Gastrodiscus is a type of fluke that has an indirect life cycle with freshwater snails as the intermediate hosts. The larvae survive in humid and wet conditions, especially in marshy or flooded fields. They swim and penetrate actively into the snails. The larvae then leave the snail, attach to the vegetation and produce cysts which are infective for the horse. The recent wet conditions in Cape Town are ideal for the snails to thrive and horses grazing along streams or on the Constantia green belt are at risk.
Most infestations don’t show any clinical signs and the pathogenic nature of Gastrodiscus has been undetermined for a long time, there are many reports of the absence of clinical disease in horses and it was originally considered to be non-pathogenic. However, it can cause weight loss, poor condition, starry coat and diarrhoea. Colic has also been reported in horses with severe infestations with caecal intussusception and typhlocolitis as a sequela. The degree of clinical signs may also not relate to the level of parasitic burden.
A special floatation test is required to test for Gastrodiscus and it will not be picked up on your routine worm egg counts. The test costs around R340 per horse, depending on sample numbers and is called a faecal sedimentation test. The R340 also includes the routine worm count for all other worms. A fresh faecal ball should be collected first thing in the morning and delivered to the shop in Meadowridge. Please remember to leave your name and horses details for the laboratory forms. The results take approx. 12-24 hours and high counts of strongylids or ascarids eggs (other species of worms) will also be noted on your test.
A positive test for Gastrodiscus will confirm a diagnosis in your horse and we recommend treating these horses. Horses that test negative, however, may still have immature parasites. The test is designed to detect worm eggs, so if your horse grazes in a high-risk area and shows clinical signs of a possible worm burden, we recommend retesting these horses in 6-8 weeks. We do not recommend treating horses with an undetermined worm burden as the product is not registered for use in horses, it is a ruminant medication.
There are no licensed products, we currently recommend Tramizan, which is an “Off label” or not licensed oral medication for use in equines. It contains the active ingredient Oxyclozanide which is effective for the treatment of Gastrodiscus positive horses. Please do not try and buy this product off the shelf, please get the required dose per horse from your vet. You need to retreat the horse after 72 hours horse, so you will need to pick up two doses per positive horse.
Controlling fluke infestations in your horse involves keeping horses away from areas where they may be contracting the cysts. Grazing on the green belt or drinking water from the streams where the snails live is obviously the origin of infestation in most horses. It is not practical to try and eradicate the snail or to not access some areas of the green belt. Our recommendation is to test your horses twice a year to determine the level of infestation and whether your horse needs treatment. This needs to be more focussed in the wet months as the fluke larvae will desiccate quickly under dry conditions. Be aware of your horse’s water source and dams or stagnant water should be fenced off where possible.
Please contact us should you have any further queries.