Failure of injectable ivermectin to control psoroptic mange in cattle

Comparative assessment of different ivermectin and doramectin formulations for mange control in grazing steers

Psoroptic mange causes relevant losses of productivity in cattle. Macrocyclic lactones are one of the main pharmacological tools recommended for controlling it. The aim of the current work was to compare the relationship between the pharmacokinetic behavior and the effectiveness of both ivermectin (IVM) and doramectin (DRM) following their administration as either the traditional (1 %) or long-acting (3.15-3.5 %) injectable formulations to cattle naturally infected with Psoroptes ovis. The overall work involved three trials (1, 2 and 3) carried out on commercial beef cattle farms (grazing systems). In Trial 1, 20 grazing steers with active mange infection were allocated into 2 groups (n = 10) and treated subcutaneously (SC) with either IVM (1 %) or DRM (1%) at 0.2 mg/kg. In Trial 2, 16 grazing steers with active mange divided in 2 groups (n = 8) were treated SC with either IVM 1 % (0.2 mg/kg) or IVM 3.15 % long-acting (0.63 mg/kg). In Trial 3, 2 groups of mange infected steers (n = 8) were treated SC with either IVM 3.15 % (0.63 mg/kg) or DRM 3.5 % (0.7 mg/kg). Blood samples were collected of each experimental group and the drug systemic availability was estimated by measuring of IVM/DRM concentrations by HPLC. Skin scraping samples were collected from each animal and mites were counted at 14, 21 and 28 days post-treatment. In Trial 1, the mite density score on day 14 was significantly lower for DRM (0.60) compared to IVM (1.80) (P = 0.019). Based on the number of animals clinically cured (negative to the presence of mites), the efficacy of DRM was higher (80 %) than that obtained for IVM (10 %) (P < 0.05). DRM systemic exposure measured as AUC was 1.37-fold higher compared to IVM. In Trial 2, even though IVM exposure was significantly greater after the long-acting (3.15 %) compared to the traditional formulation (1 %), none of the treatments significantly reduced the mite density score, with a percentage of animals cured between 0 % and 37.5 % after both IVM treatments. In Trial 3, the 100 % of cured animals were achieved at day 21 (IVM 3.15 %) and at day 28 (DRM 3.5 %) post-treatment. In conclusion, DRM treatment could offer some therapeutic advantages in field situations where IVM fails to control mange. Depending on the level of susceptibility of the mite population, long-acting pharmaceutical formulations can be useful to control Psoroptic mange in cattle. The use of macrocyclic lactones for mange control in cattle should be based on appropriate diagnosis on each individual farm.

Ivermectin: recent approaches in the design of novel veterinary and human medicines

Ivermectin (IVM) is a drug widely used in veterinary and human medicine for the management of parasitic diseases. Its repositioning potential has been recently considered for the treatment of different diseases, such as cancer and viral infections. However, IVM faces some limitations to its formulations due to its low water solubility and bioavailability, along with reports of drug resistance. In this sense, novel technological approaches have been explored to optimize its formulations and/or to develop innovative medicines. Therefore, this review discusses the strategies proposed in the last decade to improve the safety and efficacy of IVM and to explore its novel therapeutic applications. Among these technologies, the use of micro/nano-drug delivery systems is the most used approach, followed by long-acting formulations. In general, the development of these novel formulations seems to run side by side in veterinary and human health, showing a shared interface between the two areas. Although the technologies proposed indicate a promising future in the development of innovative dosage forms containing IVM, its safety and therapeutic targets must be further evaluated. Overall, these approaches comprise tailoring drug delivery profiles, decreasing the risks of developing drug resistance, and supporting the application of IVM for reaching different therapeutic targets.

Unravelling Belgian Blue cattle farmers' adoption intention towards diagnostic tools: Integrating insights from behavioural economics and socio-cognitive theories

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.

New insights into the use of a mite count reduction test for the detection of therapeutic acaricide efficacy in Psoroptes ovis in cattle

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.

Resistance against macrocyclic lactones in Psoroptes ovis in cattle

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.

Acaricidal activity of plant-derived essential oil components against Psoroptes ovis in vitro and in vivo

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 LC50 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 LC90, 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.

Current therapeutic applications and pharmacokinetic modulations of ivermectin

Ivermectin is considered to be a wonder drug due to its broad-spectrum antiparasitic activity against both ectoparasites and endoparasites (under class of endectocide) and has multiple applications in both veterinary and human medicine. In particular, ivermectin is commonly used in the treatment of different kinds of infections and infestations. By altering the vehicles used in the formulations, the pharmacokinetic properties of different ivermectin preparations can be altered. Since its development, various vehicles have been evaluated to assess the efficacy, safety, and therapeutic systemic concentrations of ivermectin in different species. A subcutaneous route of administration is preferred over a topical or an oral route for ivermectin due to superior bioavailability. Different formulations of ivermectin have been developed over the years, such as stabilized aqueous formulations, osmotic pumps, controlled release capsules, silicone carriers, zein microspheres, biodegradable microparticulate drug delivery systems, lipid nanocapsules, solid lipid nanoparticles, sustained-release ivermectin varnish, sustained-release ivermectin-loaded solid dispersion suspension, and biodegradable subcutaneous implants. However, several reports of ivermectin resistance have been identified in different parts of the world over the past few years. Continuous use of suboptimal formulations or sub-therapeutic plasma concentrations may predispose an individual to resistance toward ivermectin. The current research trend is focused toward the need for developing ivermectin formulations that are stable, effective, and safe and that reduce the number of doses required for complete clinical cure in different parasitic diseases. Therefore, single-dose long-acting preparations of ivermectin that provide effective therapeutic drug concentrations need to be developed and commercialized, which may revolutionize drug therapy and prophylaxis against various parasitic diseases in the near future. The present review highlights the current advances in pharmacokinetic modulation of ivermectin formulations and their potent therapeutic applications, issues related to emergence of ivermectin resistance, and future trends of ivermectin usage.

Towards a biased mindset: An extended Theory of Planned Behaviour framework to predict farmers' intention to adopt a sustainable mange control approach

Resistance against macrocyclic lactones is emerging in Psoroptes ovis mites, the cause of psoroptic mange in sheep and cattle. Therefore, sustainable mange control approaches should be implemented to prevent or slow down resistance. To ensure a proper implementation of such approaches, it is crucial to understand the factors that may impede or facilitate adoption of these practices among farmers. A conceptual model that combines insights from the Theory of Planned Behaviour (TPB, Ajzen, 1991) - a theory that predicts human behaviour -, with insights from behavioural economics (Camerer, 2004; Samson, 2016) - a theory that assumes that behavioural biases or reasoning errors are pervasive in decision-making -, was developed to predict farmers' adoption intention. In particular, this paper examines how behavioural economics can influence farmers' beliefs related to sustainable mange control and through which pathways these biased beliefs can predict adoption intention. A cross-sectional survey study amongst 174 Belgian Blue cattle farmers has been conducted and Structural Equation Modelling was used for analyses. In particular, the model shows that farmers' positive attitudes towards a sustainable mange control method (attitude) and their perceptions of how others evaluate the sustainable control methods (subjective norms) more strongly predict adoption intention than perceived behavioural control. Additionally, the model shows that adoption intention is explained by the bandwagon bias -the belief that other farmers have a positive opinion about the control method-, and availability bias - farmers who have the belief that mange occurs often on their farm - through the determinants of TPB. Although this bandwagon bias influences farmers adoption intention, the rather low presence of availability bias might explain why adoption intention of a sustainable mange control method is limited. Next, retaining to the default treatment (default bias) influences farmers' belief that they are capable of implementing control methods on their farm (perceived behavioural control), while the belief that implementing a control method is perceived as a cost for their farm rather than being beneficial (loss aversion bias) negatively influences attitude and perceived behavioural control. We further discuss important implications that can incite farmers' adoption intention.

First evidence of resistance to macrocyclic lactones in Psoroptes ovis sheep scab mites in the UK

Ovine psoroptic mange (sheep scab) is an infection of substantial economic and animal welfare concern in the UK. Its prevalence has increased rapidly over the last 20 years and management is dependent on a small number of acaricidal compounds, many of which are also used to control a range of other endoparasites and ectoparasites. Here, the effects of the macrocyclic lactone (ML) moxidectin was considered using in vitro assays against mites from four farm populations where persistent treatment failure had been reported: two in West Wales, one from the England/Wales border and one in Herefordshire. The data demonstrate resistance in mites from all four farms. This is the first quantitative evidence of ML resistance in Psoroptes mites in the UK. Given the similarities in their mode of action it is highly likely that cross-resistance across the range of this class of compound will be found. The development of resistance to moxidectin is of considerable concern given the already high prevalence of scab infection in some regions; major difficulties in scab management should be anticipated if ML resistance becomes widely established in the UK.

The efficacy of topical ivermectin versus malation 0.5% lotion for the treatment of scabies

Objective: There are different medications for the treatment of scabies but the treatment of choice is still controversial. This study aimed at comparing the efficacy of topical ivermectin versus malation 0.5% lotion for the treatment of scabies. Methods: In total, 340 patients with scabies were enrolled, and randomized into two groups: the first group received 1% ivermectin applied topically to the affected skin and the second group received topical malation 0.5% lotion and were told to apply this twice with 1 week interval. Treatment was evaluated at intervals of 2 and 4 weeks, and if there was treatment failure at the 2-week follow-up, treatment was repeated. Results: Two application of topical ivermectin provided a cure rate of 67.6% at the 2-week follow-up, which increased to 85.2% at the 4-week follow-up after repeating the treatment. Treatment with two applications of malation 0.5% lotion was effective in 44.1% of patients at the 2-week follow-up, which increased to 67.6% at the 4-week follow-up after this treatment was repeated. Conclusion:Two application of ivermectin was as effective as single applications of malation 0.5% lotion at the 2-week follow-up. After repeating the treatment, ivermectin was superior to malation 0.5% lotion at the 4-week follow up.

Comparison of oral ivermectin versus crotamiton 10% cream in the treatment of scabies

OBJECTIVE

Scabies is a relatively contagious infection caused by a tiny mite (Sarcoptes scabiei). Products used to treat scabies are called scabicides because they kill scabies mites; some also kill mite eggs. The aim of this study was to compare the efficacy and safety of oral ivermectin versus crotamiton 10% cream for the treatment of scabies.

METHODS

In total, 320 patients with scabies were enrolled, and were randomized into two groups: the first group received a single dose of oral ivermectin 200 µg/kg body weight, and the second group were treated with crotamiton 10% cream and were told to apply this twice daily for five consecutive days. Treatment was evaluated at intervals of two and four weeks, and if there was treatment failure at the two-week follow-up, the treatment was repeated.

RESULTS

A single dose of ivermectin provided a cure rate of 62.5% at the two-week follow-up, which increased to 87.5% at the four-week follow-up after repeating the treatment. Treatment with crotamiton 10% cream was effective in 46.8% of patients at the two-week follow-up, which increased to 62.5% at the four-week follow-up after this treatment was repeated.

CONCLUSION

A single dose of ivermectin was as effective as one application of crotamiton 10% cream at the two-week follow-up. After repeat treatment, ivermectin was superior to crotamiton 10% cream at the four-week follow up. The delay in clinical response with ivermectin suggests that it may not be effective against all the stages in the life cycle of the parasite.

Risk factors for Psoroptes ovis mange on Belgian Blue farms in Northern Belgium

The parasitic mite Psoroptes ovis causes important economic losses in Belgian Blue cattle. Because mange problems vary significantly between farms, a cross-sectional questionnaire survey and subsequent farm visits were performed to identify potential risk factors for P. ovis infections on Belgian Blue farms in Flanders, Belgium. The questionnaire was sent to 1800 beef farms to evaluate the presence and severity of psoroptic mange in the herd and to assess farm management practices, including antiparasitic treatments. Subsequently, about 10% of the farms with a completed questionnaire were visited to validate the questionnaire and to retrieve supplementary information on additional management parameters, such as barn infrastructure and climate. Associations between parasitism and putative risk factors were assessed by logistic regression. Out of 1800 contacted farms, 680 (38%) completed questionnaires were received. Data were collected from 238 barns during 66 farm visits. The questionnaire results demonstrated a high farm prevalence of mange (74%; 95% CI (70.7-77.3)) and half of the farmers declared that the problem was difficult to control. Nevertheless, in only 14% of the barns a high scratching index was recorded and in most of the sampled animals (80%) the affected body surface was less than 10%. This indicates that despite the high prevalence and the difficulty to control the infection, clinical signs were often quite moderate. Logistic regression analyses of the questionnaire and the farm visit data suggested that heavily infested farms treat more intensively against mange. On most farms mange occurred the whole year round and more problems with mange were found on farms where a higher number of animals were purchased per year. In addition, the disease was more prevalent when the animals had a lower hygiene score. This score was strongly correlated with environmental hygiene, indicating that transmission of mites from the environment to the animals should not be underestimated. Conflicting results were obtained on the effect of supplementing minerals on the occurrence of mange. In this study, temperature, light intensity and relative humidity in the barns, ventilation systems, barn infrastructure, animal stocking rate and blood mineral levels were not indicated as risk factors for mange. In conclusion, maintaining a good animal hygiene and if possible, avoiding introduction of cattle may help to control psoroptic mange in Belgian Blue cattle.

Clinical features of psoroptic mange in cattle in England and Wales

The clinical signs, treatments used and spread of psoroptic mange in cattle from October 2007 until March 2011 are described. The disease was first diagnosed in South West Wales, having not been reported in Great Britain since the 1980s. The likely source was identified as a farm that had imported two animals from mainland Europe in the summer of 2006. Since that time, disease has been diagnosed on a further 22 premises, the majority in South West Wales but also in South East and Mid Wales and on one farm in England. Bought in animals harbouring the Psoroptes species mite but not showing clinical signs were considered the greatest risk of introducing the infestation into a herd. This, together with the difficulties of treatment to eliminate the parasite, means that it is unlikely that this outbreak has been controlled. There is also a continuing threat of importing the disease from abroad. The disease is not notifiable in the UK.

Generation, analysis and functional annotation of expressed sequence tags from the ectoparasitic mite Psoroptes ovis

Background

Sheep scab is caused by Psoroptes ovis and is arguably the most important ectoparasitic disease affecting sheep in the UK. The disease is highly contagious and causes and considerable pruritis and irritation and is therefore a major welfare concern. Current methods of treatment are unsustainable and in order to elucidate novel methods of disease control a more comprehensive understanding of the parasite is required. To date, no full genomic DNA sequence or large scale transcript datasets are available and prior to this study only 484 P. ovis expressed sequence tags (ESTs) were accessible in public databases.

Results

In order to further expand upon the transcriptomic coverage of P. ovis thus facilitating novel insights into the mite biology we undertook a larger scale EST approach, incorporating newly generated and previously described P. ovis transcript data and representing the largest collection of P. ovis ESTs to date. We sequenced 1,574 ESTs and assembled these along with 484 previously generated P. ovis ESTs, which resulted in the identification of 1,545 unique P. ovis sequences. BLASTX searches identified 961 ESTs with significant hits (E-value < 1E-04) and 584 novel P. ovis ESTs. Gene Ontology (GO) analysis allowed the functional annotation of 880 ESTs and included predictions of signal peptide and transmembrane domains; allowing the identification of potential P. ovis excreted/secreted factors, and mapping of metabolic pathways.

Conclusions

This dataset currently represents the largest collection of P. ovis ESTs, all of which are publicly available in the GenBank EST database (dbEST) (accession numbers FR748230 - FR749648). Functional analysis of this dataset identified important homologues, including house dust mite allergens and tick salivary factors. These findings offer new insights into the underlying biology of P. ovis, facilitating further investigations into mite biology and the identification of novel methods of intervention.