Carl Ribble

Evaluation of a nondestructive diagnostic test for Kudoa thyrsites in farmed Atlantic salmon (Salmo salar)

Abstract Postharvest myoliquefaction (soft flesh) associated with Kudoa thyrsites infections is a concern to the Atlantic salmon (Salmo salar) industry in the Pacific Northwest. Infection with this parasite is not macroscopically visible in salmon, and thus infected fish are not readily detectable on the processing line. Identification of infected fish relies on either histological or whole-mount evaluation of muscle tissue. A nondestructive, inexpensive diagnostic test for detection of K. thyrsites infection in the musculature of Atlantic salmon was evaluated in this study. The results indicated that the presence or absence of K. thyrsites in the hyohyoideus ventralis muscle of the operculum, as detected in wet-mount preparations, is a good indicator of the presence or absence of the parasite in the body musculature (fillets) of Atlantic salmon. The sensitivity and specificity of the diagnostic test were 79.0% and 94.6%, respectively. The sensitivity of the test was increased to 93% when the test was used to detect only heavily infected fillets. Therefore the presence or absence of K. thyrsites spores in the hyohyoideus ventralis muscle is a good indicator of heavily infected fish fillets, but is slightly less accurate at detecting fillets with lighter infections of K. thyrsites.

An evaluation of surface moribund salmon as indicators of seapen disease status

Abstract This observational study utilized modified mark and recapture techniques to examine the reliability of moribund fish caught at the surface of the water as indicators of the disease status of commercial salmon farms in British Columbia, Canada. The results indicate that the vast majority of fish captured at the surface are truly moribund, but that the pattern of disease in these fish can be significantly different from that seen in moribund fish not accessible to capture from the surface. In some cases, estimates of the proportional mortality attributed to specific disease categories differed by 30% between surface-caught fish and dead fish. The small number of fish caught at the surface makes it difficult to detect disease of low prevalence. In addition, the low proportion of total mortalities accessible to surface capture prior to their death makes extrapolation of disease data derived from surface samples to the entire pen tenuous. We conclude that samples of surface-catchable fish do not necessarily reveal the true disease pattern of a seapen and that future studies should be directed towards developing additional methods of disease monitoring and investigation on seafarms such as mortality surveys and behavioural observations.

Clustering of fatal fibrinous pneumonia (shipping fever) in feedlot calves within transport truck and feedlot pen groups

Abstract Feedlot owners often state that shipping fever mortality does not affect calves in a random fashion across the feedlot; instead, mortality can be abnormally high in certain truckloads of calves or in certain pens. However, these apparent “clusters” of disease might be no more than coincidental concentrations of fatal shipping fever cases selected from a truly random distribution of cases throughout the feedlot. The purpose of this study was to distinguish between these two possibilities by critically examining the pattern of fatal shipping fever affecting calves placed in a large beef feedlot. Management and mortality data from 36 339 spring-born calves entering a large commercial beef feedlot in SW Alberta, Canada from 1985 to 1988 were used for the analysis in this study. Once at the feedlot, calves were placed in pens of approximately 300 animals. Truck manifests (which include freight or cargo documentation) and feedlot processing records were used to determine the truck and auction market origin of all incoming calves. Because the prevalence of shipping fever mortality varied dramatically among years, an analysis was performed on each of the 4 years separately. To determine whether clustering occurred within the transport truck, tests of homogeneity of binomial samples were run on the truckloads of calves making up each individual pen. To determine whether clustering occurred within a pen, a test for homogeneity of binomial samples was run within each year using the proportion of mortality due to fibrinous pneumonia in each pen; the intracluster correlation coefficient was used to correct for the nested effect of truck within pen. When the incidence of fatal shipping fever was high (greater than 2%), the disease clustered within truckload groups of calves and also, one year, within pens. Further work is necessary to determine whether contagious or non-contagious factors are responsible for the clustering that was documented.

Association between cellulitis (enlarged sternal bursa) and focal ulcerative dermatitis in Ontario turkeys at the time of processing.

Abstract We conducted a processing plant survey to determine the prevalence of cellulitis (enlarged sternal bursa) and focal ulcerative dermatitis (FUD) in Ontario turkeys during the summer and to establish whether the two conditions were associated. A total of 11,772 birds from 24 different farms were observed at three processing plants in Ontario between June and August 2001. Each bird was examined for the presence of cellulitis and FUD. The severity and location of lesions were also noted. The overall prevalence of severe cellulitis (requiring either extensive trimming or condemnation of the bird) was 8.8% (95% confidence interval [CI] = 6.7, 10.9) and the overall prevalence for FUD was 22.6% (19.3, 25.9). The Pearson correlation coefficient between the prevalences of the two lesions was 0.56 (P = 0.0043), suggesting farms with a high prevalence of FUD in their birds also had a high prevalence of cellulitis. More specifically, birds with FUD were, on average, 10.8 times more likely to have cellulitis than birds without FUD (Mantel–Haenszel summary odds ratio = 10.8; 95% CI = 9.5, 12.3). Our observations suggest FUD may predispose birds to cellulitis, in which case, preventing FUD may reduce the occurrence of cellulitis condemnations in turkeys.

DESCRIPTIVE EPIDEMIOLOGY OF DETECTED ANTHRAX OUTBREAKS IN WILD WOOD BISON (BISON BISON ATHABASCAE) IN NORTHERN CANADA, 1962–2008

Abstract We inventoried and assessed historical anthrax outbreak data from 1962–2008 in wild wood bison (Bison bison athabascae) in Wood Buffalo National Park and the Slave River Lowlands (SRL), Northwest Territories, Canada. We compared these results with a 2010 outbreak in the SRL. Anthrax outbreaks have occurred in 12 of the years between 1962 and 2008 in wild wood bison with 1,515 anthrax deaths detected. The average number of carcasses found each outbreak year was 126 (range 1–363), though local averages varied. The numbers of animals found dead per outbreak declined over the past four decades. Outbreaks varied in duration from 16–44 days (average length 25.5 days). The length of an outbreak was not a determinant of the number of dead bison found, but outbreaks starting in July had more deaths than those staring in June. Males were more likely to be detected in an outbreak, outbreaks were likely not random events, and there was no relationship between outbreak size or length and location. Future surveillance activities may benefit from targeting bulls and planning surveillance activities for more than 3 wk after outbreak detection. Coordinating data collecting and recording efforts between jurisdictions may overcome historical challenges in inconsistent record keeping.

Descriptive epidemiology of fatal abomasal ulcers in Canadian beef calves

Retrospective and prospective study designs were used to compile data on 209 cases of fatal abomasal ulceration involving Canadian beef calves < 6 months of age. Retrospective studies of pathology reports and producer records provided data for two of the databases. The third was a prospective study involving necropsy submissions to privately owned veterinary clinics. Data from these three studies were used to describe the age, sex, and breed distribution of calves dying of abomasal ulcers. The monthly distribution of the cases was also described. Most (93.3%) of the fatal ulcers were perforating, the remainder (6.7%) were haemorrhagic ulcers. Calves dying of ulcers ranged in age from 5 days to 6 months, with the average being 45 days. The majority (85.6%) of the cases involved calves < 2 months of age. This age distribution of fatal ulcers closely parallels the timing of forestomach development in naturally reared beef calves, suggesting that ulcerogenesis may be related to forestomach development. The peak number of cases occurred in April and May, suggesting a possible seasonal effect. However, a cohort analysis of calves born in four different months (January, February, March, and April) indicated that season is unlikely to be a factor in fatal ulcer formation. Rather, the clustering of ulcers in April and May likely reflects the underlying age structure of the calf population—most Canadian calves are born in the spring. There was no sex predisposition for ulcer formation, nor was there any conclusive evidence to indicate a breed predilection.

Marine anemia in farmed chinook salmon (Oncorhynchus tshawytscha): Development of a working case definition

Abstract Marine anemia (plasmacytoid leukemia) is a histologically defined syndrome affecting farmed chinook salmon (Oncorhynchus tshawytscha) in British Columbia, Canada. Although the disease has received recent attention and has been diagnosed in many fish farms, past criteria for diagnosis have limited the depth and breadth of epidemiological investigations. By identifying a repeatably diagnosable subset of signs and symptoms of affected fish, a new working case definition of marine anemia was developed. This definition relied exclusively on histological features to achieve the diagnosis. The intra-observer repeatability of diagnoses using the new definition was high ( κ = 0.84). An algorithm employing gross pathological signs was created for field investigation of the disease. The algorithm was capable of predicting histological diagnosis with a reasonable level of accuracy, and was judged to be a valuable tool for diagnostic decisions. We concluded that by using the case definition created in this study together with the algorithm, the comparability and accuracy of clinical and epidemiological research of marine anemia could be improved.