Deworming Drug Resistance in Ethiopian Working Horses

Deworming Drug Resistance in Ethiopian Working Horses

Educating owners about treating horses for internal parasites is key to helping minimize parasite resistance to deworming medications.

Photo: Kristen M. Janicki, MS, PAS

Have you heard of parasite resistance to deworming medications? Probably. But, by and large, owners of working equids in certain developing countries have not. And the result is a growing problem of anthelmintic resistance in the working cart horse populations of countries like Ethiopia.

Ethiopian researchers have learned that the classic antiparasitic drugs ivermectin and especially fenbendazole are losing their efficacy in treating internal parasites in the northwest region of their country. And this, they said, is likely due to drug management errors resulting from a lack of education.

“Since most cart horse owners are poor and illiterate, they are less prepared to manage this problem,” said Seyoum Zewdu, MSc, DVM, of the Department of Paraclinical Studies in the Faculty of Veterinary Medicine at the University of Gondar, in Ethiopia. “So, the parasites will affect the health and welfare of the animal. Moreover, when drug resistance happens, it incurs further money losses for the owner as he or she searches for other control methods and deals with mortality and loss of economic power.”

Study Overview

In their study, Zewdu and his fellow researchers randomly selected 140 working horses in Gondar for parasite testing. They found 45 positive cases—32% of their selected sample. Then, they separated the parasite-infected horses into three treatment groups:

  • Ivermectin,
  • Fenbendazole, or
  • No treatment (as a control).

The team treated the horses according to their body weights and re-evaluated the animals 14 days later.

The researchers found that ivermectin had the best results, eliminating 97% of the parasite load, Zewdu said. However, scientific studies always rely on what is known as a “confidence interval,” which takes into consideration the possibility of errors and unknowns to create a range of percentages (minimum and maximum). As such, the lower range limit of this ivermectin confidence interval is just under 90%--meaning it’s possible that as many as 10% of parasites remained after ivermectin treatment. And that, said Zewdu, qualifies as showing parasitic resistance to treatment.

Fenbendazole results were far more obvious. The drug resulted in a 79% drop in parasite load, Zewdu said, clearly an indication of treatment resistance.

Potential for Undertreatment

Meanwhile, owner questionnaires revealed that they tended to guess at their horses’ weight or not take it into consideration at all when treating their horses, Zewdu said. This is likely results in undertreatment, which gives the parasites a chance to develop resistance.

Furthermore, the owners chose to treat the horses as a solution to various physical problems such as poor hair coat, weakness, or colic, he added. Most bought their products from an open market or private seller rather than via veterinarian’s prescription.

Fenbendazole causes particular concerns for resistance because owners mix the drug into the feed and, therefore, can’t control the actual quantity that the horse is ingesting, Zewdu said. This could also lead to resistance.

However, the problem, he said, is not one of lack of willingness but lack of education.

“Equines are the life of African poor people and farmers,” Zewdu said. “They are used for transportation of goods and human beings. Particularly, horses around urban areas are the economy sources of the cart horse owner’s families. They are essential as packing animals.”

Take-Home Message

Further steps should include education programs which prevent too-frequent treatments and underdosing, and which encourage alternation with other anthelmintic drugs, said Zewdu.

“Education programs are essential in order to make equine owners aware of the impact of drug resistance on animal health and the economy,” he said. “These programs should be implemented by integrating the traditional knowledge of the owners. That will contribute to convincing owners’ perceptions regarding the significance of these approaches to controlling parasites and underscore the owners’ responsibility in helping control such problems.”

About the Author

Christa Lesté-Lasserre, MA

Christa Lesté-Lasserre is a freelance writer based in France. A native of Dallas, Texas, Lesté-Lasserre grew up riding Quarter Horses, Appaloosas, and Shetland Ponies. She holds a master’s degree in English, specializing in creative writing, from the University of Mississippi in Oxford and earned a bachelor's in journalism and creative writing with a minor in sciences from Baylor University in Waco, Texas. She currently keeps her two Trakehners at home near Paris. Follow Lesté-Lasserre on Twitter @christalestelas.

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