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In an era of highly productive herds, performance monitoring and planned health strategies, parasitic diseases were predicted to become a thing of the past. Parasites remain ubiquitous, of course, and eradicating them from farms is not feasible or economically viable, so the impacts of subclinical disease on performance continue. However, acute clinical cases of parasitism are something that, even 25 years ago, were supposed to be consigned to history.1
Highly effective anthelmintics were to ensure this, and while that narrative has been unravelling for some time for gastrointestinal nematodes in sheep, goats and cattle,2 anthelmintics still seem to be working against the lungworm Dictyocaulus viviparus. By now, this parasite should be confined to the museum, or at least be a rare and notable clinical diagnosis, like thromboembolic colic caused by Strongylus vulgaris – a parasite suppressed by the long-term use of macrocyclic lactone anthelmintics in practice.3
However, a new study by McCarthy and van Dijk, summarised on p 642 of this issue of Vet Record, tells us otherwise.4 Not only is D viviparus clinging on, but cases actually increased between the 1980s and 2014. This is despite the absence of reported anthelmintic resistance and the availability of a vaccine.
Using Veterinary Investigation Diagnosis Analysis (VIDA) data,5 compiled from diagnoses at veterinary investigation laboratories run by the APHA and Scotland’s Rural College, McCarthy and van Dijk found that not only have cases increased but seasonal shifts and changes in the age of affected animals have also occurred.
Cases traditionally peak between July and October, as warm conditions and summer grazing allow parasite larvae to build up on pastures. This still seems to be true in Scotland, …
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