# Variability in the anthelmintic efficacy of levamisole against gastrointestinal nematodes of cattle, sheep and goats in South Darfur, Sudan

## TL;DR

This study found that levamisole is effective against gastrointestinal worms in cattle but not in sheep and goats in South Darfur, Sudan.

## Contribution

The study provides new evidence on anthelmintic resistance in small ruminants and evaluates statistical models for resistance detection.

## Key findings

- Levamisole was effective against gastrointestinal nematodes in cattle but not in sheep and goats.
- Resistance in goats was confirmed through both field and experimental trials.
- Statistical models showed better fit when using individual efficacy estimates over common efficacy assumptions.

## Abstract

This study evaluated the efficacy of levamisole against gastrointestinal nematodes (GINs) in cattle, sheep and goats in five regions from South Darfur, Sudan, based on faecal egg count reduction tests (FECRTs) and coprocultures. Levamisole efficacy was examined in 45 cattle (8 mg/kg dose) from Bulbul, 22 sheep (8 mg/kg dose) from Nyala Domaia and 117 goats (10 and 12 mg/kg doses) from Bulbul (n = 25), Kass (n = 21), Nyala Domaia (n = 40) and Tulus (n = 31), all naturally infected with GINs. Moreover, the efficacy was evaluated in goats (n = 10) experimentally infected with a local Haemonchus contortus Um Dafuq isolate and treated with an 8 mg/kg dose. Faecal samples were collected before treatment (day 0) and day 12 after treatment for natural infection trials, while different collection times were used for experimentally infected goats.

A parametric FECRT model with individual efficacy and parametric and non-parametric models with common efficacy assigned levamisole susceptibility to strongyle nematodes in cattle. However, all three models classified strongyles in goats as resistant to 10 and 12 mg/kg in Bulbul, Kass and Nyala Domaia, with lower 90% confidence intervals (CIs) of 77.7 – 94.4% and upper 90% CIs of 86.6 – 97.5%. Discrepancies occurred between the models in sheep in Nyala Domaia and goats in Tulus. The experimental infection trial in goats supported findings from goat field trials. Host species and sex were significant factors in resistance (P < 0.05). Using simulated data, a power analysis to detect resistance or susceptibility showed a power above 80.0% if at least 10 animals were used, overdispersion was low and the true efficacy was < 97.0% or > 99.2%, respectively. Model fit comparisons revealed that the individual efficacy eggCounts models fitted the data significantly (P < 0.05) better than the common efficacy models. Mild cholinergic toxicity was recorded in one sheep and seven goats, particularly those that received the 12 mg/kg dose.

The GINs of cattle were levamisole susceptible, whereas those of sheep and goats were resistant. Caution is advised with dose adjustments in desert sheep and goats. Research into combination anthelmintics and targeted selective treatment is recommended to address resistance in South Darfur.

The online version contains supplementary material available at 10.1186/s12917-026-05320-2.