Mechanisms of acaricide resistance in ticks

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

Potenciais vacinas contra Rhipicephalus microplus : uma alternativa ao controle químico?

Rhipicephalus (Boophilus) microplus is a hard tick endemic in livestock-growing regions and causes economic losses in the largest beef-producing countries, including Brazil, Mexico, Argentina, Australia and Uruguay. The use of chemical acaricides is still the main strategy to control R. microplus infestations. Nevertheless, immunological control of R. microplus with an anti-tick vaccine is a suitable alternative and has manifold advantages because it can avoid drug-resistance and the presence of acaricide residues in milk, beef and in the environment. Indeed, vaccines based on the Bm86 antigen have had relative commercial and technical success to control R. microplus in some regions. Although, the efficacy of such vaccines varies among tick populations and is insufficient to provide an acceptable level of protection. Therefore, the need to search for better antigens is impelling. This review focused on the restrictions imposed on the use of acaricides in Brazil and in the European Union, as well as on the impacts of Bm86-based vaccines on R. microplus control. The efficacy of experimental anti-tick vaccines (based on subolesin, glutathione S-transferase, ferritin 2; voltage-dependent anion channel; aquaporin, 60 S acidic ribosomal protein, metalloprotease and trypsin) that can elicit an immune response against the physiological functions of various ticks is discussed.O Rhipicephalus (Boophilus) microplus é um carrapato duro que é endêmico de regiões de pecuária e causa perdas econômicas nos maiores países produtores de carne bovina, incluindo Brasil, México, Argentina, Austrália e Uruguai. O uso de acaricidas ainda é a principal estratégia para controlar infestações por R. microplus. No entanto, o controle imunológico do R. microplus com uma vacina contra carrapatos é uma alternativa adequada e possui diversas vantagens, por evitar a seleção de populações de carrapato resistentes a drogas, evitar a presença de resíduos de acaricidas no leite, na carne e no ambiente. As vacinas baseadas no antígeno Bm86 tiveram relativo sucesso comercial e técnico no controle do R. microplus em diversas regiões. No entanto, a eficácia dessas vacinas varia entre as populações de carrapatos e é insuficiente para fornecer um nível aceitável de proteção. Portanto, há uma necessidade de procurar novos antígenos. Esta revisão foca nas restrições impostas ao uso de acaricidas no Brasil e na União Europeia, bem como nos impactos das vacinas baseadas em Bm86 no controle do R. microplus. Também é discutida a eficácia de vacinas anti-carrapatos experimentais (baseadas em subolesina, glutationa S-transferase, ferritina 2; canal aniônico dependente de voltagem; aquaporina, proteína ribossômica ácida 60S, metaloprotease, tripsina) que podem elicitar uma resposta imune contra as funções fisiológicas de vários carrapatos

Modulação da resposta imune do hospedeiro pelos carrapatos

Os carrapatos são ectoparasitos hematófagos que acarretam grandes prejuízos à produção animal. Também causam danos na saúde humana e animal pela transmissão de agentes causadores de doenças. O principal método de controle desses parasitos é baseado no uso de acaricidas. O controle imunológico surge como um método alternativo promissor. Para o sucesso desse controle, moléculas fundamentais na fisiologia do carrapato devem ser identificadas. Carrapatos da família Ixodidae podem se alimentar sobre os hospedeiros por períodos de mais de duas semanas, ativando, assim, a imunidade inata e adaptativa, como também respostas hemostáticas desses animais parasitados. Contudo, durante o curso da infestação, os carrapatos são hábeis em evadir essas defesas naturais dos hospedeiros. A saliva dos carrapatos possui um efeito inibitório sobre a ativação do sistema complemento, a inflamação e a coagulação sanguínea. Porém, são relativamente recentes os estudos na caracterização de componentes da saliva dos carrapatos com funções anticomplemento e anticoagulantes. Nos últimos anos, diversas proteínas vêm sendo descritas com essas atividades na saliva dos carrapatos, revelando um papel fundamental dessas moléculas na sobrevivência desses parasitos. Essas proteínas constituem um alvo potencial para o combate aos carrapatos

Produção do anticorpo monoclonal BrBm2 para caracterização de um antígeno de intestino de Boophilus microplus

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A physiologic overview of the organ‑specific transcriptome of the cattle tick Rhipicephalus microplus

To further obtain insights into the Rhipicephalus microplus transcriptome, we used RNA-seq to carry out a study of expression in (i) embryos; (ii) ovaries from partially and fully engorged females; (iii) salivary glands from partially engorged females; (iv) fat body from partially and fully engorged females; and (v) digestive cells from partially, and (vi) fully engorged females. We obtained > 500 million Illumina reads which were assembled de novo, producing > 190,000 contigs, identifying 18,857 coding sequences (CDS). Reads from each library were mapped back into the assembled transcriptome giving a view of gene expression in different tissues. Transcriptomic expression and pathway analysis showed that several genes related in blood digestion and host-parasite interaction were overexpressed in digestive cells compared with other tissues. Furthermore, essential genes for the cell development and embryogenesis were overexpressed in ovaries. Taken altogether, these data offer novel insights into the physiology of production and role of saliva, blood digestion, energy metabolism, and development with submission of 10,932 novel tissue/cell specific CDS to the NCBI database for this important tick species

Putative target sites in synganglion for novel ixodid tick control strategies

Acaricide resistance is a global problem that has impacts worldwide. Tick populations with broad resistance to all commercially available acaricides have been reported. Since resistance selection in ticks and their role in pathogen transmission to animals and humans result in important economic and public health burden, it is essential to develop new strategies for their control (i.e., novel chemical compounds, vaccines, biological control). The synganglion is the tick central nervous system and it is responsible for synthesizing and releasing signaling molecules with different physiological functions. Synganglion proteins are the targets of the majority of available acaricides. In this review we provide an overview of the mode-of-action and resistance mechanisms against neurotoxic acaricides in ticks, as well as putative target sites in synganglion, as a supporting tool to identify new target proteins and to develop new strategies for tick control

Ecology and Genetic Identification of Freshwater Turtles in Pakistan

Background: The turtle population plays an important role in sustaining the water ecosystem by minimizing pollution from water. The identification and molecular investigation of freshwater fauna is essential for conservation of the species that are near to extinction. The quality of water, type of flora, fauna, and environmental condition are the major factors that directly affect the distribution of freshwater turtles. Studies on the species diversity and habitat of freshwater turtle have not been focused previously in the region. The present study was the first conducted to estimate the habitat and genetic diversity of freshwater turtles using 12S rRNA (ribosomal RNA) gene in Pakistan.Materials, Methods & Results: A total of 26 samples were collected from various localities using hand net, cast net, gills net, steel hooks, thick chemical wire, using chicken intestine and small fishes. The collected turtle specimens were morpho-taxonomically categorized into two genera, Lissemys punctata andersoni (n=13, 50%) and Nilssonia gangetica (n=13, 50%). The collected species showed an aggressive and active behavior in captivity during summer. Genomic DNA was extracted from collected specimens and used in PCR reaction by using specific primers for the amplification of short fragments of 12S rRNA gene. Analysis of generated sequences confirmed the existence of L. p. andersoni in the region. The generated sequences of L. p. andersoni correspond to Clad A and showed a close resemblance among different species of the genus Lissemys.Discussion: This study is the first investigation about the habitat and of the endemic turtle species L. p. andersoni and N. gangetica in Pakistan. The genetic identification followed by phylogenetic analysis based on 12S rRNA partial genes revealed a closest similarity with the sequences generated for the same species from the neighboring countries. This study provided information to conduct further molecular studies that are essential to provide significant genetic data about turtle species.Keywords: turtle, ecology, diversity, phylogeny, Pakistan

Rabbits as animal models for anti-tick vaccine development : a global scenario

Studies evaluating candidate tick-derived proteins as anti-tick vaccines in natural hosts have been limited due to high costs. To overcome this problem, animal models are used in immunization tests. The aim of this article was to review the use of rabbits as an experimental model for the evaluation of tick-derived proteins as vaccines. A total of 57 tick proteins were tested for their immunogenic potential using rabbits as models for vaccination. The most commonly used rabbit breeds were New Zealand (73.8%), Japanese white (19%), Californians (4.8%) and Flemish lopeared (2.4%) rabbits. Anti-tick vaccines efficacy resulted in up to 99.9%. Haemaphysalis longicornis (17.9%) and Ornithodoros moubata (12.8%) were the most common tick models in vaccination trials. Experiments with rabbits have revealed that some proteins (CoAQP, OeAQP, OeAQP1, Bm86, GST-Hl, 64TRP, serpins and voraxin) can induce immune responses against various tick species. In addition, in some cases it was possible to determine that the vaccine efficacy in rabbits was similar to that of experiments performed on natural hosts (e.g., Bm86, IrFER2, RmFER2, serpins and serine protease inhibitor). In conclusion, results showed that prior to performing anti-tick vaccination trials using natural hosts, rabbits can be used as suitable experimental models for these studies