Investigating a Sprague-Dawley rat-based anthelmintic assay using Trichostrongylus colubriformis

In vivo anthelmintic assay models are essential for evaluating candidate compounds in target species. Several rodent-helminth systems have been developed, with the Cobb-Wistar rat-T. colubriformis model emerging as promising for early-stage screening. Although this model has demonstrated utility, the development of an alternative model using a more widely accessible rat strain represents a valuable opportunity for advancing in vivo screening of anthelmintics. This study evaluated different immunosuppressants and regimens to identify treatments yielding the highest and most consistent worm burdens in experimentally infected Sprague-Dawley rats. Thirty rats were assigned to five groups (n = 6). Group 1 received unmedicated feed (negative control), while Groups 2, 3, and 4 received hydrocortisone acetate (HCA) in their diet at 60 ppm, 80 ppm, and a two-phase regimen of 200 ppm followed by 60 ppm, respectively. Group 5 received intramuscular methylprednisolone acetate (MPA) on three occasions. All animals were orally infected with T. colubriformis third-stage larvae, and necropsies were performed on Day 13 post-infection to recover worm burdens. Treatment had no effect on worm counts. The 80-ppm HCA group produced the highest mean burden with high variance; the 200:60 ppm group showed lower counts but less variance, and the 60-ppm HCA and MPA groups were comparable to controls. There was insufficient evidence to support the Sprague-Dawley rat-T. colubriformis model but, given the results of this study, further investigation and development are warranted.