank milk selenium (Se) concentration (BTSe) with average daily milk yield, milk fat and milk protein, bulk tank somatic cell count (BTSCC), and the probability of being a Staphylococcus aureus-positive herd. Bulk tank milk samples collected between March 2007 and February 2008 were evaluated for BTSCC, S. aureus culture status, and BTSe. Mean BTSe was 0.51 ± 0.15 µmol/L; no herds were classified as deficient or marginal based on BTSe. Bulk tank milk Se was unconditionally associated with milk production; however, adjusting by region indicated a confounding effect of this variable. There was no relationship between BTSe and BTSCC. Higher values of BTSe were associated with lower risk of being a S. aureus-positive herd, possibly as a result of a more robust udder immune response, or as a result of providing Se at a higher rate as one component of an udder health program that reduces risk of being S. aureus positive.

Who let the dogs out? Exploring the spatial ecology of free-roaming domestic dogs in western Kenya.

The spatial ecology of free-roaming dogs determines their role in the transmission of zoonoses. This study describes the geographic range of and identifies sites frequently visited by free-roaming domestic dogs in western Kenya. Eight sites in Busia county, western Kenya, were selected. At each site, ten dog-keeping households were recruited, a questionnaire was administered, and a GPS logger was fixed around the neck of one dog in each household. Loggers were programmed to capture the dog's position every minute, for five consecutive days. Individual summaries of GPS recordings were produced, and the daily distance traveled was calculated. 50% and 95% utilization distribution isopleths were produced, and the area within these isopleths was extracted to estimate the size of the core and extended Home Ranges (HRs), respectively. Linear regression analyses were performed to identify factors associated with the movement parameters. The centroid points of the 10, 50, and 90% isopleths were reproduced, and the corresponding sites identified on the ground. Seventy-three dogs were included in the final analyses. The median daily distance traveled was 13.5km, while the median core and extended HRs were 0.4 and 9.3 ha, respectively. Older dogs had a larger extended HR and traveled more daily, while the effect of sex on dog movement depended on their neutering status. Dogs spent most of their time at their household; other frequently visited sites included other household compounds, fields, and rubbish dumps. One of the centroids corresponded to a field located across the international Kenya-Uganda border, emphasizing the fluidity across the border in this ecosystem. Multiple dogs visited the same location, highlighting the heterogeneous contact networks between dogs, and between dogs and people. The field data presented are of value both in understanding domestic dog ecology and resource utilization, and in contextualizing infectious and parasitic disease transmission models.

Quantitative epidemiology: progress and challenges.

This manuscript is derived from a presentation at the 2006 AVEPM--Schwabe Symposium which honoured the 2006 recipient of the Calvin Schwabe Award--Dr. S. Wayne Martin. Throughout his career, Dr. Martin was instrumental in furthering the development of quantitative epidemiology. This manuscript highlights some of the recent advances in quantitative methods used in veterinary epidemiology and identifies some of the challenges we still face in the use of these methods. Areas discussed are: methods for analyzing hierarchical data, Bayesian methods, survival analysis and integrating causal thinking and statistical analyses.

Relationships among milk urea-nitrogen, dietary parameters, and fecal nitrogen in commercial dairy herds.

Our study objective was to determine the ability of milk urea-nitrogen concentrations ([MUN]) to predict fecal nitrogen concentrations ([Fecal N]) in commercial dairy herds. A total of 83 dairy herds were each visited 3 times within 48 h after a monthly herd milk test. For each farm visit, forages were sampled for nutrient analyses, which were entered into a computerized ration evaluator, and fecal samples were taken per rectum from each of 6 cows (2 early-, 2 mid-, and 2 late-lactation). Fecal samples were pooled, mixed, and analyzed for nitrogen content. Fecal nitrogen concentrations were compared with the routinely measured nutritional parameters from the ration evaluation, and the herd average [MUN] for the previous milk test date using mixed linear regression analyses. Total protein supplied in the ration was significantly positively associated with [Fecal N], but herd average [MUN] was not associated (P > 0.10) with [Fecal N].

Estimate of the direct production losses in Canadian dairy herds with subclinical Mycobacterium avium subspecies paratuberculosis infection.

The objective of this study was to estimate the annual losses from Mycobacterium avium subspecies paratuberculosis (MAP) for an average, MAP-seropositive, Canadian dairy herd. A partial-budget simulation model was developed with 4 components of direct production losses (decreased milk production, premature voluntary culling, mortality, and reproductive losses). Input values were obtained primarily from a national seroprevalence survey of 373 Canadian dairy farms in 8 of 10 provinces. The model took into account the variability and uncertainty of the required input values; consequently, it produced probability distributions of the estimated losses. For an average Canadian dairy herd with 12.7% of 61 cows seropositive for MAP, the mean loss was $2992 (95% C.I., $143 to $9741) annually, or $49 per cow per year. Additional culling, decreased milk production, mortality, and reproductive losses accounted for 46%, 9%, 16%, and 29% of the losses, respectively. Canadian dairy producers should use best management practices to reduce these substantial annual losses.

Canadian veterinarians' use of analgesics in cattle, pigs, and horses in 2004 and 2005.

Anecdotal evidence suggests that many veterinarians may not use analgesics in livestock for routine surgical procedures or painful disease states. To investigate this, we conducted a national mail survey of a random sample of 1431 Canadian veterinarians (response rate, 50.1%). Questions primarily concerned veterinarians' analgesic usage for common surgeries and medical conditions in beef and dairy cattle, pigs, and horses, and attitudes toward pain management. More than 90% of veterinarians used analgesic drugs for equine surgeries, for cesarean section in sows and cows, and for bovine claw amputation and omentopexy. However, in these and other categories, the analgesics used were often inadequate, and many veterinarians did not give analgesics to young animals. When castrated, < 0.001% of piglets received analgesia, compared with 6.9% of beef calves and 18.7% of dairy calves < or = 6 mo of age, 19.9% of beef calves and 33.2% of dairy calves > 6 mo of age, and 95.8% of horses. Respondents largely agreed that there are no long-acting, cost-effective analgesics available for use in livestock (median rating 8/10; interquartile range 4-9), and that the long or unknown withdrawal periods of some drugs outweighed the benefits of using them (median rating 7/10; interquartile range 4-9). The results indicate an urgent need for veterinarians to manage pain in livestock better. Continuing education would help, as would an increase in the number of approved, cost-effective analgesic drugs with known withdrawal periods.

Factors affecting Canadian veterinarians' use of analgesics when dehorning beef and dairy calves.

Data collected through a national, randomized mail survey (response rate 50%) were used to identify reasons why veterinarians were likely (i) to use analgesic drugs when dehorning calves, and (ii) to perceive dehorning without analgesia as very painful. Logistic regression analysis indicated that veterinarians were more likely to be analgesic users the more they perceived that dehorning without analgesia was painful (OR = 1.7, P < 0.001). Other positive influences were if the veterinarian worked in British Columbia or Alberta (OR = 5.9, P = 0.005), and if they were primarily in dairy practice (OR = 3.7, P = 0.012) rather than beef practice. This effect of dairy practice was negated if the veterinarian also perceived that owners were unwilling to pay for analgesia (interaction term: OR = 0.25, P = 0.038). Veterinarians were also less likely to perceive dehorning without analgesia as very painful if they perceived that owners were unwilling to pay (OR = 0.58, P = 0.029). However, this effect on pain perception was offset by concern for personal safety (OR = 2.7, P = 0.015). The results are consistent with the relatively high level of outreach about animal welfare among farmers and veterinarians in the western provinces. The results confirm that many veterinarians' approach to pain management for dehorning is influenced considerably by concern about cost. However, pain management for dehorning is not expensive and there is unequivocal evidence that dehorning calves without pain management causes significant distress. Continuing education of veterinarians should help to increase analgesic usage.

Spatial analysis of land use impact on ground water nitrate concentrations.

In spatial analyses of causes or health effects of environmental pollutants, small units of analyses are usually preferred for internal environmental homogeneity reasons but can only be done when fine resolution data are available for most units. Objectives of this study were to determine which land use practices were spatially associated with ground water nitrate concentrations across Prince Edward Island (PEI), Canada, and which spatial aggregation is the preferred unit of analyses. Nitrate concentrations were determined for 4855 samples from private wells. Validated field-by-field land use data were available. Average nitrate concentration and percentage of area for the 14 major land use categories in PEI were determined for each of three spatial aggregations: watersheds based on topography and hydrology; freeform polygon boundaries based on similar neighboring nitrate concentrations; and 500-m buffer zones around each well. Results showed that the percentages of potato, grain, and hay coverage were positive predictors of ground water nitrate concentrations. Percentage of blueberry was a marginally significant negative predictor in the watershed and freeform polygon models, and percentage of residential coverage was a positive predictor in the freeform polygon and buffer zone models. Spatial autocorrelation was present in the freeform polygon and buffer zone models even after land use was taken into account. In conclusion, analyses based on watersheds produced the best predictive model with the percentages of land cover of potato, hay, and grain being significantly associated with ground water nitrate concentrations, and the percentages of blueberry, clear-cut woodland, and other agriculture being marginally significant.

Assessment of antimicrobial transfer from treated to untreated mammary gland quarters by use of high-pressure liquid chromatography for detection of cloxacillin in milk samples from nonlactating dairy cows.

OBJECTIVE: To determine whether half-udder intramammary infusion of cloxacillin results in transfer of cloxacillin from treated to untreated mammary gland quarters within nonlactating cows, and, if so, at what concentrations, and to determine whether selection of ipsilateral versus diagonal-contralateral quarters for treatment affects cloxacillin transfer among quarters. ANIMALS: 20 Holstein-Friesian cows from a dairy herd. PROCEDURES: A within-cow half-udder comparison trial was used in which 2 of 4 mammary gland quarters (ipsilaterally or diagonally) received an intramammary infusion of cloxacillin on day 1 of the nonlactating period. Three days later, milk samples were taken from all untreated quarters and high-pressure liquid chromatography was used to detect and quantify milk cloxacillin concentrations. RESULTS: Cloxacillin was detected in 25% of all untreated mammary gland quarters. Mean cloxacillin concentration in untreated quarters was below minimum inhibitory concentrations for targeted mastitis pathogens. No significant difference in cloxacillin concentrations was found in the ipsilateral or diagonal treatment groups. CONCLUSIONS AND CLINICAL RELEVANCE: Within-cow half-udder comparison trials are valid for antimicrobial trials in nonlactating cows, although transfer of antimicrobials does occur in trace concentrations. Ipsilateral or diagonal-contralateral treatment designs perform similarly. This type of design is economical for researchers, although care must be taken to account for within-cow clustering of mammary gland quarter data.

Efficacy of using an internal teat sealer to prevent new intramammary infections in nonlactating dairy cattle.

OBJECTIVE: To determine whether insertion of an internal teat sealer (ITS) at the end of lactation would prevent development of new intramammary infections (IMIs) during the nonlactating period. DESIGN: Controlled clinical trial. ANIMALS: 939 Holstein-Friesian dairy cows from 16 herds. PROCEDURES: Results of bacteriologic culture of milk samples collected 14 days prior to the end of lactation were used to assign cows to groups (group 1 = negative results for all quarters; group 2 = positive results for > or = 1 quarter). Quarters of cows in group 1 were treated with an ITS or a single intramammary dose of cloxacillin; quarters of cows in group 2 were treated with cloxacillin in conjunction with an ITS or with cloxacillin alone. Milk samples were collected at the end of lactation and within 8 days after calving. RESULTS: Regardless of whether the outcome of interest was new IMIs caused by any pathogens, major pathogens, environmental pathogens, or streptococci other than Streptococcus agalactiae, quarters in group 2 treated with both cloxacillin and an ITS were less likely to develop a new IMI than were quarters treated with cloxacillin alone. For cows in group 1, no significant difference in risk of new IMIs was found between treatments. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that for dairy cattle with an IMI late in the lactation period, intramammary administration of cloxacillin at the end of lactation followed by insertion of an ITS enhanced protection against development of new IMIs, compared with use of cloxacillin alone.

Using and interpreting diagnostic tests.

Diagnostic tests are invaluable to the practice of veterinary medicine. Using them correctly and interpreting the results appropriately depend on having a good understanding of the basic principles outlined in this article. Topics covered include sensitivity and specificity, agreement among tests, using multiple tests, and other issues related to the use and interpretation of diagnostic tests. The most important principle is recognition that the interpretation of test results varies across populations and requires an estimate of the prevalence of the infection (or disease) in the population being studied.

Factors affecting the use of postincisional analgesics in dogs and cats by Canadian veterinarians in 2001.

Factors affecting the postincisional use of analgesics for ovariohysterectomy (OVH) in dogs and cats were assessed by using data collected from 280 Canadian veterinarians, as part of a national, randomized mail survey (response rate 57.8%). Predictors of analgesic usage identified by logistic regression included the presence of at least 1 animal health technician (AHT) per 2 veterinarians (OR = 2.3, P = 0.004), and the veterinarians' perception of the pain caused by surgery without analgesia (OR = 1.5, P < 0.001). Linear regression identified the following predictors of veterinarians' perception of pain: the presence of more than 1 AHT per 2 veterinarians (coefficient = 0.42, P = 0.048) and the number of years since graduation (coefficient = -0.073, P < 0.001). Some of these risk factors are similar to those identified in 1994. The results suggest that continuing education may help to increase analgesic usage. Other important contributors may be client education and a valid method of pain assessment.

Perioperative use of analgesics in dogs and cats by Canadian veterinarians in 2001.

A random sample of 652 Canadian veterinarians was surveyed to determine perioperative use of analgesics in dogs and cats following common surgeries. The response rate was 57.8%. With the exception of taildocking in puppies, at least 85% of animals received preincisional analgesics, and 30% to 98.1% received postincisional analgesics. A similar survey was conducted in 1994; since then, analgesic usage has increased markedly, as have ratings of the pain caused by different surgeries. In 2001 most veterinarians (62%) used at least 2 classes of analgesic perioperatively. However, strong opioids, local anesthetics, and alpha-2 agonists were underused, and there was an overreliance on weak opioids (butorphanol, meperidine). Up to 12% of veterinarians did not use any analgesics. Nationally, this may have affected many animals monthly; for example, approximately 6000 dogs or cats undergoing ovariohysterectomy. Continuing education (provincial level) and review articles were considered effective ways to inform veterinarians about optimal analgesic practices.

Management factors affecting stereotypies and body condition score in nonracing horses in Prince Edward Island.

In North America, there are few representative data about the effects of management practices on equine welfare. In a randomized survey of 312 nonracing horses in Prince Edward Island (response rate 68.4%), owners completed a pretested questionnaire and a veterinarian examined each horse. Regression analyses identified factors affecting 2 welfare markers: body condition score (BCS) and stereotypic behavior. Horses' BCSs were high (mean 5.7, on a 9-point scale) and were associated with sex (males had lower BCSs than females; P < 0.001) and examination date (P = 0.052). Prevalences of crib biting, wind sucking, and weaving were 3.8%, 3.8%, and 4.8%, respectively. Age (OR = 1.07, P = 0.08) and hours worked weekly (OR = 1.12, P = 0.03) were risk factors for weaving. Straw bedding (OR = 0.3, P = 0.03), daily hours at pasture (OR = 0.94, P = 0.02), and horse type (drafts and miniatures had a lower risk than light horses; P = 0.12) reduced the risk of horses showing oral stereotypies. Some of these results contradict those of other studies perhaps because of populations concerned.

Multiple imputation in veterinary epidemiological studies: a case study and simulation.

The problem of missing data occurs frequently in veterinary epidemiological studies. Most studies use a complete case (CC) analysis which excludes all observations for which any relevant variable have missing values. Alternative approaches (most notably multiple imputation (MI)) which avoid the exclusion of observations with missing values are now widely available but have been used very little in veterinary epidemiology. This paper uses a case study based on research into dairy producers' attitudes toward mastitis control procedures, combined with two simulation studies to evaluate the use of MI and compare results with a CC analysis. MI analysis of the original data produced results which had relatively minor differences from the CC analysis. However, most of the missing data in the original data set were in the dependent variable and a subsequent simulation study based on the observed missing data pattern and 1000 simulations showed that an MI analysis would not be expected to offer any advantages over a CC analysis in this situation. This was true regardless of the missing data mechanism (MCAR - missing completely at random, MAR - missing at random, or NMAR - not missing at random) underlying the missing values. Surprisingly, recent textbooks dealing with MI make little reference to this limitation of MI for dealing with missing values in the dependent variable. An additional simulation study (1000 runs for each of the three missing data mechanisms) compared MI and CC analyses for data in which varying levels (n=7) of missing data were created in predictor variables. This study showed that MI analyses generally produced results that were less biased on average, were more precise (smaller SEs), were more consistent (less variability between simulation runs) and consequently were more likely to produce estimates that were close to the "truth" (results obtained from a data set with no missing values). While the benefit of MI varied with the mechanism used to generate the missing data, MI always performed as well as, or better than, CC analysis.

Effects of seropositivity for bovine leukemia virus, bovine viral diarrhoea virus, Mycobacterium avium subspecies paratuberculosis, and Neospora caninum on culling in dairy cattle in four Canadian provinces.

The purpose of this research was to determine the effects of seropositivity for exposure to bovine leukemia virus (BLV), bovine viral diarrhoea virus (BVDV), Mycobacterium avium subspecies paratuberculosis (MAP) and Neospora caninum (NC) on overall and reason-specific culling in Canadian dairy cattle. Serum samples from, approximately, 30 randomly selected cows from 134 herds were tested for antibodies against BLV, MAP and NC using commercially available ELISA test kits, while 5 unvaccinated cattle over 6 months of age were tested for antibodies to bovine viral diarrhoea virus (BVDV). For analyzing the time (in days) to culling of cows after the blood testing, a two-step approach was utilized, non-parametric (Kaplan-Meier survival graphs) visualization and then semi-parametric survival modelling (Cox proportional hazards model), while controlling for confounding variables and adjusting for within herd clustering. For all reasons of culling, MAP-seropositive cows had a 1.38 (1.05-1.81, 95% C.I.) times increased hazard of culling compared to MAP-seronegative cows. Seropositivity for the other pathogens was not associated with an increased risk of overall culling. Among cows that were culled because of either decreased reproductive efficiency or decreased milk production or mastitis, MAP-seropositive cows were associated with 1.55 (1.12-2.15, 95% C.I.) times increased hazard compared to MAP-seronegative cows. Among cows that were culled because of reproductive inefficiency, NC-seropositive cows had a 1.43 (1.15-1.79, 95% C.I.) times greater hazard than NC-seronegative cows. Among cows that were culled because of decreased milk production, cows in BVDV-seropositive herds had a 1.86 (1.28-2.70, 95% C.I.) times increased hazard compared to cows in BVDV-seronegative herds. BLV-seropositive cows did not have an increased risk of reason-specific culling as compared to BLV-seronegative cows. No significant interaction on culling among seropositivity for the pathogens was detected, but only a limited number of cows tested seropositive for multiple pathogens. Results from our research will help in better understanding the economic impacts of these pathogens and justification for their control.

Risk factors for outbreaks of infectious salmon anemia in farmed Atlantic salmon, Salmo salar.

Infectious salmon anemia (ISA) is a viral disease occurring in farmed Atlantic salmon (Salmo salar) that is characterized by lethargy, anorexia, anemia and death. To control the disease in New Brunswick, Canada, 7.5 million fish from outbreak cages have been destroyed since 1997. Despite changes made by farmers, 2002 was the worst year ever for ISA losses in the region. We evaluated the associations between potential risk factors and ISA outbreaks in the Atlantic-salmon sites in New Brunswick. This was a multilevel study in which the site-level design was a retrospective cohort study while the cage-level design was a modified case-cohort study. The questionnaire was divided into site-level questions, cage-level questions and hatchery information. The important factors identified by this study can be categorized as environmental, farmer controlled or industry controlled according to the capacity to change or eliminate them. Environmental risk factors such as increasing the depth of the net (if nets were 3m, OR=3.34) are for the most part dictated by site location. Wild pollock (Pollachius virens) in the cage reflects the number of wild pollock that live in the site location. If there were >or=1000 pollock in the cage, the odds of disease in the cage increased 4.43-fold. Risk factors that are under farm control include increasing the number of times that the salmon are treated for sea lice (OR=3.31 if lice treatments are 99 g) and improving on the adaptation of smolts to seawater to reduce post-transfer mortalities (OR=4.52 if there was at least one cage with post-transfer mortalities >5%). The industry-controlled factors need to be addressed by the industry as a whole. Organizing boat travel to minimize the time and frequency of boats travelling to or by sites currently is being reviewed. This will be extremely important because the OR=9.43 if processing boats travel within 1 km of the site and the OR=4.03 if the site has dry feed delivered by the feed company. Because the hazard ratio increased stepwise from 1 if the nearest neighbor with ISA was >or=5 km up to 5.5 if the nearest site with ISA was within 0.5 km, increasing the distance between sites might be necessary for effective control.

Application of surveillance data in evaluation of diagnostic tests for infectious salmon anemia.

Infectious salmon anemia (ISA) is a viral disease in farmed Atlantic salmon Salmo salar, characterized by lethargy, anorexia, anemia and death. Test methods used for regulatory decisions to remove infected cages include the indirect fluorescent antibody test (IFAT), the reverse transcription-polymerase chain reaction test (RT-PCR), and virus isolation (VI). However, no thorough evaluation of these diagnostic tests has been carried out on field samples. The objective of this study was to evaluate the sensitivity and specificity of ISA diagnostic tests as individual tests and in combinations, using data collected by the provincial government surveillance program. Because a 'gold standard' reference test for ISA was not available, cage status was based on clinical disease records. A pool of fish from negative farms that had never had clinical ISA and a pool of fish from positive cages that were experiencing an outbreak of clinical ISA were obtained and assumed to be uninfected and infected respectively. A total of 1071 fish were used in this study. Depending on the test's cut-off value, the sensitivity and specificity for histopathology ranged from 30 to 73 and 72 to 99% respectively. IFAT had sensitivities and specificities in the range of 64 to 83 and 96 to 100% respectively. For the RT-PCR, sensitivity and specificity were 93 and 98% respectively. Test performances were also evaluated in series and in parallel combinations. Sensitivities are maximized when tests are evaluated in parallel, and ranged from 75 to 98%. Specificities are maximized when the tests are evaluated in series, and ranged from 99 to 100%. Current surveillance testing protocols should be reviewed to capitalize on this newly available information on test characteristics.