Revisiting anthelmintic resistance in sheep flocks from São Paulo State, Brazil.

Haemonchus contortus and Trichostrongylus colubriformis are the most important gastrointestinal nematodes causing serious losses in sheep production of tropical and subtropical regions. Prophylaxis of gastrointestinal nematode infections is based on anthelmintics use, but their frequent administration selects multiple-resistant parasites. To evaluate how the situation has changed over the last decades, the anthelmintic resistance status of gastrointestinal nematodes in sheep flocks was assessed in the current study and compared to previous surveys. In each one of the 15 flocks evaluated, animals (n ≥ 7) were allocated into at least five groups and treated as follows: 1) untreated control; 2) albendazole; 3) levamisole; 4) ivermectin; and 5) monepantel. If more animals were available, two additional groups were included: 6) closantel, and 7) moxidectin. The faecal egg count reduction test (FECRT) was carried out to evaluate the pre- and post-treatment using the SHINY tool. Haemonchus spp. was the most prevalent nematode from faecal cultures. The mean efficacy of albendazole was 40%. Only in two farms, levamisole presented a relatively high percentage of reduction in the FECRT about 90%, while ivermectin and moxidectin presented the worst mean efficacy of 34% and 21% among all farms, respectively. Like other anthelmintics, closantel demonstrated low efficacy (63%) across all farms evaluated. Monepantel presented an overall mean efficacy of 79%, but it was the only anthelmintic that presented efficacy ≥95%, in five farms. The results revealed that gastrointestinal nematodes with multiple anthelmintic resistance were prevalent in all 15 sheep herds. The research suggests that nematodes are becoming more and more resistant to various anthelmintic compounds, which has made the problem worse. This circumstance highlights the necessity to put into practice sustainable and long-lasting methods to prevent gastrointestinal nematode infections in sheep husbandry.

Abomasal RNA-seq reveals a strong local cellular response in suckling lambs with resistance against Haemonchus contortus.

Santa Ines (SI) and Ile de France (IF) sheep are known to be resistant and susceptible to Haemonchus contortus infection, respectively. Several studies have shown some genes as potential biological markers for sheep resistance against gastrointestinal nematodes using molecular tools, including transcriptomic analysis. In this study, we sequenced the polyadenylated RNA of the abomasal tissue of SI and IF suckling lambs to identify mucosa-specific transcript alterations between breeds artificially infected with H. contortus. Naïve SI (n = 4) and IF (n = 4) lambs were artificially infected every other day, over a period of 52 days, from 14 to 66 days old, with a total of 5,400 H. contortus infective larvae. Fundic abomasal tissue samples were collected at 68 days old, and submitted to high-throughput RNA sequencing (RNA-seq). Differential expression analysis (P value < 0.001 and False Discovery Rate (FDR) < 0.05) between SI and IF samples identified 292 genes, most of which showed greater expression in SI lambs. To help annotate and assign possible function to differentially expressed genes (DEGs), we used previously available single-cell RNA-seq (scRNA-seq) data from ovine abomasal mucosa to putatively identify cell types and possible mechanisms involved in resistance to H. contortus. In particular, genes associated with endothelial and tuft cells showed the greatest increases in expression in SI relative to IF lambs. SI lambs had higher percentages of tuft cells than IF lambs in the fundic abomasal mucosa. Although we found innate immunity (cell-mediated in mucosa) acting as a protagonist in impairing H. contortus infection, a stronger acquired immune response was being modulated at an earlier stage by SI lambs. We suggest that the complex connection between innate and adaptive immunity is via cellular antigen processing and presentation (APP). Based on comparison with scRNA-seq data, SI lambs showed a robust APP mechanism characterized mainly by greater T cell APP, macrophage differentiation, and cytokine signalling. We identified potential mechanisms and markers to advance knowledge for selection of H. contortus resistance at a very early age, in SI as well as in other commercial sheep breeds.

Influence of targeted selective anthelmintic treatment on the productive performance of wool and hair lambs naturally infected with gastrointestinal nematodes in Brazil.

Targeted selective treatment (TST) is an alternative method to reduce the use of anthelmintics and delay the development of resistant nematode populations. However, there is limited information on the actual effects of this type of treatment on livestock productivity. The objective of this study was to evaluate the production performance of Santa Ines (hair) and Ile de France (wool) lambs naturally infected with gastrointestinal nematodes (GIN) under TST based on packed cell volume (PCV) versus suppressive anthelmintic treatments. Thirty-eight lambs were divided into two treatment groups: Suppressive treatment, animals were drenched with monepantel every two weeks and TST, animals were treated with the same anthelmintic when they presented PCV ≤ 20%. Feces, blood, and weight were measured weekly to determine eggs per gram of feces, PCV, total plasma protein, and weight gain. After animals were slaughtered, carcasses were weighed to determine carcass yield. In the TST group, substantial productive losses of approximately 21.3% in the wool and 25.9% in the hair lambs were observed in body weight compared to their counterparts. Significant differences in hematological variables occurred over the experimental period, especially in the wool lambs under TST. Favorable environmental conditions enabled infective larvae to survive and thrive on pasture. Haemonchus contortus and intestinal nematodes were the most common parasites found in the Ile de France lambs and the Santa Ines lambs, respectively. Although TST prevented mortality, it did not prevent production losses. Both breeds showed a significant drop in production due to GIN parasitism.

Diagnosis of Oestrus ovis infestation in sheep by PCR and enzyme-linked immunosorbent assay.

The aim of this study was to assess the suitability of PCR and ELISA as diagnostic method in young sheep naturally infested by Oestrus ovis larvae. The experiment was carried out from December 2020 to April 2021 with 39 lambs divided into two groups: infested (n = 26) and control treated group (n = 13). The infested group did not receive treatment against oestrosis, and the control group was treated with closantel (10 mg/kg orally) every 28 days in order to keep the animals as free as possible of O. ovis infestation. The clinical signs varied among animals regardless of the number of recovered larvae of each lamb, however, the thick mucus and mucopurulent nasal discharge scores were less frequent in lambs from treated group. There was no correlation between the nasal discharge score and the number of O. ovis recovered larvae (R² = 0.012, P = 0.165). Three control treated animals only presented first instar larvae (L1) (1 - 4 larvae/animal) which were smaller than L1 found in the lambs of the infested group. Ninety-two percent of the lambs from infested group (24/26) were parasitized by O. ovis with number ranging from 1 to 54 larvae per animal. A gradual increase in plasma IgG (anti-antigen of O. ovis larvae) levels of animals from infested group after the third week of the trial was observed, whereas the control lambs had low levels of IgG until the end of the experiment. The PCR had low sensitivity (26 %) and high specificity (100 %), and it presented poor agreement (k = 0.177) with the larvae detection after the lamb slaughter. The oestrosis clinical signs were not related to larvae infestation intensity and ELISA showed a greater advantage over the PCR technique in identifying animals that are carrying O. ovis.

Early-onset immune response to Haemonchus contortus infection in resistant Santa Ines suckling lambs compared with susceptible Ile de France.

Santa Ines, an indigenous Brazilian hair sheep, in comparison with European sheep breeds (e.g., Ile de France), show greater resistance against gastrointestinal nematode (GIN) infections, mainly to Haemonchus contortus. Here we bring novel findings that address some gaps regarding the resistance traits involved in the development of the immunity of young lambs in the first few weeks of life to H. contortus infection. This study aimed to compare parasitological, humoral, and local effector cell-mediated responses, also the histopathological differences in the abomasal mucosa of Santa Ines (SI) and Ile de France (IF) suckling lambs serially infected with H. contortus. Parasitological variables, local and circulating humoral immunity, and local cellular response were evaluated in naïve Santa Ines (n = 14) and Ile de France (n = 12) lambs, randomized into four groups: infected SI (n = 8), non-infected control SI (n = 6), infected IF (n = 8) and non-infected control IF (n = 4). Lambs from infected groups were first infected at 14 days old, and multiple infections were conducted every second day, until the age of 66 days old (52 days post first infection). In comparison with infected Ile de France, infected Santa Ines lambs had lower mean eggs per gram of faeces, lower total H. contortus worm burden, lower females' length, greater abomasal lymph node weight, greater mucosal thickness in the fundus, and also higher counts of eosinophils in the fundus, and mast cells and globule leukocytes in both fundic and pyloric mucosa of the abomasum. Intrabreed differences were observed into the infected Santa Ines group, with three of the eight lambs classified as highly resistant for displaying H. contortus burden ranging only from 1 to 42 worms. Overall, Santa Ines suckling lambs showed great resistance against H. contortus infection in comparison with Ile de France lambs, being able to mount a robust innate immune response at an early age, and before weaning.

Effect of antihelminths with contrasting efficacy against gastrointestinal nematodes on the live-weight gain of young Nellore cattle.

We estimated the losses caused by gastrointestinal nematode (GIN) infections in young Nellore cattle born in three consecutive calving seasons (Cycles I, II and III). Three groups of animals: Group 1 - free from GIN using 2.5 mg/kg of albendazole sulfoxide; Group II - free from Oesophagosomum radiatum using 0.2 mg/kg of ivermectin but infected with ivermectin-resistant Haemonchus placei and Cooperia spp.; and Group III - non-treated experimental control animals, infected with all GIN, were observed over a period of 12 months. Male and female calves were evaluated starting before weaning when the animals were an average of approximately four months of age. In Cycle I, only females were evaluated. All the animals continued to graze on pastures of Urochloa spp. (= Brachiaria). All the groups showed median faecal egg counts of fewer than 250 eggs per gram (EPG), and no clinical signs of parasitic gastroenteritis were observed. The blood variables were within the normal ranges, and no calf presented anaemia. In most of the samplings, the median EPGs were significantly lower (P < 0.05) in the group treated with albendazole. Throughout the experiment, the most prevalent parasite observed in the control group was Cooperia spp., followed in decreasing order by Haemonchus spp., O. radiatum and Trichostrongylus spp. All the groups of calves exhibited weight gain throughout the trials with control group displaying the lowest body weight gain. Body weight variables between the albendazole- and ivermectin-treated groups were not significantly different (P > 0.05). After weaning, females animals in albendazole and ivermectin treated groups exhibited higher body weights, 20.4% and 22.7%, respectively, than those of the control group. Likewise, males treated with albendazole and ivermectin exhibited 27.6% and 25.8%, respectively, more body weight gain than animals under control group. Because the main difference between the ivermectin and the control groups was the O. radiatum parasitism, most of the losses in the control group were possibly due to this nematode species. Nevertheless, the other nematodes species that occurred in relatively high intensities in control group could also have an additive effect in such losses.

Haematological variables of Santa Ines and Ile de France suckling lambs: Influence of Haemonchus contortus infection / Variáveis hematológicas de cordeiros lactentes Santa Inês e Ile de France: influência da infecção por Haemonchus contortus

Haemonchus contortus is the major gastrointestinal parasite of sheep raised in tropical and subtropical areas worldwide. This trial aimed to evaluate the influence of H. contortus infection on the bone marrow response of Santa Ines (SI) and Ile de France (IF) suckling lambs experimentally infected with H. contortus. Fourteen SI lambs and 12 IF lambs were randomized in four groups: infected SI (n=8), non-infected SI (n=6), infected IF (n=8) and non-infected IF (n=4). Lambs of infected groups were submitted to 27 infections, conducted every two days, from 14 to 68 days of age, and each lamb received a total of 5400 H. contortus infective larvae (L3). Ten blood samples were obtained during the experimental period to be used for erythrocyte and leukocyte counts, packed cell volume and total plasma protein estimation. Additionally, it was carried out a differential leukocyte count. Lambs from control groups did not shed eggs in faeces all over the experiment, while infected Santa Ines and Ile de France lambs presented means of 2963 EPG (Eggs Per Gram of faeces) and 8175 EPG in the last sampling (P<0.05), respectively. Infected Santa Ines lambs had an increase in eosinophil release, however differences (P<0.05) on circulation number in comparison with infected Ile de France lambs were identified only in the last sampling (54 days post first infection). The mild H. cortortus infection did not produce significant changes in the blood variables of the Ile de France and Santa Ines suckling lambs.(AU)

Haemonchus contortus é o principal parasita gastrintestinal de ovinos criados em áreas tropicais e subtropicais. Este estudo objetivou avaliar a influência da infecção por H. contortus na resposta medular de cordeiros lactentes das raças Santa Inês (SI) e Ile de France (IF) infectados experimentalmente com H. contortus. Quatorze cordeiros SI e 12 cordeiros IF, foram distribuídos em quatro grupos: SI infectado (n=8), SI não infectado (n=6), IF infectado (n=8) e IF não infectado (n=4). Cordeiros dos grupos infectados foram submetidos a 27 infecções, realizadas a cada dois dias, do 14º até 68º dia de vida, com um total de 5400 larvas infectantes (L3) de H. contortus por animal. Foram realizadas 10 coletas de sangue ao longo do período experimental para determinação do volume globular, proteínas plasmáticas totais, contagem de eritrócitos e leucócitos, além do diferencial de leucócitos. Cordeiros controles não infectados não eliminaram ovos nas fezes durante todo o experimento, enquanto que os cordeiros Santa Ines e Ile de France infectados apresentaram em média 2963 ovos por grama de fezes (OPG) e 8175 OPG na última coleta (P<0,05), respectivamente. Cordeiros Santa Inês infectados tiveram um aumento na produção de eosinófilos, mas diferenças (P<0.05) no número de eosinófilos sanguíneos em comparação a cordeiros Ile de France infectados foram detectadas somente na última coleta (54 dias após a primeira infecção). A infecção leve por H. cortortus não induziu alterações significativas nas variáveis sanguíneas de cordeiros lactentes Ile de France e Santa Inês.(AU)

Peripartum Phenomenon in Crioula Lanada Sheep Susceptible and Resistant to Gastrointestinal Nematodes.

This study aimed at evaluating parasitological and blood variables in native breed Crioula Lanada sheep belonging to the same herd, to identify and compare susceptible or resistant individuals to gastrointestinal nematodes during gestation and lactation phases. For this purpose, 18 Crioula sheep were used within 2 years of evaluation, in which blood and feces samples and weight of the animals were taken from their 4th month of gestation until the weaning of their lambs, in the 4th month postpartum. Feces samples were used for counting eggs per gram of feces (EPG) and, thus, to identify 12 resistant ewes (EPG < 1,000) and 6 susceptible (EPG > 1,000) to gastrointestinal nematodes. The identification of infective larvae was also performed. Blood was used for analysis of packed cell volume (PCV), eosinophil count, total plasma protein, and immunoglobulin G level against Haemonchus contortus infective larvae. The Kruskal-Wallis non-parametric comparison test was used to evaluate the differences between days of parturition and linear mixed-effects model using package lme4 in R to evaluate the groups. The main parasite species observed in the feces samples were Haemonchus, Trichostrongylus, Oesophagostomum, Ostertagia, and Cooperia in similar proportions in both groups. Susceptible ewes presented peaks of EPG at the beginning of lactation and lower PCV values throughout the study. No difference between groups was observed concerning other blood variables or body weight, but some changes were observed along with the gestation and lactation phases within each group. The physiological response of sheep to nematode infection is a useful tool to identify the most susceptible individuals within the same breed and herd and to select the most genetically resistant individuals.

Repeated vaccination against Haemonchus contortus provides continuous protection to young grazing sheep.

Haemonchus contortus is the most important gastrointestinal nematode in the tropics and subtropics causing huge economic losses to the small ruminant industry. Vaccination is potentially a sustainable approach to control this parasite and the performance of Barbervax® a vaccine containing integral membrane glycoproteins from H. contortus intestinal cells, was evaluated in naturally infected grazing sheep during their development from sucking lambs to adults. The sheep were randomly assigned to two groups: Vaccine and Control. The Vaccine group were vaccinated 23 times over the course of this two-year trial at intervals of 3-6 weeks. They responded with anti-vaccine specific antibodies, had 80 % lower Haemonchus egg counts and were less anaemic compared with the controls. Packed cell volumes (PCV) were always greater than 25 % in the vaccinated sheep but averaged between 23 % and 24 % in the controls. Total plasma protein values were higher in the vaccinated group from the third vaccination until the end of the trial. Throughout the trial, 88 % of the control sheep were drenched (average of 3.1 drenches per treated animal) but only 57 % of vaccinates, needed a salvage anthelmintic treatment (average of 1.9 drenches per treated animal), however, between group no differences in body weight were observed. In summary, these results indicate that a continuous course of Barbervax® can provide lambs with substantial year-round protection against H. contortus until they reached adulthood.

Long spelling periods are required for pasture to become free of contamination by infective larvae of Haemonchus contortus in a humid subtropical climate of São Paulo state, Brazil.

The objective of this trial was to evaluate the period of spelling necessary for a pasture to become free of contamination by infective larvae of gastrointestinal nematodes (GIN) of sheep, in different seasons of the year, as well as to determine when the greatest pasture contamination occurs and how long it lasts. An area was divided into four paddocks, one for each season (spring, summer, autumn, and winter). In order to contaminate the paddocks with free living stages of GIN, eight ewes, naturally infected, grazed on each paddock for 14 consecutive days, starting on the following dates: autumn, on April 4, 2017; winter, on July 4, 2017; spring, on September 26, 2017; summer, on January 2, 2019. At the beginning and end of the grazing period, faecal samples were taken directly from the rectums of the ewes to count eggs per gram of faeces (EPG) and for faecal cultures. Every 14 days pasture samples were collected to assess the number of infective larvae (L3) per kilogram of dry matter. At the end of the 14 day ewe grazing period, 21 stakes were placed where there were faeces on the paddock. Subsequently, every 14 days, the faeces located at three of the stakes were collected and the L3 were recovered. After the exit of the ewes, monthly, two tracer lambs, free of helminth infection, were allocated into the paddock for 14 days. At the end of this period they were housed in covered stalls for 28 days. Faeces from the lambs were collected for individual EPG counting and faecal culture at 21 and 28 days after grazing. Infective larvae recuperation was observed from faeces and pasture in all seasons. In the autumn, spring, and summer, high EPG counts were observed in the first tracer lambs (8521, 4800, and 8064 EPG, respectively), while in winter, high infection (14132 EPG) of the animals was observed only from the second pair of tracer lambs. For a pasture to become "clean", 322 days, 350 days, 294 days, and 182 days following contamination were necessary, respectively, in the autumn, winter, spring, and summer. In autumn, spring, and summer, massive contamination of the pasture with L3 occurred soon after an area had been grazed by infected sheep, while in winter this took a little longer. The contamination persisted, approximately, from a minimum of six months post contamination in summer to up to almost one year post contamination in winter.

Is there competition between Haemonchus contortus and Haemonchus placei in a pasture grazed by only sheep?

This study aimed to evaluate the dynamics of Haemonchus contortus and Haemonchus placei infections and hybridization between these species in grazing sheep without contact with cattle. On January 14, 2014, sixteen young sheep were infected with 4000 infective H. placei third-stage larvae L3; 11 days later, another group n = 16 was infected with 4000 H. contortus L3. The establishment rates of H. contortus and H. placei L3 were, on average, 61.6 % and 56.8 %, respectively, in the permanent sheep. After the establishment of patent infections, all permanent sheep were allocated together in the same clean pasture where they grazed for the next 12 months. Euthanasia of a sample of the permanent sheep was performed every three months: in May, August, November and February. Two weeks before the sheep were removed for euthanasia, 2 worm-free tracer sheep were introduced to the pasture to evaluate the larval population in the field. The tracer sheep grazed alongside the permanent sheep for 2 weeks. Then, they were housed indoors for 20 days; at the end of this period, they were euthanized. Parasites were recovered from the permanent and tracer sheep and identified using morphological and molecular techniques. A total of 432 worms (from permanent and tracer animals) were analyzed by PCR using species-specific primer pairs. Of these specimens, only two (0.46 %) male worms were identified as hybrids: one was recovered from a permanent animal euthanized in August and the other from a tracer sheep that grazed in May. The last detection of adult H. placei worms occurred in sheep euthanized in May (approximately 3.5 months after the beginning of the grazing period). The morphological evaluation of the L3 produced in fecal cultures showed that H. placei were progressively replaced by H. contortus populations starting in March. The last trace of H. placei L3 was found in August, when a small percentage (0.5 %) of infective larvae with H. placei morphology was identified in a fecal culture. In conclusion, hybridization between H. contortus and H. placei can occur in the field during coinfection. It was demonstrated that H. placei established successfully in artificially infected worm-free sheep; however, with concomitant natural reinfection with H. contortus, the H. placei population showed a rapid decrease and was eliminated within a few months in an environment without cattle.

Lagochilascaris minor (Nematoda, Ascarididae) in a domestic cat in a coastal city of the state of São Paulo.

This paper describes the discovery of Lagochilascaris minor parasitizing a stray cat (Felis catus) in São Sebastião, a coastal city in the state of São Paulo, Brazil. The cat presented fistulas with purulent secretion in the ventral cervical region. A thorough evaluation revealed nematodes in the site. The parasites were removed, amounting to a total of about 100 specimens. The parasite species was identified based on measurements and morphological characteristics of adult worms. This report of parasitism by L. minor in domestic cats in the state of São Paulo reinforces the need for greater attention to this parasitosis, given the increase in cases among carnivores in Brazil.

Parasitism in Angus x Nellore heifers in a silvopastoral system.

The influence of shade in the silvopastoral system on the performance and degree of parasitism by endo- and ectoparasites in Angus x Nellore heifers was assessed. The experiment was conducted with 72 heifers, with an initial mean weight of 276 ± 5.67 kg and 9 months of age, in a total area of 25 ha, divided into 12 paddocks, with three treatments and four replicates. The experimental design was a randomized complete block design, to evaluate the conventional grazing system (CGS) without shade and silvopastoral systems with simple line (SPS1) or triple lines (SPS3) of eucalyptus. The evaluations were carried out every 28 days, from June 2017 to April 2018. During the trial, the number of eggs per gram of feces (EPG) presented a gradual increase in the three systems. Differences (P < 0.05) in the variables analyzed were recorded only in two occasions: the CGS group EPG mean ± standard error (1269 ± 105) was higher than the SPS1 group mean (402 ± 129 EPG) in March, and tick average of the CGS group (13 ± 2.7) was lower than the SPS3 (32 ± 5.3) in October. There were no significant differences (P ≥ 0.05) between groups in relation to horn fly counts, the numbers of infective nematode larvae on pasture, hematological variables, and weight gain. It was concluded that in comparison with the CGS system, the shading in the SPS1 and SPS3 systems did not have any major influence on the degree of parasitism or in the performance of the heifers.

Assessment of biophysical properties of Haemonchus contortus from different life cycle stages with atomic force microscopy.

Atomic force microscopy (AFM) was used in this work to investigate the ultrastructural and mechanical characteristics of Haemonchus contortus, the major gastrointestinal nematode that infects small ruminants worldwide. The biophysical characterization of this species is extremely important in order to reveal mechanisms of action of drugs and to classify its ultrastructure and biomechanical properties. High-resolution topographic images by AFM as well as data on biomechanical properties of cuticles were obtained at different stages of H. contortus. The results reveal details of the mechanical and structural properties of this nematode never observed before for nematodes parasite with other microscope techniques. Qualitative and quantitative reductions in the elasticity of the larvae stage egg were compared with those of the morulae stage, and the increased adhesion of unsheathed L3 were compared with the same stage of sheathed larvae. The results presented here open possibilities for understanding the mechanisms of drug and biomolecular actions that can be used to control infections caused by H. contortus.

Differences in immune responses to Haemonchus contortus infection in the susceptible Ile de France and the resistant Santa Ines sheep under different anthelmintic treatments regimens.

Understanding the immunological basis of resistance to gastrointestinal nematode infections in livestock is important in order to develop novel methods of parasite control such as vaccination or genetic selection for parasite resistance. The present study aimed to investigate differences in immune response between parasite resistant Santa Ines and susceptible Ile de France sheep breeds to natural Haemonchus contortus infection. Parasitological parameters, humoral immunity, local and circulating cellular immune responses were evaluated in 19 Santa Ines and 19 Ile de France lambs undergoing different anthelmintic treatments regimens: suppressive treatments (SUP) or targeted selective treatments (TST) over a 5-month grazing period. Santa Ines lambs had significantly lower Haemonchus faecal egg count and worm burden compared to Ile de France regardless of treatment regime. In addition, circulating blood eosinophils count and parasite-specific IgG levels were significantly higher and more rapidly induced in Santa Ines lambs. Abomasal immune responses were generally greater in the resistant breed, which had significantly higher levels of parasite-specific IgA in mucus, and elevated number of globule leukocytes and CD3+ T cells within the abomasal mucosal. Furthermore, numbers of POU2F3+ epithelial cells, a tuft-cell specific transcription factor, were also elevated in the Santa Ines breed, suggesting that this breed is better able to initiate T-helper type 2 immune responses within the abomasum. In conclusion, the differential immunological responses detailed here are relevant to understanding resistance to gastrointestinal nematodes in other host breeds, as well as to resistance breeding as a sustainable control approach for parasitic infections.

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.

A panel of microsatellite markers to discriminate and study interactions between Haemonchus contortus and Haemonchus placei.

Haemonchus contortus and Haemonchus placei are two closely related economically important parasites of ruminants. Their close morphological similarity, common occurrence as co-infections and ability to hybridize makes definitive diagnosis and epidemiological studies in field populations challenging. In this paper, we describe the development of a panel of microsatellite markers that can be used to discriminate and study the genetics of these two parasite species in co-infections and mixed field populations. We have identified two additional microsatellites (Hp52 and Hp53), in addition to three previously reported microsatellites (Hcms3561, Hcms53265 and Hcms36) that have a discrete set of alleles between the two species. Multilocus genotyping of worms with this 5 marker panel from 3 geographically diverse H. placei isolates and 4 geographically diverse H. contortus populations allows unambiguous species assignment of individual worms. This panel of markers should provide a valuable resource in studying the biology and epidemiology of these important ruminant parasite species in the field.

Time required by different anthelmintics to reach expected efficacy levels in horses infected by strongyles.

The aim of this study was to determine the time required by different anthelmintic agents to reduce strongyle egg shedding in horses. Fifty horses were divided into five homogenous groups based on faecal egg counts (FECs). Treatment groups received either ivermectin; moxidectin; fenbendazole; piperazine; or no treatment (control group). Faecal examinations were performed 4, 8, 12, 18, 24, 36 and 48h after the anthelmintic treatment. After this period, faecal samples were taken every 24h over the next 12days and finally on alternate days (48-h intervals) for another 14days until the end of the experiment (28days post-treatment). The faecal egg count reduction (FECR) was calculated based on the post-treatment mean FECs in the controls and treated animals. Eggs were absent from the faecal examinations beginning at 72h and 4days, respectively, following treatment with moxidectin or ivermectin. Piperazine showed an FECR greater than 95% from 48h up to 9days post-treatment, with the highest FECR value recorded at 7days post-treatment (98.1%). However, the FECR was lower than 90% in the last two samplings (26 and 28days post-treatment). The febendazole group presented the lowest efficacy with FECR below 90% in all samplings. The faecal cultures showed that at the beginning of the trial, all of the groups presented with mixed infections and were predominantly composed of cyathostomins (92.8%), followed by Strongylus vulgaris (5.6%) and Triodontophorus serratus (1.6%). Only cyathostomin larvae were identified following treatment with fenbendazole or piperazine. In conclusion, horses in the present study had a segment of the cyathostomin population with resistance to fenbendazole and piperazine. The strongyle population was susceptible to macrocyclic lactones, with cessation in egg shedding three and four days after treatment with moxidectin and ivermectin, respectively.

The effects of diet and corticosteroid-induced immune suppression during infection by Haemonchus contortus in lambs.

To evaluate the effects of Diet and corticosteroid-induced immune suppression during infection by Haemonchus contortus, 28 lambs were allocated to one of four groups treated as follows: Group Basal Diet - Normal; Group Basal Diet - Immune-Suppressed; Group Supplemented Diet - Normal; and Group Supplemented Diet - Immune-Suppressed. The Basal Diet contained Cynodon dactylon (cv. coast cross) hay with 82 g crude protein (CP)/kg dry matter (DM), which was provided to the lambs in all groups ad libitum. In addition, animals on the Supplemented Diet received daily a commercial concentrate containing 171 g CP/kg DM, which was offered in an amount corresponding to 3% of the animal's live weight. The Immune-Suppressed groups received treatments with the glucocorticoid methylprednisolone sodium succinate (1.33 mg/kg of body weight), administered weekly. All lambs received a single infection with 4000 H. contortus infective larvae (L3) and were euthanised 28 days post-infection. Differences in pH and in the short-chain fatty acid (SCFA) concentrations occurred in rumen as a result of the distinct Diets offered to lambs. Such changes, however, did not have any apparent effect on larvae exsheathment and/or larvae survival inside the rumen, with all groups presenting similar worm burdens. However, animals on the Supplemented Diet presented reductions in worm growth and faecal egg counts. There was a significant effect of the Diet on the IgG levels against total antigens of H. contortus L3 from 7 to 27 days post-infection, with supplemented animals showing higher overall mean values (P<0.05). The immunosuppressive treatments had no effect on worm burden despite the reduction in the numbers of inflammatory cells in the abomasal mucosa of the Immune-Suppressed groups. These groups showed longer worms and females with more eggs in comparison with their counterparts fed each Diet; however, only the length of males was significantly affected (P<0.05). In conclusion, the changes caused in the rumen contents by supplementation with concentrate did not impair H. contortus establishment.

Dermatobia hominis: Potencial risk of resistance to macrocyclic lactones.

Dermatobia hominis is an ectoparasite that infests various species of mammals, including cattle, impairing the quality of cowhides and leather. After observing natural infestation with D. hominis larvae in cattle on two farms in the state of São Paulo, Brazil, we evaluated the efficacy of two macrocyclic lactones, ivermectin and moxidectin, against this parasite. The drugs were administered to 10 animals in each group, following the manufacturer's instructions. The groups were: Group 1-treated with ivermectin (0.2mg/kg of body weight (BW)); Group 2-treated with moxidectin (0.2mg/kg BW); and Group 3-control (untreated). On the farm in Pardinho, a total of 12 and 16 live larvae were found in 6 and in 8 animals 10 days after the treatment with ivermectin and moxidectin, respectively, while in the control group 4 bovines had a total of 7 live larvae. On the farm in Anhembi, 2, 4 and 6 live larvae were extracted from ivermectin, moxidectin and control groups, respectively, after the treatment. This is the first report of the presence of live D. hominis larvae after the treatment of cattle with ivermectin and moxidectin in Brazil.