Syringe immersion test as in vitro bioassay against Rhipicephalus microplus: Macrocyclic lactones dose-response relationship

Background

For the diagnosis of tick sensitivity against different acaricides, there are in vitro and in vivo methods. The main in vivo method, the stable test, is considered a defining methodology. In Uruguay, the Rhipicephalus microplus (R. microplus) strain Mozo is used as the standard susceptible strain by the regulatory authorities. In vitro techniques applied both on adult and larvae stages are validated by FAO and can serve as an orientation diagnosis of the resistance profile developed in field conditions. An alternative was proposed as a modification of the larval immersion test (LIT), where syringes were used seeking to reduce the work necessary to perform the original technique, resulting in the syringe immersion test (SIT).

Aim

The aim of this study was to expand the SIT for the characterization of sensitivity to Macrocyclic Lactones (MLs) in R. microplus and provide information on field strain sensitivity of R. microplus larvae.

Methods

Log-logistic dose-response model for Ivermectin (IVM), Doramectin (DRM), and Moxidectin (MOX) were performed using concentrations ranging from 0.01 to 20.0 ppm (n = 6, 3 replicates per level on each drug). Larvae sensitivity results were determined after 24 hours of incubation at 27°C/90% RH, counting live/dead larvae. The final model will be decided as the best fit according to the model selection AIC criteria for each drug. Pharmacodynamic parameters [lower limit, slope, and effective dose at different levels (ED20, ED50, ED80, and ED95)] and its 95% confidence interval were considered for drug comparison.

Results

Dose-response models were fitted for IVM, DRM, and MOX. MOX had the lowest ED50 of the three drugs, implying that MOX is of higher potency (two folds) when compared to IVM and DRM on R. microplus larvae using SIT. DRM had a different slope compared to IVM and MOX (p < 0.05), while IVM and MOX showed a similar slope (p > 0.05).

Conclusion

This study allowed us to standardize the technique for larvae immersion for each ML, granting a new tool for in vitro test as a screening technique for tick sensitivity.

Acaricidal activity and clinical safety of arecoline hydrobromide on calves infested with cattle tick Rhipicephalus microplus (Acari: Ixodidae)

The objective of the present study was to determine the acaricidal activity of arecoline hydrobromide against cattle tick Rhipicephalus microplus infesting calves. in vivo efficacy of arecoline emulsified with polysorbate-80 (2%) was evaluated using ear bag method with the effective dose of 12.5 mg/mL applied on ear pinna of calves infested with ticks. Control group received polysorbate-80 (2%) after larvae infestation, however, reference group received deltamethrin (0.5 %). The experiment was continued for six days (144 h) and treatment of drug was given twice a day. Daily observation of calves was done to count the number of ticks after treatment. Acute dermal toxicity study for test drug was performed on wistar rats. Clinical safety of arecoline was determined by examining hematological profile and skin irritancy assay for calves infested with ticks. Results showed that arecoline significantly (p < 0.01) reduced the number of ticks attached to ear pinna of calves. Fewer number of ticks remained on calves skin at 120 h and 144 h were 8.09 and 6.21, respectively after treatment with arecoline in comparison to control group. Treatment of animals with arecoline hydrobromide significantly (p < 0.01) restored the hematological profile of animals as hemoglobin (Hb) level was 9.01 g/100 mL, PVC was 29.24 %, TEC and TLC were 5.23 and 7.19 106/cumm, respectively as compared to the control group having Hb 9.48 g/100 mL, PVC 31.60 %, TEC 5.64 10⁶/cumm and TLC 7.27 10⁶/cumm. Arecoline showed no toxicity while applied on wistar rats. The drug was mild irritative for an initial 20 min to the calves after that no redness or erythema was seen on the skin of the animals. Thus, arecoline hydrobromide may be an effective alternative to be used as herbal ectoparasiticide for the eradication of R. microplus ticks.

Preventive measures of canine leishmaniosis in Italy: Attitudes of veterinarians based on a questionnaire

There are several topical ectoparasiticides, drugs, supplements and vaccines that protect dogs against sand fly bites and/or reduce the risk of Leishmania infantum infection. This large variety of products and the absence of comparative studies mean that veterinarians are often faced with uncertainty. The aim of the study was to characterise the attitudes of veterinarians towards leishmaniosis prevention in client-owned dogs in Italy. A web-based questionnaire was prepared with 28 questions covering the working environment of veterinarians, advice given to owners regarding topical ectoparasiticides, advice on systemic prevention, and the use of diagnostic tests on which to base advice for prevention. The questionnaire was emailed to 9,426 veterinarians and answers were collected after 100 days. A total of 542 questionnaires were returned (response percentage 5.8 %): 54.8 % of the veterinarians considered their working area to be endemic, 29.3 % examined dogs from urban areas, and 42.3 % diagnosed ≥10 dogs/year with leishmaniosis. Those veterinarians who diagnosed ≥10 dogs/year with leishmaniosis were more likely to consider their working area to be endemic, whereas those who examined dogs mainly from urban areas were less likely to consider the area to be endemic. Veterinarians who considered the working area to be endemic were more prone to prescribe ectoparasiticides throughout the year, including collars and spot-on products and a combination of the two, vaccine alone or vaccine and domperidone combined, and used qualitative serological Leishmania tests. The attitude of veterinarians did not differ whether dogs were from urban or rural areas. In conclusion, veterinarians who consider their working area to be endemic or who frequently diagnose dogs with leishmaniosis tend to adopt more comprehensive strategies, and their attitudes are not influenced by the origin of the dogs: urban or rural. Overall, in Italy the attitudes of veterinarians in relation to canine leishmaniosis prevention appear to vary considerably.

Efficacy of fluralaner spot-on solution for the treatment of Ctenocephalides felis and Otodectes cynotis mixed infestation in naturally infested cats

BACKGROUND

Cats can be infested with several ectoparasite species, especially Ctenocephalides felis and Otodectes cynotis. The aim of this study was to evaluate the efficacy of a single topical application of fluralaner against C. felis and O. cynotis natural infestation in stray (study 1) and owned (study 2) cats in central and southern Italy.

RESULTS

The number of live fleas found on each cat on Day 0 ranged from 1 to more than 30 (arithmetic mean live flea count = 11.9 in study 1; 14.6 in study 2) while no live fleas were found on days 7 and 84 post topical application of fluralaner. The number of live mites found on each cat on Day 0 ranged from 1 to 42 (arithmetic mean live mite count = 6.4 in study 1; 8.9 in study 2) while no live mites were found on days 7 and 84 post topical application of fluralaner.

CONCLUSIONS

Topical fluralaner completely eliminated fleas and ear mites from infested cats and was 100% effective against both parasites up to 84 days after treatment.

Itching for change: Embracing modern flea and tick product development

The development and regulatory approval of ectoparasiticides, including flea and tick control products, involves decades-old methods and the use of large numbers of animals to evaluate toxicity and efficacy. Animals also are used to rear (breed and feed) fleas and ticks for later use in testing. Non-animal methods for regulatory-required testing and rearing currently exist and, with further development, others could soon become available. Here we provide an overview of the state-of-the-science of non-animal methods for rearing and regulatory-required efficacy testing of flea and tick control products. Several remaining challenges as well as recommendations on the steps needed to replace animals in the evaluation of these products are discussed.

Effect of uncertainty in total parasite infestation on accuracy and precision of estimates of ectoparasiticide efficacy

In animal studies of ectoparasiticide efficacy the total number of parasites with which experimental animals are infested is not always equal to the intended number of parasites (usually n=50 per experimental animal in the case of ticks, and n=50 or n=100 in the case of fleas). That is, in the practical implementation of a study protocol, the infestation of experimental animals may be subject to variability so that total infestation is not known precisely. The purpose of the present study is to assess the impact of this variability on the accuracy and precision of efficacy estimates. The results of a thorough simulation study show clearly that uncertainty in total parasite infestation - of the magnitude encountered in well-controlled animal studies - has virtually no effect on the accuracy and precision of estimators of ectoparasiticide efficacy.

Accuracy and precision of alternative estimators of ectoparasiticide efficacy

While there is consensus that the efficacy of parasiticides is properly assessed using the Abbott formula, there is as yet no general consensus on the use of arithmetic versus geometric mean numbers of surviving parasites in the formula. The purpose of this paper is to investigate the accuracy and precision of various efficacy estimators based on the Abbott formula which alternatively use arithmetic mean, geometric mean and median numbers of surviving parasites; we also consider a maximum likelihood estimator. Our study shows that the best estimators using geometric means are competitive, with respect to root mean squared error, with the conventional Abbott estimator using arithmetic means, as they have lower average and lower median root mean square error over the parameter scenarios which we investigated. However, our study confirms that Abbott estimators using geometric means are potentially biased upwards, and this upward bias is substantial in particular when the test product has substandard efficacy (90% and below). For this reason, we recommend that the Abbott estimator be calculated using arithmetic means.