Tick infestation level interferes with spray formulation (organophosphate + pyrethroid) efficacy against Rhipicephalus microplus.

Due to the scarcity of information regarding the control of Rhipicephalus microplus on bovines with different tick burdens, tick counts and the efficacy of a commercial spray formulation (aspersion bath with organophosphate + pyrethroid) were evaluated for animals with a low and high tick burdens for 35 days in a stall test. Thirty-two crossbreed Bos taurus indicus x Bos t. taurus experimentally infested with R. microplus larvae were divided into four groups: T01 high infestation control, T02 high infestation treated, T03 low infestation control, and T04 low infestation treated. The bovines were kept individually in pens and R. microplus females were collected daily. All data were statistically analyzed with a significance level of 5% (P ≤ 0.05). For linear regressions, variables with P≤0.05 and the highest coefficients of determination (R2 ≥ 0.70) were considered the best descriptors. The reliability level was 95%. Tick counts differed (P<0.0001) between T01 and T02 (high infestation control vs. treated), except at day 2 (P >0.05) post-treatment, and efficacy ranged from 85.2 to 50.6%. The number of collected engorged females was lower (P<0.0001) for T04 than for T03 (low infestation treated vs. control) animals from day 3 to 29, and efficacy ranged from 95.2 to 69.8%. In addition, tick burden and efficacy were negatively correlated for both the group of animals with a high tick burden (r = -0.5256; p = 0.0012; R² = 0.2762) and the group of animals with a low tick burden (r = -0.9817; p < 0.0001; R² = 0.9638). In conclusion, a high tick burden on bovines decreases the efficacy of the tested spray acaricide.

Strategic control of cattle co-parasitized by tick, fly and gastrointestinal nematodes: Is it better to use ecto + endoparasiticide or just endectocide formulations?

Ticks, flies, and gastrointestinal helminths (GINs) significantly affect cattle productivity; thus, ectoparasiticide, endoparasiticide, and endectocide drugs have commonly been used for their control. The study aimed to compare the technical (parasites counts), productive, and financial effects of a treatment protocol comprising ecto- + endoparasiticides formulations (T01: fluazuron 2.5 mg/kg + fipronil 1.25 mg/kg and fenbendazole 5 mg/kg; n = 15) to a treatment with one formulation of endectocide (T02: ivermectin 450 µg/kg + abamectin 250 µg/kg; n = 15) over 308 days under field conditions in crossbred cattle co-parasitized by Rhipicephalus microplus, Haematobia irritans, and GINs. Bovine weight gain and return on investment (ROI) were also evaluated. Bovines from T01 received four treatments against the cattle tick and two against two GINs. For T02, four treatments were performed. Animals from T01 gained 15.4 kg more than T02 and provided a comparative ROI of 15.8. In cattle co-parasitized with R. microplus, H. irritans, and GINs, the treatment protocol used in this study with ecto- + endoparasiticidal action formulations showed better technical results regarding parasite counts and productive and financial data than the strategic treatment protocol using only an endectocide formulation.

Investigation of fecal egg counts versus worm burden and helminth fauna in cattle treated or not with macrocyclic lactones in a tropical region.

Gastrointestinal nematodes negatively impact the health and productivity of livestock. Macrocyclic lactones (MLs) are the most common class of chemicals used in helminth control programs, however, their intense use is accelerating the development of parasite resistance. For cattle, little is known regarding the relationship between fecal egg counts (FECs) and the helminth population inside the animal's gastrointestinal tract and so this study evaluated the correlation between FEC and worm burden in cattle treated or not with MLs (ivermectin 200 µg/kg, ivermectin 630 µg/kg, abamectin 200 µg/kg, doramectin 700 µg/kg and moxidectin 200 µg/kg). Animals were necropsied to determine if there were any modifications to the proportions of worm species due to chemical treatment. FECs of ML-treated and untreated animals showed significant (p ≤ 0.05 and R2 ≥0.70) positive linear correlations and substantial or perfect strength-of-agreement (LCCC ≥ 0.61) with total worms present, all of which were Haemonchus placei and Cooperia punctata. However, this correlation and strength-of-agreement did not occur when the efficacy of MLs was ≥80 % against these helminths. Among the active MLs tested, moxidectin had the weakest relationship between FEC and worm burden, except for H. placei. Analysis of the helminthological fauna found an increase of H. placei (35.6 % = 95 % CI 35.4-35.6) and a consequent decrease of C. punctata (52.5 % = 95 % CI 52.3-52.6) in untreated animals, when compared to studies carried out over 20-40 years ago, but this proportion was reversed for ML-treated animals (C. punctata 64.5 % = 95 % CI 64.4-64.8; H. placei 30.8 % = 95 % CI 30.6-30.8). It is possible that MLs mitigate this effect in the field and that C. punctata remained prevalent in cattle in different regions of Brazil.

Spatial distribution of Toxoplasma gondii in cows and associated risk factors.

The aim of the present study was to evaluate the spatial distribution of the prevalence of T. gondii in cows using the indirect immunofluorescence assay and determine associated risk factors. Serum samples were collected from 2970 cows on 263 rural farms in 223 municipalities. A questionnaire was administered to herd owners to collect data for the evaluation of risk factors associated with this disease. Mean seroprevalence of T. gondii in cows was 8.48% (95% CI: 7.48 to 9.49). The microregions with the greatest likelihood (p ≤ 0.05) of having infected animals were Anápolis, Ceres, São Miguel do Araguaia, the Federal District, Anicuns, and Vão do Paraná. The purchase of females or males for reproductive/breeding purposes was significantly associated (p ≤ 0.05) with the prevalence of T. gondii in these regions. A positive correlation (0.7618; p = 0.047) was found between the prevalence of T. gondii and total area in hectares of forests in these regions, suggesting that wild cats may be disseminating T. gondii at these sites. The present results highlight the importance of considering the meat from these animals to be an important infection route for humans who eat raw or undercooked food.

Does bathing affect tick and flea burdens and ectoparasiticide effectiveness of a spot-on formulation (fipronil + (S)-methoprene) for dogs?

This work evaluated tick and flea burdens and the efficacy of a single topical application of 10% fipronil + 9% (S)-methoprene spot-on against experimental infestations of Rhipicephalus sanguineus sensu lato and Ctenocephalides felis felis on dogs that were submitted to regular baths for 56-days post-treatment. Four treatments (n = 24) were evaluated: no chemical treatment and no bathing (T01); no chemical treatment + bathing (T02); chemical treatment and no bathing (T03) and chemical treatment + bathing (T04). Dogs were infested with adult ticks and fleas seven days pre-treatment (-7). The ectoparasites were then counted and removed on day -5, followed by a new infestation on day -2 and treatment on day 0. Ticks and fleas were then counted without removal on day 1 and counted with removal on day 2. The dogs were then repeatedly infested with both ectoparasites on days 5, 12, 19, 26, 33, 40, 47 and 54 post-treatment. Baths and ectoparasite counts with removal were performed every 48 h before and after experimental infestation, respectively. Animals of T04 had lower (P ≤ 0.05) tick burden than animals from T01 and T02 from day 2 to day 28. For fleas, the counts varied among days of the study. Dogs from T03 presented lower (P ≤ 0.05) flea burden than dogs from T01 from day 1 until day 56. The same was true for T04 when compared to T01 from day 1 to day 42. Animals of T02 greater (P ≤ 0.05) flea burden than animals of T04 in all dates post treatment. In addition, dogs from T02 presented higher (P ≤ 0.05) flea burden than T01 from day 7 to day 28 and from day 49 to day 56. In sum, the efficacy of the spot-on formulation used declined over the time against both ectoparasites. The efficacy for ticks ranged from 0.0 to 96.5% and 0.0 to 98.52% for T03 and T04, respectively. While for fleas, the efficacy of the formulation ranged from 67.41 to 100% for T03 and 40.18 to 100% for T04. So, bathing dogs that were not treated increased C. f. felis burden but not R. sanguineus s. l. burden. The residual efficacy of the product had a shorter duration against these ectoparasites for dogs that received subsequent bathing.

Biological parameters for Rhipicephalus microplus in the field and laboratory and estimation of its annual number of generations in a tropical region.

The present study aimed to evaluate biological parameters of Rhipicephalus microplus in the non-parasitic phase in both field and laboratory conditions. It also aimed to assess correlations between duration (in days) of these parameters and climatic variables (humidity, rainfall, and soil temperature) and to estimate the annual number of generations of R. microplus in a tropical region. The non-parasitic phase of R. microplus in field and laboratory conditions was evaluated throughout the course of two years. A pasture was infested with engorged female of R. microplus, and biological parameters, including female pre-oviposition, female oviposition, egg mass incubation, larval pre-hatching phase, larval maturation, and larval longevity, were evaluated concomitantly with the collection of data on climatic conditions. The same parameters were also evaluated in a climatized chamber in the laboratory. The total duration of the non-parasitic phase in the field was longer in the dry season (1st and 4th life-cycle repetitions) than in the rainy season (2nd, 3rd, and 5th repetitions). Tick biological parameters for the non-parasitic phase in the laboratory were similar to those obtained in the field during the rainy season. The evaluated biological parameters were influenced mainly by environmental and ground-level temperatures, which modified egg mass incubation, larval pre-hatching, and larval longevity periods and, consequently, the total duration of the non-parasitic phase of the tick. The annual number of generations for the tick was estimated at five per year, which is alarming because it represents an increase, and so new studies into strategic control are needed.

Frequency of bovine cysticercosis in the state of Rondônia, Brazil.

Bovine cysticercosis remains as one of the most important cause of carcasses and viscera condemnation in Brazilian slaughterhouses. However, the efficiency of post-mortem inspection for the diagnosis of this zoonotic disease is relatively low, and few available studies were performed through serological exams. This study evaluated the frequency of bovine cysticercosis in cattle herds located in different farms of the state of Rondônia, Brazil. Among the 987 animals slaughtered from 33 farms, 21 animals (Frequency: 2.13%; 95C.I. 1.23-3.03) were considered as positive through indirect ELISA and confirmed by Immunoblot tests and the cysticercosis was detected in 12 farms (36.36% - C.I. 95% 19.95-52.78). The disease was detected in the municipalities Vale do Paraíso (12.50%), Theobroma (8.11%), Guaporé (7.27%), Rolim de Moura (5.71%), Presidente Médici (5.0%), Ouro Preto do Oeste (4.69%), Nova União (1.77%), Nova Brasilândia d'Oeste (1.14%) and Ministro Andreazza (1.01%). Therefore, prophylactic measures should be taken to improve beef production, control bovine cysticercosis and reduce costs to public health in this Brazilian state.

Viability of Haemonchus placei parasitism in experimentally infected young goats.

The present study aimed to evaluate the viability of Haemonchus placei parasitism in experimentally infected goats. For that, 14 75 days old kids male Saanen kids were placed in one of the four experimental groups: GI - infected with 5000 H. placei L3 (n = 4); GII - infected with 5000 H. contortus L3 (n = 4); GIII - infected with 2500 H. contortus L3 + 2500 H. placei L3 (n = 4), and GIV - control, inoculated with distilled water (n = 2). Each kid received, orally, the infective dose in a single inoculum. Based on daily fecal egg counts, the average pre-patent period was determined as 24 days for H. contortus, and 31 days for H. placei. Regarding the Haemonchus spp. recovered at necropsy, the experimental groups GI, GII, and GIII had, respectively, an average of 25.5, 619.5, and 724.75 (120 H. placei, and 604.75 H. contortus) adult specimens, and no immature forms. Under the conditions of this study, the viability of goat infection by H. placei was confirmed, although, with low susceptibility. Nevertheless, the parasitism of this helminth species was more intense when associated with H. contortus. This fact indicates that in common grazing between cattle and young goats, when the latter end up ingesting both Haemonhcus species, especially in a mixed infection, H. placei may also parasitize them.

In vivo effect of diflubenzuron, administered via mineral salt supplementation, against Haematobia irritans and Rhipicephalus microplus parasitizing cattle.

This study involved two field trials with the aim of evaluating the efficacy of diflubenzuron, via mineral supplementation, against Haematobia irritans parasitizing cattle. Concomitantly with the main trial, a stall test was conducted to ascertain the effects of a different formulation with the same active ingredient against Rhipicephalus microplus, along with the action of diflubenzuron on the reproductive parameters of R. microplusfemales that had naturally detached from cattle. Against H. irritans, it was observed that the efficacy indexes fordiflubenzuron were low (≤ 31.3% or 44.6%) or null (0.0%) throughout the study. The anti- R. microplus efficacy of diflubenzuron, at weekly intervals, ranged from 0.0 to 13.7% over the entire experimental period. Null efficacy (0.0%) was registered for diflubenzuron in relation to the reproductive parameters of R. microplusfemales that had naturally detached from cattle. The different diflubenzuron formulations, administered via mineral salt supplementation, did not show satisfactory efficacy indexes against H. irritans and R. microplus parasitizing cattle, within the experimental design of the present study. In addition, this agent did not present any deleterious effects on the reproductive parameters of R. microplus females.

In vivo effect of diflubenzuron, administered via mineral salt supplementation, against Haematobia irritans and Rhipicephalus microplus parasitizing cattle / Efeito in vivo do diflubenzuron, administrado via sal mineral, contra Haematobia irritans e Rhipicephalus microplus parasitando bovinos

Abstract This study involved two field trials with the aim of evaluating the efficacy of diflubenzuron, via mineral supplementation, against Haematobia irritans parasitizing cattle. Concomitantly with the main trial, a stall test was conducted to ascertain the effects of a different formulation with the same active ingredient against Rhipicephalus microplus, along with the action of diflubenzuron on the reproductive parameters of R. microplusfemales that had naturally detached from cattle. Against H. irritans, it was observed that the efficacy indexes fordiflubenzuron were low (≤ 31.3% or 44.6%) or null (0.0%) throughout the study. The anti- R. microplus efficacy of diflubenzuron, at weekly intervals, ranged from 0.0 to 13.7% over the entire experimental period. Null efficacy (0.0%) was registered for diflubenzuron in relation to the reproductive parameters of R. microplusfemales that had naturally detached from cattle. The different diflubenzuron formulations, administered via mineral salt supplementation, did not show satisfactory efficacy indexes against H. irritans and R. microplus parasitizing cattle, within the experimental design of the present study. In addition, this agent did not present any deleterious effects on the reproductive parameters of R. microplus females.

Resumo O objetivo deste estudo foi avaliar a eficácia do diflubenzuron, administrado via suplementação mineral, contra Haematobia irritans parasitando bovinos, em dois testes à campo. Concomitantemente, foi realizado testes em estábulo para determinar os efeitos de uma formulação diferente, com o mesmo princípio ativo, contra Rhipicephalus microplus , bem como a ação do diflubenzuron nos parâmetros reprodutivos de fêmeas de R. microplus recolhidas após desprendimento natural do hospedeiro bovino. Contra H. irritans, foi observado que foram baixos (≤ 31,3% ou 44,6%) ou nulos (0,0%) os índices de eficácia do diflubenzuron. A eficácia anti-R. microplus do diflubenzuron, observada em intervalos semanais, variaram de 0,0% a 13,7% durante todo o período experimental. Com relação aos parâmetros reprodutivos das fêmeas de R. microplus recolhidas, foi observada eficácia nula (0,0%) para o diflubenzuron. Conclui-se que as diferentes formulações administradas via sal mineral no atual estudo, contra H. irritans e R. microplus parasitando bovinos, não apresentaram eficácia satisfatória. Este agente também não mostrou efeito deletério sobre os parâmetros reprodutivos de fêmeas de R. microplus.

Prevalence of bovine fascioliasis, areas at risk and ensuing losses in the state of Goiás, Brazil / Prevalência de fasciolose bovina, áreas de risco e perdas subsequentes no estado de Goiás, Brasil

Abstract The present study had to determine the prevalence and spatial distribution of areas at risk of bovine fascioliasis in the state of Goiás, central-western Brazil between 2007 and 2014; to evaluate the associations of some epidemiological variables with occurrences of Fasciola hepatica in animals; and to estimate the economic losses that this parasite on the cattle industry. It could be concluded that of 23,255,979 animals slaughtered, the average prevalence of F. hepatica in cattle in Goiás during the period evaluated was 0.0026% (95% CI: 0.0024-0.0028). In the State of Goias, in about then years (since when this parasite was found for the first time by other researchers in 2007), F. hepatica was diagnosed in 168 new municipalities. Using the regression analysis, the effective bovine herd size was a significant risk factor (OR= 1.21; 95% CI 1.1022-1.4510; p ≤ 0.05) for cattle to be infected with fascioliasis in the state of Goiás. The cattle-rearing industry lost approximately R$ 15,072.75 (US$ 4,785) due to condemn of livers with Fasciola in the state of Goiás. New studies need to be conducted in these regions, with the aim to identify the likelihood of presence of intermediate hosts, which might serve as a source of F. hepatica infection for definitive hosts.

Resumo O presente estudo objetivou determinar a prevalência e a distribuição espacial das áreas em risco para fasciolose bovina no Estado de Goiás, região Centro-Oeste do Brasil, entre 2007 a 2014; avaliando as associações de variáveis epidemiológicas com ocorrências da Fasciola hepatica em animais; e estimar as perdas econômicas deste parasito em bovinos. Pode-se concluir que de 23.255.979 bovinos abatidos, a prevalência média de F. hepatica durante o período avaliado foi de 0,0026% (IC 95%: 0,0024-0,0028). No Estado de Goiás, em aproximadamente 10 anos (desde quando este parasito foi encontrado pela primeira vez por outros pesquisadores em 2007), F. hepatica foi diagnosticada em 168 novos municípios. Utilizando-se a análise de regressão logística, o tamanho do rebanho apresentou-se como um fator de risco significativo (OR= 1,21; IC 95% 1,1022-1,4510; p≤0,05) para os bovinos se infectarem por F. hepatica no referido Estado. O prejuízo, devido à condenação de fígados com Fasciola nos bovinos no Estado de Goiás, foi de R$ 15.072,75 (US 4.785). Novos estudos precisam ser conduzidos nessas regiões, com o objetivo de identificar a presença de hospedeiros intermediários infectados, que podem servir como fonte de infecção por F. hepatica para hospedeiros definitivos.

Prevalence of bovine fascioliasis, areas at risk and ensuing losses in the state of Goiás, Brazil.

The present study had to determine the prevalence and spatial distribution of areas at risk of bovine fascioliasis in the state of Goiás, central-western Brazil between 2007 and 2014; to evaluate the associations of some epidemiological variables with occurrences of Fasciola hepatica in animals; and to estimate the economic losses that this parasite on the cattle industry. It could be concluded that of 23,255,979 animals slaughtered, the average prevalence of F. hepatica in cattle in Goiás during the period evaluated was 0.0026% (95% CI: 0.0024-0.0028). In the State of Goias, in about then years (since when this parasite was found for the first time by other researchers in 2007), F. hepatica was diagnosed in 168 new municipalities. Using the regression analysis, the effective bovine herd size was a significant risk factor (OR= 1.21; 95% CI 1.1022-1.4510; p ≤ 0.05) for cattle to be infected with fascioliasis in the state of Goiás. The cattle-rearing industry lost approximately R$ 15,072.75 (US$ 4,785) due to condemn of livers with Fasciola in the state of Goiás. New studies need to be conducted in these regions, with the aim to identify the likelihood of presence of intermediate hosts, which might serve as a source of F. hepatica infection for definitive hosts.

Susceptibility of Rhipicephalus (Boophilus) microplus to fluazuron (2.5mg/kg) and a combination of novaluron (2.0mg/kg)+eprinomectin (0.36mg/kg) in field studies in Brazil.

The present study aimed to determine the susceptibility of 32 R. (B.) microplus populations from Southeast, Midwest and South regions of Brazil, to fluazuron (2.5mg/kg), administered topically (pour-on). Additionally, five populations (Southeast and Midwest regions) of the southern cattle tick were evaluated using in vivo field studies, regarding their susceptibility to a new combination of novaluron (2.0mg/kg)+eprinomectin (0.36mg/kg), administered subcutaneously, compared with two positive controls (fluazuron 2.5mg/kg and eprinomectin 0.5mg/kg), both administered topically (pour-on). Selected bovines were allocated to treatment groups on day 0, and block formation was based on arithmetic means of female ticks (4.5-8.0mm long) counted on three consecutive days (-3, -2 and -1). To evaluate therapeutic and residual efficacies of these formulations, tick counts (females ranging from 4.5 to 8.0mm long) were performed on days 3, 7 and 14 post-treatment, continuing on a weekly basis until the end of each experiment. Results obtained throughout this study, utilizing field efficacy trials, allowed us to conclude that four R. (B.) microplus populations (including two in the Southeast and two in the Midwest regions) could be diagnosed as resistant, or with low susceptibility, to fluazuron (2.5mg/kg). Such fact was detected in farms where owners applied products containing this active component on cattle for at least five years, with treatment intervals of 30-55days during the rainy season. Nonetheless, in vitro studies should be performed in order to reinforce in vivo results obtained on the present study. Regarding efficacy indexes obtained by the association of eprinomectin and the novel molecule novaluron against R. (B.) microplus, none of the trials managed to obtain efficacies superior to 48%. Such results, allied to data obtained by different researchers and previously published in literature, reinforce the perception that maybe these formulations containing novaluron, in the administered dosages and treatment routes, may not be effective tools for controlling R. (B.) microplus. However, future studies must be conducted in order to support such hypothesis. Additionally, all five R. (B.) microplus populations were diagnosed as resistant, or with low susceptibility, to eprinomectin (0.5mg/kg) as well. Even though fluazuron, administered topically (pour on), is still an excellent active principle to be used against R. (B.) microplus, resistance management strategies should be quickly implemented in order to keep selection pressure in Brazil at a minimum level for this compound.

Experimental infection of calves with Haemonchus placei or Haemonchus contortus: Assessment of clinical, hematological and biochemical parameters and histopathological characteristics of abomasums.

The present study had the primary objective of evaluating clinical, hematological and biochemical parameters, as well as observing anatomical and histopathological characteristics of abomasums, from calves prime-infected with Haemonchus contortus or H. placei. Ten male Holstein newborns were subdivided in three groups (GI placebo; GII infected with H. contortus; GIII inoculated with H. placei). Eye mucosa staining was evaluated. Hematological and biochemical tests were performed on animals. The euthanasia of all ten experimental calves was performed on the 42nd day post-inoculation. Fragments were collected from each of all 10 abomasums for histopathological analysis. Discrete submandibular edema was diagnosed in animals from both infected groups (H. contortus or H. placei). However, there were no significant changes (P > 0.05) in the color of the ocular mucosa of calves from all three experimental groups across the entire experimental period. Hematological and biochemical changes diagnosed on animals could not be linked to infections by species of Haemonchus spp. Regarding histopathological exams, it was possible to diagnose hypertrophy, hyperplasia, binucleated cells, inflammatory infiltrate, multifocal hemorrhage and edema in abomasums from calves of both groups infected with H. placei and H. contortus. It can, thus, be concluded that not only are calves susceptible to infections by both Haemonchus species, but they can also present clinical changes and similar anatomic histopathological lesions independent of being infected by Haemonchus placei or Haemonchus contortus. These results reflect a negative effect on helminth control by mixed grazing between sheep and cattle, especially when using calves.

Spatial distribution and risk factors for Toxoplasma gondii seropositivity in cattle slaughtered for human consumption in Rondônia, North region, Brazil.

The present study aimed to evaluate Toxoplasma gondii seroprevalence in cattle slaughtered for human consumption from rural properties in the state of Rondônia, North region, Brazil; the seroprevalence was determined using indirect immunofluorescence assays (IFATs). Additionally, spatial distribution and risk factors associated with toxoplasmosis were also analyzed. Of the 1000 cattle serum samples examined, 53 (5.3%) were determined to be seropositive for T. gondii with antibody titers (IgG) ≥64. In regard to results of the studied risk factors (presence of cats, cats with free access to cattle, breeding system, animal's gender, consumption of raw milk by humans on the property and cattle abortion in the last 12 months) and the odds ratio (OR) of each of these factors influencing cattle to acquire toxoplasmosis, only animals raised on a feeder/stocker/backgrounder system presented a higher probability of being seropositive for T. gondii (OR≥1, P=0.04) than cattle raised only in a feeder/stocker system. There was no association between the occurrence of reproductive problems and T. gondii seropositivity. Based on results obtained in the Brazilian state of Rondônia, it could be concluded that the presence of cats and their contact with cattle on each property, cattle breeding purpose and cattle abortion in the last 12 months were not considered risk factors for T. gondii infection in cattle. Considering that the presence of T. gondii was detected in animals slaughtered in the state of Rondônia, consuming raw or undercooked meat from seropositive cattle should be considered a route of transmission of T. gondii to humans. However, the prevalence of toxoplasmosis diagnosed in cattle from this state (5.30%) is lower than the prevalence of toxoplasmosis observed in South, Southeast and Center-West regions of Brazil, which may vary between 48.5% and 71.0%. The low prevalence of toxoplasmosis in cattle is highlighted in Rondônia, which is the sixth largest state for cattle slaughtering in Brazil and is responsible for producing 20% of all cattle meat exported by Brazil.

Population dynamics and evaluation of the partial selective treatment of crossbreed steers naturally infested with Rhipicephalus (Boophilus) microplus in a herd from the state of Minas Gerais in Brazil.

The present study aimed to evaluate the population dynamics of Rhipicephalus (Boophilus) microplus over a period of 13 months on a rural property located in the state of Minas Gerais in southeastern Brazil. Animals were treated for ticks indoors by whole body spraying when R. (B.) microplus had an average count equal or more than 30 ticks. The study also evaluated the possibility of a partial selective treatment for bovines to control R. (B.) microplus in which only a percentage of the population would be treated (specifically those bovines with tick counts of ≥20. Moreover, we examined the percentage of the population of R. (B.) microplus present on experimental bovines that did not come into contact with the chemical compounds used in the partial selective treatment. We concluded that in this particular region of Brazil, the crossbreed steers support up to five R. (B.) microplus generations per year and that the number of generations was primarily affected by the pluviometric precipitation. We sprayed the bovines with chemicals seven times during the course of the study. The results of the partial selective treatment method revealed that during the rainy and the dry periods, 42.1% to 60.0% and 61.9% to 79.2% of the animals, respectively, fulfilled the criteria to receive a chemical treatment to reduce the number of cattle ticks. In consideration of the need to slow the development of tick resistance with the chemical compounds used in the spraying treatment, the results showed that the percentage of animals that did not require treatment is not relevant. This was evidenced by the result that bovines that presented tick counts of ≥20 during the dry and rainy periods represented 91.5% and 90.6% of the total recorded R. (B.) microplus populations, respectively. Only 8.7% of the tick population remained free from exposure to acaricides during the 13 months of the study, which is an important point when considering the adoption of the partial selective treatment method. Future studies with larger herds must be conducted on these topics; however, our results suggest that the partial selective treatment method most likely will not slow the development of resistance in this R. (B.) microplus population against the chemical compound used in this study.

Experimental infection of calves with Haemonchus placei and Haemonchus contortus: Assessment of parasitological parameters.

The present study evaluated the viability and possible effects of Haemonchus contortus infections in experimentally prime infected calves, comparing them to infections by Haemonchus placei. Ten male Holstein newborns were used. All calves were individually weighed for subsequent group formation, in which two animals were kept as a control group, inoculated with water (GI); four animals were inoculated with 10,000 third stage (L3) Haemonchus contortus larvae (GII); and the remaining four calves were inoculated with 10,000 third stage (L3) H. placei larvae (GIII). All experimental animals were necropsied on the 42nd day after inoculation. Based on results obtained by the present study, it can be concluded that bovine calves were susceptible to infections by both Haemonchus species (placei and contortus). H. contortus presented an inferior pre-patent period when compared to H. placei. No significant difference (P>0.05) was observed between Haemonchus burdens recovered from both infected groups (GII and GIII). Moreover, H. contortus females maintained an egg production rate similar to H. placei females in young animals, which can contribute to pasture contamination by both Haemonchus species. This could possibly lead to negative reflexes on helminth control based on a mixed pasture with bovines and ovines, especially when it involves younglings.

Ten years later: Evaluation of the effectiveness of 12.5% amitraz against a field population of Rhipicephalus (Boophilus) microplus using field studies, artificial infestation (Stall tests) and adult immersion tests.

Using field trials, artificial infestations (Stall tests) and in vitro adult immersion tests, the present study evaluated the acaricidal efficacy of 12.5% amitraz administered via whole body spraying against a Rhipicephalus (Boophilus) microplus population that did not have any contact with chemical products belonging to this acaricide family for 10 years (approximately 40 generations). Two natural infestation trials, two artificial infestation trials (Stall tests) and two adult immersion tests were performed in two different stages in 2005 and 2015. Between 2002 and 2015, the bovine herd of this property was formed by approximately 450 animals from the Simmental breed that were divided into nine paddocks formed by Cynodon dactylon (L.) Pers. For the natural infestation experiments in 2005 and 2015, we selected nearly 70 animals naturally infested with ticks from the same herd that belonged to the "São Paulo" farm located in São José do Rio Pardo, São Paulo, Brazil. Field studies were performed in the same paddock (9). To evaluate anti-R. (B.) microplus activity in the artificially infested cattle (Stall tests) and adult immersion tests, two experiments of each methodology were performed at CPPAR (the Center of Research in Animal Health located on the FCAV/UNESP campus in Jaboticabal, São Paulo, Brazil) in 2005 and 2015. R. (B.) microplus used in the artificial infestation, and adult immersion test experiments were obtained from paddocks 1-9 in 2005 and 2015 from the commercial farm where the field studies were performed. Based on the obtained results, it was possible to conclude that amitraz use in rotation with pyrethroids every 28 days for three consecutive years (2002-2004) previous to the beginning of the first trial (2005) was sufficient to generate a R. (B.) microplus strain resistant to amitraz. Moreover, using field trials, artificial infestations (Stall tests) and adult immersion tests, we verified that 40 generations of the tick species with no contact to the aforementioned compound (amitraz) were not sufficient to revert or modify the efficacy/resistance of amitraz for this analyzed R. (B.) microplus strain. The reversion of amitraz efficacy values in R. (B.) microplus may only occur when resistance of the field strain is incipient. Alternatively, the differences in the results may be due to differences in the Rhipicephalus spp. species between current study locations. Therefore, future studies must be performed to prove this hypothesis.

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.

Endectocide activity of a pour-on formulation containing 1.5 per cent ivermectin +0.5 per cent abamectin in cattle.

The present work aimed to evaluate, through ten different studies, the therapeutic efficacy of a new pour-on formulation, containing 1.5 per cent ivermectin +0.5 per cent abamectin, against parasites of cattle. Results obtained on trials against Rhipicephalus (Boophilus) microplus showed that the pour-on combination of 1.5 per cent ivermectin +0.5 per cent abamectin obtained superior efficacy indexes against this ectoparasite, when compared with formulations containing 0.5 per cent ivermectin, 1 per cent ivermectin and the combination of 1 per cent abamectin +20 per cent levamisole. The results of efficacy of the ivermectin+abamectin and the 0.5 per cent ivermectin against Haematobia irritans were similar. Against Cochliomyia hominivorax larvae, all pour-on formulations tested (1.5 per cent ivermectin +0.5 per cent abamectin, 0.5 per cent ivermectin and 0.5 per cent abamectin), as well as 1 per cent doramectin administered subcutaneously, were considered ineffective. Cattle medicated with 1.5 per cent ivermectin +0.5 per cent abamectin, pour-on, remained free from parasitism by Dermatobia hominis larvae during 42 days (96 per cent efficacy), while values superior to 90 per cent were obtained by 0.5 per cent ivermectin (92 per cent) and 0.5 per cent abamectin (93 per cent) until the 42nd and 35th days post treatment, respectively. Against Haemonchus placei and Oesophagostomum radiatum, the pour-on of ivermectin+abamectin showed better efficacy than the 0.5 per cent ivermectin and 0.5 per cent abamectin. As to Cooperia punctata, there was no difference regarding efficacy results obtained by the avermectins combination and abamectin. The pour-on combination of 1.5 per cent ivermectin +0.5 per cent abamectin obtained high efficacy against R. (B.) microplus, D. hominis and some species of cattle gastrointestinal helminths when compared with formulations of 0.5 per cent ivermectin and 0.5 per cent abamectin administered through the same route.