First evaluation and detection of ivermectin resistance in gastrointestinal nematodes of sheep and goats in South Darfur, Sudan

Mohammedsalih, K. M.; Ibrahim, A. I. Y.; Juma, F.-R.; Abdalmalaik, A. A. H.; Bashar, A.; Coles, G.; von Samson-Himmelstjerna, G.; Krücken, J.

doi:10.1101/2024.03.20.585868

bioRxiv · 10.1101/2024.03.20.585868

First evaluation and detection of ivermectin resistance in gastrointestinal nematodes of sheep and goats in South Darfur, Sudan

Mohammedsalih, K. M.·Ibrahim, A. I. Y.·Juma, F.-R.·Abdalmalaik, A. A. H.·Bashar, A.·Coles, G.·von Samson-Himmelstjerna, G.·Krücken, J.

View original source ↗Export metadata ↓

Abstract

In Sudan, resistance to benzimidazoles has been reported recently in cattle and goats from South Darfur. Herein, ivermectin efficacy against gastrointestinal nematodes (GINs) was evaluated in sheep and goats in three study areas in South Darfur. The faecal egg count reduction test (FECRT) was used to evaluate the efficacy of ivermectin in sheep and goats naturally infected with GINs in the region of Bulbul (goats: n=106), Kass (goats: n=40) and Nyala (Domaia (sheep: n=47, goats: n=77) and the University farm (goats: n=52)), using different treatment plans, and the efficacy was evaluated 12 days after treatment. Ivermectin efficacy was also evaluated in goats experimentally infected using local Haemonchus contortus isolates from Kass and Nyala. Nematodes surviving ivermectin treatment in goats in Bulbul and Nyala were harvested and larvae used to infect worm-free male sheep (n=6, [≤]6 months old). Infected sheep were dosed subcutaneously with ivermectin every eight days with increasing doses from 0.2 mg/kg to 1.6 mg/kg bodyweight (bw). Reduced ivermectin efficacy was identified in sheep and goats in the four study locations. Using a paired statistic, the efficacy of a therapeutic dose in sheep was 75.6% (90% upper credible limit (UCrL): 77.5%), while twice the recommended dose led to a reduction of 92.6% (90% UCrL: 93.3%). In goats, the FECRs of a therapeutic dose were 72.9 - 95.3% (90% UCrL range: 73.6 - 95.7%) in Bulbul, Nyala Domaia, Nyala University farm and Kass. Twice the dose recommended for goats in Bulbul revealed a 90% UCrL of 87.6%. All post-treatment faecal cultures contained only Haemonchus spp. larvae. The experimental infection trials in sheep and goats supported our findings from field trials and calculated upper 90% CrL of below 98.9%. For the first time highly ivermectin resistant H. contortus populations have been identified in sheep and goats in Sudan, and resistance was experimentally confirmed.

Source connections

Published article ↗

Explore related subjects

zoology Preprint

Keep this discovery

Explore connections, maps & timelines

BibTeX RIS

Mohammedsalih, K. M., Ibrahim, A. I. Y., Juma, F.-R., Abdalmalaik, A. A. H., Bashar, A., Coles, G., von Samson-Himmelstjerna, G., Krücken, J.. 2024-03-24. First evaluation and detection of ivermectin resistance in gastrointestinal nematodes of sheep and goats in South Darfur, Sudan. https://doi.org/10.1101/2024.03.20.585868

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related preprints

bioRxiv2026

Comparing the Influence of Habitat Configuration on Population Connectivity and Genetic Structure Using Congeneric Species Across Multiple Taxa

Abstract Habitat configuration influences population connectivity and, consequently, genetic structure. River networks provide heterogeneous, hierarchically arranged environments that shift drastically from upstream to downstream. We compared congeneric species across Ephemeroptera, Plecoptera, and Trichoptera, emphasizing longitudinal replacement (upstream to downstream) and the rarely studied wet rock (hygropetric) habitats. We surveyed six rivers on the Muroto Peninsula, Japan, qualitatively sampling aquatic insects at 63 sites. Cluster analysis based on the environmental data classified surveyed sites into four clusters. We analyzed a total of 10 species from four genera that exhibit longitudinal replacement patterns within genera. Genetic analyses based on the mitochondrial cytochrome c oxidase subunit I region revealed that upstream species showed higher genetic diversity than downstream species. In contrast, species adapted to hygropetric exhibited the lowest genetic differentiation among all habitat types. A novel contribution of this study is the inclusion of hygropetric species. The surprisingly low differentiation in hygropetric species suggests high connectivity, similar to lentic species. By comparing congeneric taxa across orders within environmentally similar rivers, we reduce phylogenetic and environmental confounds, strengthening inference that habitat configuration and dispersal traits jointly shape genetic structure. These findings provide a new perspective on riverine spatial ecology and underscore the importance of microhabitat-aware comparisons for evolutionary inference.

zoology↗

bioRxiv2026

Late lactation represents the main window for sow-to-piglet transmission of persistent gut strains

The gut microbiota plays a key role in piglet health, and maternal microbial transmission may represent a promising lever to shape early-life microbiota and prevent post-weaning digestive disorders. This study aimed to better characterize sow-to-piglet microbiota transmission and persistence using a long-read metabarcoding approach targeting the 16S-ITS-23S region. Fecal samples (n = 204) were collected from 17 families, a family being as sow and three of her piglets, at multiple stages: late gestation (G110), early (L6) and late lactation (L28) for sows; early lactation (L6), late lactation (L28), and 5 days post-weaning for piglets. To approximate strain-level resolution, a putative strain (PS) approach was developed by clustering ASVs (n = 6064) affiliated with the same species based on abundance covariance (r > 0.9), resulting in 4857 PS. Piglet microbiota progressively diversified during lactation and converged toward that of sow. In sows, 27 {+/-} 6% of PS were persistent from late gestation to late lactation. In piglets, only 4.2 {+/-} 2.5% of PS persisted from d6 to 5 days post-weaning. Persistent PS in piglets were mainly affiliated with Limosilactobacillus reuteri and Lactobacillus amylovorus followed with Holdemanella porci and H. biformis, Lentihominibacter hominis and Dorea formicigenerans. Shared PS were significantly higher within families than between unrelated pairs (p < 0.05). Maternal transmission peaked at the end of lactation (35 {+/-} 7% at L28). Persistent transmitted PS represented 2.7 {+/-} 1.6% (d6-post-weaning) and 15.4 {+/-} 5.6% (d28-post-weaning). Early-transmitted persistent PS were mainly affiliated with Limosilactobacillus reuteri, Lactobacillus amylovorus, and Paraeggerthella hominis, whereas late-transmitted persistent PS were associated with Prevotella spp., Sphaerochaeta globosa, and Bariatricus comes. These findings highlight the significance of maternal transmission in shaping the post-weaning microbiota and identify late lactation as a critical window for microbiota transfer.

zoology↗

bioRxiv2026

RISC-Bound Small RNA Sequencing Provides Insights into Guide Strand Selection and siRNA Trimming and Tailing Following Insecticidal dsRNA Delivery

RNA interference (RNAi) offers a sequence-specific approach to pest control. In insects, Dicer-2 processes double-stranded RNA (dsRNA) into small interfering RNA (siRNA) duplexes, from which the RNA-induced silencing complex (RISC) retains a guide strand. Only antisense-loaded RISC can mediate cleavage of the target transcript. However, how sequence features shape the RISC-bound siRNA pool in pests remains poorly understood, limiting opportunities for sequence optimization. Here, we profiled RISC-bound siRNAs following injection of 34 insecticidal dsRNAs targeting 11 essential genes in Tribolium castaneum larvae. We computationally reconstructed 7,879 siRNA pairs and examined associations between sequence features and strand bias. Differences in GC identity at terminal paired positions 1 to 5, used as a proxy for local thermodynamic asymmetry, correlated with strand bias, with the strongest correlations at the first two paired positions. ORF targeting and reduced predicted antisense self-folding were also associated with higher antisense fractions. Analysis of non-templated terminal additions revealed predominantly 3-prime uridylation, a known signature of small RNA turnover, along with putative 3-prime trimming. Among ORF-associated siRNA pairs, sense strands showed higher relative U-tailing abundance, based on 3-prime uridylated and putatively trimmed-and-3-prime-uridylated reads relative to perfect 21-nt reads, than antisense strands. Antisense strands with the least predicted self-folding also showed low relative U-tailing abundance. These observations are consistent with sequence-dependent contributions from both guide-strand selection and differential post-RISC-loading siRNA retention, although a causal link remains to be established. The identified associations provide a basis for testing whether dsRNA sequence optimization can improve pest control efficacy and reduce off-target activity.

zoology↗