Background: Psoroptic mange is an important disease in Belgian Blue cattle. Treatment failure of macrocyclic lactones against Psoroptes ovis has been reported, but clear evidence of in vivo resistance is lacking. This study assessed the efficacy of macrocyclic lactone products on 16 beef farms in Belgium and the Netherlands in vivo and in vitro. Methods:On each farm a group of animals (n = 7-14) with psoroptic mange was treated with two subcutaneous injections of a macrocyclic lactone product with 7-10 days interval (15 farms) or a single injection with a long-acting macrocyclic lactone (1 farm). In vivo efficacy was assessed by the reduction in mite counts, clinical index (proportion of the body surface affected by lesions), the proportion of the animals with negative mite counts after the first treatment round and the number of treatment rounds needed to obtain zero mites counts in all animals. A mite population was categorized as sensitive when the mite count reduction after the first treatment round > 95% and the lower limit of the uncertainty interval > 90%. Resistance was detected when both parameters were below their threshold and suspected when one parameter was too low. In vitro knockdown and mortality were evaluated in a contact test. Results:The proportion of the animals with negative mite counts after the first treatment round varied from 0 to 80%. All farms needed two or more treatments rounds to obtain zero mite counts on all animals. Clinical index only started to reduce after the second treatment round. Mite populations from three farms were categorized as sensitive, one as suspected resistant and 12 as resistant. No correlation was found between in vitro lethal dose 50 and knockdown dose 50 values and in vivo efficacy parameters. Conclusions:Unambiguous treatment failure was detected on 12 out of 16 farms, confirming the presence of macrocyclic lactone resistance on Belgian Blue beef farms. In vitro parameters could not discriminate the farms based on their in vivo sensitivity. The mean reduction in mite counts and the lower limit of the confidence interval are proposed as parameters to identify acaricide resistance.

Background Treatment of Psoroptes ovis in cattle is limited to topical acaricides or systemic treatment with macrocyclic lactones. Treatment failure of macrocyclic lactones has been reported. The aim of this study was to evaluate a potential alternative treatment against P. ovis . Methods The acaricidal activity against P. ovis of four plant-derived essential oil components, i.e. geraniol, eugenol, 1,8-cineol and carvacrol, was assessed in vitro and in vivo . In vitro contact, fumigation and residual bioassays were performed. In addition, 12 Belgium Blue cattle were artificially infested and treated topically once a week for three successive weeks with carvacrol in Tween-80 (treatment group) or with Tween-80 alone (control). The efficacy of carvacrol was determined by the reduction in lesion size and mite counts. Six additional animals were topically treated with carvacrol to assess local adverse reactions. Results Three components showed a concentration-dependent acaricidal activity in a contact assay, with LC 50 of 0.56, 0.38 and 0.26% at 24 h for geraniol, eugenol, and carvacrol, respectively. However, 1,8-cineol showed no activity at any of the tested concentrations in a contact bioassay. In a fumigation bioassay, carvacrol killed all mites within 50 min after treatment, whereas geraniol, eugenol and 1,8-cineol needed 90 to 150 min. Following a 72 h incubation period in a residual bioassay, carvacrol killed all mites after 4 h of exposure to LC 90, while geraniol and eugenol killed all mites only after 8 h exposure. Based on these results, carvacrol was further assessed in vivo . Mite counts in the treatment group were reduced by 98.5 ± 2.4% at 6 weeks post-treatment, while in the control group the mite population had increased. Topical application of carvacrol only caused mild and transient erythema 20 min after treatment. No other side effects were observed. Conclusions Considering the strong acaricidal activity of carvacrol in vitro and in vivo and the mild and transient local side effects, carvacrol shows potential as an acaricidal agent in the treatment of P. ovis in cattle.

Macrocyclic lactone resistance in Psoroptes ovis mites, causing psoroptic mange, is emerging in beef cattle. Therefore, diagnostic tools that can indicate macrocyclic lactone resistance should be implemented at farms in order to control these parasitic infections and slow down emerging resistance. Unfortunately, the adoption of such tools remains relatively poor. This study explores which beliefs, and behavioural biases that misconstrue these beliefs, underlie farmers' adoption intention. Five semi-structured focus groups were conducted with Belgian Blue cattle farmers (n = 38). Inductive analysis revealed that farmers' positive attitudes towards acaricides use and risk perception towards acaricide resistance made them rather reluctant to implement diagnostic tools. In addition, farmers' susceptibility to acaricide resistance occurring on their farm was weakened by the optimism and availability bias. Deductive analysis revealed that economic reasons, usefulness of the diagnostic tool and contribution to animal wellbeing motivated farmers to adopt such tools (i.e., behavioural beliefs). However, the loss aversion and time discounting bias weakened farmers' beliefs related to economic reasons. The veterinarian was seen as the responsible actor for implementing diagnostic tools, while colleague-farmers' opinion related to the diagnostic tool was also valued (i.e., normative beliefs). The latter belief was strengthened by the bandwagon-effect bias. Farmers' beliefs about economic costs related to the diagnostic tool tended to hinder adoption intention, while the veterinarian's assistance motivated farmers to implement such tools (i.e., control beliefs). The loss aversion bias also strengthened farmers' control beliefs related to the diagnostic tools' perceived costs. As such, this article provides more insights into the (ir)rational factors shaping farmers' intention to adopt diagnostic tools. These insights might help animal health organisations to design communication strategies to stimulate the adoption of diagnostic tools on beef cattle farms.

Psoroptic mange is a common disease of livestock, caused by Psoroptes ovis. Compared to Holstein–Friesian (HF) cattle, the Belgian Blue (BB) cattle breed is highly susceptible to the infestation. However, the mechanism for this difference is still unclear. To determine the factors responsible for this breed susceptibility, the immune response to P. ovis was studied in experimentally infested BB and HF cattle, using clinical signs, histology, immunohistochemical profiling and gene expression analysis of skin biopsies. The mite numbers and lesion area of BB cattle were greater than in HF during the whole study period. Significant influxes of eosinophils in the epidermis and dermis were detected in comparison with the pre-infestation samples in both breeds, with significantly higher eosinophils in BB at 6 weeks post infestation (wpi). Mast cell numbers were unaffected at all stages of infestation in HF, but were significantly elevated relative to pre-infestation in BB cattle at 2 and 6 wpi. The more pronounced cutaneous eosinophilia and higher IL-4 levels at 6 wpi in BB cattle suggest that a Th2-type immune response is underlying the higher susceptibility of the BB breed. In naturally infested BB cattle, development of the psoroptic mange lesions and eosinophils and CD3+ T cell areas were severely depressed after anti-inflammatory treatment with dexamethasone. Together, these results suggest that a stronger Th2-type immune response to P. ovis causes the skin lesions in psoroptic mange in BB cattle and that local anti-inflammatory treatment could potentially be an alternative to control the pathology caused by this parasite.

Background Psoroptic mange is an important disease in beef cattle, and Belgian Blue cattle are particularly susceptible. Treatment failure of macrocyclic lactones against Psoroptes ovis has been reported, but clear evidence of in vivo resistance is still lacking. This study was conducted to investigate the efficacy of macrocyclic lactone products in 16 beef farms in Belgium and The Netherlands in vivo and in vitro . Methods On each farm a group of animals (n= 7-14) with psoroptic mange was treated with two subcutaneous injections of a macrocyclic lactone product with 7-10 days interval (15 farms) or a single injection with a long-acting macrocyclic lactone (1 farm). In vivo efficacy was assessed by the reduction in mite counts and clinical index (estimated proportion of the body surface affected by lesions), the proportion of the animals with negative mite counts after the first treatment round and the number of treatment rounds needed to obtain zero mites counts in all animals. A mite population from a given farm was categorized as sensitive when the mite count reduction after the first treatment round >95% and the lower limit of the uncertainty interval >90%. Resistance was detected when both parameters were below the threshold. Resistance was suspected when only one was below its threshold. In vitro knock-down and mortality was evaluated in a contact test. Results The proportion of the animals with negative mite counts after the first treatment round varied from 0-80%. All farms needed two or more rounds of treatments to obtain zero mite counts on all animals. Clinical index had a high variation and only started to reduce after the second treatment round. Mite populations from three farms were categorized as sensitive, one as suspected resistant and the other 12 as resistant. No correlation was found between in vitro lethal dose 50 and knock-down dose 50 values and any parameter of in vivo efficacy. Conclusions Unambiguous treatment failure was detected on 12/16 beef farms, confirming the presence of macrocyclic lactone resistance on Belgian Blue beef farms. In vitro parameters could not discriminate the farms based on their in vivo sensitivity. The mean reduction in mite counts and the lower limit of the confidence interval are proposed as most useful parameters to identify acaricide resistance.

Background Psoroptic mange is an important disease in Belgian Blue cattle. Treatment failure of macrocyclic lactones against Psoroptes ovis has been reported, but clear evidence of in vivo resistance is lacking. This study assessed the efficacy of macrocyclic lactone products on 16 beef farms in Belgium and the Netherlands in vivo and in vitro . Methods On each farm a group of animals ( n = 7–14) with psoroptic mange was treated with two subcutaneous injections of a macrocyclic lactone product with 7–10 days interval (15 farms) or a single injection with a long-acting macrocyclic lactone (1 farm). In vivo efficacy was assessed by the reduction in mite counts, clinical index (proportion of the body surface affected by lesions), the proportion of the animals with negative mite counts after the first treatment round and the number of treatment rounds needed to obtain zero mites counts in all animals. A mite population was categorized as sensitive when the mite count reduction after the first treatment round > 95% and the lower limit of the uncertainty interval > 90%. Resistance was detected when both parameters were below their threshold and suspected when one parameter was too low. In vitro knockdown and mortality were evaluated in a contact test. Results The proportion of the animals with negative mite counts after the first treatment round varied from 0 to 80%. All farms needed two or more treatments rounds to obtain zero mite counts on all animals. Clinical index only started to reduce after the second treatment round. Mite populations from three farms were categorized as sensitive, one as suspected resistant and 12 as resistant. No correlation was found between in vitro lethal dose 50 and knockdown dose 50 values and in vivo efficacy parameters. Conclusions Unambiguous treatment failure was detected on 12 out of 16 farms, confirming the presence of macrocyclic lactone resistance on Belgian Blue beef farms. In vitro parameters could not discriminate the farms based on their in vivo sensitivity. The mean reduction in mite counts and the lower limit of the confidence interval are proposed as parameters to identify acaricide resistance.

BackgroundPsoroptic mange is an important disease in beef cattle, and Belgian Blue cattle are particularly susceptible. Treatment failure of macrocyclic lactones against Psoroptes ovis has been reported, but clear evidence of in vivo resistance is still lacking. This study was conducted to investigate ML efficacy in 16 beef farms in Belgium and The Netherlands in vivo and in vitro. MethodsOn each farm a group of animals (n= 7-14) with clinical psoroptic mange was treated with two subcutaneous injections of a macrocyclic lactone with 7-10 days interval (15 farms) or a single injection with a long-acting macrocyclic lactone (1 farm). In vivo efficacy was assessed by the reduction in mite counts and clinical index (part of the body affected by lesions), the cure rate after the first treatment round and the number of treatment rounds needed to cure all animals. In vitro knock-down and mortality was evaluated in a contact test. ResultsCure rates after the first treatment round varied from 0-80%. All farms needed two or more rounds of treatments to obtain full efficacy. Clinical index had a high variation and only started to reduce after the second treatment round. Only three farms were categorized as susceptible with a mean mite count reduction>95% and a lower limit of the uncertainty interval>90%. One farm had a mean reduction>95%, but its lower limit of the confidence interval was <90%. All other farms had mean reductions<95% and lower limits of their uncertainty intervals<90%. No correlation was found between in vitro lethal dose 50 and knock-down dose 50 values and any parameter of in vivo efficacy. ConclusionUnambiguous treatment failure was detected on 12/16 beef farms, confirming the presence of macrocyclic lactone resistance in Belgian Blue beef farms. In vitro parameters could not discriminate the farms based on their in vivo susceptibility. The mean reduction in mite counts and the lower limit of the confidence interval stood out as most useful parameter to identify acaricide resistance.

When used for the evaluation of drug efficacy against Psoroptes ovis , the diagnostic performance of different sampling strategies for a mite count reduction test (MCRT) remains unclear. In the present study, a novel simulation framework was constructed that accounted for relevant biological features of P. ovis infestations in cattle and that was parameterized with field data from 16 farms (154 animals). Second, this framework was applied to explore the impact of study specific factors (number of animals, number of sampled lesions, and number of scrapings per lesion) and biological factors (mite infestation intensity and size of lesions) on the diagnostic performance of MCRT. Its outcome provided a basis to determine the diagnostic performance of MCRT when it was applied according to the World Association for the Advancement in Veterinary Parasitology (WAAVP) and the European Medicine Agency (EMA) guidelines, and to formulate recommendations to ensure a good diagnostic performance of the MCRT. For both guidelines, the MCRT allowed to correctly detect (power 80%) reduced and normal efficacy when the therapeutic efficacy was <70%, and ≥95%, respectively. The results highlighted a reliable diagnostic performance of the MCRT when performed as recommended by WAAVP and EMA for the detection of normal drug efficacy. When used for the detection of reduced efficacy, therapeutic efficacies between 70% and 90% could not be detected with sufficient reliability. The diagnostic performance can be improved by increasing the total number of skin scrapings (increasing the number of animals, number of sampled lesions and/or number of samples per lesion). In order to help researchers and veterinarians to optimize the design of the MCRT to their field settings, the findings were translated into a simple tool.