Establishing the discriminating concentration for permethrin and fipronil resistance in Rhipicephalus sanguineus (Latreille) (Acari: Ixodidae), the brown dog tick

Determination of the discriminant doses to identify resistance to fipronil, flumethrin and coumaphos, in Rhipicephalus sanguineus s.l. (Acari: Ixodidae) from Mexico

Rhipicephalus sanguineus s.l. is an intra- and peridomiciliary tick of medical and veterinary importance, whose control is carried out through the application of various ixodicides, to which it can develop resistance. The objective of this work was to determine the discriminant doses (d.d.) to identify resistance against three ixodicides - fipronil, flumethrin and coumaphos - in R. sanguineus s.l. larvae originating from Mexico. Engorged ticks were collected from naturally infested dogs residing in rural communities in five Mexican states; the dogs had no history of recent treatment with ixodicides. All ticks were identified as R. sanguineus s.l. They were incubated for 25 days and their progeny was used in the larval package test (LPT) to be exposed to d.d. as determined in Rhipicephalus microplus, and those that were susceptible were analyzed using the LPT with six concentrations, for fipronil from 0.1 to 0.003125%, for flumethrin from 0.02 to 0.000625% and for coumaphos from 0.4 to 0.0125%. Mortality was analyzed with Probit methodology, to calculate the 50 and 99% lethal concentrations (LC50 and LC99). The d.d. was determined as a consensus value by multiplying the LC99 value × 2. Nine double susceptible samples (fipronil + flumethrin) and one triple susceptible sample (fipronil + flumethrin + coumaphos) were found; the d.d. determined were fipronil 0.05%, flumethrin 0.01% and coumaphos 0.43%. These doses can be used to rapidly and inexpensively identify resistant populations in samples collected in the field.

Phenotypic and genotypic characterization of dog tick Rhipicephalus sanguineus sensu lato (Acari: Ixodidae) resistance to deltamethrin in Benin

The aim of this study was to evaluate the phenotypic and genotypic resistance of Rhipicephalus sanguineus sensu lato to deltamethrin in dogs in the municipality of Natitingou in Benin. In this study, the collection and identification of ticks, Larval Packet Test and specific allele PCR were the main methods used. A total of 41 dogs were examined and 420 ticks were collected in six areas which includes: Tchrimina, Yokossi, Boriyoure, Berécingou, Péporiyakou and Perma. Three species of ticks were identified and they include: R. sanguineus s.l., Rhipicephalus microplus and Haemaphysalis spp. However, R. sanguineus s.l. was the most abundant tick species (9.85) and had the highest parasitic intensity (10.36). The results of the Larval Packet Test showed that the larvae of R. sanguineus s.l. developed a phenotypic resistance against deltamethrin, particularly in the Bérécingou area where resistance ratios of LC50 and LC95 of R. sanguineus s.l. compared to a susceptible strain were 1.591 (1.025-3.054) and 65.339 (20.235-579.825) respectively. The molecular study of the sodium channel gene revealed three genotypes namely the susceptible genotype (SS), the heterozygous genotype (SR) and the resistant genotype (RR), which correlates with the phenotypic results. This information is fundamental to improve monitoring and resistance management strategies of R. sanguineus s.l. ticks to pyrethroids.

Practices employed by veterinary practitioners for controlling canine gastrointestinal helminths and ectoparasites

The present study attempted to evaluate the practical experience and methods employed by Brazilian veterinary practitioners for control of parasites. Twenty-one questions were asked of 403 veterinary practitioners based in different climatic zones with reference to parasite epidemiology from the country. Administration of a combination of drugs at three-month intervals was the most common regime recommended for prophylaxis against gastrointestinal helminths, with a single treatment repeated after 15 days. Routine prophylaxis against dog ectoparasites was recommended by 82.4% veterinary practitioners, and 46.6% changed the drug compound used. Monthly prophylaxic treatments for ectoparasites, using systemic, topical and/or collar-impregnated drugs, was recommended by 21.5% veterinary practitioners. Side-effects of ectoparasiticide-impregnated collars were suspected by 58% of the veterinary practitioners. Isoxazolines were the most frequently used chemical group to treat ectoparasites in dogs. Poor efficacy of fipronil in controlling ticks was suspected by 79.5% of the veterinary practitioners. The isoxazolines and combination of anthelmintic compounds are the most common drugs to prevent or treat ectoparasites and gastrointestinal nematodes, respectively. The suspect of the inefficacy of antiparasitic drugs is shared among the veterinary practitioners from part of Brazil. Guidelines are needed, specifically for the control of gastrointestinal helminths and ectoparasites in Brazilian dogs.

Evaluation of Fipronil Susceptibility in the Lone Star Tick (Acari: Ixodidae)

The lone star tick, Amblyomma americanum Linnaeus, is ubiquitously present in the southeastern United States and will readily parasitize humans and companion animals. Fipronil is the active ingredient in several topically applied products used to manage ticks and fleas on companion animals. Reducing ectoparasite infestations on companion animals decreases the risk that pathogens vectored by these pests are transmitted to these animals and their owners. However, dependence on acaricides can promote the development of resistance. In this study, the Food and Agriculture Organization of the United Nations larval packet test was used to determine the lethal concentration (LC) values and discriminating concentration (DC) for fipronil in the lone star tick. The DC was calculated as 0.02080%. The low magnitude of the DC value suggests that fipronil is an effective active ingredient for A. americanum management. With the LC and DC values determined, emergent resistance can be monitored, potentially allowing for intervention should tolerance develop in A. americanum populations that are in frequent contact with humans and their companion animals.

Identification of permethrin and etofenprox cross-tolerance in Rhipicephalus sanguineus sensu lato (Acari: Ixodidae)

BACKGROUND

The brown dog tick, Rhipicephalus sanguineus sensu lato (Latreille; Acari: Ixodidae), is a peridomestic ectoparasite of dogs and occasionally humans. In some populations, lack of integrated pest management practices and overuse of pesticides has resulted in high levels of resistance to multiple active ingredients. In this study, we established the etofenprox discriminating concentration (DC) and three additional screening concentrations to evaluate resistance status. Using mortality results, cross-resistance was investigated in brown dog tick populations from five geographically disparate regions, including Asia, Africa, Europe, North America, and the Caribbean, following exposure to the DC for both etofenprox and permethrin separately. Subsequently, using both larval packet tests and molecular methods, etofenprox resistance was investigated.

RESULTS

The etofenprox DC was set at 0.51%, which allows for the rapid screening of peridomestic brown dog tick populations for resistance to this active ingredient. Cross-tolerance to two sodium channel-inhibiting pesticides, permethrin and etofenprox, was observed in one population.

CONCLUSION

Our study has provided a single etofenprox concentration that can be used in larval packet tests to determine resistance status in collected peridomestic brown dog ticks, which is particularly important when a single to a few engorged adult ticks are provided for evaluation. Although metabolic resistance is presumed to be the primary resistance mechanism, a sodium channel mutation also confers tolerance to etofenprox at the DC. © 2019 Society of Chemical Industry.

Annotated List of the Hard Ticks (Acari: Ixodida: Ixodidae) of New Jersey

Standardized tick surveillance requires an understanding of which species may be present. After a thorough review of the scientific literature, as well as government documents, and careful evaluation of existing accessioned tick collections (vouchers) in museums and other repositories, we have determined that the verifiable hard tick fauna of New Jersey (NJ) currently comprises 11 species. Nine are indigenous to North America and two are invasive, including the recently identified Asian longhorned tick, Haemaphysalis longicornis (Neumann, 1901). For each of the 11 species, we summarize NJ collection details and review their known public health and veterinary importance and available information on seasonality. Separately considered are seven additional species that may be present in the state or become established in the future but whose presence is not currently confirmed with NJ vouchers. We compare our list of hard ticks in NJ with those from neighboring states (Connecticut, New York, Pennsylvania, Delaware, and Maryland), discuss the importance of vouchers in tick research and surveillance, and examine the likelihood and public health consequences of additional hard tick species becoming established in NJ.

A randomised, blinded, controlled field study to assess the efficacy and safety of lotilaner tablets (Credelio™) in controlling fleas in client-owned dogs in European countries

Background

Lotilaner is a novel isoxazoline developed for oral administration to dogs. In laboratory studies, lotilaner was shown to be safe and to produce a rapid flea and tick knockdown, with a sustained speed of kill for at least a month post-treatment. A study was undertaken to demonstrate the efficacy, safety and palatability of three monthly doses of lotilaner flavoured chewable tablets (Credelio™, Elanco) in controlling fleas under field conditions in Europe.

Methods

Dogs were enrolled at 17 veterinary clinics across Germany, Hungary and Portugal. Qualifying households having no more than three dogs and one primary dog with at least five fleas was randomised 2:1 to a lotilaner (minimum dose rate 20 mg/kg) or a topical fipronil group (administered per label). There were 128 and 64 households allocated to the lotilaner and fipronil groups, respectively. Treatments were dispensed to owners on Days 0, 28 and 56; supplementary household dogs received the same treatment as the primary dog. Post-enrollment flea counts and flea allergy dermatitis (FAD) assessments were made on primary dogs on Days 14, 28, 56 and 84. Efficacy calculations were based on geometric mean percent reductions of live flea counts versus pre-treatment counts on Day 0. The safety and palatability of lotilaner tablets were also assessed.

Results

Lotilaner efficacy was 99.1, 99.5, 99.9 and 99.8% on Days 14, 28, 56 and 84, respectively. Corresponding reductions for fipronil were 93.4, 91.2, 94.4 and 97.0%. Lotilaner was superior to fipronil at all post-Day 0 assessments (t₍₁₈₆₎ ≥ 3.43, P ≤ 0.0007). At every post-treatment assessment, at least 90% of lotilaner-treated dogs were flea-free (98.4% on Day 84); fewer than 90% of fipronil group dogs were flea-free on the same time points. Lotilaner flavoured chewable tablets were palatable, and both products were well tolerated. Lotilaner alleviated or eliminated clinical signs of FAD, including pruritus.

Conclusions

Under field conditions in Europe, lotilaner flavoured chewable tablets were greater than 99% effective in eliminating fleas from dogs at the first post-treatment assessment (Day 14). Efficacy was maintained through Day 84, with corresponding improvements in FAD. Lotilaner tablets were palatable and safe and provided superior flea control to fipronil.

Electronic supplementary material

The online version of this article (10.1186/s13071-017-2479-8) contains supplementary material, which is available to authorized users.

First report of amitraz and cypermethrin resistance in Rhipicephalus sanguineus sensu lato infesting dogs in Mexico

Engorged female Rhipicephalus sanguineus sensu lato (Ixodida: Ixodidae) were collected from dogs in the state of Yucatán, Mexico. Fourteen tick populations were collected from dogs at seven veterinary clinics, four residential homes and three cattle farms. The larval immersion test was used in the progeny of collected adult females to test susceptibility to amitraz and cypermethrin. Dose-mortality regressions, 50% lethal concentrations (LC₅₀ ), confidence intervals and slope were estimated by probit analysis. For amitraz, 12 tick populations (85.7%) were classified as resistant and low inter-population variation in the phenotypic level of resistance was evident [resistance ratios (RRs) at LC₅₀ : 1.0-13.0]. For cypermethrin, 12 tick populations (85.7%) were classified as resistant and substantial inter-population variation in the phenotypic level of resistance was evident (RRs at LC₅₀ : 1.0-104.0). Thus, amitraz resistance in R. sanguineus s.l. is common, but generally occurs at low levels; however, alarmingly high levels of cypermethrin resistance are present in R. sanguineus s.l. populations in dogs in Yucatán, Mexico. The intensive use of both acaricides to control ectoparasites on dogs is likely to lead to more serious resistance problems that may cause high levels of control failure in the future.

Evaluation of the in vitro expression of ATP binding-cassette (ABC) proteins in an Ixodes ricinus cell line exposed to ivermectin

Background

Ticks are among the most important vectors of pathogens causing human and animal disease. Acaricides are used to control tick infestation, although there are increasing reports of resistance. Recently, over-expression of ATP-binding cassette (ABC) transporter proteins (P-glycoproteins, PgP) has been implicated in resistance to the acaricide ivermectin in the ticks Rhipicephalus (Boophilus) microplus and Rhipicephalus sanguineus sensu lato. Ixodid tick cell lines have been used to investigate drug resistance mechanisms. The aim of the present study was to evaluate expression of several PgPs in the Ixodes ricinus-derived cell line IRE/CTVM19 and to determine modulation of expression following treatment with ivermectin.

Findings

IRE/CTVM19 cells were treated with different concentrations of ivermectin (0, 11, 22 or 33 μM) and incubated for 10 days. Evaluation of viability and relative expression of ABCB1, ABCB6, ABCB8 and ABCB10 genes were carried out at day 10 post treatment. Cell viability ranged between 84 % and 92 % with no significant differences between untreated and treated cells. qRT-PCR showed that ABC pump expression was not significantly modulated by ivermectin treatment. Expression of the ABCB8 PgP subfamily revealed a biphasic trend, based on the ivermectin concentration. ABCB6 and ABCB10 gene expression was not modulated by ivermectin treatment and ABCB1 expression was not detected.

Conclusions

This is the first report of PgP expression in an I. ricinus-derived tick cell line. Development of an in vitro model for the study of acaricide resistance mechanisms would greatly facilitate screening for drug resistance in ticks.