A longitudinal study of Besnoitia besnoiti infections and seasonal abundance of Stomoxys calcitrans in a dairy cattle farm of southwest France

Bovine besnoitiosis, caused by the cyst-forming apicomplexan Besnoitia besnoiti, is commonly reported in some restricted regions of South-Western Europe, and in larger regions of Africa and Asia. This infection is thought to be transmitted by blood feeding insects and is responsible for major economic losses in cattle production. A recent emergence in Europe, notified in the Centre of France, Spain and Germany, has attracted more attention to this disease. Clinical signs could appear in some animals; however, many infected cattle remain asymptomatic or show scleral-conjunctival cysts (SCC) only. Recent development of serological methods allows carrying out seroepidemiological field studies. In this respect, a long-term investigation was performed in a dairy cattle farm localized in an enzootic area of besnoitiosis of South-western France between March 2008 and May 2009. The objective was to estimate the seasonal pattern of B. besnoiti infections based on the presence of SCC and serology (ELISA and Western blot). In parallel, an entomological survey was conducted to describe population dynamics of Stomoxys calcitrans and Tabanidae species. The seroprevalence determined by Western blot in a cohort of 57 animals continuously present during the whole survey increased from 30% in March 2008 to 89.5% in May 2009 and was always higher than the prevalence based on clinically assessed SCC. New positive B. besnoitia seroconversions occurred throughout the year with the highest number in spring. In addition, many seroconversions were reported in the two months before turn-out and could be associated with a high indoors activity of S. calcitrans during this period.

Evaluation of farm-level parameters derived from animal movements for use in risk-based surveillance programmes of cattle in Switzerland

BACKGROUND: This study focused on the descriptive analysis of cattle movements and farm-level parameters derived from cattle movements, which are considered to be generically suitable for risk-based surveillance systems in Switzerland for diseases where animal movements constitute an important risk pathway. METHODS: A framework was developed to select farms for surveillance based on a risk score summarizing 5 parameters. The proposed framework was validated using data from the bovine viral diarrhoea (BVD) surveillance programme in 2013. RESULTS: A cumulative score was calculated per farm, including the following parameters; the maximum monthly ingoing contact chain (in 2012), the average number of animals per incoming movement, use of mixed alpine pastures and the number of weeks in 2012 a farm had movements registered. The final score for the farm depended on the distribution of the parameters. Different cut offs; 50, 90, 95 and 99%, were explored. The final scores ranged between 0 and 5. Validation of the scores against results from the BVD surveillance programme 2013 gave promising results for setting the cut off for each of the five selected farm level criteria at the 50th percentile. Restricting testing to farms with a score ≥ 2 would have resulted in the same number of detected BVD positive farms as testing all farms, i.e., the outcome of the 2013 surveillance programme could have been reached with a smaller survey. CONCLUSIONS: The seasonality and time dependency of the activity of single farms in the networks requires a careful assessment of the actual time period included to determine farm level criteria. However, selecting farms in the sample for risk-based surveillance can be optimized with the proposed scoring system. The system was validated using data from the BVD eradication program. The proposed method is a promising framework for the selection of farms according to the risk of infection based on animal movements.