Dinâmica populacional de Rhipicephalus (Boophilus) microplus (Canestrini, 1887) em bovinos mestiços mantidos em pastagens de Brachiaria decumbens no município de Formiga, Minas Gerais

Pós-graduação em Medicina Veterinária - FCAV

Acaricidal effects of fluazuron (2.5 mg/kg) and a combination of fluazuron (1.6 mg/kg) + ivermectin (0.63 mg/kg), administered at different routes, against Rhipicephalus (Boophilus) microplus parasitizing cattle

The present study aimed to evaluate the acaricidal efficacy of fluazuron (2.5 mg/kg), administered as a pour-on, in comparison to an injectable formulation containing fluazuron (1.6 mg/kg) + ivermectin (0.63 mg/kg), against Rhipicephalus (Boophilus) microplus in naturally and experimentally infested cattle. Two studies were conducted with different tick strains, one with artificial infestations (Stall Test, using leight animals per group) and one with natural infestations (utilizing ten animals per group): In both studies, the animals were randomized, according to average tick counts performed on days -3, -2 and -1, into four groups: T01, negative control (saline solution); T02, pour-on fluazuron (2.5 mg/kg); T03: subcutaneous fluazuron (1.6 mg/kg) + ivermectin (0.63 mg/kg); and T04 subcutaneous ivermectin (0.63 mg/kg). Based on obtained results, and considering the utilized tick strains, it was possible to conclude that the pour-on fluazuron (2.5 mg/kg) formulation demonstrated high acaricidal efficacy, with protection periods ranging from 49 to 77 days against Rhipicephalus (Boophilus) microplus. On the other hand, for the injectable fluazuron (1.6 mg/kg) + ivermectin (0.63 mg/kg) formulation, it was not possible to observe elevated anti-R. (B.) microplus effect on both artificial and experimental infestation studies. Results observed for this combination were similar or inferior to those obtained by subcutaneous ivermectin (0.63 mg/kg). Future studies with this formulation containing fluazuron (1.6 mg/kg) + ivermectin (0.63 mg/kg), regarding pharmacokinetic and/or bioavailability profiles, or even studies analyzing both this active principles separately, are needed, seeking to better understand the effects of such combination against Rhipicephalus (Boophilus) microplus parasitizing cattle. (C) 2015 Elsevier Inc. All rights reserved.

A comparison of three different methodologies for evaluating Rhipicephalus (Boophilus) rnicroplus 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 (R) FC 30, Ouro Fino Agronegocios; and 60% Dichlorvos + 20% Chlorpyriphos-Ectofos (R), Vallee Saude 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.) micro plus 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.) micro plus. 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. (C) 2014 Elsevier B.V. All rights reserved.

Susceptibility of Rhipicephalus (Boophilus) microplus to ivermectin (200, 500 and 630 mu g/kg) in field studies in Brazil

The present study aimed to determine the susceptibility of 17 Rhipicephalus (Boophilus) microplus populations, originating in the Southeast and Southern regions of Brazil, to different ivermectin concentrations (200, 500 and 630 mu g/kg), administered through subcutaneous or topical (pour-on) routes. R. (B.) microplus populations from the states of Minas Gerais (seven populations), Sao Paulo (seven populations) and Parana (three populations) were chosen for the tests. The selected cattle were allocated to treatment groups on day 0, and block formation was based on the arithmetic mean of female ticks (4.5-8.0 mm long) counted on three consecutive days (-3, -2 and -1). To evaluate the therapeutic and residual efficacies of these formulations, tick counts (females ranging from 4.5 to 8.0 mm long) were performed on days 3,7 and 14 post-treatment, and continued on a weekly basis thereafter until the end of each experiment. The results obtained throughout this study, utilizing field efficacy studies, allowed us to conclude that the resistance of R. (B.) microplus against 200 and 500 mu g/kg ivermectin is widely disseminated because all tick populations that had contact with these specific concentrations were diagnosed as resistant. However, it is possible to infer that R. (B.) microplus resistance against 630 mu g/kg ivermectin was also widespread, diagnosed at six of ten analyzed properties. Resistance of these ectoparasites to 630 mu g/kg ivermectin is most likely emerging in three other populations of R. (B.) microplus. Strategies of resistance management need to be quickly determined to keep the selection pressure at a minimum level in Brazil. (C) 2014 Elsevier B.V. All rights reserved.

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.

Effects of different spray formulations on the reproductive parameters of engorged Rhipicephalus (Boophilus) microplus females detached from experimentally infested cattle

This present study aimed to evaluate the deleterious effects of some commercially available spray formulations (15% Cypermethrin+25% Chlorpyriphos+1% Citronellal and 8% Cypermethrin+60% Ethion) on the reproductive parameters of engorged Rhipicephalus (Boophilus) microplus females that detached from experimentally infested cattle. The following reproductive parameters of engorged female ticks were analyzed: female weight, egg mass weight, percentage of hatchability, percentage of reduction in oviposition, percentage of reduction in hatchability, reproductive efficiency and percent control/efficacy of formulations for reproductive parameters. Our findings showed that although the strain R. (B.) microplus used in both experiments was thought to be sensitive to the test compounds because of the acaricidal efficacy observed throughout these trials, it was not possible to observe overall deleterious effects on the reproductive parameters of this tick species with both spray formulations. However, the 8% Cypermethrin+60% Ethion showed short-term significant effects on the weight of female ticks between the 14th and 16th days post-treatment and the weight of female and the egg mass weight between the 20th and 22nd days post-treatment. New studies should be conducted to show if these results regarding the reproductive parameters of fully engorged R. (B.) microplus females, combined with the acaricidal efficacy can be sufficient to reduce the number of chemical treatments administered to cattle.

Resistência do Rhipicephalus (Boophilus) microplus aos carrapaticidas: revisão de literatura

O carrapato Rhipicephalus (Boophilus) microplus é o principal ectoparasito de bovinos e esta associado à transmissão de doenças, causando grandes prejuízos econômicos a indústria da pecuária no geral. O surgimento de populações de carrapatos R.(B) microplus resistentes aos carrapaticidas comerciais é um problema observado em muitas propriedades rurais no mundo, gerando um prejuízo de aproximadamente US$ 7 bilhões por ano. O uso correto dos princípios ativos carrapaticidas existentes e conhecimento das diversas formas de resistência do R. (B) microplus a estes princípios são de grande valia para prevenir ou então diagnosticar precocemente o aparecimento da resistência nas diversas populações deste ectoparasita.

Estudo do nível de infecção por Babesia bovis e Babesia bigemina em bovinos da raça Canchim naturalmente infestados com o carrapato Rhipicephalus (Boophilus) microplus

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Purification and characterization of Hb 98-114: A novel hemoglobin-derived antimicrobial peptide from the midgut of Rhipicephalus (Boophilus) microplus

The antimicrobial activity of hemoglobin fragments (hemocidins) has been reported in a variety of models. The cattle tick Rhipicephalus (Boophilus) microplus is a blood sucking arthropod from where the first in vivo-generated hemocidin was characterized (Hb 33-61). In the present work we identified a novel antimicrobial peptide from the midgut of fully engorged R. (B.) microplus females, which comprises the amino acids 98-114 of the alpha subunit of bovine hemoglobin, and was designated Hb 98-114. This peptide was active against several yeast and filamentous fungi, although no activity was detected against bacteria up to 50 mu M of the synthetic peptide. Hb 98-114 was capable of permeabilizing Candida albicans cell membrane and had a fungicidal effect against this yeast. Circulardichroism (CD) and nuclear magnetic resonance (NMR) experiments showed that Hb 98-114 has a random conformation in aqueous solution but switches to an alpha-helical conformation in the presence of sodium dodecyl sulfate (SDS). This alpha helix adopts an amphipathic structure which may be the mechanism of cell membrane permeabilization. Importantly, Hb 98-114 may play an important role in defending the tick midgut against fungal pathogens and is the first hemocidin with specific antifungal activity to be characterized. (C) 2012 Elsevier Inc. All rights reserved.

WOOD NATURAL RESISTANCE OF SEVEN FOREST SPECIES TO WHITE ROT CAUSED BY Pycnoporus sanguineus

This research evaluated the natural resistance of Platanus x acerifolia, Luehea divaricate, Carya illinoinensis, Peltophorum dubium, Araucaria angustifolia, Eucalyptus grandis and Hovenia dulcis, to accelerated decay of the white-rot fungus Pycnoporus sanguineus. The Specific Density at 12% was determinated. The accelerated decay test was conducted with glass bottles (capacity of 500 mL) filled with 100 g of moist soil, autoclaved, and kept at 25 degrees C. The initial establishment of fungal colonies on plates was supported by samples of Pinus elliottii sapwood. In this study, three samples of dimensions 9.0 x 25.0 x 25.0 mm were used for each species evaluated and, after 16 weeks of incubation, the percentage loss of mass was calculated. The degree of natural resistance was performed according to the percentages of mass loss. The results obtained from weight loss were compared by Tukey test at 5%. The natural resistance of woods was not influenced by specific gravity The wood of Carya illinoinensis, Eucalyptus grandis, Platanus x acerifolia, Luehea divaricata and Peltophorum dubium were classified as very resistant, Houvenia dulcis as resistant and Araucaria angustifolia as moderate resistant.

Pathogenicity of Metarhizium anisopliae towards Rhipicephalus (Boophilus) microplus under laboratory and field conditions

Metarhizium anisopliae is one of the most studied agents of biological control of several arthropod plagues, including the cattle tick Rhipicephalus (Boophilus) microplus. Studies have been conducted to assess the fungal complex infection process towards its hosts. To accomplish that, mutant strains overexpressing or lacking assumed determinant genes for the process were constructed over the years. A fundamental experiment to demonstrate a particular gene or set of genes participation is the bioassay. The comparison of bioassays using wild and engineered strains is an essential tool to affirm a given gene is crucial in the process. Therefore, the in vitro bioassays should mimic the results obtained in tests under field conditions. In this study, tests under laboratory and filed conditions were done and a correlation analysis was performed in order to statistically validate in vitro bioassays. Tick egg laying, larvae hatching and host mortality were recorded in each experiment through 21 days, both under laboratory and field conditions. In all cases, M. anisopliae treatments were statistically different from the control treatments. A linear regression analysis was performed between the cases. Laboratory results showed a statistically significant correlation with the field conditions using the Pearson's Correlation Test (P < 0.01 host mortality - 0.969, tick egg laying - 0.977 and larvae hatching - 0.956). These results legitimize the in vitro bioassays and, therefore, constitute them as a valid tool for studying this fungus behavior, so they can be used to infer M. anisopliae response towards R. (Boophilus) microplus.

Applicability of in vitro bioassays for the diagnosis of ivermectin resistance in Rhipicephalus microplus (Acari: Ixodidae)

The applicability of laboratory bioassays to diagnose ivermectin (IVM) resistance in Rhipicephalus microplus was evaluated. Adult immersion tests (AITs), larval immersion tests (LITs) and larval packet tests (LPTs) were performed to characterise the effects of ivermectin toxicity on adults and larvae of a susceptible reference strain. The AIT was determined to be a reasonable assay but requires a large number of individuals to attain interpretable results. The LIT and LPT were validated with an IVM resistant strain, revealing resistance ratios (RRs) of 6.73 and 1.49, respectively. In a field survey, nine different populations of cattle tick from the states of Sao Paulo and Mato Grosso do Sul, Brazil, were analysed with the LIT. Populations without previous exposure to ivermectin exhibited RRs between 0.87 and 1.01. Populations previously exposed to IVM showed RRs between 1.83 and 4.62. The LIT was more effective at discriminating between resistant and susceptible populations than the LPT. The use of the LIT is recommended for the diagnosis of ivermectin resistance in R microplus. (C) 2011 Elsevier B.V. All rights reserved.

Acaricidal action of destruxins produced by a marine-derived Beauveria felina on the bovine tick Rhipicephalus (Boophilus) microplus

The increasing resistance of Rhipicephalus (Boophilus) microplus tick to commercial insecticides requires alternative methods for the control of this cattle plague. The enthomopathogenic fungus Beauveria feline produces destruxins in culture media, cyclic depsipeptides which display an array of biological activities. The present investigation aimed to evaluate the acaricide action of destruxins isolated from B. felina culture media on R. (B.) microplus engorged females. B. felina was grown in MF medium under 19 different growth conditions. HPLC-PDA analysis of chromatographic fractions obtained from the 19 different growth media extracts indicated the presence of destruxins in all lipophylic fractions. Such fractions were combined and subjected to separation by HPLC. Fractions containing distinct destruxins composition were tested against R. (B.) micro plus. Two fractions, composed of destruxin Ed(1) and pseudodestruxin B and/or pseudodestruxin C (fraction P1) as well as by hydroxyhomodestruxin B and/or destruxin D and/or roseotoxin C (fraction P7), displayed 30% and 28.7% acaricidal efficacy, respectively. This activity profile in such low concentration is adequate to consider destruxins as potential leading compounds to be developed for tick biological control. (C) 2012 Elsevier Inc. All rights reserved.

Isolation of a Pax-6 homolog from the ribbonworm Lineus sanguineus.

The Pax-6 genes of vertebrates and Drosophila encode transcription factors with highly conserved paired- and homeodomains. They are expressed in the nervous system and the developing eyes. Loss-of-function mutations in mammals and flies lead to a reduction or absence of the eyes. By ectopic expression of Pax-6 in Drosophila ectopic eyes can be induced, indicating a determinative role in eye morphogenesis. We have isolated a Pax-6 homolog of the ribbonworm Lineus sanguineus. This gene shares extensive sequence identity and several conserved splice sites with the mammalian and Drosophila genes. During head regeneration the L. sanguineus Pax-6 homolog is expressed in the central nervous system, in the cerebral organ, and in the eye region. These findings support the hypothesis that Pax-6 was present in primitive metazoa before the evolutionary separation of vertebrates and arthropods and suggest a fundamental role in eye and central nervous system development.

The genera Boophilus, Rhipicephalus, and Haemaphysalis (ixodiadae) of the new world,

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