Resistance In Gastrointestinal Nematodes Research Articles

Anthelmintic resistance and novel control options in equine gastrointestinal nematodes.

Control of equine nematodes has relied on benzimidazoles (BZs), tetrahydropyrimidines and macrocyclic lactones. The intensive use of anthelmintics has led to the development of anthelmintic resistance (AR) in equine cyathostomins and Parascaris equorum. Field studies indicate that BZ and pyrantel resistance is widespread in cyathostomins and there are also increasing reports of resistance to macrocyclic lactones in cyathostomins and P. equorum. The unavailability of reliable laboratory-based techniques for detecting resistance further augments the problem of nematode control in horses. The only reliable test used in horses is the fecal egg count reduction test; therefore, more focus should be given to develop and validate improved methodologies for diagnosing AR at an early stage, as well as determining the mechanisms involved in resistance development. Therefore, equine industry and researchers should devise and implement new strategies for equine worm control, such as the use of bioactive pastures or novel feed additives, and control should increasingly incorporate alternative and evidence-based parasite control strategies to limit the development of AR. This review describes the history and prevalence of AR in equine nematodes, along with recent advances in developing resistance diagnostic tests and worm control strategies in horses, as well as giving some perspective on recent research into novel control strategies.

Resistance of gastrointestinal nematodes to five different active principles in sheep infected naturally in São Paulo State, Brazil

This study evaluated the efficacy of commercially available anthelmintic drugs by calculating the percent reduction of eggs per gram (EPGR%) and appropriate statistical tests. A total of 350 animals selected from five commercial sheep farms was divided in seven groups with 10 animals each: Group 1 - control, Group 2 - Albendazole (5 mg/kg); Group 3 - Levamisole hydrochloride (5 mg/kg); Group 4 - Ivermectin (0.2 mg/kg); Group 5 - Moxidectin (0.2 mg/kg); and Group 6 - Closantel (10 mg/kg); Group 7 - Ivermectin + Levamisole + Albendazole (200 mcg/kg Ivermectin, 7.5 mg/kg Levamisole and 5 mg/kg Albendazole). EPG percent reduction was determined between day zero and day 10 after treatment had started and compared between groups. It was observed that, practically, almost all the tested drugs had some level of parasitic resistance while Moxidectin was the most effective during treatment. The results show that more sustainable procedures such as pasture rotation system, plant‑based products, certain fungi and earthworms need to be adopted to reduce parasitism and anthelmintic resistance in ovine herds.

Genome wide association study reveals new candidate genes for resistance to nematodes in Creole goat

An alternative control for gastrointestinal nematode (GIN) infection in goats can be achieved by genetic improvement of the host resistance through identification of genes controlling the resistance mechanisms and their use in breeding programs under a marker-assisted selection or gene introgression frameworks. In this context, we aimed to develop genome wide association studies (GWAS) for resistance to H. contortus in Creole goats from Guadeloupe to identify possible candidate genes associated with GIN resistance in this population. Resistance was characterized by the fecal egg counting (FEC). A total of 182 Creole goats were phenotyped for FEC and genotyped through Illumina Goat SNP50 BeadChip. After SNP quality control analysis, 46,643 SNP markers were used for GWAS. The significant associations were identified by fitting a linear mixed model. A total of seven QTL (on the chromosomes 4, 6, 11, and 17) associated to FEC were reported and candidate genes recording was performed at these positions. The identified genes were related to the intestine damage (PROM1), inflammation process (FGFBP1), immune response (LIMCH1), hemorrhage control (ADAMTS3), and muscle weakness (SUCLG1). Network analysis provided annotation results linking all identified candidate genes, which are biologically related to resistance mechanisms approaching H. contortus infections.

PCR-based genotyping of SNP markers in sheep.

Single nucleotide polymorphisms (SNPs) are the main type of variation in genome, enabling them to be associated with traits of economic importance in livestock. Genome-wide association studies (GWAS) have led to the discovery of SNPs associated with desirable traits in sheep. However, in these studies, SNPs are genotyped by high-throughput methods in genome scale, which are expensive and require sophisticated equipment and analysis methods. Therefore, the goal of this study was to develop a reliable, rapid, and inexpensive polymerase chain reaction (PCR)-based method to genotype a medium number of animals for a few candidate SNPs previously associated with desirable phenotypes in sheep by GWAS, using markers associated with gastrointestinal nematode resistance as a model. DNA extracted from white-blood cells of 150 sheep was submitted to PCR amplification followed by agarose gel electrophoresis and determination of banding pattern. Tetra-primer ARMS-PCR was successfully optimized after changes in annealing temperature; annealing and extension times; concentration of MgCl2 and DNA; ratios of inner, outer, forward and reverse primer; and addition of adjuvants, for genotyping the OAR2_14765360, OAR6_81718546, OAR11_62887032, and OAR12_69606944 SNPs in sheep. An extensive optimization of tetra-primer ARMS-PCR resulted in a suitable, simple, cost-effective PCR-based method of genotyping four SNP markers previously detected by chip arrays.

Anthelmintic efficacy of glycolipid biosurfactant produced by Pseudomonas plecoglossicida: an insight from mutant and transgenic forms of Caenorhabditis elegans.

The current research focuses on the production and characterization of glycolipid biosurfactant (GB) from Pseudomonas plecoglossicida and its anthelmintic activity against Caenorhabditis elegans. The GB was purified and characterized by Fourier Transform Infrared Spectroscopy (FTIR) and Gas Chromatography and Mass Spectrometry (GC-MS) analysis. Anthelmintic activity of GB was studied at six different pharmacological doses from 10 to 320µg/mL on C. elegans. Exposure of different developmental stages (L1, L2, L3, L4 and adult) of C. elegans to the GB reduced the survivability of worms in a dose and time-dependent manner. Adult and L4 worms were least susceptible, while L1, L2 and L3 were more susceptible to GB when compared to the untreated control. An increased exposure period drastically reduced the survival rate of worms and reduction in LC50 value. The GB significantly inhibited the development of C. elegans with an IC50 value of 53.14µg/mL and even reduced the adult body length and egg hatching. Fecundity rate of the worms treated with GB at 20, 40 and 80µg/mL decreased from 261.90 ± 3.21 to 239.70 ± 5.58, 164.20 ± 5.94 and 44.80 ± 6.22 eggs per worm, respectively. Besides the toxicological effects, prolonged exposure to GB significantly decreased (p ≤ 0.0001) the lifespan of wild type worms under standard laboratory conditions. Additionally, GB was found to be lethal towards ivermectin and albendazole resistant C. elegans strains. Overall, the data indicated that the GB extracted from P. plecoglossicida could be utilized for the control of non-susceptible and resistant gastrointestinal nematodes towards broad spectrum anthelmintic drugs, ivermectin and albendazole.

Anthelmintic resistance in gastrointestinal nematodes of goats in an organized farm from Mhow, Madhya Pradesh

Anthelmintic resistance in gastrointestinal nematodes of goats in an organized farm from Mhow, Madhya Pradesh

Anthelminthic resistance of gastrointestinal nematodes in sheep to monepantel treatment in central region of Rio Grande do Sul, Brazil

ABSTRACT: Given the numerous reports of anthelminthic resistance of sheep nematodes to different anthelmintic compounds, this study aimed to evaluate the resistance status of gastrointestinal nematodes from naturally infected sheep to monepantel in the state of Rio Grande do Sul. Four farms that present extensive raising system and absence of anthelmintic treatment for 60 days were selected for the study. Lambs that present counts of eggs per gram of feces (EPG) ≥200 (sensitivity of 50 EPG) one day (D-1) before the treatment were select for the study and randomly separated into two groups, a control group and an experimental group treated with monepantel. Feces were collected 9 days after the treatment (D+9) for EPG counts and fecal culture. The monepantel was 100% effective only on 2. The efficacy found on farm 1, 3, and 4 were 2.82%, 25.8%, and 78.4%, respectably. There were no viable larvae post-treatment at farm 2, but the genera Haemonchus, Trichostrongylus, Cooperia, and Strongyloides were resistant to it at the other farms. This study shows the presence of parasites resistant to the treatment with monepantel, pointing to the importance of monitoring its efficacy in sheep flocks of Rio Grande do Sul, Brazil.

Anthelmintic resistance in gastrointestinal nematodes of goats in southern Mozambique

Small ruminant production is significantly constrained by gastrointestinal parasites once they cause serious production and economic losses for both small-scale and large-scale farmers in the developing world. The control of helminth parasites is most exclusively based on the use of anthelmintics for the economic production of ruminants. However, the resistance of nematodes to the commonly used groups of anthelmintics represents a threat to the production, particularly for small ruminants. The objective of this study was to assess the efficacy of albendazole, the most frequently used anthelmintic in Gaza and Maputo provinces in the southern region of Mozambique, in gastrointestinal nematodes of goats between November and December, 2016. Eleven goat farms in Gaza (n = 5) and Maputo (n = 6) were surveyed. The faecal egg count reduction test was used to assess the efficacy of the drug. The flocks were considered resistant when the reduction in eggs per gram of faeces was less than 95% and the lower limit of the confidence interval was less than 90%. Resistance to albendazole was detected in 60% (3/5) of the farms in Gaza province and 83.3% (5/6) of the farms in Maputo province. The percentage of faecal egg count reduction varied from 51 to 97% in Maputo and from 0 to 100% in Gaza in the farms surveyed. In pre-treatment coprocultures, Haemonchus spp., Oesophagostomum spp. and Trichostrongylus spp. were the predominant nematode species. Post-treatment larval cultures indicated that Haemonchus spp. and, to a lesser extent, Oesophagostomum spp. and Trichostrongylus spp., were resistant to albendazole. This study provided further evidence that anthelmintic resistance of gastrointestinal nematode parasites in goats is currently a problem of great significance in this region of the country and that appropriate measures must be taken to reverse the situation. Key words: Albendazole, efficacy, gastrointestinal parasites, small ruminants, Mozambique.

Resistência anti-helmíntica em nematoides gastrintestinais de ovinos

The objective was to verify the existence of antihelminthic resistance in gastrointestinal nematodes of sheep in properties of the municipalities of Janaúba and Nova Porteirinha. The experiment was conducted at 4 properties, and was done as coproparasitological analyzes in fecal samples of 88 animals. In the farms (A and B) there was a division of the animals into two groups: control and immersion and in farms (C and D) in three groups: control, ivermectin and albendazole. Each group has 6 animals. The reduction of fecal grain contamination (RCOF) was determined based on the specific formula, indicating a percentage greater than or equal to 95%. There was resistance of the gastrointestinal nematodes to albendazole in the two properties in which it was tested and ivermectin in three of the four properties. In farm C, ivermectin showed efficacy of 97%. The most prevalent nematode was Haemonchus contortus.

Evaluation of a refugia-based strategy in pastured Stocker cattle treated with LongRange®

Anthelmintic resistance (AR) in gastrointestinal nematodes of cattle is becoming increasingly prevalent worldwide, so there exists a need to develop novel approaches to manage and slow this progression. Refugia are the proportion of the worm population not selected by drug treatment, and the greater the proportion of the worm population left untreated (in refugia), the slower the progression of AR. Sources of refugia include worms in animals left untreated, stages of parasites not affected by the treatment, and free-living stages in the environment (e.g. eggs/larvae on pasture). Studies in sheep demonstrate that managing refugia will reduce the progression of AR without negatively impacting the health or productivity of the flock. However, many of these strategies are impractical for use with cattle, and consequently have not been tested or widely implemented in cattle. One refugia-based strategy with good potential applicability to the cattle industry is 'selective non-treatment’ where a percentage of the herd is deliberately left untreated. In this study, we examined the use of a selective non-treatment strategy in Stocker cattle.

Prevalence of gastrointestinal nematode resistance to avermectin anthelmintics on beef cattle operations in Georgia

Anthelmintic resistance is a worldwide problem in all livestock systems, with most reports of resistance in cattle parasites being to the macrocyclic lactone (ML) drug class. Several prevalence studies performed internationally demonstrate that anthelmintic resistance in cattle parasites is a growing problem, however, no similar studies have been performed in the US. The primary objective of this study was to gain data on the prevalence of ML resistance in gastrointestinal nematode (GIN) parasites on beef cattle farms in Georgia. We also wanted to test the efficacy of combination anthelmintic therapy in these same herds, and use these data as a basis for educational outreach programs for beef producers in Georgia.

Synergistic interaction of ten essential oils against Haemonchus contortus in vitro

Anthelmintic resistance in sheep gastrointestinal nematodes is a worldwide problem. Multi-drug resistant haemonchosis is the most serious impediment for small ruminant systems, and there are no new drug candidates currently under development. Molecules from natural sources have demonstrated anthelmintic activity against parasites. In this work, the monoterpenoids carvacrol, carvone, cineole, linalool, limonene, and thymol and the phenylpropanoids cinnamaldehyde, anethole, vanillin, and eugenol were assessed individually or in mixtures of ten binary, three ternary, and three quaternary combinations using the in vitro egg hatch assay with eggs of a multi-drug resistant strain of Haemonchus contortus. The main objective of this study was to identify the most effective interaction among essential oils with the greatest individual anthelmintic efficacy and to determine the most powerful combinations. The essential oils were ranked by their 50% lethal concentration (LC50) as follows (mg/mL): cinamaldehyde (0.018), anethole (0.070), carvone (0.085), carvacrol (0.11), thymol (0.13), linalool (0.29), vanillin (0.57), eugenol (0.57), cineole (4.74), and limonene (207.5). Quantification of synergism, additive effect, and antagonism were calculated for binary, ternary, and quaternary combinations. The best anthelmintic effect resulting from synergistic activity among 16 different combinations was for cinnamaldehyde:carvacrol (CL50 0.012mg/mL) and anethole:carvone (CL50 0.013mg/mL). These results indicate that these binary combinations would be promising to be tested in sheep infected with H. contortus.

Utilization of composite fecal samples for detection of anthelmintic resistance in gastrointestinal nematodes of cattle

Recent reports indicate that anthelmintic resistance in gastrointestinal nematodes of cattle is becoming increasingly prevalent worldwide. Presently, the fecal egg count reduction test (FECRT) is the only means available for detection of resistance to anthelmintics in cattle herds at the farm level. However, the FECRT is labor and cost intensive, and consequently is only rarely performed on cattle farms unless for research purposes. If costs could be reduced, cattle producers might be more likely to pursue drug resistance testing on their farms. One approach to reducing the cost of the FECRT, is the use of composite fecal samples for performing fecal egg counts (FEC), rather than conducting FEC on fecal samples from 15 to 20 individual animals. In this study FECRT were performed on 14 groups of cattle using both individual and composite FEC methods To measure how well the results of composite sampling reproduce those of individual sampling, Lin’s Concordance Correlation Coefficient was utilized to describe both the linear relationship between methods and the slope and y-intercept of the line relating the data sets. There was little difference between the approaches with 98% agreement in mean FEC found between methods Mean FEC based on individual counts ranged between 0 and 670.6 eggs per gram of feces, indicating that the results of this study are applicable to a wide range of FEC levels. Standard error of the mean FEC and range of FEC are reported for each group prior to and following treatment to describe the variability of the data set. There was greater than 95% agreement in drug efficacy between individual and composite sampling methods, demonstrating composite sampling is appropriate to evaluate drug efficacy. Notably, for all groups tested the efficacy calculated by composite sampling was within the 95% confidence interval for efficacy calculated using individual sampling. The use of composite samples was shown to reduce the number of FEC required by 79%. These data demonstrate that pooling fecal samples from a group of cattle and then performing repeated FEC on that composite sample yields results very similar to performing individual FEC on those same animals, while substantially reducing the cost of performing a FECRT as compared to individual fecal samples. Furthermore, we have developed suggested methods for using composite samples in a FECRT, provided a cost comparison for this methodology, and described potential issues associated with the use of composite samples that must be considered.

Quantification of resistant alleles in the \u03b2-tubulin gene of field strains of gastrointestinal nematodes and their relation with the faecal egg count reduction test

BackgroundBenzimidazole (BZ) resistance in gastrointestinal nematodes is associated with a single nucleotide polymorphism (SNP) at codons 167, 198 and 200 in the isotype 1 of beta-tubulin gene although in some species these SNPs have also been associated with resistance to macrocyclic lactones. In the present study we compared the levels of resistance in Teladorsagia circumcincta and Trichostrongylus colubriformis by means of the faecal egg reduction test (FECRT) and the percentage of resistant alleles obtained after pyrosequencing. The study was conducted in 10 naturally infected sheep flocks. Each flock was divided into three groups: i) group treated with albendazole (ABZ); ii) group treated with ivermectin (IVM); iii) untreated group. The number of eggs excreted per gram of faeces was estimated at day 0 and 14 post-treatment.ResultsResistance to ABZ was observed in 12.5% (1/8) of the flocks and to IVM in 44.4% (4/9) of them. One flock was resistant to both drugs according to FECRT. Coprocultures were performed at the same dates to collect L3 for DNA extraction from pooled larvae and to determine the resistant allele frequencies by pyrosequencing analysis. In T. circumcincta, SNPs were not found at any of the three codons before treatment; after the administration of ABZ, SNPs were present only in two different flocks, one of them with a frequency of 23.8% at SNP 167, and the other 13.2% % at SNP 198. In relation to T. colubriformis, we found the SNP200 before treatment in 33.3% (3/9) of the flocks with values between 48.5 and 87.8%. After treatment with ABZ and IVM, the prevalence of this SNP increased to 75 and 100% of the flocks, with a mean frequency of 95.1% and 82.6%, respectively.ConclusionThe frequencies observed for SNP200 in T. colubriformis indicate that the presence of resistance is more common than revealed by the FECRT.

The use of Eucalyptus staigeriana nanoemulsion for control of sheep haemonchosis

ABSTRACT: Sustainable control of gastrointestinal nematodes (GIN) in small ruminants has been based on the use of alternative methods, including targeted selective treatment, such as FAMACHA. Another GIN control alternative is the use of herbal medicines, although in many cases their use is based on empirical knowledge. Biopolymer nanoformulations has been investigated to maximize the essential oil effects against sheep gastrointestinal nematodes. The aim of the present study was to combine a Eucalyptus staigeriana essential oil nanoemulsion (EsNano) with FAMACHA as an alternative control for sheep haemonchosis. The study was performed over six months at a commercial sheep farm located in a semiarid region of Northeast Brazil. Initially, a fecal egg count reduction test (FECRT) in sheep with levamisole, ivermectin and oxfendazole in sheep was performed used to determine the most effective anthelmintic to use as the positive control. Levamisole has been selected because it showed efficacy superior to 95%. EsNano was obtained and then its physicochemical properties were characterized. The average (±SE) size of the particles in the nanoemulsion was 276.8 (±12.3) nm with bimodal distribution and polydispersity. Nine visits were performed, from April to September 2013, with an interval of 17 days. One hundred sixty-two male and female sheep were divided into three groups (n=54 each) and were treated when FAMACHA score was 3, 4, or 5: G-EsNano 250mg kg-1 EsNano; G-Lev 7.5mg kg-1 levamisole (positive control), and G-Neg was not treated (negative control). Feces from sheep were collected to quantify the number of eggs per gram of feces (epg) and to identify nematode genera. Sheep weight gain was monitored. The epg data for each group and the average sheep weight gains were analyzed by variance analysis and compared with the Tukey’s test (P<0.05). Significant difference between the number of animals treated with EsNano and levamisole was not observed in any visit (P>0.05). The epg variation was similar in the G-EsNano and G-Lev groups on visits (P>0.05), except the second and fifth evaluation in the epg groups were significantly different (P<0.05). Haemonchus spp. was the most prevalent nematode. There was no significant weight gain in any of the treated groups (P<0.05). The combination of phytotherapy and FAMACHA can be an alternative to minimize the use of synthetic anthelmintics to control resistant GIN populations of small ruminants.

Benzimidazole resistance within red deer, roe deer and sheep populations within a joint habitat in Hungary

The anthelmintic resistance of gastrointestinal nematodes is one of the most important, economic risk factors in grazing ruminant systems, all over the world. We have infinitesimal information about the resistance status of nematodes in deer species. Our aim was to determine the presence of BZ resistance in the generalist worm, Haemonchus contortus in pastured sheep and free ranging red and roe deer by RFLP-PCR method based on the detection Phe200Tyr single nucleotide polymorphism. By investigation of 70 worms from each host species, the homozygous susceptible genotype was the most representative in the red deer (100%), the homozygous resistant genotype was most prevalent in the sheep (68.6%) and moderate in the roe deer (17.1%), while the heterozygous genotype was observed in equal proportion in the sheep and roe deer (28.6%). Our results suggest that overlapping habitats of sheep flocks and roe deer could contribute to the occurrence and spread of resistant allele within wildlife.

The first reported case of resistance of gastrointestinal nematodes to benzimidazole anthelmintic in goats in Poland

Fecal egg count reduction (FECR) test with albendazole and egg hatch test (EHT) with thiabendazole (TBZ) were performed in a dairy goat herd suspected of anthelmintic resistance to benzimidazoles. The herd had been regularly dewormed with fenbendazole for 5 previous years and despite that it remained infected with several species of gastrointestinal nematodes (Trichostrongylus colubriformis, Teladorsagia circumcincta, and Haemonchus contortus). Albendazole was administered per os at dose of 20 mg/kg to 10 goats (treated group), while 10 other goats remained untreated (control group). Fecal egg count (FEC) was determined using McMaster egg counting method before and 7 days after the treatment in the treated group, and once (at the latter moment) in the control group. EHT was performed on the pooled rectal sample collected from treated goats. EHT comprised the negative control and 7 consecutive concentrations of TBZ (0.05, 0.1, 0.2, 0.3, 0.5, 1.0, 2.0 μg/ml) according to the standard procedure. Two hundred eggs/larvae were counted to determine percentage of unhatched eggs, which was adjusted by the natural mortality. TBZ dose effective in preventing hatching of 50% of eggs (ED50) was determined using the log-probit transformation. Median FEC (range) before the treatment was 1000 (250–3450) epg in the treated group and dropped to 150 (50–500) epg after the treatment (p=0.005). Median FEC (range) after the treatment was also significantly lower in the treated than in control group (p=0.009), where it was 725 (0–5050) epg. FECR between the treated and control group was 81% (95% CI: 49%, 93%). FECR in the treated group was 83% and 74% based on average and individual approach, respectively. ED50 value of TBZ was 0.78 μg/ml. Only H. contortus persisted in the treated group after treatment. The results indicate resistance of H. contortus to a benzimidazole anthelmintic, which is the first such case reported in Polish goats.

Genome-wide SNP analysis using 2b-RAD sequencing identifies the candidate genes putatively associated with resistance to ivermectin in Haemonchus contortus

BackgroundThe excessive and uncontrolled use of anthelmintics, e.g. ivermectin (IVM) for the treatment of livestock parasites has led to widespread resistance in gastrointestinal nematodes, such as Haemonchus contortus. There is an urgent need for better management of drug-use in nematode control and development of novel anthelmintics. Discovery and identification of anthelmintic resistance-associate molecules/markers can provide a basis for rational anthelmintics-use and development of novel drugs. Recent studies have shown that ivermectin resistance in H. contortus is likely to be multi-genic in nature except for several genes coding for IVM target and efflux pump. However, no other IVM resistance-associated genes were characterized by conventional methods or strategies. In the present study we adopted a new strategy, i.e. using genome-wide single nucleotide polymorphism (SNP) analysis based on 2b-RAD sequencing, for discovering SNPs markers across the genomes in both IVM susceptible and resistant isolates of H. contortus and identifying potential IVM resistance-associated genes.ResultsWe discovered 2962 and 2667 SNPs within both susceptible and resistant strains of H. contortus, respectively. A relative lower and similar genetic variations were observed within both resistant and susceptible strains (average π values were equal to 0.1883 and 0.1953, respectively); whereas a high genetic variation was found across both strains (average π value was equal to 0.3899). A significant differentiation across 2b-RAD tags nucleotide sites was also observed between the two strains (average FST value was equal to 0.3076); the larger differences in average FST were observed at SNPs loci between coding and noncoding (including intronic) regions. Comparison between resistant and susceptible strains revealed that 208 SNPs loci exhibited significantly elevated FST values, 24 SNPs of those loci were located in the CDS regions of the nine genes and were likely to have signature of IVM directional selection. Seven of the nine candidate genes were predicted to code for some functional proteins such as potential IVM target and/or efflux pump proteins, component proteins of receptor complex in membrane on neuromuscular cells, and transcriptional regulation proteins. Those genes might be involved in resistance to IVM.ConclusionsOur data suggest that candidate genes putatively associated with resistance to IVM in H. contortus may be identified by genome-wide SNP analysis using 2b-RAD sequencing.

Anthelmintic resistance in ruminants: development, diagnostics, and procedures

Anthelmintic resistance of gastrointestinal nematodes in small ruminants, but also in cattle and horses, is now found worldwide. The reason for increasing anthelmintic resistance is, in particular, the extensive use of all the anthelmintic agents available on the market. A non-targeted use leads to the selection of naturally occurring resistance genes within parasite populations. The most practical method for evaluating the efficacy of an anthelmintic is the fecal egg-count reduction test. To reduce the rate of anthelmintic resistance development, the available active substances must be applied less and in a targeted manner. When applying targeted (selective) treatment, part of the herd is left untreated. Therefore, it is necessary to identify the animals that require treatment for health or economic reasons. To decide on anthelmintic treatment, findings can be collected from single animals or from a group of animals in a herd. To determine which groups of animals are to be treated within a herd (targeted treatment), pooled fecal samples (cattle and small ruminants), serum pepsinogen concentration (cattle), or Ostertagia ostertagi antibodies in the bulk milk (cattle) can be analyzed. For individual animal (targeted selective) treatment, criteria including fecal egg count (cattle and small ruminants), conjuctival color as an indicator for infection with Haemonchus contortus (FAMACHA®, small ruminants), body condition in adult animals (small ruminants), weight gain in juvenile animals (cattle and small ruminants), and the consistency of the feces (small ruminants) are used. These decision criteria can also be combined to enhance the informative value. Furthermore, an efficacy test of the anthelmintics used should be performed regularly at the beginning of the pasture season. During the pasture season, a low infection pressure should be maintained by pasture management strategies. The goal of sustainable parasite management is the reduction of anthelmintic treatment while maintaining the productivity and health of the animals and thus a longer effectiveness of the available drugs.

Molecular identification of abomasal bacteria associated with genetic resistance and susceptibility to Haemonchus contortus infection in sheep

The widespread occurrence of anthelmintic-resistant gastrointestinal nematodes (GINs), particularly Haemonchus contortus, in sheep production systems has magnified the need to identify and develop alternative control strategies. Strategies include the selection of genetically GIN-resistant sheep and the implementation of biological parasite control to reduce dependence on anthelmintic drugs. In this study, we aimed to establish the molecular identity of bacterial communities present in the abomasum of sheep classified as resistant or susceptible to H. contortus, an abomasal parasite. Thirty-eight sheep were experimentally infected with L3 Haemonchus contortus and analyzed for fecal egg count (FEC) and hematocrit (Ht) to establish haemonchosis resistance or susceptibility. Four resistant sheep (RS) and four susceptible sheep (SS) were selected for microbial sampling and subsequent phylogenetic analysis. Molecular identification of the bacteria was based on amplification of the bacterial 16S rRNA gene, construction of a 16S rDNA clone library, and subsequent gene sequencing. Significant differences (p = 0.05) were observed in the occurrence of different phyla identified in RS and SS libraries: Firmicutes (61.4% and 37.2%, respectively), Proteobacteria (10.2% and 37.2%, respectively), Bacteroidetes (12.8% and 5.8%, respectively), and unclassified bacteria (12.8% and 17%, respectively). Differences between the proportions of bacterial communities present in the RS and SS pool samples were observed, contributing as a first step toward the assessment of the association between the gastrointestinal tract microbiota and nematode resistance in sheep.