Integration of ITS-2 rDNA nemabiome metabarcoding with Fecal Egg Count Reduction Testing (FECRT) reveals ivermectin resistance in multiple gastrointestinal nematode species, including hypobiotic Ostertagia ostertagi, in western Canadian beef cattle.

A large-scale Fecal Egg Count Reduction Test (FECRT) was integrated with ITS-2 rDNA nemabiome metabarcoding to investigate anthelmintic resistance in gastrointestinal nematode (GIN) parasites in western Canadian beef cattle. The study was designed to detect anthelmintic resistance with the low fecal egg counts that typically occur in cattle in northern temperate regions. Two hundred and thirty-four auction market-derived, fall-weaned steer calves coming off pasture were randomized into three groups in feedlot pens: an untreated control group, an injectable ivermectin treatment group, and an injectable ivermectin/oral fenbendazole combination treatment group. Each group was divided into six replicate pens with 13 calves per pen. Individual fecal samples were taken pre-treatment, day 14 post-treatment, and at monthly intervals for six months for strongyle egg counting and metabarcoding. Ivermectin treatment resulted in an 82.4% mean strongyle-type fecal egg count reduction (95% CI 67.8-90.4) at 14 days post-treatment, while the combination treatment was 100% effective, confirming the existence of ivermectin-resistant GIN. Nemabiome metabarcoding of third-stage larvae from coprocultures revealed an increase in the relative abundance of Cooperia oncophora, Cooperia punctata, and Haemonchus placei at 14 days post-ivermectin treatment indicating ivermectin resistance in adult worms. In contrast, Ostertagia ostertagi third-stage larvae were almost completely absent from day 14 coprocultures, indicating that adult worms of this species were not ivermectin resistant. However, there was a recrudescence of O. ostertagi third stage larvae in coprocultures at three to six months post-ivermectin treatment, which indicated ivermectin resistance in hypobiotic larvae. The calves were recruited from the auction market and, therefore, derived from multiple sources in western Canada, suggesting that ivermectin-resistant parasites, including hypobiotic O. ostertagi larvae, are likely widespread in western Canadian beef herds. This work demonstrates the value of integrating ITS-2 rDNA metabarcoding with the FECRT to enhance anthelmintic resistance detection and provide GIN species- and stage-specific information.

Effects of naturally acquired gastrointestinal nematode infection on bovine viral diarrhea virus vaccine-directed antibody response in western Canadian feedlot cattle.

Objective: To determine how gastrointestinal nematode (GIN) infection, reflected by fecal egg counts and Ostertagia ostertagi serum antibody titers, is associated with the antibody response to bovine viral diarrhea virus type 1 (BVDV-1) vaccine antigen in fall-weaned feedlot cattle from western Canada. Animals: Cross-sectional study with 240 steer calves derived from an auction market. Procedure: At feedlot arrival, calves were given a commercial vaccine containing modified live BVDV-1. Serum neutralization antibody titers against BVDV-1 antigens were determined in individual blood samples collected pre-vaccination and 21 d after vaccination. A modified Wisconsin sugar floatation method was used to obtain individual calf GIN egg counts in fecal samples on arrival. Antibody titers against O. ostertagi were determined using an enzyme-linked immunosorbent assay in on-arrival blood samples. Results: Fecal egg counts and O. ostertagi titers were not associated with vaccine antibody-fold changes. Similarly, fecal egg counts and O. ostertagi titers were not associated with vaccine-induced seroconversion. Conclusions: The relatively low GIN burdens, reflected by the overall low fecal egg counts in these fall-weaned feedlot calves, did not have measurable adverse effects on the humoral immune response to BVDV-1 vaccine antigens. Clinical relevance: An adequate response to vaccination is important for cattle welfare and productivity. Conditions that negatively affect this response may vary regionally, such as GIN infection. Understanding this is essential. Although subclinical intestinal parasitism did not noticeably affect the antibody response in these steers, higher GIN burdens and actual immune protection from clinical disease remain to be investigated.

Effets d'une infection par des nématodes gastro-intestinaux d'origine naturelle sur la réponse en anticorps dirigés par le vaccin contre le virus de la diarrhée virale bovine chez les bovins des parcs d'engraissement de l'Ouest canadien. Objectif: Déterminer comment l'infection par les nématodes gastro-intestinaux (GIN), reflétée par le nombre d'oeufs fécaux et les titres d'anticorps sériques d'Ostertagia ostertagi, est associée à la réponse en anticorps à l'antigène du vaccin contre le virus de la diarrhée virale bovine de type 1 (BVDV-1) chez les bovins en parc d'engraissement sevrés à l'automne de l'Ouest canadien. Animaux: Étude transversale auprès de 240 veaux bouvillons issus d'un marché aux enchères. Procédure: À leur arrivée au parc d'engraissement, les veaux ont reçu un vaccin commercial contenant du BVDV-1 vivant modifié. Les titres d'anticorps sériques neutralisants contre les antigènes BVDV-1 ont été déterminés dans des échantillons de sang individuels prélevés avant la vaccination et 21 jours après la vaccination. Une méthode de Wisconsin modifiée de flottation au sucre a été utilisée pour obtenir le nombre d'oeufs GIN de chaque veau dans les échantillons fécaux à l'arrivée. Les titres d'anticorps dirigés contre O. ostertagi ont été déterminés à l'aide d'un dosage immuno-enzymatique dans des échantillons de sang à l'arrivée. Résultats: Le nombre d'oeufs fécaux et les titres d'O. ostertagi n'étaient pas associés aux modifications du titre d'anticorps vaccinaux. De même, le nombre d'oeufs fécaux et les titres d'O. ostertagi n'étaient pas associés à la séroconversion induite par le vaccin. Conclusion: Les charges relativement faibles de GIN, reflétées par le faible nombre global d'oeufs fécaux chez ces veaux d'engraissement sevrés à l'automne, n'ont pas eu d'effets indésirables mesurables sur la réponse immunitaire humorale aux antigènes du vaccin BVDV-1. Pertinence clinique: Une réponse adéquate à la vaccination est importante pour le bien-être et la productivité des bovins. Les conditions qui affectent négativement cette réponse peuvent varier selon les régions, telles que l'infection par les GIN. Comprendre cela est essentiel. Bien que le parasitisme intestinal subclinique n'ait pas sensiblement affecté la réponse en anticorps chez ces bouvillons, des charges de GIN plus élevées et une protection immunitaire réelle contre la maladie clinique restent à étudier.(Traduit par Dr Serge Messier).

An optimized swine dysentery murine model to characterize shedding and clinical disease associated with "Brachyspira hampsonii" infection.

BACKGROUND: The development of a mouse model as an in vivo pathogenicity screening tool for Brachyspira spp. has advanced the study of these economically important pathogens in recent years. However, none of the murine models published to date have been used to characterize the clinical signs of disease in mice, instead focusing on pathology following oral inoculation with various Brachyspira spp. The experiments described herein explore modifications of published models to characterize faecal consistency, faecal shedding and pathology in mice challenged with "Brachyspira hampsonii" clade II (Bhamp). METHODS AND RESULTS: In Experiment 1, 24 CF-1 mice were randomly allocated to one of three inoculation groups: sham (Ctrl), Bhamp, or B. hyodysenteriae (Bhyo; positive control). Half of each group was fed normal mouse chow (RMH) while the other received a low-zinc diet (TD85420). In Experiment 2, eight CF-1 mice and nine C3H/HeN mice were divided into Ctrl or Bhamp inoculation groups, and all fed TD85420. In Experiment 1, mice fed TD85420 demonstrated more severe mucoid faeces (P = 0.001; Kruskal Wallis) and faecal shedding for a significantly greater number of days (P = 0.005; Kruskal Wallis). Mean faecal scores of Bhamp inoculated mice trended higher than Ctrl (P = 0.06; Wilcoxon rank-sum) as did those of Bhyo mice (P = 0.0; Wilcoxon rank-sum). In Experiment 2, mean faecal scores of inoculated CF-1 mice were significantly greater than in C3H mice (P = 0.049; Kruskal Wallis) but no group differences in faecal shedding were observed. In both experiments, mice clustered based on the severity of colonic and caecal histopathology but high lesion scores were not always concurrent with high fecal scores. CONCLUSION: In our laboratory, CF-1 mice and the lower-zinc TD85420 diet provide a superior murine challenge model of "Brachyspira hampsonii" clade II.