Anthelmintic resistance in nematode parasites from goats in Spain

First Report of Anthelmintic Resistance in Gastrointestinal Nematodes in Goats in Romania

Currently, there are three classes of anthelmintics most commonly used in small ruminants: the benzimidazoles (BZs), macrocyclic lactones (MLs) and cholinergic agonists (especially levamisole; LEV). The widespread use of those products has led to the emergence of drug-resistant parasite strains which represents a serious threat to the livestock industry. In the present study, we describe for the first time a case of resistance to anthelmintics in goats in Romania. The study was carried out in 2021 in a dairy goat herd from the Transylvania region. Two types of diagnostic methods were used to confirm anthelmintic resistance (AR). First, the faecal egg count reduction test (FECRT), an in vivo AR diagnostic method, was used to evaluate the efficacy of eprinomectin (EPM). The results of this test were analysed applying two different calculative methods that are used only in treated animals (without the control group). Furthermore, two in vitro methods were used: the egg hatch test (EHT) for the detection of resistance to BZs, and the larval development test (LDT) for detection of resistance to all three classes of anthelmintics. The results of FECRT indicate the resistance of gastrointestinal nematodes (GINs) to EPM in both calculative methods (FECR₁ = -88% and FECR₂ = -202%). In addition, the results obtained for ivermectin aglycone (IVM-AG) in LDT also indicate resistance to drugs from MLs group, especially avermectins. Similarly, the results of in vitro methods (EHT and LDT) indicate resistance to BZs in this herd. LEV was the only drug that stopped the development of L3 larvae 100% (LDT). H. contortus was the only nematode species found in coproculture after EPM treatment. Furthermore, H. contotus L3 larvae was the only species found in the wells with the highest concentrations of thiabendazole (TBZ) and IVM-AG in LDT. This suggests that resistance to both BZs and MLs was present for that species.

Multiple Anthelmintic Resistance at a Goat Farm in Slovakia

Cases of parasite resistance to the main classes of anthelmintics are increasingly reported from small ruminants at farms in Europe. We visited a goat farm in Slovakia in November 2019 with suspected parasite problems that reduced productivity and performed an in vivo faecal egg count reduction test (FECRT) and an in vitro larval development test (LDT) for all three main classes of anthelmintics. The lowest efficacy (60 %) detected by FECRT was for ivermectin (IVM). Benzimidazole (BZ) efficacy ranged between 80.3 and 86.5 %, and levamisole (LEV) efficacy was 94 %. The results from the in vivo FECRT test were confirmed by the in vitro LDT. Minimum inhibitory concentration (MIC) 173.6 ng/ml for IVM several times exceeded the recommended threshold of 21.6 ng/ml. Mean LD₅₀ for BZ was equal to the threshold concentration, but the other threshold criteria indicated a low level of resistance in the population. The LDT did not indicate the presence of resistance only for LEV. The MIC 1.0 μg/ml for LEV was evaluated as susceptible with respect to species composition. Teladorsagia was the dominant genus after treatment with BZ, IVM, and LEV. Haemonchus contortus was identifi ed after treatment with BZ and LEV.

Haemonchus contortus Susceptibility and Resistance to Anthelmintics in Naturally Infected Egyptian Sheep

PURPOSE

Susceptibility and resistance of Haemonchus contortus to anthelmintic drugs, including ivermectin, levamisole, and albendazole in naturally infected sheep were investigated.

METHODS

Three sets of assays were conducted to detect drug efficacy. Firstly, in vivo estimation of drug resistance to H. contortus was explored in 80 sheep naturally infected with H. contortus. Sheep were divided into four equal groups (20 sheep for each group): the first group was treated with albendazole (5.00 mg/kg BW), the second with levamisole (7.50 mg/kg BW), the third with ivermectin (0.20 mg/kg BW), and the fourth group served as the untreated control. Fecal egg reduction test (FERT) was done at days 7 and 14 after treatment. Secondly, for in vitro egg hatching assay (EHA), H. contortus eggs from naturally infected sheep were collected and treated with 0.0002, 0.002, 0.02, 0.2, and 2.0 µg/mL albendazole. Thirdly, molecular detection of the albendazole resistance gene in adult male H. contortus worms and larvae from infected sheep was carried out using allele-specific PCR.

RESULTS

The FECRT results showed that the drug efficacy was 86.84% for albendazole and 100% for both levamisole and ivermectin. The result of EHA showed that eggs did not hatch at 2.0 µg/mL albendazole concentration. Molecular findings showed two forms, including H. contortus homozygous susceptible (SS) and heterozygous (RS) of "β-tubulin" gene at 200 sites, which were recorded in both single male worms and larvae.

CONCLUSION

H. contortus, which was susceptible to levamisole and ivermectin, had developed resistance to albendazole.

Exploring benzimidazole resistance in Haemonchus contortus by next generation sequencing and droplet digital PCR

Anthelmintic resistance in gastrointestinal nematode (GIN) parasites of grazing ruminants is on the rise in countries across the world. Haemonchus contortus is one of most frequently encountered drug-resistant GINs in small ruminants. This blood-sucking abomasal nematode contributes to massive treatment costs and poses a serious threat to farm animal health. To prevent the establishment of resistant strains of this parasite, up-to-date molecular techniques need to be proposed which would allow for quick, cheap and accurate identification of individuals infected with resistant worms. The effort has been made in the previous decade, with the development of the pyrosequencing method to detect resistance-predicting alleles. Here we propose a novel droplet digital PCR (ddPCR) assay for rapid and precise identification of H. contortus strains as being resistant or susceptible to benzimidazole drugs based on the presence or absence of the most common resistance-conferring mutation F200Y (TAC) in the β tubulin isotype 1 gene. The newly developed ddPCR assay was first optimized and validated utilizing DNA templates from single-worm samples, which were previously sequenced using the next generation PacBio RSII Sequencing (NGS) platform. Subsequent NGS results for faecal larval cultures were then used as a reference to compare the obtained values for fractional abundances of the resistance-determining mutant allele between ddPCR and NGS techniques in each sample. Both methods managed to produce highly similar results and ddPCR proved to be a reliable tool which, when utilized at full capacity, can be used to create a powerful mutation detection and quantification assay.

Benzimidazole resistance in helminths: From problem to diagnosis

Helminth parasites cause significant morbidity and mortality in endemic countries. Given the severity of symptoms that helminths may elicit in the host, intervention with prophylactic and therapeutic measures is imperative. Treatment with benzimidazoles is the most widely used means of combatting these parasites. However, widespread use of these drugs can select for drug-resistant parasite strains. In this review, we approach the problem of benzimidazole resistance in helminths in both humans and animals, focusing on the properties of the drug, the molecular mechanisms of drug resistance and how resistance is diagnosed.

A telephone survey of internal parasite control practices on sheep farms in Spain

A telephone survey of farmers was conducted to determine current internal parasite control practices on sheep farms in Spain; the farmers were interviewed by their veterinarians. Anthelmintic choice was largely on veterinary advice and dominated by benzimidazoles and macrocyclic lactones. Anthelmintic rotation was separated into: no rotation (42% of farms); annual rotation (36%); rotate within year (20%); and rotate every second year (2%). The mean annual number of treatments varied subtly by region; ewes and rams 1.6-2.1, replacement lambs 1.7-2.1. Anthelmintics are administered primarily during spring and early summer (47% of treatments), and autumn (41%). Thirty-two percent of farmers introduced sheep to their properties and more than half did not quarantine drench the arrivals.

Management and environmental factors related to benzimidazole resistance in sheep nematodes in Northeast Spain

A survey to determine the level of parasite resistance to benzimidazoles (BZ) under field conditions was performed on 107 commercial sheep farms located in the Aragon region of northeast Spain. Resistance was measured using the discriminant dose, a simplified form of the in vitro egg hatch assay (EHA). Taking into account the spatial structure of the data, a multivariate approach was applied to management and environmental variables as well as to their relationships with BZ resistance levels compiled from each flock. Results estimated that 11% of flocks had resistant parasite populations, although we suspected the presence of BZ-resistant parasite strains in 98% of the sample. Resistance levels were more similar among the nearest flocks, suggesting a contagious spatial distribution of resistance (i.e., resistance at neighbouring farms was not independent from one another). Management variables such as frequency of deworming, grazing in private pastures and underdosing were positively related to resistance levels, whereas only the use of BZ was negatively related to resistance levels, likely because BZ were replaced by other anthelmintics in flocks where reduced BZ efficacy was suspected. In addition to climatic conditions and seasonality, land use was an environmental variable associated with observed BZ resistance levels. Generally, resistance was highest in cooler and wetter areas but was lower in flocks sampled during January-March compared to flocks sampled in April-June or October-December. Variation partitioning procedures showed that the variation of resistance explained by the effect of environmental variables was higher than management variables. The effects of both variable groups, however, highly overlapped with the spatial structure of resistant levels, which suggests that a considerable amount of the effects attributable to both variable groups may be actually due to the spatial distribution of resistance. The resistance variation explained by the spatial component suggested that other uncontrolled factors acting at short spatial scale (e.g., common management and environmental variables; the importation of resistant strains and their posterior spread across neighbouring flocks; the selection history of the worms carried out by historical management events previous to this survey; and genetic, physiological or both types of parasite population variation) could yield this contagious spatial structure of BZ resistance. Although further research is needed, both seasonal variation and the dependence of resistance levels among neighbouring flocks should be taken into account in the design of future research or observational resistance programmes to minimise spatial and temporal pseudo-replication. Thus, research would avoid biased estimations of resistance prevalence or of its relationship with putative factors.

Multiple anthelmintic resistance on a goat farm in Hawassa (southern Ethiopia)

A study was conducted to determine the presence of anthelmintic resistance on Hawassa University goat farm in southern Ethiopia. The 180 goats were stratified by age and sex and randomly assigned to treatment groups (albendazole, tetramisole and ivermectin and untreated control). Each treatment group included 15 goats and treatments were administered according to weight of each goat with 7.5 mg/kg bw albendazole, 22.5 mg/kg bw tetramisole and 0.2 mg/kg bw ivermectin dose rates recommended by scientists. Faecal samples were collected on day 0 before treatment, and again on day 12 post treatment. Efficacy of all the drugs was assessed on day 12 post treatment by faecal egg count reduction test (FECRT). Multiple anthelmintic resistance in Haemonchus spp. against albendazole, tetramisole and ivermectin was recorded in all age categories of the goats. Likewise, Trichostrongylus/Teladorsagia spp. showed resistance against ivermectin. Coprocultures from all pre- and post-treatments revealed the predominance of Haemonchus spp. Resistance against anthelmintics is attributed to the high frequency of treatment and low dosage of treatment practices on the farm. Large scale studies, however, are needed to assess the current status of anthelmintic resistance against the most commonly used anthelmintics in different agroecology, species of animals and management systems in Ethiopia.

Resistance of trichostrongyles to benzimidazoles in Italy: a first report in a goat farm with multiple and repeated introductions

Anthelmintic resistance is widely distributed in small ruminants throughout the world. The extension of resistance seems lower in southern European countries and has not been reported previously in Italy. In the present study, resistance to benzimidazoles, levamisole and ivermectin was evaluated in a multi-breed goat farm of southern Italy. The farm had a history of repeated goat introductions from other flocks and a moderate regimen of anthelmintic treatments using alternatively the three above-mentioned drugs. Resistance of gastrointestinal strongyles was studied on the basis of faecal egg counts, egg hatch assay and necropsies. Resistance to anthelmintics was evidenced for benzimidazoles only, and Trichostrongylus colubriformis was the only resistant strongyle species. Single drug and single species resistance suggest that resistance is on its beginning and that measures for reducing the spread of resistance are of interest and should be promoted.

Effect of nematophagous fungusDuddingtonia flagransand energy supplementation on the epidemiology of naturally infected kids

Gastrointestinal (GI) nematode infection is a major constraint for grazing livestock production. The increasing prevalence and severity of anthelmintic-resistant nematodes in many parts of the world has led to a search for non-chemical control options. Under experimental conditions, the nematophagous fungus Duddingtonia flagrans is emerging as an alternative to chemotherapy for the control of GI nematode infection in biological production systems. Also, recent information points to the role of energy nutrition to increase the immune response against GI nematode infection. In this study the effect of D. flagrans and energy supplementation on the epidemiology of GI nematode infections is explored on grazing kids. Four groups of 10, 4-month old goats were turned out on infected pasture in the early spring and allocated to four separate paddocks where they were rotationally grazed for 16 weeks. One of these groups (F) received 0.5 x 10(6) D. flagrans spores/kg BW/d. Another group (S) was supplemented with 100 g barley grain per day. A third group (F+S) received both nematophagous fungi and barley supplement treatments simultaneously while the fourth group (C) was used as a non-treated control. Both nematophagous fungi and barley supplement had a significant effect (P<0.01) on reducing pasture infectivity, faecal egg excretion and worm burdens at slaughter that was particularly evident for Trichostrongylus colubriformis. The combination of both treatments showed a synergistic effect on the control of gastrointestinal nematode infections. At slaughter, the average total post-mortem worm count of the F+S group was reduced by 65% compared with the non-treated control. The results herein show that D. flagrans can act as an efficient biological control agent against kid GI nematode infections on pasture, which could further improve carcass characteristics. While small amounts of energy supplement can also reduce kid infection, the effect of D. flagrans as a biological control agent appeared clearly enhanced both in magnitude and duration by energy supplementation. This has clear implications for grazing animals and provides an efficient method for the practical control of parasitic nematodes in biological production systems.

Anthelmintic resistance: The state of play revisited

Helminthosis is one of the major constraints in the successful wool and mutton industry throughout the world. Anthelmintic Resistance (AR) is said to have been established when previously effective drug ceases to kill exposed parasitic population at the therapeutically recommended dosages. Anthelmintic resistance is almost cosmopolitan in distribution and it has been reported in almost all species of domestic animals and even in some parasites of human beings. Some of the most important species of parasites of small ruminants in which AR has been reported include: Haemonchus spp., Trichostrongylus spp. Teladorsagia spp., Cooperia spp. Nematodirus spp., and Oesophagostomum spp. All the major groups of anthelmintics have been reported for development of variable degrees of resistance in different species of gastrointestinal nematodes. This paper describes the global scenario of prevalence and methods used for detection of AR in small ruminants. Different mechanisms and contributory factors for the development of AR are discussed. Various options and alternate strategies for the control and/or delay in the onset of AR are suggested in the light of available information.

Anthelmintic resistance in trichostrongylid nematodes of sheep farms in Northwest Spain

A survey to determine the prevalence of anthelmintic resistance in nematode parasites of sheep against the three main families of anthelmintics (benzimidazoles, macrocyclic lactones and imidazothiazoles) was carried out from January 1999 to December 2003 involving 85 flocks in Northwest (NW) Spain. In the study on prevalence of resistance to benzimidazoles, faecal egg count reduction test (FECRT) showed there was resistance in 8 (12.7%) flocks, 1 (1.6%) was suspected, and 54 (85.7%) were susceptible. The results indicated that 9 flocks (34.61%) showed resistance, 1 (3.85%) showed suspected resistance, and 16 (61.54%) were susceptible to the imidazothiazoles. Against macrocyclic lactones, resistance was observed in 8 flocks (15.69%), 4 (7.84%) showed suspected resistance and 39 (76.47%) were susceptible. None of the flocks used in the study showed resistance to the three families of anthelmintics. Nevertheless, six were recorded as resistant or suspected of being resistant to two of these families of anthelmintics. Egg hatch assay (EHA) and FECRT were carried out jointly on 61 flocks, although EHA was done on a total of 83 farms. The results showed that 15 (18.07%) of the 83 flocks were resistant, with egg death 50 over 0.1 microg/ml thiabendazole, and 68 (81.93%) were susceptible to benzimidazoles. When the results between FECRT and EHA were compared, both techniques showed good correlation in field studies. Faecal cultures performed pre- and post-treatment indicated that Teladorsagia and Trichostrongylus were the main genera.

Anthelmintic resistance on goat farms in Georgia: efficacy of anthelmintics against gastrointestinal nematodes in two selected goat herds

Gastrointestinal nematode (GIN) parasitism is a major constraint to production of goats in the southeastern United States. The conventional method of control used by producers in this region is frequent use of anthelmintics during the warm season. Overuse of anthelmintics has led to an increase in the incidence of anthelmintic resistance in many parts of the world, but data on prevalence of anthelmintic resistance in GIN of goats in the southeastern United States are very limited. To address this issue, anthelmintic efficacy was determined in goat herds at the Fort Valley State University, Agricultural Research Station (FVSU-ARS) and the University of Georgia, College of Veterinary Medicine (UGA-CVM) using fecal egg count reduction (FECR) tests and DrenchRite((R)) larval development assays (LDA). At FVSU-ARS, 2-year-old Spanish goat does were randomly allocated to one of nine different treatment groups (n = 10): albendazole (ABZ; 20mg/kg body weight (BW)), fenbendazole (FBZ; 20mg/kg BW), ivermectin (IVM; 0.4 mg/kg BW), doramectin (DRM; 0.4 mg/kg BW), moxidectin (MOX; 0.4 mg/kg BW), levamisole (LEV; 12 mg/kg BW), morantel tartrate (MOR; 10mg/kg BW), a combination of IVM (0.4 mg/kg BW) and ABZ (20 mg/kg BW), and untreated controls. At UGA-CVM, goats were randomly allocated to one of five different treatment groups (n = 8): ABZ (20 mg/kg BW), IVM (0.4 mg/kg BW), MOX (0.4 mg/kg BW), LEV (12 mg/kg BW), and untreated controls. All drugs in both experiments were administered orally. Anthelmintic efficacy was calculated by comparing 14-day post-treatment FEC of treated and control animals, and percent reductions were interpreted using the World Association for the Advancement of Veterinary Parasitology guidelines for resistance. For the LDA, nematode eggs were isolated from pooled fecal samples of untreated control goats in each herd and used to perform DrenchRite((R)) assays. In the FVSU-ARS herd, MOX, LEV, the combination of IVM and ABZ, IVM, DRM, ABZ, MOR, and FBZ reduced FEC by 100, 91, 88, 78, 76, 62, 48, and 10%, respectively. In the UGA-CVM herd, MOX, LEV, ABZ and IVM, reduced FEC by 100, 94, 87, and 0%, respectively. In both herds moxidectin was the only drug tested that was fully effective. Results of the LDA were in agreement with results of the FECR tests for both herds. These data demonstrate the presence of GINs resistant to all three major anthelmintic classes in both goat herds.