Anthelmintic resistance of horse strongyle nematodes to fenbendazole in Lithuania.

BACKGROUND: Control of strongyle infections presents a global challenge for horse practitioners due to the development of anthelmintic resistance (AR), however comprehensive information on AR in Lithuania is still lacking. The aim of this study was to assess the current situation of fenbendazole (FBZ) AR in horses at stable level in Lithuania. RESULTS: Faecal samples from 121 horses from six stables were examined using the Mini-FLOTAC method. Of these, 89 horses met the inclusion criteria that included strongyle faecal egg counts (FEC) exceeding 200 eggs per gram (EPG). Faecal egg count reduction tests (FECRTs) were performed in these. AR was evaluated at horse stable level based on faecal egg count reduction (FECR) and the lower limit of the 95% credible interval (LLCI) using the Bayesian hierarchical model. This study confirmed that strongylids (Cyathostominae (CYA)) resistant to FBZ are pervasive in Lithuania. FBZ was ineffective in three of the six stables (FECR 77.1-79.0%; 49.8-99.8 LLCI), was suspected to be ineffective in one stable (FECR 93.6%; 85.4-100 LLCI) and was effective (FECR 99.8-100%; 99.8-100 LLCI) in two stables. FEC showed a significant (P < 0.01) difference between the treatment and control groups. Only CYA larvae were detected in larval cultures derived from strongyle-positive faecal samples collected 14 days after treatment of a test group with FBZ. CONCLUSION: This in vivo study showed that resistance to FBZ in the treatment of strongyle nematodes is prevalent in horse stables in Lithuania. These findings should guide the implementation of more sustainable management of strongyle infections in horses in Lithuania.

Does the in vitro egg hatch test predict the failure of benzimidazole treatment in Haemonchus contortus?

Considerable research has been directed towards optimising in vitro tests that can diagnose resistance in pre-parasitic stages of parasites. The objective of this study was to compare the in vivo faecal egg count reduction test (FECRT), the in vitro egg hatch test (EHT), and the molecular determination of the frequency of a codon 200 allele of ß-tubulin isotype 1 associated with benzimidazole resistance in larval stages of Haemonchus contortus obtained from infected goats. Animals were infected with composite infective doses representing 10, 20, 30, 40, 60, and 80% resistant alleles. Faecal samples for the EHT were collected on 28, 33, and 35 days post-infection. The results of the in vivo FECRT indicated that albendazole treatment reduced infections consisting of composite doses of 10, 20, 30, 40, 60, and 80% larvae of the resistant isolate by 91.3, 78.0, 63.3, 48.4, 36.5, and 41.4%, respectively. The drug concentration at which 50% of the eggs were prevented from developing hatching larvae (ED50) in the in vitro EHT varied from 0.09 ± 0.01 to 15.63 ± 12.10 µg/mL thiabendazole. The results of the in vitro EHT indicated that the test could estimate in vivo resistance well. The EHT could thus accurately estimate the in vivo efficacy of the drug and percentage of the resistance allele in the population using hatching parameters in delineation doses. This finding was also supported by comparing the FECRT data to the hatching percentages in the EHT on 30 goat farms in Slovakia with natural mixed infections of gastrointestinal parasites.

TITLE: Le test d'éclosion des œufs in vitro prédit-il l'échec du traitement au benzimidazole pour Haemonchus contortus ? ABSTRACT: Des efforts de recherche considérables ont été consacrés à l'optimisation des tests in vitro permettant de diagnostiquer la résistance des parasites aux stades préparasitaires. L'objectif de cette étude était de comparer le test de réduction du nombre d'œufs fécaux in vivo (TRNOF), le test d'éclosion des œufs in vitro (TEO) et la détermination moléculaire de la fréquence d'un allèle du codon 200 de l'isotype 1 de la ß-tubuline associé à résistance au benzimidazole au stade larvaire d'Haemonchus contortus, obtenus à partir de chèvres infectées. Les animaux ont été infectés avec des doses infectieuses composites représentant 10, 20, 30, 40, 60 et 80 % d'allèles résistants. Des échantillons de matières fécales ont été prélevés pour le TEO aux jours 28, 33 et 35 après l'infection. Les résultats de la TRNOF in vivo ont indiqué que le traitement à l'albendazole réduisait respectivement de 91,3, 78,0, 63,3, 48,4, 36,5 et 41,4 % les infections composées de doses composites de 10, 20, 30, 40, 60 et 80 % de larves de l'isolat résistant. La concentration de médicament à laquelle 50 % des œufs ont été empêchés de développer des larves qui éclosent (DE50) dans le TEO in vitro variait de 0,09 ± 0,01 à 15,63 ± 12,10 µg/mL de thiabendazole. Les résultats du TEO in vitro ont indiqué que le test pouvait correctement estimer la résistance in vivo. Le TEO a ainsi pu estimer avec précision l'efficacité in vivo du médicament et le pourcentage de l'allèle de résistance dans la population en utilisant des paramètres d'éclosion dans les doses de délimitation. Cette constatation a également été étayée par la comparaison des données du TRNOF aux pourcentages d'éclosion dans le TEO sur 30 élevages de chèvres en Slovaquie, avec des infections mixtes naturelles de parasites gastro-intestinaux.

Anthelmintic resistance in small ruminants in the Nordic-Baltic region.

Gastrointestinal nematodes (GIN) in small ruminants result in production losses, and consequently economic losses, and are an animal welfare problem in most countries in the Nordic-Baltic region. Intensive use of anthelmintics to control helminth infections has led to anthelmintic resistance (AR), which has become a major issue in many European countries. Several studies have been performed in countries in the Nordic-Baltic region (e.g. Denmark, Sweden, Norway and Lithuania) showing increasing/emerging levels of AR. The aim of this paper is to provide an overview of the problem of AR on sheep and goat farms in the Nordic-Baltic region. This region has a limited number of registered anthelmintics. However, researchers in this area have discovered some surprising findings, such as ivermectin (IVM) resistance on a farm that had never used IVM. In Sweden there is evidence of macrocyclic lactone (ML)-resistant Haemonchus contortus being introduced with sheep imported from the Netherlands. As elsewhere in the world, the livestock trade appears to be contributing to the spread of AR in the region and isolated cases of multidrug-resistant cases have also been reported. This is surprising given that the frequency of treatments here is much lower than in other countries where sheep production is economically more important. The prevailing nematodes are Haemonchus, Teledorsagia and Trichostrongylus, while on some farms Haemonchus is dominant and clinical haemonchosis has increasingly been observed in recent decades. The reasons for this are unclear, but are probably related to this parasite's propensity to rapidly develop drug resistance and a general lack of awareness of the problem, possibly in combination with global warming and the increased livestock trade within the EU. In addition, domestic interactions through contacts with wildlife ruminants, alpacas may also be a contributing factor for transmission of AR.

Anthelmintic resistance of horse strongyle nematodes to ivermectin and pyrantel in Lithuania.

BACKGROUND: With intensive use of anthelmintic drugs in recent decades, anthelmintic resistance (AR) in horse nematodes is becoming a growing issue in many countries. However, there is little available information about the parasites, treatment practices or AR in the horse population in Lithuania. The aim of this study was to assess the current situation of AR on horse farms in Lithuania. The study was conducted in 25 stables on horses with a strongyle faecal egg count (FEC) of ≥ 200 eggs per gram. A faecal egg count reduction test (FECRT) was performed on each farm after administration of ivermectin (IVM) or pyrantel (PYR). RESULTS: The efficacy of IVM was comparatively high, with 98.8% of 250 horses having a zero egg count 14 days after treatment. Two conditions were used to interpret the FECRT results for PYR: firstly, resistance was determined when FECR was < 90% and the lower 95% confidence interval (LCL) was < 80%, and secondly when in addition the upper confidence level (UCL) was < 95%. Under the first condition, resistance against PYR was found in five stables (25% of all tested herds), while when considering the UCL as well, resistance was only detected in two stables (8%). The FEC showed a significant (P < 0.01) difference between the treatment and control groups. Only cyathostomin larvae were detected in larval cultures derived from strongyle-positive faecal samples collected 14 days after treatment of a test group with PYR. CONCLUSIONS: This in vivo study showed that PYR resistance is prevalent on horse farms in Lithuania, while the efficacy of IVM still appears to be unaffected. However, further studies of ivermectin resistance are needed. These findings should guide the implementation of more sustainable management of strongyle infections in horses in Lithuania.

A comparison of two different anthelmintic treatment regimens against natural gastrointestinal nematode infections on two Lithuanian sheep farms.

BACKGROUND: According to targeted treatment (TT), the whole flock is dewormed based on knowledge of the risk, or parameters that quantify the mean level of infection, whereas according to targeted selective treatment (TST), only individual animals within the grazing group are treated, based on parasitological, production and/or morbidity parameters. The aim of this study was to compare two different treatment protocols on sheep farms in Lithuania. The study was conducted from 15 April to 31 October 2014 on three sheep farms. On the TT (the whole flock) and T(S)T (with FECs ≥ 300, respectively) farms all adult animals were treated orally with fenbendazole irrespective of EPG counts before the grazing season. The second treatment was applied with injectable ivermectin on both farms. However, on the TT farm all sheep were also treated on 2nd August regardless of their EPG counts, while on the T(S)T farm only those animals with an EPG ≥ 300 were treated on 1 July using a threshold of ≥ 300 EPG. No treatments were administered on the control farm (n = 1) during the study. RESULTS: Spring treatment of ewes significantly reduced nematode faecal egg counts (FEC) both on the TT and T(S)T farms, with the benefit of lowering pasture contamination with infective L3 stage larvae at the start of grazing season, while it remained significantly higher on the control farm. The positive effect of the spring treatment of ewes was reflected by increased body weight gains (BWG) in lambs in the first half of the grazing season. Following the second treatment, the weight gains in lambs on the T(S)T farm were higher compared to lambs on the TT farm, while BWG in the control lambs started to decrease. The difference was also substantiated by the body condition scores (BCS) and dag scores (DS) of lambs, which were highest on the T(S)T farm compared with those on the control and TT farms. CONCLUSIONS: The results of this study show that both treatment strategies were useful in reducing clinical effects (BCS and DS) of gastrointestinal nematode parasitism and increasing the performance in lambs. Furthermore, on the T(S)T farm some of animals were left in refugia, helping to slow down the development of anthelmintic resistance (AR) in future.

Prevalence of anthelmintic resistance on Lithuanian sheep farms assessed by in vitro methods.

BACKGROUND: This study examines the prevalence of drug resistance in gastrointestinal nematodes to macrocyclic lactones (ML) and benzimidazoles (BZ) in Lithuanian sheep using sensitive and precise in vitro methods. The survey was conducted from August 2013 to November 2014. Thirty-three farms with sheep previously treated with BZ and ivermectin (IVM) were included in the study. On 12 farms where only BZ were used, egg hatch discrimination dose testing (EHDDT) was conducted to detect anthelmintic resistance (AR) to BZ. On eight farms where only ML were used, micro agar larval development testing (MALDT) was conducted to detect AR to ivermectin (IVM). On the remaining 13 farms, where both classes of drugs were used, EHDDT and MALDT were both applied to detect multidrug resistance to BZ and IVM. RESULTS: BZ-resistant gastrointestinal nematodes were found on all 25 farms with a previous history of BZ use. High levels of resistance (>40 % of hatching) were recorded on 36 % of these farms, and low levels (<20 % of hatching) on 40 % of farms. IVM-resistant populations were found on 13 out of 21 sheep farms using this drug. Of these 13 farms with AR to IVM, low levels of resistance (<30 % development) were recorded on 84.6 % of farms and high levels (>30 % development) on 15.4 % of farms. No resistance to IVM was recorded on 38.1 % of farms. Multi-drug resistance was detected on five farms out of 13 (38.5 %) using both classes of drugs. CONCLUSIONS: The present study demonstrates the existence of AR to BZ and ML on Lithuanian sheep farms thus confirming results in a previous in vivo study. Cases of multi-drug resistance were recorded in the present study and require further consideration. An appropriate strategy for anthelmintic treatment, measures to prevent gastrointestinal nematode infection and a better understanding of the management practices associated with resistance may slow down further development of AR.