An ultrasonographic scoring method for transabdominal monitoring of ascarid burdens in foals
Nielson M.K., Donoghue E.M., Stephens M.L., Stowe C.J., Donecker J.M. and Fenger C.K.
High ascarid burdens can lead to impaction and adversely affect foal welfare and lead to costly interventions. The aims of this study were to develop a technique for quantifying ascarid burdens in foals and use this in a treatment study and cost-benefit analysis.
Using a portable ultrasound machine and convex probe, the scan focused on three regions; immediately caudal to the xiphoid, halfway between the xiphoid and umbilicus and immediately cranial to the umbilicus. The left parainguinal region was also examined if no small intestine had been visualised in the first three locations. The number of ascarid worms visualised was assigned a score from none (score 1) to more than three sections of worm cuticle seen in less than 5cm (score 4).
The quality of the assessment was also scored from A to F based on the amount of small intestine visualised on scan. Over 80% of examinations resulted in useful images with scores of C or above. Ultrasound examinations were repeated every two weeks until the end of the study. Every month one foal was euthanased and all stages of Parascaris worms counted. The technique was able to reliably identify burdens of more than ten ascarid worms. The ultrasound scores were found to change in line with faecal counts, both peaking at around 5 months. Between 5 and 7 months, faecal egg counts reduced to zero; however, ascarid burdens were still visualised on ultrasonography, supported by the presence of worms in the intestines of several foals of this age at necropsy.
A treatment trial was conducted in parallel: foals were randomly assigned to one of three treatment groups: oxibendazole, ivermection and no treatment. A significant reduction in ascarid burdens identified by ultrasonographic scoring was found from Day 3 to 5, and there was a significant reduction in faecal ascarid counts. There was no difference in post-treatment ultrasound scores between the different groups. Within this foal population, theultrasonographic method was cost-effective when the prevalence rate of ascarid impactions was less than 5%.
A scoring system using a straightforward, quick and potentially cost-effective ultrasonographic technique can be used to reliably detect clinically significant ascarid burdens.