Population replacement of benzimidazole-resistant Haemonchus contortus with susceptible strains: evidence of changes in the resistance status.

The spread of anthelmintic resistance (AR) in nematode populations threatens the viability of sheep production systems worldwide, and warrants the adoption of sensitive, practical, and standardized tests to detect AR. The aim of this study was to characterize the replacement of an Haemonchus contortus population resistant to benzimidazoles (BZDs) by a susceptible one, by means of both phenotypic and genotypic techniques. Phenotypic methods to assess BZD resistance included in vivo tests, such as the fecal egg count reduction test (FECRT), and in vitro tests, such as the egg hatch assay (EHA). Additionally, genotypification of polymorphisms associated with BZD resistance by sequencing a fragment of the isotype 1 ß-tubulin gene was carried out. The initial, BZD-resistant population (initial Balcarce population) exhibited an egg count reduction (ECR) of 59.3%. Following refugium replacement, the final population (final Balcarce population) exhibited an ECR of 95.2%. For the initial Balcarce population, the median effective dose (ED50) for the EHA was 0.607 µg thiabendazole (TBZ)/mL, with a rate of eclosion at a discriminating dose (EDD) of 0.1 µg TBZ/mL of 76.73%. For the final Balcarce population, ED50 was 0.02 µg TBZ/mL, and EDD was 1.97%. In the initial population, 93% of the analyzed individuals exhibited genotypic combinations associated with BZD resistance (53% Phe/Phe167-Tyr/Tyr200, 37% Phe/Tyr167-Phe/Tyr200, and 3% Phe/Tyr167-Glu/Leu198). Conversely, no combination associated with resistance was found in individuals from the final population. All of the tests were useful for detecting AR to BZDs. The results from the genetic and phenotypical studies were consistent, and the resulting information greatly aided in interpreting the outcomes of the population replacement and the potential impact of this strategy on management of AR.

Phytochemicals in Gastrointestinal Nematode Control: Pharmacokinetic-Pharmacodynamic Evaluation of the Ivermectin plus Carvone Combination.

A wide variety of plant-derived phytochemicals with anthelmintic effects have been described. Most of them have shown activity against parasites in vitro but have not been extensively explored in vivo. The aim of the current work was to study the pharmacokinetic-pharmacodynamic relationship of the combined administration of carvone (R-CNE) and ivermectin (IVM) to lambs. Three trials were conducted to evaluate the pharmacological interaction between R-CNE and IVM in lambs infected with resistant nematodes. Drug concentrations were measured in plasma, target tissues, and H. contortus by HPLC with fluorescent (IVM) and ultraviolet (R-CNE) detection. The effect of both compounds on parasites was estimated by the fecal egg count reduction. Coadministration with R-CNE significantly increased the plasma bioavailability of IVM. R-CNE showed a moderate anthelmintic effect, which was greater on the susceptible isolate of H. contortus. After the combination of R-CNE and IVM as an oral emulsion, both compounds were quantified in H. contortus recovered from infected lambs. However, R-CNE concentrations were much lower than those reported to achieve anthelmintic effects in the in vitro assays. Optimization of the pharmaceutical formulation, dose rate, and administration schedule is needed to take advantage of the intrinsic anthelmintic activity of phytochemicals.

Recovery of fenbendazole efficacy on resistant Haemonchus contortus by management of parasite refugia and population replacement.

The recovery of fenbendazole efficacy against Haemonchus contortus was attempted in a sheep intensive production system, using a strategy of population replacement in which the initial absolute efficacy of fenbendazole was 0%. The strategy was based on managing the parasite populations in refugia. Firstly, the resistant parasite population was reduced by means of anthelmintic treatments with efficacious drugs (Phase I), then a new, susceptible population was introduced in summer by way of artificially infected lambs at weaning, which were left to graze on the experimental pasture for eleven months (Phase II). Lastly, the impact of the replacement strategy, in terms of benzimidazole efficacy, was measured (Phase III). Faecal egg counts from permanent lambs and worm burdens as a measure of pasture infectivity from tracer lambs were determined throughout the study. During Phase I, faecal egg counts diminished from a peak of 2968 (300-7740) epg to 0 epg at the end, while adult worm burdens of H. contortus were reduced from 2625 (800-5100) to 0, which showed that the treatment strategy used in Phase I was effective in reducing the resistant population. These parameters also showed that good levels of pasture contamination and infectivity were achieved in Phase II, as faecal egg counts of up to 7275 (3240-13080) epg and adult worm burdens of 500 (200-800) H. contortus were reached. The absolute benzimidazole efficacy on H. contortus estimated at 16 months post-population replacement (Phase III) was 97.58%. The results lead to the conclusion that the recovery of anthelmintic efficacy of fenbendazole against a resistant population of H. contortus may be achieved by means of a strategy based on management of refugia and a subsequent introduction of a susceptible population. This strategy might be translatable to other resistant nematode genera.

Methotrexate pharmacogenetics in Uruguayan adults with hematological malignant diseases.

BACKGROUND: Individual variability is among the causes of toxicity and interruption of treatment in acute lymphoblastic leukemia (ALL) and severe non-Hodgkin lymphoma (NHL) patients under protocols including Methotrexate (MTX): 2,4-diamino-N10-methyl propyl-glutamic acid. METHODS: 41 Uruguayan patients were recruited. Gene polymorphisms involved in MTX pathway were analyzed and their association with treatment toxicities and outcome was evaluated. RESULTS: Genotype distribution and allele frequency were determined for SLC19A1 G80A, MTHFR C677T and A1298C, TYMS 28bp copy number variation, SLCO1B1 T521C, DHFR C-1610G/T, DHFR C-680A, DHFR A-317G and DHFR 19bp indel. Multivariate analysis showed that DHFR-1610G/T (OR=0.107, p=0.018) and MTHFR677T alleles (OR=0.12, p=0.026) had a strong protective effect against hematologic toxicity, while DHFR-1610CC genotype increased this toxicity (OR=9, p=0.045). No more associations were found. CONCLUSIONS: The associations found between gene polymorphisms and toxicities in this small cohort are encouraging for a more extensive research to gain a better dose individualization in adult ALL and NHL patients. Besides, genotype distribution showed to be different from other populations, reinforcing the idea that genotype data from other populations should not be extrapolated to ours.