Status of Porcine circovirus diseases in western Canada. (2007)

Following the epizootic herd outbreaks in the mid-1990s (1), western Canada entered a period of quiescence during which time Porcine circovirus diseases (PCVD) were rarely diagnosed in North America. During this time, PCVD caused devastating disease throughout Europe and in many non-European countries. Following the reemergence of PCVD in eastern Canada in 2004/2005, sporadic, but sometimes devastating, outbreaks were reported in the west. To characterize the severity and extent of PCVD in western Canada, a brief descriptive survey of practicing veterinarians of the Western Canadian Association of Swine Veterinarians (WCASV) was undertaken in May 2006. Thirty-seven herd health veterinarians in 15 of 25 solicited veterinary practices (60% response) representing practices in all 4 western provinces participated in the survey. Collectively, the respondents provided consulting services for 862 herds, which, cumulatively, represented over 440 000 sows and 4.05 million feeding pigs, approximately 63% of western Canada’s hog inventory, based on 2005 Statistics Canada data (2). In 121 herds (14%), representing approximately 43 845 inventoried sows and 638 000 hogs marketed annually, PCVD was reported to be a clinical entity (defined as sufficient to require ongoing attention of the farm management and veterinarians). By farm type, clinical disease was most prevalent in finisher farms (n = 49; 5.7%) and farrow-to-finish herds (n = 54; 6.3%). Restriction fragment length polymorphism (RFLP) genetic analysis (3) had been undertaken in 37 affected and 31 nonaffected farms and Porcine circovirus (PCV)2-321 had been identified in 59% and 19% of clinically affected and non-affected herds, respectively. By contrast, PCV2-422-like strains had been identified in 14% and 71% of clinically affected and nonaffected herds, respectively, and multiple strains had been identified in 27% and 10% of clinically affected and nonaffected herds, respectively. The disease was noted in pigs aged between 5 and 17 wk, most commonly between 8 and 14 wk (Figure 1). The most common clinical signs of PCVD included, in order of frequency: wasting, pallor, diarrhea, and dyspnea (Figure 2). On affected farms, mortality levels were estimated to be increased over the historic baseline by 5.0%, 4.0%, and 6.5% in nursery (weaning–30 kg), grower (30–75 kg), and combined grower-finisher (30–120 kg) stages, respectively. Elevated morality in the finisher stage (75–120 kg) was rarely reported. While PCV2 infection is present on virtually all farms, clinical expression is enhanced by numerous infectious and noninfectious cofactors. When asked which cofactors contributed to clinical expression in PCVD-affected herds in western Canada, respondents identified concurrent disease, poor environment or husbandry, and overcrowding most frequently (Table 1). The results of this survey indicate that in May 2006, PCVD was a sporadic (affecting about 14% of western Canadian farms), but economically significant, disease on the majority of affected farms. More recent informal communication with several western Canadian veterinarians suggests that the prevalence of epizootic PCVD is increasing in western Canada.



Figure 1

Bars represent the number of respondents reporting clinical signs of Porcine circovirus diseases for each week of age on the affected farms in their practice as reported by their herd health veterinarians.





Figure 2

Bars represent the relative severity of clinical signs of Porcine circovirus diseases (PCVD) or lesions on PCVD-affected farms in western Canada as reported by their herd health veterinarians. Veterinarians ranked each clinical sign or lesion from 0–3 ...





Table 1

Perceived health and production factors associated with the expression of clinical signs of Porcine circovirus diseases (PCVD) on affected farms in western Canada as identified by herd health veterinarians