Epidemiology and risk factors for exposure to gastrointestinal nematodes in dairy herds in northwestern Europe.

In this survey, the epidemiology of gastrointestinal (GI) nematodes in dairy herds in five northwestern European countries was studied using a standardized Ostertagia ostertagi ELISA applied on bulk-tank milk, and a common questionnaire. The levels of exposure to GI nematodes were high in Belgium, the UK and Ireland, intermediate in Germany and low in Sweden, with a mean (95% confidence interval) ELISA result (ODR) of 0.83 (0.82-0.84) in Belgium, 0.82 (0.79-0.84) in the UK and 0.80 (0.78-0.83) in Ireland; significantly higher than the mean ODR of 0.66 (0.65-0.68) in Germany and 0.52 (0.51-0.53) in Sweden. Taking into account previous literature, these regional differences are likely to be systematic. Regional variations in exposure were significantly explained by differences in management (grazing time per day, mowing, the months of turnout, housing and anthelmintic treatment). However, after controlling for these factors, significant regional differences in levels of exposure remained, suggesting an importance for climate (temperature, rainfall) and unmeasured management factors. This study emphasizes that GI nematode-induced production losses should be considered on a large percentage of northwest European dairy herds. Proposals are made for the development of region-specific monitoring and control strategies. Further advances in this area are likely to come from intervention studies that investigate the feasibility of control measures and from studies on the potential effects of climatic conditions on shifts in levels of exposure between years and regions.

Assessment of the within- and between-laboratory repeatability of a commercially available Ostertagia ostertagi milk ELISA.

The objectives of this study were (1) to assess the within- and between-laboratory repeatability of a commercially available antibody-detection Ostertagia ostertagi ELISA (SVANOVIR(O). ostertagi-Ab, Svanova, Uppsala) and (2) to investigate if the assay could be further simplified by reading optical density at a single instead of double wavelength. A total of 80 bulk-tank milk samples were divided into aliquots and tested in duplicate per ELISA plate on 3 different days in 4 different laboratories (Bristol, Ghent, Hannover, Uppsala). The within- and between-laboratory repeatability of the ELISA was assessed by random effect models and the amount of variance attributable to each source of variation (duplicate within plate, day, laboratory and sample) was expressed as a proportion of the total between-sample variance. Overall, the within-laboratory repeatability was good in each laboratory with a proportion of total between-sample variance that could be attributed to assay variability of 5% in Ghent to 27% in Bristol. The between-laboratory repeatability was high: 15% of the total between-sample variance was attributable to the duplicate, 1% to the day, 2% to the laboratory and 82% to the sample. The range of deviations expected to include 95% of the observations when the same sample is tested in different laboratories was -0.23 to 0.23. The mean difference between the ODR values when the optical density was read at a single or double wavelength was -0.002 and the 95% confidence interval included zero. This study demonstrates that the SVANOVIR(O). ostertagi ELISA has a good repeatability and can be further simplified by reading optical density at a single instead of double wavelength. However, the observed variations in the within-laboratory repeatabilities suggest that regular ring testing is necessary when different laboratories cooperate in a same monitoring programme.

Bacteria isolated from parasitic nematodes--a potential novel vector of pathogens?

Bacterial pathogens are ubiquitous in soil and water - concurrently so are free-living helminths that feed on bacteria. These helminths fall into two categories; the non-parasitic and the parasitic. The former have been the focus of previous work, finding that bacterial pathogens inside helminths are conferred survival advantages over and above bacteria alone in the environment, and that accidental ingestion of non-parasitic helminths can cause systemic infection in vertebrate hosts. Here, we determine the potential for bacteria to be associated with parasitic helminths. After culturing helminths from fecal samples obtained from livestock the external bacteria were removed. Two-hundred parasitic helminths from three different species were homogenised and the bacteria that were internal to the helminths were isolated and cultured. Eleven different bacterial isolates were found; of which eight were indentified. The bacteria identified included known human and cattle pathogens. We concluded that bacteria of livestock can be isolated in parasitic helminths and that this suggests a mechanism by which bacteria, pathogenic or otherwise, can be transmitted between individuals. The potential for helminths to play a role as pathogen vectors poses a potential livestock and human health risk. Further work is required to assess the epidemiological impact of this finding.