Publications (3)7.74 Total impact
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Article: Ivermectin resistance status and factors associated in Rhipicephalus microplus (Acari: Ixodidae) populations from Veracruz, Mexico.
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ABSTRACT: The objectives of the present study were to (1) determine the status of resistance or susceptibility to ivermectin (IVM) in Rhipicephalus microplus tick populations in Veracruz, Mexico, (2) determine the level of resistance (resistance ratios [RR] and lethal concentrations for 50% [LC(50)] and 99% [LC(99)]) mortality in each R. microplus population, and (3) identify factors associated with resistance. Populations of R. microplus were sampled from 53 cattle farms to evaluate their resistance using the larval immersion test. Mortality data were subjected to probit analysis to calculate LC(50) and LC(99). Resistance ratios were calculated in relation to a susceptible reference strain. A logistic regression model was used to evaluate the relation between resistance and possible associated factors. Thirteen tick populations were susceptible to ivermectin, eighteen had incipient resistance and twenty-two had significant resistance. RR(50) of the susceptible tick populations varied from 0.59 to 1.07. The populations that showed the highest level of resistance were: ANTE (RR(50)=8.21; RR(99)=46.0), PALO (RR(50)=6.25; RR(99)=35.47), P.VIE (RR(50)=5.89; RR(99)=180.3), AURO (RR(50)=5.36; RR(99)=13.82 and CEDR (RR(50)=4.11; RR(99)=26.47). Cattle farms that used macrocyclic lactones ≥4 times per year were more likely to develop R. microplus resistant to ivermectin (OR=13.0; p=0.0028). In conclusion, more than two-thirds of the farms sampled in Veracruz, Mexico, showed some level of ivermectin-resistant R. microplus populations and the number of ML applications per year is factor associated with the resistance of R. microplus to IVM.Veterinary Parasitology 06/2012; 190(1-2):210-5. · 2.58 Impact Factor -
Article: First report of a Rhipicephalus microplus tick population multi-resistant to acaricides and ivermectin in the Mexican tropics.
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ABSTRACT: We document the presence of a Rhipicephalus microplus tick population resistant to acaricides (organophosphates (OP), synthetic pyrethroids (SP), amitraz) and macrocyclic lactones (ML) (ivermectin). Engorged females of R. microplus were collected from a cattle farm in Veracruz, Mexico, to evaluate acaricide and ivermectin resistance. The modified larval packet test (LPT) was used to detect OP (chlorpiriphos and diazinon) and SP (flumethrin, deltamethrin and cypermethrin) resistance and the larval immersion test (LIT) to detect resistance to amitraz and ivermectin. Both, LPT and LIT were performed twice at different times with different collected samples. Mortality data with ivermectin were subjected to probit analysis to obtain lethal concentrations and resistance ratios (RR) using an ivermectin-susceptible strain (Deutch) as a reference. The R. microplus population showed resistance to all acaricides tested, with different mortalities at the discriminate dose: chlorpiriphos (1%), diazinon (24.2%), flumethrin (92.8%), deltamethrin (94.2%), cypermethrin (98.0%) and amitraz (1.5%). The studied tick population also showed resistance to ivermectin with a resistance ratio at 99% of 9.58 and 6.52 in the first and second evaluation, respectively. We report for the first time a R. microplus population in Mexico with different levels of resistance to OP, SP, amidines (Am) and ivermectin. The uncontrolled use of these products in the study area may promote the complete failure of tick control within a short period of time.Veterinary Parasitology 07/2011; 183(3-4):338-42. · 2.58 Impact Factor -
Article: In vitro acaricidal effect of tannin-rich plants against the cattle tick Rhipicephalus (Boophilus) microplus (Acari: Ixodidae).
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ABSTRACT: The objectives of this study were to evaluate the in vitro acaricidal effects of lyophilized extracts of four tannin rich plants (Acacia pennatula, Piscidia piscipula, Leucaena leucocephala and Lysiloma latisiliquum) against diverse stages of Rhipicephalus (Boophilus) microplus, and to asses whether tannins were involved in the acaricidal effect using polyethylene glycol (PEG) to block tannins. Larval immersion (LIT) and adult immersion (AIT) tests were used to evaluate the acaricidal effect of each of the lyophilized extracts against larval and adult stages of R. microplus respectively. Larvae and adult ticks were exposed to increasing concentrations of each plant extract (0, 1200, 2400, 4800, 9600 and 19,200 μg ml(-1)) for 10 min. Larval mortality was recorded at 48 h post-incubation. Adult mortality was recorded daily over 14 days, at which point their reproductive efficiency was evaluated. PEG was added to the extracts to verify whether tannins were involved in the acaricidal effect. The effect on egg laying inhibition and larval mortality was analyzed using the GLM procedure in SAS. A Kruskal-Wallis test was used to assess the effect of PEG on LIT results. Calculation of the lethal concentration 50 (LC50) was performed using a probit analysis. All extracts reduced the viability of R. microplus larval stages (P<0.001), and viability was restored with the addition of PEG suggesting an important role of tannins in the acaricidal effect (P<0.001). The LC50 values of L. latisiliquum and P. piscipula plant extracts were 6.402 and 2.466 μg ml(-1). None of the tannin-rich plant extracts affected adult mortality (P>0.05). Lysiloma latisiliquum extract inhibited egg hatching of R. microplus (P<0.01). Tannin-rich plant extracts from A. pennatula, P. piscipula, L. leucocephala and L. latisiliquum showed potential acaricidal activity. Further in vivo studies are needed to confirm this finding.Veterinary Parasitology 09/2010; 175(1-2):113-8. · 2.58 Impact Factor
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Institutions
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2010–2011
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National Autonomous University of Mexico
- School of Veterinary Medicine and Zootechnics
Mexico City, The Federal District, Mexico
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