Predicting the unpredictable? A climate-based model of the timing of peak pasture infectivity for Dictyocaulus viviparus.

Outbreaks of cattle lungworm disease (Dictyocaulus viviparus) are explosive and costly. The unpredictability of the disease often encourages farmers to apply blanket anthelmintic treatments to the herd, which impede the acquisition of immunity, increase the risk of drug resistance, and interfere with efforts to reduce anthelmintic use against ubiquitous gastrointestinal nematodes. Improving our understanding of the factors which lead to a high risk of infection with lungworm, (including climatic pressure), would support a more targeted management. We present GLOWORM-FL-DV, the first mathematical model of the free-living stages of D. viviparus. The ecology of D. viviparus is unique compared with other strongylid nematodes due to its relationship with Pilobilus spp. fungi, which enhance the transmission potential. The role of the fungi was therefore incorporated into the model framework, informed by laboratory observations of Pilobolus spp. development and sporulation. The thermal niche of D. viviparus was characterised based on published and laboratory observations. Mortality of parasitic larvae increased significantly below 0oC, and larval development occurred above 1.4oC, whereas the estimated minimum temperature for migration via Pilobolus spp. was 8.8oC. Model predictions were compared with antibody levels in bulk milk tank samples collected at two-weekly intervals from eight dairy herds across Great Britain over two grazing seasons. The model predicted high levels of larval abundance on pasture 46 days (38-52 days) before a rise in antibody levels and 22-26 days before the onset of clinical signs. The model assesses the impact of climate and weather on lungworm larval availability at pasture and provides a framework for the development of a risk forecasting system. This could help to focus vigilance for clinical signs at high-risk times and facilitate the targeted use of anthelmintics to prevent outbreaks, in support of sustainable parasite control.

Initial assessment of the economic burden of major parasitic helminth infections to the ruminant livestock industry in Europe.

We report a European wide assessment of the economic burden of gastrointestinal nematodes, Fasciola hepatica (common liver fluke) and Dictyocaulus viviparus (bovine lungworm) infections to the ruminant livestock industry. The economic impact of these parasitic helminth infections was estimated by a deterministic spreadsheet model as a function of the proportion of the ruminant population exposed to grazing, the infection frequency and intensity, the effect of the infection on animal productivity and mortality and anthelmintic treatment costs. In addition, we estimated the costs of anthelmintic resistant nematode infections and collected information on public research budgets addressing helminth infections in ruminant livestock. The epidemiologic and economic input data were collected from international databases and via expert opinion of the Working Group members of the European Co-operation in Science and Technology (COST) action COMbatting Anthelmintic Resistance in ruminants (COMBAR). In order to reflect the effects of uncertainty in the input data, low and high cost estimates were obtained by varying uncertain input data arbitrarily in both directions by 20 %. The combined annual cost [low estimate-high estimate] of the three helminth infections in 18 participating countries was estimated at € 1.8 billion [€ 1.0-2.7 billion]. Eighty-one percent of this cost was due to lost production and 19 % was attributed to treatment costs. The cost of gastrointestinal nematode infections with resistance against macrocyclic lactones was estimated to be € 38 million [€ 11-87 million] annually. The annual estimated costs of helminth infections per sector were € 941 million [€ 488 - 1442 million] in dairy cattle, € 423 million [€ 205-663 million] in beef cattle, € 151million [€ 90-213 million] in dairy sheep, € 206 million [€ 132-248 million] in meat sheep and € 86 million [€ 67-107 million] in dairy goats. Important data gaps were present in all phases of the calculations which lead to large uncertainties around the estimates. Accessibility of more granular animal population datasets at EU level, deeper knowledge of the effects of infection on production, levels of infection and livestock grazing exposure across Europe would make the largest contribution to improved burden assessments. The known current public investment in research on helminth control was 0.15 % of the estimated annual costs for the considered parasitic diseases. Our data suggest that the costs of enzootic helminth infections which usually occur at high prevalence annually in ruminants, are similar or higher than reported costs of epizootic diseases. Our data can support decision making in research and policy to mitigate the negative impacts of helminth infections and anthelmintic resistance in Europe, and provide a baseline against which to measure future changes.