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.

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.

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)

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.