Resumo
Background: In several countries, including Brazil, the livestock industry plays a key role in the country's economy. Brazil has the second largest bovine herd in the world and the biggest commercial herd. Ticks are an ongoing problem for both large operation cattle producers and small family farmers. Rhipicephalus microplus causes expressive losses in cattle breeding, since it occurs in important beef production zones like South America, Africa, and Oceania. Some of the negative consequences of tick infestation to cattle breeding are anemia, loss in milk and beef production, and transmission of Babesia bovis and B. bigemina. Significant losses are caused by the cattle tick (R. microplus) in several regions of the world, costing around US$ 3.3 billion per year to the Brazilian livestock industry alone. The tick control methods are mainly based on synthetic acaricides. However, the improvement of current tick control requires the identification of new molecular targets in tick physiology and development of molecule compounds to target important physiology pathways. The strategies proposed to address this issue are expand the knowledge about the molecules involved in the detoxification of chemicals to enhance the efficacy of the acaricides as well as to develop new compounds for chemical control. Review: Tick control is currently based on chemical acaricides; however, effective control and prevention of tick infestation remain distant goals. In recent decades, a progressive decrease in the efficiency of acaricides due to drug resistance has been observed. Acaricide resistance is an evolutionary adaptation, which implies the existence of behavioral and physiological mechanisms that allow the survival of resistant individuals. Four resistance mechanisms are described: behavioral resistance, reduced drug penetration, target site insensitivity and increased drug detoxification. Augmented drug detoxification may be due to increased activity of enzymes or transporters due to increased gene expression or mutations in some genes. Research focus on mechanisms of acaricide resistance in ticks characterized detoxification pathways based on (1) increased activity of enzymes (cytochrome p450, esterase and GST) which play a role in biochemically altering acaricides towards decreased toxicity and, (2) enhanced excretion of the modified less toxic compounds. To bypass the current problems, a better understanding of the biology, physiology, and molecular biology of the mechanisms of resistance to acaricides is fundamental to prolong their efficiency in controlling ticks. Moreover, identifying the genes and proteins associated with resistance can support in the development of more sensitive diagnostic methods to identify acaricide resistance, as well as improving control strategies. Discussion: In the last years, many researchers have been studying resistance mechanisms and important advances have been made which showed that, in several tick species, ABC transporters, esterases, P-450 cytochromes and glutathione-S-transferases participate in acaricide resistance. The characterization of the alterations in the targets in tick physiology and identification of new drugs with potential to tick control are crucial goals to increase tick control
Assuntos
Animais , Piretrinas/administração & dosagem , Resistência a Inseticidas/fisiologia , Rhipicephalus , Esterases , Glutationa S-Transferase pi , Inseticidas Organofosforados , Acaricidas/administração & dosagemResumo
Field samples of Rhipicephalus (Boophilus) microplus from the state of Rio Grande do Sul, Brazil, were assessed using the following methods: larval packet test (LPT), larval immersion test (LIT) and syringe immersion test (SIT). The following parameters were determined for each population and for the Mozo susceptible reference strain: lethal concentration for 50% (LC50) with its 95% confidence interval (95% CI), regression line slope and resistance ratio (RR). Using the LPT, only one population was susceptible to amitraz, presenting a RR of 1.9. Using the same technique, the other populations presented RRs of between 92.9 and 3445.8 and were considered resistant. The LC50 of the Mozo strain calculated using the LPT, LIT and SIT was 2.9, 27.3, and 52.7 µg/mL, respectively. In general, a good fit to the probit statistical model was only achieved using the LPT. The results obtained in this study impair recommendations for using the LIT and SIT to diagnose amitraz resistance in R. (B.) microplus populations. Additional studies are required to improve the sensitivity of these tests in relation to the LPT.
Amostras de Rhipicephalus (Boophilus) microplus coletadas à campo no Rio Grande do Sul, Brasil, foram analisadas pelos seguintes métodos: teste do pacote de larvas (TPL), teste de imersão de larvas (TIL) e teste de imersão em seringas (TIS). Os seguintes parâmetros foram determinados para cada população e para a amostra referência suscetível Mozo: concentração letal para 50% (CL50) e seu intervalo de confiança de 95% (IC95%), inclinação da reta de regressão e os fatores de resistência (FR). Pelo TPL, apenas uma população foi sensível ao amitraz, com FR de 1,9. Utilizando a mesma técnica, as outras amostras apresentaram FR entre 92,9 e 3445,8 sendo consideradas resistentes. As CL50 da cepa Mozo calculadas por meio do TPL, TIL e TIS foram 2,9, 27,3 e 52,7 µg/mL, respectivamente. De forma geral, a adequação ao modelo estatístico de probitos só foi alcançada com o uso do TPL. Os resultados obtidos no presente estudo limitam a recomendação de uso do TIL e TIS para diagnóstico de resistência ao amitraz em populações de R. (B.) microplus. Estudos adicionais são necessários para aprimorar a sensibilidade destes testes em relação ao LPT.
Assuntos
Animais , Bioensaio/métodos , Inseticidas/farmacologia , Rhipicephalus/efeitos dos fármacos , Toluidinas/farmacologia , Larva/efeitos dos fármacos , Testes de Sensibilidade ParasitáriaResumo
Horn fly resistance to pyrethroid insecticides occurs throughout Brazil, but knowledge about the involved mechanisms is still in an incipient stage. This survey was aimed to identify the mechanisms of horn fly resistance to cypermethrin in Mato Grosso do Sul state, Brazil. Impregnated filter paper bioassays using cypermethrin, synergized or not with piperonyl butoxide (PBO) and triphenyl phosphate (TPP), were conducted from March 2004 to June 2005 in horn fly populations (n = 33) from all over the state. All populations were highly resistant to cypermethrin, with resistance factors (RF) ranging from 89.4 to 1,020.6. Polymerase chain reaction (PCR) assays to detect the knockdown resistance (kdr) mutation also were performed in 16 samples. The kdr mutation was found in 75% of the tested populations, mostly with relatively low frequencies (<20%), and was absent in some highly resistant populations. Addition of TPP did not significantly reduce the LC50 in any population. However, PBO reduced LC50s above 40-fold in all tested populations, resulting in RFs ≤ 10 in most cases. Horn fly resistance to cypermethrin is widespread in the state, being primarily caused by an enhanced activity of P450 mono-oxygenases and secondarily by reduced target site sensitivity.
Resistência da mosca-dos-chifres a inseticidas piretróides ocorre em todo o país, entretanto, o conhecimento sobre os mecanismos envolvidos é ainda incipiente. Este estudo objetivou identificar os mecanismos de resistência desta mosca à cipermetrina em Mato Grosso do Sul. Bioensaios utilizando papéis impregnados com cipermetrina, isoladamente ou sinergizada por butóxido de piperonila (PBO) ou trifenil fosfato (TPP), foram realizados de março∕2004 a junho∕2005 em 33 populações. Todas as populações apresentaram elevada resistência à cipermetrina, com fatores de resistência (FR) variando de 89,4 a 1.020,6. Ensaios de reação em cadeia da polimerase (PCR) visando a detecção de kdr ("knockdown resistance") foram realizados em 16 amostras. A mutação kdr foi detectada em 75% das populações, geralmente em baixas frequências (<20%) e ausente em algumas populações resistentes. A adição de TPP não reduziu significativamente a CL50 em nenhuma população. Entretanto, o PBO reduziu em mais de 40 vezes a CL50 de todas as populações testadas, resultando em FR ≤ 10 na maioria dos casos. Resistência da mosca-dos-chifres à cipermetrina encontra-se disseminada no estado, sendo causada primariamente por um aumento da atividade de P450 mono-oxigenases e secundariamente pela redução da sensibilidade do sítio de ação do inseticida.
Assuntos
Animais , Inseticidas/farmacologia , Muscidae/efeitos dos fármacos , Piretrinas/farmacologia , Brasil , Resistência a InseticidasResumo
Cattle ticks Rhipicephalus (Boophilus) microplus are mainly controlled in Brazil by means of acaricide products, without any official policies in this regard. Acaricides continue to be sold indiscriminately, and this has contributed towards making the problem of resistance widespread, thus making diagnosis and monitoring of tick resistance essential. Here, bioassays (larval packet test) were performed on tick populations from the states of Rio Grande do Sul and Mato Grosso do Sul regarding their susceptibility to cypermethrin, deltamethrin and flumethrin. All the tick samples tested showed resistance to cypermethrin (10) (resistance factor (RF) ranging from 5.6 to 80.3) and deltamethrin (10) (RF ranging from 2.4 to 83.1). Six out of eight populations were resistant to flumethrin (RF ranging from 3.8 to 8.2). PCR molecular analyses did not show any T2134A mutations in the voltage-gated sodium channel gene, in any of the sampled populations. The results from this study highlight the critical status of resistance of the cattle tick to synthetic pyrethroids in the regions studied. Further studies are needed to identify the mechanisms responsible for the resistant phenotypes observed in the bioassays. This was the first detection of flumethrin resistance in Brazil.
O controle do carrapato Rhipicephalus (Boophilus) microplus no Brasil é feito principalmente com produtos acaricidas, sem uma política de controle oficial. A venda destes produtos continua ocorrendo de maneira indiscriminada, o que tem contribuído para generalizar o problema da resistência em todo o país, tornando essencial seu diagnóstico e monitoramento. Bioensaios (teste do pacote de larvas) foram conduzidos com populações de carrapatos do Rio Grande do Sul e Mato Grosso do Sul, com relação à sua suscetibilidade a três princípios ativos piretróides. Todas as amostras analisadas mostraram resistência à cipermetrina (10), com fatores de resistência (FR) de 5,6 a 80,3, e à deltametrina, com FR variando de 2,4 a 83,1. Seis das oito amostras foram resistentes à flumetrina (FR de 3,8 a 8,2). Análises moleculares utilizando PCR demonstraram que em todas as populações amostradas não foram encontrados alelos com a mutação T2134A no gene do canal de sódio controlado por voltagem. Os resultados deste estudo evidenciam a situação crítica da resistência do carrapato bovino ao grupo dos piretróides sintéticos nas regiões estudadas. Novos estudos são necessários para identificar os mecanismos responsáveis pelos fenótipos resistentes observados nos bioensaios. Este é o primeiro relato da resistência a flumetrina no Brasil.