A systematic review and meta-analysis of factors associated with anthelmintic resistance in sheep.

BACKGROUND Anthelmintic drugs have been widely used in sheep as a cost-effective means for gastro-intestinal nematode (GIN) control. However, growing anthelmintic resistance (AHR) has created a compelling need to identify evidence-based management recommendations that reduce the risk of further development and impact of AHR. OBJECTIVE To identify, critically assess, and synthesize available data from primary research on factors associated with AHR in sheep. METHODS Publications reporting original observational or experimental research on selected factors associated with AHR in sheep GINs and published after 1974, were identified through two processes. Three electronic databases (PubMed, Agricola, CAB) and Web of Science (a collection of databases) were searched for potentially relevant publications. Additional publications were identified through consultation with experts, manual search of references of included publications and conference proceedings, and information solicited from small ruminant practitioner list-serves. Two independent investigators screened abstracts for relevance. Relevant publications were assessed for risk of systematic bias. Where sufficient data were available, random-effects Meta-Analyses (MAs) were performed to estimate the pooled Odds Ratio (OR) and 95% Confidence Intervals (CIs) of AHR for factors reported in ≥2 publications. RESULTS Of the 1712 abstracts screened for eligibility, 131 were deemed relevant for full publication review. Thirty publications describing 25 individual studies (15 observational studies, 7 challenge trials, and 3 controlled trials) were included in the qualitative synthesis and assessed for systematic bias. Unclear (i.e. not reported, or unable to assess) or high risk of selection bias and confounding bias was found in 93% (14/15) and 60% (9/15) of the observational studies, respectively, while unclear risk of selection bias was identified in all of the trials. Ten independent studies were included in the quantitative synthesis, and MAs were performed for five factors. Only high frequency of treatment was a significant risk factor (OR=4.39; 95% CI=1.59, 12.14), while the remaining 4 variables were marginally significant: mixed-species grazing (OR=1.63; 95% CI=0.66, 4.07); flock size (OR=1.02; 95% CI=0.97, 1.07); use of long-acting drug formulations (OR=2.85; 95% CI=0.79, 10.24); and drench-and-shift pasture management (OR=4.08; 95% CI=0.75, 22.16). CONCLUSIONS While there is abundant literature on the topic of AHR in sheep GINs, few studies have explicitly investigated the association between putative risk or protective factors and AHR. Consequently, several of the current recommendations on parasite management are not evidence-based. Moreover, many of the studies included in this review had a high or unclear risk of systematic bias, highlighting the need to improve study design and/or reporting of future research carried out in this field.

[Overview of helminth problems in domestic ruminants in Switzerland]

Potent anthelmintics were introduced into the Swiss market several decades ago. Despite this, gastrointestinal nematodes (GIN), lungworms and the large liver fluke (Fasciola hepatica) can successfully inhabit Swiss ruminant farms. This is mainly due to a high reproductive capacity as well as very efficient survival strategies. In addition some species readily develop anthelmintic resistance. GIN-infections in young cattle are under comparatively good control. However, prophylactic measures are compromised where adult stock is also affected due to incomplete development of immune protection. Under these circumstances control measures must include all age groups. This results in fewer helminths in refugia thus may accelerate the development of anthelmintic resistance. This review aims to present a synopsis of the significance of the major helminth infections obtained on pasture by large and small ruminants in Switzerland. Currently available strategies for strategic helminth control are summarized and an outlook is given on new developments which might expand the spectrum of control measures relevant for veterinary practice in the future.

Equine parasite control under prescription-only conditions in Denmark - Awareness, knowledge, perception, and strategies applied.

Due to widespread development of anthelmintic resistance in equine parasites, recommendations for their control are currently undergoing marked changes with a shift of emphasis toward more coprological surveillance and reduced treatment intensity. Denmark was the first nation to introduce prescription-only restrictions of anthelmintic drugs in 1999, but other European countries have implemented similar legislations over recent years. A questionnaire survey was performed in 2008 among Danish horse owners to provide a current status of practices and perceptions with relation to parasite control. Questions aimed at describing the current use of coprological surveillance and resulting anthelmintic treatment intensities, evaluating knowledge and perceptions about the importance of various attributes of parasite control, and assessing respondents' willingness to pay for advice and parasite surveillance services from their veterinarians. A total of 1060 respondents completed the questionnaire. A large majority of respondents (71.9%) were familiar with the concept of selective therapy. Results illustrated that the respondents' self-evaluation of their knowledge about parasites and their control associated significantly with their level of interest in the topic and their type of education (P<0.0001). The large majority of respondents either dewormed their horses twice a year and/or performed two fecal egg counts per horse per year. This approach was almost equally pronounced in foals, horses aged 1-3 years old, and adult horses. The respondents rated prevention of parasitic disease and prevention of drug resistance as the most important attributes, while cost and frequent fecal testing were rated least important. Respondents' actual spending on parasite control per horse in the previous year correlated significantly with the amount they declared themselves willing to spend (P<0.0001). However, 44.4% declared themselves willing to pay more than what they were spending. Altogether, results indicate that respondents were generally familiar with equine parasites and the concept of selective therapy, although there was some confusion over the terms small and large strongyles. They used a large degree of fecal surveillance in all age groups, with a majority of respondents sampling and/or treating around twice a year. Finally, respondents appeared willing to spend money on parasite control for their horses. It is of concern that the survey suggested that foals and young horses are treated in a manner very similar to adult horses, which is against current recommendations. Thus, the survey illustrates the importance of clear communication of guidelines for equine parasite control.