A case-control study of risk factors for bovine cysticercosis in Danish cattle herds.

Bovine cysticercosis (BC) is a zoonotic, parasitic infection in cattle. Under the current EU meat inspection regulation, every single carcass from all bovines above 6 weeks of age is examined for BC. This method is costly and makes more sense in countries with higher number of BC-infected animals than in countries with few lightly infected cases per year. The aim of the present case-control study was to quantify associations between potential herd-level risk factors and BC in Danish cattle herds. Risk factors can be used in the design of a risk-based meat inspection system targeted towards the animals with the highest risk of BC. Cases (n = 77) included herds that hosted at least one animal diagnosed with BC at meat inspection, from 2006 to 2010. Control herds (n = 231) consisted of randomly selected herds that had not hosted any animals diagnosed with BC between 2004 and 2010. The answers from a questionnaire and register data from the Danish Cattle Database were grouped into meaningful variables and used to investigate the risk factors for BC using a multivariable logistic regression model. Case herds were almost three times more likely than control herds to let all or most animals out grazing. Case herds were more than five times more likely than control herds to allow their animals access to risky water sources with sewage treatment plant effluent in proximity. Case herds were also more likely to share machinery or hire contractors than control herds. The risk decreased with increasing herd size probably because the larger herds generally tend to keep cattle indoors in Denmark. The results are useful to guide future data recording that can be supplied by the farmer as food chain information and then be used for differentiated meat inspection in low- and high-risk groups, enabling development of risk-based meat inspection systems.

Occurrence and factors associated with bovine cysticercosis recorded in cattle at meat inspection in Denmark in 2004-2011.

Current EU regulation requires that every bovine carcass is examined for bovine cysticercosis (BC) at meat inspection. This is costly and might be superfluous at low BC prevalence. However, from a consumer view-point it may be important to identify and manage infected carcasses to avoid human infection. If relevant data could be effectively used to classify animals with respect to their risk of being infected, then the current meat inspection could be replaced by a more cost-effective system targeting high-risk animals. This study aimed to (1) describe the distribution of BC cases in the Danish cattle population, (2) estimate the animal level prevalence (3) provide descriptive statistics of potential risk factors for BC, and (4) determine attributable risks and fractions of selected risk factors potentially useful for a future risk-based meat inspection system. In total, 348 cases of BC were recorded among all cattle slaughtered (n=4,090,661) in Denmark between 2004 and 2011. The true animal level prevalence of BC was estimated to be 0.06%. The herd of origin of the cases were defined as the herd in which the animals spent most of their lifetimes. The detected cases were found to originate from 328 herds, with a maximum of two cases per herd indicating sporadic occurrence. Even though organic farming was associated with a higher risk (RR=1.9 in univariable analysis) of BC-positive animals being detected at slaughter, the population attributable fraction showed that only 5% of the animals with BC could be attributed to organic farming practices at the level of organic farming practiced in Denmark in the study period. Thus, organic farming status was not a suitable risk factor to use to target future risk-based meat inspection. However, 54% of the animals with BC in the cattle population were attributed to female gender. Increasing age at slaughter was also associated with high risk of BC. There may be overlaps between these effects in animals with multiple risk factors. Other underlying factors such as grazing patterns might explain the risk factors and attribution results found in this study. However, grazing practices are currently not recorded in the Danish cattle database. Therefore, animal level risk factors such as age and gender together with other risk factors such as grazing practices might be included as food chain information, required to be provided by the farmer prior to slaughter. The challenges and opportunities of this approach should be investigated further.