Nemabiome metabarcoding reveals differences between gastrointestinal nematode species infecting co-grazed sheep and goats.

Our current understanding of differences in the epidemiology of gastrointestinal nematode (GIN) species in co-grazed sheep and goats is inadequate with reference to the development of sustainable control strategies. The next-generation metabarcoding sequencing method referred to as the 'nemabiome' allows some of these differences to be explored to describe the intensity of co-infecting GIN species. We applied this platform to study sheep and goats that were co-grazed on Guinea grass pasture in northeastern Brazil. Co-grazed goats and sheep were treated with a monepantel anthelmintic, then exposed to the same gastrointestinal nematode species. Overall, there were differences in the prevalence of GIN species identified in the sheep and goats; Trichostrongylus colubriformis and Teladorsagia circumcincta predominated in goat kids, while Haemonchus contortus predominated in adult does, ewes and lambs once burdens became re-established after anthelmintic treatment. Description of the pattern of re-infection following anthelmintic treatment was prevented by the unpredicted poor efficacy of 2.5 mg/kg and 5 mg/kg, respectively, of monepantel against O. columbianum and T. circumcincta in lambs, and T. circumcincta adult does. Differences in drug efficacy between host age and species groups may be important when considering sustainable GIN control strategies for co-grazed animals. The aggregated FECs of the adult does and goat kids representing re-established GIN burdens, were higher than those of the co-grazed adult ewes and lambs. This implies that there are inherent differences in GIN species adaptation to the two naïve small ruminant host species, and shows the need for better understanding of the factors giving rise to this situation associated with exposure to infective larvae and host responses. At the start of the study, the adult does were co-infected with several GIN species, with the highest intensity of T. circumcincta, contrasting with the situation in the adult ewes, in which H. contortus predominated. However, once burdens became re-established after treatment, H. contortus predominated in both adult does and ewes. This demonstrates the potential for host burdens of H. contortus to establish and predominate after anthelmintic treatment when burdens of co-infecting GIN species are low.

First case of monepantel resistant nematodes of sheep in Sweden.

In this study, we describe for the first time monepantel (MOP) resistance in gastrointestinal nematodes (GIN) in a Swedish sheep flock. On the farm, which had recurrent problems with Haemonchus contortus infection, the efficacy of most available anthelmintics (AH) in Sweden (i.e. ivermectin, albendazole, levamisole and monepantel), was monitored. This was done with the faecal egg count reduction test (FECRT) on three different occasions between August 2017 and April 2020. Although, MOP was used in ewes for the first time in this herd in October 2018 and then demonstrated to be highly efficacious (100% reduction), MOP-resistant worms (52% reduction) appeared in lambs already in April 2020. Resistance was detected only after two further rounds of treatment of the lambs after weaning. It is assumed that a contributing factor to this extremely rapid development was related to the fact that ewes and lambs treated during the housing period were let out on clean pasture after treatment. The ewes were treated during the housing period 2018 and grazed a clean pasture the following spring. The same ewes were treated a second time after housing 2018. The lambs were grazed with these ewes in summer 2018 and after weaning they were treated and moved to another clean pasture during the fall 2018. Anthelmintic resistance was also confirmed on two occasions to different compounds of ivermectin and once to albendazole, but not to levamisole which was tested twice. In conclusion, this is the first description of triple resistance to AH drugs in GIN of sheep in Sweden.

The intake of dry cashew apple fiber reduced fecal egg counts in Haemonchus contortus-infected sheep.

Helminthiasis is a common disease in which parasite resistance is frequently caused by inadequate administration of anthelmintics in small ruminant production. Since phytotherapy may be an adjuvant for parasite control, we assessed whether the ingestion of cashew apple fiber (Anacardium occidentale) would reduce Haemonchus contortus infection in Santa Inês sheep. Twenty-one male sheep with mean age of 240 ±â€¯9.7 days were dewormed, infected with 4000 L3 of H. contortus Embrapa2010 (day 0 - D0) and on D28 were divided into three equally sized experimental groups: 1) control (no treatment), 2) treated with anthelmintic (monepantel, 2.5 mg/kg PV) and 3) cashew apple fiber (0.3% BW) for 7 days of adaptation plus 28 days (D63). The animals were weighed weekly for diet adjustment and individual EPGs were performed twice a week. Corn silage was given ad libitum after each animal had eaten all the cashew apple fiber, which always occurred due to its palatable flavor. The silage, cashew apple fiber and leftovers were weighed daily and the samples were analyzed for dry matter. In cashew apple fiber, the total polyphenol contents were determined spectrophotometrically and the phenol compounds were identified by LC-MS. Cashew apple fiber contained 93.6% DM, 13.0% CP, 68.7% NDF, 47.6% FDA, 1.3% MM, 1.9% EE and 22.3% LIG. Twenty phenolic compounds were detected, among them phenolic acids and flavonoids, including glycosylated ones. The general EPG averages were statistically different among control, anthelmintic and cashew groups (3449, 14 and 2070, respectively), while the mean total weight gain did not differ (3.21, 3.20 and 1.94 kg, respectively) (p < 0.05). In relation to the control group, the anthelmintic showed efficacy of 99.6% and the cashew apple fiber 40.8%. Phenolic compounds appear to play an important role in the anthelmintic activity of cashew apple fiber. Thus, its use as an adjuvant in the control of H. contortus can be encouraged in regions where it is available at low cost, mitigating the use of veterinary drugs, reducing environmental contamination by agroindustrial residues and promoting the more sustainable production of small ruminants.

Supplementation with dry Mimosa caesalpiniifolia leaves can reduce the Haemonchus contortus worm burden of goats.

Gastrointestinal nematodes (GINs) cause considerable economic losses in grazing goat herds. At present, GIN control cannot rely on conventional anthelmintic (AH) drugs because parasites have developed resistance against such drugs. Thus, alternative control methods are being sought to reduce the dependence on AH. Many tannin-rich plants exhibit AH activity and may be used as alternatives for GIN control. Mimosa caesalpiniifolia is a tannin-rich shrub consumed by small ruminants in Brazil. This study evaluated the in vivo AH effect of M. caesalpiniifolia leaf powder supplementation on GIN egg fecal excretion and worm burden in goats. Plant leaves were harvested, dried and ground to obtain a powder. Twenty-four castrated male goats, aged six to eight months, with a mean body weight of 15.0 ±â€¯2.5 kg were used in the experiment. Animals were infected orally with 16,000 larvae comprising 50% Haemonchus spp., 41% Trichostrongylus spp. and 9% Oesophagostomum spp. Once the infection was patent, the goats were distributed into four groups of six animals. The control group received concentrate without condensed tannins (CTs) and did not receive any drench against GINs. The monepantel group received concentrate without CTs and were drenched once with monepantel. The other two groups received the M. caesalpiniifolia leaf powder in two periods of seven consecutive days (days 1-7 and 14-21), with one of the groups also receiving 10 g of polyethyleneglycol (PEG)/day. The animals were weighed weekly, and individual fecal eggs counts (FECs) were performed daily. After 28 days, the animals were humanly slaughtered, and the worm burden was estimated. Although live weight gain and FECs did not differ among the groups (P > 0.05), post-mortem worm counts showed a reduction in Haemonchus contortus adult worm burden (57.7%) in goats of the CT group compared to control goats (P < 0.05). The addition of PEG did not diminish AH activity in the CT + PEG group (66.9% reduction compared to the control). No AH effect against other GIN species was found. The result for the addition of PEG suggested that the observed AH activity was associated with plant secondary compounds, as opposed to CTs. As expected, no AH effect against Oesophagostomum columbianum was found for the monepantel group showed. Thus, feeding dry leaves of M. caesalpiniifolia represent a promising alternative for the control of GIN infections in goats.

Monepantel resistant Trichostrongylus colubriformis in goats in Brazil.

In a farm where Trichostrongylus colubriformis in sheep had been found resistant to monepantel (MNP), we aimed to evaluate the efficacy against gastrointestinal nematodes in a controlled efficacy test (CT) and a fecal egg count reduction test (FECRT) in goats. We used 15 (CT) and 30 goats (FECRT), naturally infected, and equally divided into control and treated groups. The efficacy of MNP in the CT against Haemonchus contortus, Trichostrongylus axei and Cooperia curticei was 100%. For T. colubriformis, the efficacy was 90.5% in goats treated with 2.5mg/kg, and 88.1% in goats treated with 3.5mg/kg. In the FECRT, the overall reduction was 91% (2.5mg/kg) and 90% (3.75mg/kg). In the fecal cultures, Trichostrongylus spp. larvae represented 25% (pre-treatment) and 15% (post-treatment) of the larvae in the control group, but they were 75% (2.5mg/kg) and 98% (3.75mg/kg) of the recovered larvae after MNP treatment. In accordance with published standards, and based on FECRT and CT, MNP was considered ineffective against T. colubriformis in the studied flock.

Development of Haemonchus contortus resistance in sheep under suppressive or targeted selective treatment with monepantel.

This study examined the development of resistance to anthelmintics in Haemonchus contortus in lambs under suppressive or selective treatment regimens that included monepantel. Twenty Ile de France and 20 Santa Ines lambs were allocated to two anthelmintic treatment regimens, based on body weight and nematode faecal egg counts (FEC): targeted selective treatment (TST) or suppressive treatment, both with monepantel. Lambs of the TST group were treated individually when they presented with a packed cell volume (PCV) ≤20%. On 7 October 2016, the lambs were allocated to clean pastures, where they grazed in separated paddocks by group until late February 2017. The experimental area was contaminated with nematodes that were introduced with the experimental Ile de France and Santa Ines lambs, naturally infected with gastrointestinal nematodes. To maintain the grazing lambs in the suppressive treatment group and their pasture as free of worms as possible, these lambs were treated with anthelmintics before being allocated to their paddock and then were periodically treated with monepantel. However, the use of a suppressive treatment regimen that included monepantel over a period of 3 months resulted in the emergence of a population of resistant H. contortus. In the TST group, there was a rapid and progressive reduction in the efficacy of monepantel, which at the end of the experiment was only 76%. The Ile de France lambs were all treated one or more times during the experiment, whereas only two Santa Ines lambs in the TST required treatment. In conclusion, a population of H. contortus resistant to monepantel emerged quickly during the rainy season, even when sheep were submitted to selective treatment.

Combination of SL327 and Sunitinib Malate leads to an additive anti-cancer effect in doxorubicin resistant thyroid carcinoma cells.

BACKGROUND: Receptor tyrosine kinases (RTKs) play crucial roles in numerous cancer cell processes including cell survival, proliferation, and migration. MEK1/2 MAPK kinases are very important for cancer survival and development. Anaplastic thyroid carcinoma (ATC) is a deadly type of thyroid cancer and there are no very effective systemic treatment strategies for ATC so far. Also, ATC can easily become resistant to therapy of traditional therapeutic drugs for ATC, such as doxorubicin. Drug combination treatment could be a promising therapeutic strategy for ATC, especially for drug resistant ATC. METHODS: We explored the combination effect between a MEK1/2 inhibitor SL327 and a multi-targeted RTK inhibitor Sunitinib Malate in doxorubicin resistant ATC cells using cell viability assay, cell migration assay, nuclei morphology and caspase-3 activity analysis, as well as in vivo tumor growth assay. RESULTS: There is a significant additive effect between SL327 and Sunitinib Malate in reducing viability, increasing apoptosis, and suppressing migration of doxorubicin-resistant ATC cells. Importantly, combination of SL327 and Sunitinib Malate induced significant additive suppression of in vivo doxorubicin-resistant ATC tumor growth. CONCLUSIONS: Our results suggest that the combination of MEK1/2 inhibitor and RTK inhibitor is promising for treatment of ATC especially doxorubicin-resistant ATC. The combination might not only enhance the anti-cancer efficacy, but also reduce the side effects and overcome drug resistance developed in ATC treatment. All these might provide useful information for clinical therapeutics of ATC.

Lack of efficacy of monepantel against Trichostrongylus colubriformis in sheep in Brazil.

Multiple drug resistance of nematodes against anthelmintics has become one of the most important economic problems in sheep production worldwide. The aim of this experiment was to evaluate the efficacy of monepantel (2.5mg/kg) against gastrointestinal nematodes in fecal egg count reduction test (FECRT) and controlled efficacy test (CT) in naturally infected sheep. We used 30 sheep for the FECRT and 20 sheep for the CT, equally divided into control and treated groups. In the FECRT, the reduction was 98%. Larval identification of pre-treatment coprocultures revealed 100% Haemonchus spp. for both control and treated groups. Post-treatment culture of treated sheep was 100% Oesophagostomum spp., but only few larvae were recovered. In the control group, they were 99% Haemonchus spp and 1% Oesophagostomum spp. larvae. Based on the FECRT, Haemonchus spp. was considered susceptible to monepantel. The efficacy of monepantel in the CT against Haemonchus contortus and Trichostrongylus axei was 100% and against Cooperia curticei was 99.7%. For Trichostrongylus colubriformis, the efficacy was -21.5%. In both treated and untreated animals, Oesophagostomum columbianum was recovered from the large intestines. Based on FECRT and CT and in accordance with WAAVP standards, monepantel was ineffective against T. colubriformis and O. columbianum, but effective against H. contortus, T. axei and C. curticei in the studied flock.

Alcohol alters the activation of ERK1/2, a functional regulator of binge alcohol drinking in adult C57BL/6J mice.

BACKGROUND: Binge alcohol drinking is a particularly risky pattern of alcohol consumption that often precedes alcohol dependence and addiction. The transition from binge alcohol drinking to alcohol addiction likely involves mechanisms of synaptic plasticity and learning in the brain. The mitogen-activated protein kinase (MAPK) signaling cascades have been shown to be involved in learning and memory, as well as the response to drugs of abuse, but their role in binge alcohol drinking remains unclear. The present experiments were designed to determine the effects of acute alcohol on extracellular signaling-related kinases (ERK1/2) expression and activity and to determine whether ERK1/2 activity functionally regulates binge-like alcohol drinking. METHODS: Adult male C57BL/6J mice were injected with ethanol (EtOH) (3.0 mg/kg, intraperitoneally) 10, 30, or 90 minutes prior to brain tissue collection. Next, mice that were brought to freely consume unsweetened EtOH in a binge-like access procedure were pretreated with the MEK1/2 inhibitor SL327 or the p38 MAPK inhibitor SB239063. RESULTS: Acute EtOH increased pERK1/2 immunoreactivity relative to vehicle in brain regions known to be involved in drug reward and addiction, including the central amygdala and prefrontal cortex. However, EtOH decreased pERK1/2 immunoreactivity relative to vehicle in the nucleus accumbens core. SB239063 pretreatment significantly decreased EtOH consumption only at doses that also produced nonspecific locomotor effects. SL327 pretreatment significantly increased EtOH, but not sucrose, consumption without inducing generalized locomotor effects. CONCLUSIONS: These findings indicate that ERK1/2 MAPK signaling regulates binge-like alcohol drinking. As alcohol increased pERK1/2 immunoreactivity relative to vehicle in brain regions known to regulate drug self-administration, SL327 may have blocked this direct pharmacological effect of alcohol and thereby inhibited the termination of binge-like drinking.

Inhibition of ERK1/2 signaling prevents epileptiform behavior in rats prone to audiogenic seizures.

It has recently been proposed that extracellular signal-regulated kinases 1 and 2 (ERK1/2) are one of the factors mediating seizure development. We hypothesized that inhibition of ERK1/2 activity could prevent audiogenic seizures by altering GABA and glutamate release mechanisms. Krushinsky-Molodkina rats, genetically prone to audiogenic seizure, were recruited in the experiments. Animals were i.p. injected with an inhibitor of ERK1/2 SL 327 at different doses 60 min before audio stimulation. We demonstrated for the first time that inhibition of ERK1/2 activity by SL 327 injections prevented seizure behavior and this effect was dose-dependent and correlated with ERK1/2 activity. The obtained data also demonstrated unchanged levels of GABA production, and an increase in the level of vesicular glutamate transporter 2. The study of exocytosis protein expression showed that SL 327 treatment leads to downregulation of vesicle-associated membrane protein 2 and synapsin I, and accumulation of synaptosomal-associated protein 25 (SNAP-25). The obtained data indicate that the inhibition of ERK1/2 blocks seizure behavior presumably by altering the exocytosis machinery, and identifies ERK1/2 as a potential target for the development of new strategies for seizure treatment. Extracellular signal-regulated kinases 1 and 2 (ERK1/2) are one of the factors mediating seizure development. Here we report that inhibition of ERK1/2 by SL 327 prevented seizure behavior and this effect was dose-dependent and correlated with ERK1/2 activity. Accumulation of VGLUT2 was associated with differential changing of synaptic proteins VAMP2, SNAP-25 and synapsin I. The obtained data indicate that the inhibition of ERK1/2 alters neurotransmitter release by changing the exocytosis machinery, thus preventing seizures.

First report of monepantel Haemonchus contortus resistance on sheep farms in Uruguay.

BACKGROUND: On two farms it was noted that after routine treatment with monepantel, fecal egg counts failed to drop. This was accompanied by lambs mortality due to Haemonchus contortus infection. The aim of this work was to evaluate the efficacy of monepantel to control gastrointestinal nematodes (GIN) in two sheep farms, in Uruguay. FINDINGS: A Fecal Egg Count Reduction Test (FECRT) was subsequently performed at the Experimental Stations Glencoe of INIA Tacuarembó (Farm 1) and Sheep Unit of INIA La Estanzuela (Farm 2) using the World Association for the Advancement of Veterinary Parasitology guidelines. On Farm 1 the FECRT was performed using 6-8 month old Corriedale or Merino Dohne x Corriedale male lambs naturally infected with GIN. On day 0 pre-treatment, three groups of 15 lambs each were selected, blocked by fecal egg count level (FEC) and randomly assigned to one of the following: Group 0 = untreated control, Group 1 = treated with monepantel (Zolvix®, Novartis Animal Health Inc.) from stock previously purchased; Group 2 = treated with monepantel from stock provided by the supplier, at the recommended dose of 2.5 mg/kg of body weight. Fecal samples were collected directly from the rectum from each lamb on day 0 and on day 9 post-treatment. On Farm 2, the FECRT was conducted on a group of 8 month old male lambs Milchschaff x Finn. At this farm, 10 lambs were randomly allocated to be treated with monepantel (Group 1) and 10 lambs were randomly allocated to remain as untreated control (Group 0) using the same protocols as Farm 1. On farm 1 the FECR was 0.0% (95% CI = 0.0-49.0) and 42.0% (95% CI = 0.0-75.0) for Group 1 and Group 2 respectively. For Farm 2, the FECR was 82.1% (95% CI = 36.0-99.0). Haemonchus spp was the resistant genus. CONCLUSIONS: Poor effcicacy of monepantel in treating GIN parasites was demonstrated on both farms.

Monepantel: the most studied new anthelmintic drug of recent years.

Monepantel (MOP), a new anthelmintic drug from a group of amino-acetonitrile derivatives, has been intensively studied during last years. Many authors examined this new drug from different perspectives, e.g. efficacy against different species and stages of parasites, mode of action, metabolism, pharmacokinetics, toxicity, resistance, ecotoxicity, etc. MOP is an anthelmintic for livestock (currently only sheep and goats), with molecular mode of action which is different to all other anthelmintics. MOP has a broad-spectrum of activity against gastrointestinal nematodes of sheep, including adults and L4 larvae of the most important species. The key feature of MOP is its full effectiveness against strains of nematodes resistant to benzimidazoles, levamisole, macrocyclic lactones and closantel. After oral administration, MOP is quickly absorbed into the bloodstream and quickly metabolized to MOP sulfone that has a similar efficacy as the parent molecule. Several other MOP metabolites formed in ovine hepatocytes were described. MOP and its metabolites are considered to be non-toxic to environment and its components, such as soil microflora, aquatic organisms, dung organisms, vegetation, etc. The aim of the presented review was not to collect all reported data but to bring an overview of various approaches in the study of MOP and to evaluate their principal results.

Lack of efficacy of monepantel against Teladorsagia circumcincta and Trichostrongylus colubriformis.

After reports of the apparent failure of monepantel to reduce the egg counts of goats on a farm in the lower North Island of New Zealand, faecal egg count reduction tests were conducted in goats and lambs resident on the property, and a confirmatory, slaughter study was conducted using 12 sheep, sourced elsewhere, that were grazed on the farm for approximately 5 weeks. In the egg count reduction test in goats, 8 animals were given monepantel at 3.9 mg/kg (just over 1.5× the sheep dose rate of 2.5mg/kg), whilst four received 7.7 mg/kg (just over 3× the sheep dose). In the egg count reduction test in sheep, 15 lambs were treated with 3.0mg/kg of monepantel. For the confirmatory study, the sheep were housed indoors for 2 weeks before half were treated with 2.9 mg/kg monepantel and the animals were killed for worm counts 9 days later. There was no evidence of efficacy in either egg count reduction test, or in the goats, the two dose rates used appeared equally ineffective. Likewise, there were no significant reductions in egg counts or worm burdens in the slaughter study. Monepantel was ineffective against at least two gastrointestinal nematode species, Teladorsagia circumcincta and Trichostrongylus colubriformis. These findings represent the first report from the field of resistance having developed to the anthelmintic monepantel with severe resistance developing in more than one species after being administered on 17 separate occasions to different stock classes and in less than 2 years of the product first being used on the farm in question.

Anthelmintic resistance in Northern Ireland (I): prevalence of resistance in ovine gastrointestinal nematodes, as determined through faecal egg count reduction testing.

The prevalence of anthelmintic resistance in Northern Ireland sheep flocks was evaluated between July and October 2011. Sampling kits were sent to 172 flock owners and returns were received from 91. Within this survey population, 27 flock owners used benzimidazole products, 10 used levamisole products, 15 used avermectin products, 26 used milbemycin products and 4 flock owners used the amino acetonitrile derivative, Monepantel. The remaining 9 flock owners used combination drenches (broad spectrum wormer plus fasciolicide). However, 15 sets of samples were ineligible for faecal egg count reduction testing due to either too low an egg count or insufficient faecal volume. Treatment efficacy below 95%, indicating significant resistance, was detected in 81% (n=24) of flocks tested for benzimidazole resistance; in 14% (n=1) of flocks tested for levamisole resistance; and in 50% (n=7) and 62% (n=13) of flocks tested for avermectin and milbemycin resistance, respectively. Monepantel resistance was absent in all (n=3) flocks tested. Combination products (broad spectrum nematocide plus flukicide) containing levamisole were entirely effective, while treatment efficacy below 95% was detected in 60% (n=3) of flocks where the nematocide in the combination product was a benzimidazole. Where parasite identification based on coproculture was completed, Trichostrongylus was the dominant genus detected in all cases post-treatment, indicating the occurrence of anthelmintic-resistant Trichostrongylus spp. populations. Benzimidazole efficacy was highest in treating Trichostrongylus spp. (51%) and lowest when treating Teladorsagia spp. Levamisole was 100% effective in treating Cooperia, but ineffective (0%) in treating Trichostrongylus spp. Avermectin efficacy was highest when treating Haemonchus contortus (100%) and Teladorsagia spp. (73%), with a marginally lower efficacy against Trichostrongylus spp. (71%). Moxidectin efficacy was 33% against Trichostrongylus spp., 68% against Teladorsagia spp., 97% against Cooperia spp. and 100% against Haemonchus contortus infections.

The comparative efficacy of abamectin, monepantel and an abamectin/derquantel combination against fourth-stage larvae of a macrocyclic lactone-resistant Teladorsagia spp. isolate infecting sheep.

Anthelmintic resistance by gastrointestinal nematodes of sheep continues to be an issue of global interest. While the recent introduction in some countries of one or two new anthelmintic classes (amino-acetonitrile derivatives [AAD] and spiroindoles [SI]) has been welcomed, it is important that there is no relaxation in parasite control and the management of drug resistance. Monepantel (an AAD) was the first new anthelmintic to be approved for use (New Zealand, 2009) and was followed a year later in the same country by a combination of derquantel (a SI) and abamectin. The present study determined the efficacy of the new anthelmintic products and abamectin against fourth-stage larvae of macrocyclic lactone-resistant Teladorsagia spp. in lambs. Efficacies were calculated by comparing post-mortem nematode burdens of treated animals with those of untreated control sheep, and were 98.5, 86.3 and 34.0% for monepantel, abamectin/derquantel and abamectin, respectively. The nematode burdens of monepantel- and abamectin/derquantel-treated sheep were significantly lower than those sheep treated with abamectin and the untreated controls. Similarly, the burden of the monepantel group was significantly lower than that of the abamectin/derquantel group. These findings provide an opportunity to reinforce the recommendation that farmers and animal health advisors need to know the resistance status of nematode populations on subject farms to ensure effective control programs are designed and implemented. Such control programs should include an appropriate choice of anthelmintic(s), monitoring parasite burdens for correct timing of treatments, and pasture management to reduce larval challenge balanced with the maintenance of drug-susceptible populations in refugia.

The efficacy of monepantel against naturally acquired inhibited and developing fourth-stage larvae of Teladorsagia circumcincta in sheep in the United Kingdom.

The inhibition of Teladorsagia and other nematode genera at the early fourth-stage is a biological process that allows the parasites to survive in their host in a dormant state when prevailing conditions may otherwise kill them or prevent their progeny from surviving in the external environment. A study was conducted in Scotland to evaluate the efficacy of monepantel, an amino-acetonitrile derivative, against natural infections of inhibited fourth-stage Teladorsagia spp. larvae. At necropsy it was determined that the untreated control sheep were additionally infected with developing fourth-stage Teladorsagia spp. larvae and this is the first published evidence on the efficacy of monepantel against natural infections of this parasite and stage. The study sheep, which had grazed on naturally contaminated pastures since birth, were transferred to indoor housing after a subset of animals was examined to confirm the presence of inhibited larvae within the study population prior to the experiment. After 14 days of housing, monepantel was orally administered at 2.5 mg/kg to half of the animals. The sheep were necropsied seven days later and their parasite burdens recovered for the determination of efficacy, which was 99.7% for the inhibited stages and 99.3% for the developing fourth-stages. In conclusion, monepantel dosed orally at 2.5 mg/kg is a highly effective treatment against naturally acquired infections of inhibited and developing fourth-stage larvae of Teladorsagia spp.

Modelling the benefits of a new class of anthelmintic in combination.

Since 2009 two new classes of anthelmintics have been registered for use in sheep in New Zealand. This raises challenging questions about how such new actives should be used, not only to minimise the development of resistance to them, thereby ensuring their availability as effective treatments for as long as possible, but also to minimise the further development of resistance to the other anthelmintic classes. One strategy which appears to offer considerable potential for slowing the development of resistance is the use of combinations of different anthelmintic classes, although this approach remains contentious in some countries. The potential benefit of using anthelmintics in combination is particularly relevant to two recently released anthelmintic compounds because one, monepantel, is presently only available as a single active product while the other, derquantel, is only available in combination with abamectin. A simulation modelling approach was used to investigate the potential benefits of using anthelmintics in combination. The rate at which resistance develops to a new 'active' when used alone was compared to an equivalent compound used in combination with a second compound from an alternative class (in this case, abamectin), when various levels of resistance occur to the second active. In addition, the potential of a new active to reduce further development of resistance to the second compound in the combination was evaluated. Finally, the use of combinations as compared to sequential or rotational use patterns, in the presence of side resistance between two actives was investigated. The modelling simulations suggest a significant advantage to both compounds when they are used in combination, especially if both initially have high efficacy. The development of resistance to the new active was delayed, although to a lesser extent, even when the efficacy of the second active in the combination was only 50%. Under a 'low-refugia' management environment resistance to all actives developed more rapidly, and the advantage of using actives in combination was reduced. When used in conjunction with other resistance management strategies, a combination containing a new active prevented further development of resistance to the older class. Using actives in combination was superior to using them individually either sequentially or in rotation, even in the presence of side-resistance between the two anthelmintic classes.