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6. Spatiotemporal heterogeneity of Rhipicephalus microplus resistance to chemical acaricides at intra‐farm level: A case study using ivermectin.

Author

Morel, Nicolas, Torrents, Jorgelina, Sarli, Macarena, Rossner, Maria V., Lifschitz, Adrián L., and Nava, Santiago

Subjects
*CHEMICAL resistance, *IXODIDAE, *MITES, *TICK control, *RHIPICEPHALUS, *IVERMECTIN
Abstract

The aim of this work was to analyse the spatiotemporal heterogeneity of Rhipicephalus microplus (Canestrini, 1888) (Acari: Ixodidae) resistance to chemical acaricides at intra‐farm level under different environmental (favourable and unfavourable areas for tick development) and management (different schemes of acaricides applications) conditions using ivermectin as a model. The in vitro larval immersion test (LIT) was used to determine quantitatively the levels of resistance to ivermectin in the different populations and subpopulations of R. microplus analysed. In the first case study, differences in resistance levels among tick samples within the same paddock across time and among tick samples from different paddocks were recorded. These results stress the importance of taking successive samples so that they represent the spatial and temporal variabilities in the levels of resistance that can occur within the same farm. In a second case study, the evolution of resistance in R. microplus subpopulations subjected to strategic and threshold control methods based on the application of three annual treatments with alternation of chemical groups was compared. No changes in resistance/susceptibility status were observed in both tick subpopulations. These results show that the application of a particular drug once a year within a scheme of alternation with other chemical groups could be an appropriate strategy to delay the development of resistance. Data of the third case study showed that environmental constraints is not only a key modulator of R. microplus abundance but could also affect the evolution of resistance in the tick populations. The decreasing trend of LC50 values in the tick subpopulation not exposed to chemical treatments but also in that subpopulation exposed to three annual chemical treatments under unfavourable environmental conditions allow us to hypothesise that environmental constraints can modify the levels of resistance in a tick population because it can constitute a stronger selection factor than the treatments themselves. [ABSTRACT FROM AUTHOR]

Published
2024
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9. Efecto del control estratégico de la garrapata común del bovino Rhipicephalus (Boophilus) microplus sobre la ganancia de peso en vaquillas Braford en el noreste de Argentina

Author

Rossner, Maria Victoria, Torrents, Jorgelina, Morel, Nicolas, Prieto, Paula Noelia, Lottero, F., Mangold, Atilio Jose, and Nava, Santiago

Subjects
Rhipicephalus (Boophilus) microplus, Garrapatas, Región Noroeste, Argentina, Weight Gain, Ticks, Raza Braford, Plagas de Animales, Ganado Bovino, Control de Plagas, Rhipicephalus, Metastigmata, Ganancia de Peso, Cattle, Pest Control, Pests of Animals
Abstract

El objetivo de este trabajo fue analizar el impacto del control estratégico de Rhipicephalus microplus sobre la ganancia de peso de vaquillas Braford en el noreste de Argentina. Se realizaron dos experimentos con un diseño similar en localidades de Corrientes (Colonia Tabay) y Chaco (Colonia Benítez). Los distintos grupos de vaquillas fueron sujetos a esquemas de control estratégico que consistieron en la aplicación de tres o cuatro productos garrapaticidas entre agosto y diciembre, y se compararon el número de garrapatas y la ganancia diaria de peso (GDP) entre estos y un grupo testigo que no recibió garrapaticidas. En Colonia Tabay, en los dos grupos tratados con esquemas de control estratégico la GDP fue significativamente mayor que en el grupo testigo con mayor nivel de infestación con garrapatas. El grupo sujeto a control estratégico en Colonia Benítez también tuvo una GDP significativamente mayor que el grupo testigo. Las diferencias en las GDP entre los grupos de animales sujetos a control estratégico y aquellos mantenidos como grupos testigo fluctuó entre 0.09 y 0.149 kg/día. Para el período evaluado en este trabajo (nueve meses), la aplicación del control estratégico contra R. microplus implicó una ganancia diferencial con respecto a los grupos sin tratamientos de 29 y 42 kg en promedio en las vaquillas de Colonia Tabay y de 25 kg en aquellas de Colonia Benítez. De los resultados se desprende que la aplicación de esquemas de tratamientos estratégicos para controlar la infestación con R. microplus en el noreste de Argentina contribuye a disminuir significativamente la abundancia de garrapatas y posibilita obtener mejores ganancias de peso vivo en bovinos en crecimiento al prevenir altos niveles de parasitación en los animales. The objective of this study was to analyze the impact of the strategic control of Rhipicephalus microplus on body weight gain of Braford heifers in northeastern Argentina. Two experiments with a similar design were carried out in Corrientes (Colonia Tabay) and Chaco (Colonia Benítez) Provinces. Strategic control schemes were applied different groups of heifers with the application of three or four treatments with chemical acaricides between August and December, and the number of ticks and the daily weight gain (GDP) were compared between them and with a control group without treatments. In Colonia Tabay, the GDP in the two groups treated with strategic control schemes was significantly higher than in the control group, which had higher level of infestation with ticks. The group subjected to strategic control in Colonia Benítez also had a significantly higher GDP than the control group. Differences in GDP between groups subjected to strategic control and control groups fluctuated between 0.09 and 0.149 kg/day. The application of strategic control against R. microplus implied a differential mean weight gain regarding the groups without treatments of 29 and 42 kg in Colonia Tabay heifers and 25 kg in Colonia Benítez. The results show that the application of strategic treatment schemes to control infestation with R. microplus in northeastern Argentina contributes to significantly reduce the abundance of ticks and enable obtain better body weight gains in growing cattle by preventing high levels of parasitism on animals. EEA Colonia Benitez EEA Rafaela Fil: Rossner, Maria Victoria. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Colonia Benítez; Argentina Fil: Torrents, Jorgelina. Universidad Nacional del Litoral. Facultad de Ciencias Veterinarias; Argentina Fil: Morel, Nicolas. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Rafaela; Argentina Fil: Morel, Nicolas. Instituto de Investigación de la Cadena Láctea (IDICAL, INTA-CONICET); Argentina Fil: Prieto, Paula Noelia. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Colonia Benítez; Argentina Fil: Lottero, F. Fundación Correntina para la Sanidad Animal; Argentina Fil: Mangold, Atilio José. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Rafaela; Argentina Fil: Mangold, Atilio José. Instituto de Investigación de la Cadena Láctea (IDICAL, INTA-CONICET); Argentina Fil: Nava, Santiago. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Rafaela; Argentina Fil: Nava, Santiago. Instituto de Investigación de la Cadena Láctea (IDICAL, INTA-CONICET); Argentina

Published
2022

10. Influence of the cattle body weight estimation for drug dosing on the pharmacokinetic and efficacy of ivermectin against Rhipicephalus (Boophilus) microplus.

Author

Miró, María Victoria, Sarli, Macarena, Rossner, María Victoria, Gómez, Viviana, Toffaletti, José, Torrents, Jorgelina, Lifschitz, Adrián, and Nava, Santiago

Subjects
CATTLE weight, RHIPICEPHALUS, IVERMECTIN, BODY weight, PHARMACOKINETICS, DRUG efficacy
Abstract

This study aimed to evaluate how the method of body weight estimation of a herd (average vs individual) for drug dosing may affect the pharmacokinetics and therapeutic efficacy of ivermectin 3.15% against Rhipicephalus (Boophilus) microplus. The trial was performed in two populations of R. (B.) microplus with different levels of susceptibility to ivermectin: San Martín (SM) (incipient resistance) and Colonia Benítez (CB) (susceptible). Twenty-one (SM) and forty-two (CB) 12-month-old Braford heifers, naturally infested with R. (B.) microplus, were individually weighed and divided into three groups (G). G1 and G2 were treated with a dose of ivermectin 3.15% (IVOMEC GOLD®) at a dose rate of 630 µg/kg of body weight (1 mL/50 kg). G1 received a uniform dose of ivermectin calculated according to the average of the individual body weights. G2 received a dose of ivermectin calculated according to the exact body weight of each animal. G3 were the control group. Ivermectin concentrations were measured from blood samples from day 1 to day 21 post-treatment. The efficacy of the treatment was evaluated by counting female ticks. In both populations the differences in the doses of ivermectin administered did not affect the pharmacokinetics and therapeutic efficacy of the drug. Nevertheless, it is necessary to avoid the sub-dosage of cattle to reduce the selection pressure for resistance on the tick populations. [ABSTRACT FROM AUTHOR]

Published
2022
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11. Two novel Ehrlichia(Rickettsiales: Anaplasmataceae) strains detected in ticks (Ixodida, Ixodidae) and opossums (Didelphimorphia: Didelphidae) in Argentina

Author

Tarragona, Evelina L., Flores, Fernando S., Lamattina, Daniela, Torrents, Jorgelina, Sebastian, Patrick S., and Nava, Santiago

Abstract

The aim of this study is to determine if there is circulation of microorganisms of the genus Ehrlichiain opossums Didelphis albiventrisand their ticks from the Humid Chaco in Argentina. Blood samples of 15 specimens of the opossum D. albiventriswere analysed. Immature stages of the ticks Amblyomma ovale(Larvae=26; Nymphs=10), Amblyomma sculptum(Larvae=86; Nymphs=6) and Ornithodorossp. cf. O. mimon(Larvae=90) were also analyzed. DNA was extracted individually from blood samples and ticks. Molecular detection of Ehrlichiaagents was performed targeting two different loci: 16S rRNA and dsb gen. The phylogenetic analyses showed that the Ehrlichiasp. detected in D. albiventrisin this study is identical to Ehrlichiasp. strain Natal previously detected in two marsupials from Brazil. Furthermore, a new Ehrlichia strain was amplified from an A. ovalenymph (named as Ehrlichiasp. strain El Bagual) which is phylogenetically closely related to a strain of Ehrlichiasp. detected in Bradypus tridactylusin Brazil. The findings of the current study represent the first report of these two strains of Ehrlichiafor Argentina, showing that the diversity of Ehrlichiaspp. is greater than previously assumed. Further studies should determine the epidemiological relevance of these findings.

Published
2022
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12. Analysis of sequence variations in the GABA gated chloride gene associated with resistance to fipronil in Rhipicephalus (Boophilus) microplusticks from Argentina

Author

Sarli, Macarena, Torrents, Jorgelina, Morel, Nicolás, and Nava, Santiago

Abstract

This study aimed to evaluate the sequence variations of the GABA-Cl gene of Rhipicephalus (Boophilus) microplusticks from Argentina with different resistance levels to fipronil. Genomic DNA was obtained from engorged females (n = 50) of fipronil-susceptible and resistant tick field populations from five localities in northern Argentina. Tick populations were tested for fipronil resistance by in vitro larval packet test. DNA encoding amino acid residues 264–360 of the GABA-Cl was amplified by PCR. PCR products were sequenced and the translated amino acid sequences were aligned and compared among each other and with sequences of the GABA-Cl belonging to the Brazilian and Uruguayan reference strains fipronil-susceptible (Mozo) and resistant (RFSan and Juarez). All the GABA-Cl amino acid sequences obtained from the R. microplusspecimens from Argentina were identical, regardless of the fipronil resistance-susceptibility status of each population. Mutations present in GABA-Cl sequence of RFSan and Juarez strains were not present in any of the populations from Argentina analyzed. These results indicate the failure of this gene as a molecular marker of resistance to fipronil, at least in the R. micropluspopulations from northern Argentina.

Published
2022
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