Gastrointestinal parasites are a leading cause of disease in all grazing livestock, including camelids. The blood-feeding nematode, Haemonchus contortus, is especially devastating, because it can cause anemia and death. Lisa Williamson, DVM, and her colleagues from the University of Georgia studied hundreds of llamas and alpacas on 26 farms in the southeastern United States and is not necessarily reflective of the rest of the country. They found that ivermectin and benzimidazole resistance is common in Haemonchus contortus isolates from camelids, but many are still sensitive to levamisole and moxidectin. Levamisole effectively treated camelids with levamisole-sensitive Haemonchus contortus burdens. No adverse effects were seen in any treated camelids. Of note, oral morantel tartrate, a dewormer that is related to levamisole, and more widely available, showed a great deal of inconsistency in efficacy at all doses studied. Further studies showed that orally administered moxidectin also safely and effectively reduced moxidectin-sensitive Haemonchus contortus worms in alpacas and llamas. In contrast, moxidectin injected subcutaneously was much less effective than oral moxidectin treatment. The “take home” message is that it is important to treat gastrointestinal parasites with either orally administered levamisole or orally administered moxidectin (not the injectable form) to maximize effectiveness.
Another big “take home” message is that we need to avoid accelerating drug resistance by using these remaining effective drugs judiciously. The way producers can help slow resistance is by only medicating animals with moxidectin and/or levamisole that need treatment based on clinical signs or fecal egg count data, not the entire herd, and certainly not on a repeated basis at given times during the year! The FAMACHA system has been validated to detect anemia related to Haemonchus contortus burdens in camelids. This parameter, as well as body condition score, and fecal consistency can be used to make good selective treatment decisions. Treatment decisions for your animals should be made with your veterinarian as each farm's parasite concerns are unique. There is no one blanket protocol that is appropriate for all farms.
To read more about strategies to control this problem, read the full text of Dr. Williamson’s article about drug resistant worms, which is available on the Alpaca ResearchFoundation website.