A new approach to characterization of the resistance of populations of Rhipicephalus microplus (Acari: Ixodidae) to organophosphate and pyrethroid in the state of Minas Gerais, Brazil

Tick treatment practices in the field: Access to, knowledge about, and on-farm use of acaricides in Laikipia, Kenya

The prevention of tick-borne diseases is a major challenge for livestock production globally. Tick control strategies include the use of acaricides, but the prescribed strategies do not achieve the desired results in several countries, including Kenya. To better understand how tick treatment practices, contribute to reported tick treatment failures, we assessed livestock owners' acaricide procurement, level of knowledge about acaricides and tick resistance, and how they apply acaricides. We also assessed the quality of the commonly available acaricides. We focused on three livestock systems in Laikipia County, Kenya: two private ranches; one community ranch whose members communally graze their cattle and acquire and apply acaricides; and individual livestock owners in two pastoral communities who individually graze their cattle and acquire and apply acaricides. Through interviews and focus group discussions we assessed; access to acaricides, livestock owners' knowledge, and acaricide use practices; interview data were triangulated with participant observations (n = 107). We analysed nine commonly used acaricides to determine the active ingredient concentration and we determined the concentration of active ingredients in acaricide dilutions collected on farms. All livestock owners had access to and used chemical acaricides for tick control, predominantly amitraz-based. Private ranchers bought one amitraz-based acaricide in bulk directly from the manufacturer, while all other livestock owners bought from agrovet shops. The livestock owners acquired knowledge about acaricides from their own experiences and through experience-based recommendations from peers, but not from the technical information provided by the manufacturers and agrovet shops. All pastoral livestock frequently changed acaricide brand and active ingredient class. A large majority of pastoralists (86%) mixed acaricide brands within and across active ingredient classes; a smaller majority (56%) mixed acaricides with crop pesticides and insecticides. Our lab tests confirmed the content description on the labels bought from agrovet shops. However, on-farm acaricide dilutions from all three livestock systems deviated from the level recommended for effective treatment. If too diluted, the acaricide does not kill ticks, promoting resistance development. If too concentrated, this increases environmental contamination and raises public health concerns. Livestock owners lack a technical understanding of the functioning of acaricides, compromising their use and effectiveness. The widely adopted mixing of acaricides with insecticides and pesticides raises serious health concerns.

Plant-Derived Natural Compounds for Tick Pest Control in Livestock and Wildlife: Pragmatism or Utopia?

Ticks and tick-borne diseases are a significant economic hindrance for livestock production and a menace to public health. The expansion of tick populations into new areas, the occurrence of acaricide resistance to synthetic chemical treatments, the potentially toxic contamination of food supplies, and the difficulty of applying chemical control in wild-animal populations have created greater interest in developing new tick control alternatives. Plant compounds represent a promising avenue for the discovery of such alternatives. Several plant extracts and secondary metabolites have repellent and acaricidal effects. However, very little is known about their mode of action, and their commercialization is faced with multiple hurdles, from the determination of an adequate formulation to field validation and public availability. Further, the applicability of these compounds to control ticks in wild-animal populations is restrained by inadequate delivery systems that cannot guarantee accurate dosage delivery at the right time to the target animal populations. More work, financial support, and collaboration with regulatory authorities, research groups, and private companies are needed to overcome these obstacles. Here, we review the advancements on known plant-derived natural compounds with acaricidal potential and discuss the road ahead toward the implementation of organic control in managing ticks and tick-borne diseases.

Menace of acaricide resistance in cattle tick, Rhipicephalus microplus in India: Status and possible mitigation strategies

Livestock in general and dairy sector in particular plays a vital role in the Indian economy and in the socio-economic development of millions of people. Rhipicephalus microplus, a one-host and the most prevalent cattle tick in various agro climatic zones of India. This tick species is responsible for severe economic losses to livestock owners both through the direct effects of blood sucking, injection of toxins and indirectly by transmitting pathogens. Due to inadvertent and indiscriminate use of chemicals to kill ticks, field tick population has developed resistance to almost all chemicals that are used to manage them. The intention of this review is to provide the current status of resistance in ticks, the possible mechanisms of resistance operating in the tick population, factors contributing to the development of resistance and the managemental strategies.

Cattle herd shearing can help to control Rhipicephalus microplus ticks

Given the difficulties of controlling the tick Rhipicephalus microplus due to acaricide resistance, this study aimed to ascertain whether shearing could reduce infestation in cattle. 17 taurine cattle were sheared on the anterior third of one randomly selected side. Shearing was undertaken using a machine with a blade, leaving coats with a thickness of 1 mm. Subsequently, eight evaluations were performed once a week, counting adult females of R. microplus with a diameter > 4.5 mm on the anterior third of both sides (shorn and unshorn). The coat length was also monitored by taking five hair samples from each animal fortnightly (1, 15, 29, 43 and 57 days post shorn) from a central area of both shoulders (shorn and unshorn). The tick counts and hair length data were transformed for normalisation and were analysed using mixed models. The tick and hair length means were significantly higher for the unshorn side. Tick counts were significantly lower on the sheared side until the fifth evaluation, with the final three presenting no differences between the sides. The hair length was significantly lower for the sheared side during the five evaluations. We conclude that as the hair length increased, there was also an increase in the number of ticks on the sheared side. Although this method is not practical for large herds, it can be deemed an option in extreme conditions of tick infestation. In addition, the study reinforces the suggestion that the selection and/or use of cattle with shorter hairs may contribute to reduced tick infestation.

Molecular markers and their application in the monitoring of acaricide resistance in Rhipicephalus microplus

Monitoring acaricide resistance and understanding the underlying mechanisms are critically important in developing strategies for resistance management and tick control. Identification of single nucleotide polymorphisms in the acaricide-resistant associated gene of Rhipicephalus microplus has enabled the development of molecular markers for detection and monitoring of resistance against different types of acaricide. There are many molecular markers developed for resistance monitoring, including mutations on target genes such as sodium channel, acetylcholinesterase, carboxylesterase, β-adrenergic octopamine receptor, octopamine-tyramine etc. Molecular genotyping through molecular markers can detect the presence of resistance-associated genes in a tick population before it reaches high frequency. This review aims to provide an update on the various molecular markers discovered to date from different regions of the world.

Management and control of parasites on dairy farms in northwestern region of São Paulo state

Dairy cattle farming is of great economic and social importance in all Brazilian's regions. Parasites can reduce milk productivity, especially the tick Rhipicephalus (Boophilus) microplus. This study consisted of a questionnaire answered by 40 milk producers in the northwestern region of the State of São Paulo. The aim was to ascertain how these producers controlled ticks and other parasites. Very many of them knew nothing about the biological cycle of the cattle tick or about strategic control or acaricide efficacy tests. The majority (87.5%) controlled ticks at a high frequency, without technical criteria and care to apply the acaricide. Spraying was the most used mode of acaricide application (95%) and endectocides were used by 45%. Cattle tick fever was the harm most associated with ticks (87.5%) followed closely by screwworm (77.5%). However, 65% were satisfied with their tick control. About the control of others parasites, all dewormed at least twice a year their animals; 65% were controlling horn fly; 40% had problems with screwworm. The interviewers had in general good level of education and the farms generally exhibited a high degree of technology for milk production on pasture because half of them received technical assistance frequently.

Emergence of multi-acaricide resistant Rhipicephalus ticks and its implication on chemical tick control in Uganda

Background

Acaricide failure has been on the rise in the western and central cattle corridor of Uganda. In this study, we identified the tick species associated with acaricide failure and determined their susceptibility to various acaricide molecules used for tick control in Uganda.

Methods

In this cross sectional study, tick samples were collected and identified to species level from 54 purposively selected farms (from 17 districts) that mostly had a history of acaricide failure. Larval packet test was used to screen 31 tick populations from 30 farms for susceptibility at discriminating dose (DD) and 2 × DD of five panels of commercial acaricide molecules belonging to the following classes; amidine, synthetic pyrethroid (SP), organophosphate (OP) and OP-SP co-formulations (COF). Resistance was assessed based on World Health Organization criteria for screening insecticide resistance.

Results

Of the 1357 ticks identified, Rhipicephalus (Rhipicephalus) appendiculatus and Rhipicephalus (Boophilus) decoloratus were the major (95.6 %) tick species in farms sampled. Resistance against SP was detected in 90.0 % (27/30) of the tick populations tested. Worryingly, 60.0 % (18/30) and 63.0 % (19/30) of the above ticks were super resistant (0 % mortality) against 2 × DD cypermethrin and deltamethrin, respectively. Resistance was also detected against COF (43.3 %), OP chlorfenvinphos (13.3 %) and amitraz (12.9 %). In two years, 74.1 % (20/27) of the farms had used two to three acaricide molecules, and 55.6 % (15/27) rotated the molecules wrongly. Multi-acaricide resistance (at least 2 molecules) was detected in 55.2 % (16/29) of the resistant Rhipicephalus ticks and significantly associated with R. decoloratus (p = 0.0133), use of both SP and COF in the last 2 years (p < 0.001) and Kiruhura district (p = 0.0339). Despite emergence of amitraz resistance in the greater Bushenyi area, it was the most efficacious molecule against SP and COF resistant ticks.

Conclusion

This study is the first to report emergence of super SP resistant and multi-acaricide resistant Rhipicephalus ticks in Uganda. Amitraz was the best acaricide against SP and COF resistant ticks. However, in the absence of technical interventions, farmer-led solutions aimed at troubleshooting for efficacy of multitude of acaricides at their disposal are expected to potentially cause negative collateral effects on future chemical tick control options, animal welfare and public health.

Electronic supplementary material

The online version of this article (doi:10.1186/s13071-015-1278-3) contains supplementary material, which is available to authorized users.

Multiple mutations in the acetylcholinesterase 3 gene associated with organophosphate resistance in Rhipicephalus (Boophilus) microplus ticks from Punjab, India

The organophosphate (OP) resistance status in Rhipicephalus (Boophilus) microplus ticks collected from seventeen districts located in the northwestern Indian state, Punjab were characterized using three data sets (bioassay, biochemical and molecular assays). Adult immersion test (AIT) was adopted and the resistance factors (RF) for the field isolates were determined. Resistance to malathion was detected in 12 isolates among which 11 showed level I resistance status while level II status was recorded in one isolate (RF of 5.35). To understand the possible mechanism of resistance development, acetylcholinesterase (AChE) activity and gene sequences of the AChE3 were analyzed. A significantly (P<0.001) higher level of percent uninhibited AChE activity was recorded in all field isolates (36.36±0.46-43.77±1.21) in comparison to the susceptible population (29.39±0.40). The AChE activity was positively correlated with RF against malathion with a correlation coefficient (r) of 0.359. Analysis of nucleotides and their deduced amino acids sequences of partial AChE3 gene revealed the presence of six amino acid substitutions (I48L, I54V, V71A, I77M, S79P and R86Q). Three novel amino acid substitutions (V71A, I77M and S79P) in partial AChE3 gene were also identified in some of the isolates which may possibly have a role in OP resistance development. The PCR-RFLP assay with HaeIII revealed the presence of restriction site corresponding to R86Q mutation in all the field isolates along with an additional restriction site in seven field isolates corresponding to V71A mutation. The results of the study indicate the involvement of both insensitive AChE and higher percent uninhibited AChE activity as the possible mechanism in these field isolates.

Effect of a spray formulation on the reproductive parameters of a susceptible population of Rhipicephalus (Boophilus) microplus

The number of studies emphasizing the possible damage that acaricidal spray formulations can cause on engorged female ticks' reproductive parameters is small. The present study evaluated the deleterious effects of a spray formulation (dichlorvos 60% + chlorpyrifos 20%) on the reproductive parameters of a susceptible population of Rhipicephalus (B.) microplus females, using the Stall Test. The ticks were allocated randomly to treatments according to the mean numbers of females detached from each cow on days -3, -2 and -1 and the cattle pen location. The numbers of engorged female ticks that naturally detached from the cattle were counted daily from day 1 to day 30. For each group, 20 detached engorged female ticks or the available number collected daily were evaluated regarding reproductive parameters. Associations of organophosphates demonstrated elevated acaricidal efficacy, as well as deleterious effects on the reproductive parameters of R. (B.) microplus females. The engorged female weight (days 1 to 7), weight of egg masses (days 5 to 10) and larval hatching percentage (days 5 to 19) were decreased (P ≤ 0.05). It is possible that a formulation can lead to deleterious effects on R. (B.) microplus females when the tick population analyzed shows elevated sensitivity towards a particular formulation. However, further studies need to be conducted.

A comparison of three different methodologies for evaluating Rhipicephalus (Boophilus) microplus susceptibility to topical spray compounds

This study aimed to compare three different methodologies (Adult Immersion Tests, field trials with naturally infected animals, and a Stall Test using artificially infested cattle) to evaluate the efficacy of two topical formulations that we administered as whole body sprays (15% Cypermethrin+30% Chlorpyriphos+15% Fenthion-Colosso(®) FC 30, Ouro Fino Agronegócios; and 60% Dichlorvos+20% Chlorpyriphos-Ectofós(®), Vallée Saúde Animal Ltd.), against a susceptible strain of Rhipicephalus (Boophilus) microplus. To achieve this objective, two natural infestation trials were conducted, as well as two artificial infestation trials (Stall Tests) and two Adult Immersion Tests (AIT). The AIT results showed that both spray formulations achieved 100% efficacy against R. (B.) microplus fully engorged females. However, when observing results obtained by field trials (natural infestations) and Stall Tests, none of these topically applied compounds reached 100% efficacy or affected the reproductive capacity of the fully engorged female ticks. Additional studies must be conducted to compare these in vivo methodologies with different in vitro techniques, such as the Larval Packet Test. However, based on results obtained here, we can conclude that depending on the spray formulations used, the AIT can overestimate acaricidal efficacy and values of reproductive efficiency of such compounds against R (B.) microplus. Specifically, when dealing with spray formulations in the Stall Tests, the period of residual action can increase because these animals are sheltered from contact with environmental factors that might interfere with the efficacy of the products tested. It may be necessary to take in vivo trial results into consideration (such as field trials with naturally infested animals or Stall Tests) to standardize a specific in vitro assay, such as the Adult Immersion Test.

Effects of fluazuron (2.5 mg/kg) and a combination of fluazuron (3.0 mg/kg) + abamectin (0.5 mg/kg) on the reproductive parameters of a field population of Rhipicephalus (Boophilus) microplus on experimentally infested cattle

The current study assessed the deleterious effects of two formulations of fluazuron (2.5 mg/kg fluazuron and a combination of 3.0 mg/kg fluazuron + 0.5 mg/kg abamectin) on the reproductive parameters of engorged Rhipicephalus (Boophilus) microplus females that naturally detached from experimentally infested cattle in two experiments. Based on the obtained results, it can be concluded that fluazuron (2.5 mg/kg) showed deleterious effects only on the hatchability percentage in the period of 2-7 post-treatment days of this ectoparasite's engorged females. On the other hand, the fluazuron (3.0 mg/kg) + abamectin (0.5 mg/kg) combination presented harmful effects over reproductive parameters of this tick species. Further studies should be performed with a known tick population (reference susceptible strain) to determine the effect of these formulations on the reproductive parameters and to elucidate if this field population is fluazuron resistant.