By Roger J. Klingenberg
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Nematodes are among the most common parasites diagnosed in reptiles, with more than five hundred reptile forms identified. Larval forms migrate through the body. Adult nematodes are typically thought of as worms. Because of their ubiquitous nature, several drugs have been adapted to treat them.
Because ivermectin is strictly contraindicated in chelonians of all types, Bodri, Nolan, and Skeeba (1993) set out to investigate a related drug that could be used in turtles and tortoises. Milbemycin is a macrolide antibiotic formed by the fermentation of Streptomyces hygroscopicus aurolacrimosis and is somewhat similar to ivermectin, one of the avermectins produced by Streptomyces avermitilis. The compound has negligible activity as an antibiotic, but it is insecticidal, is acaricidal (active against mites), and provides anthelmintic activity at very low concentrations.
Milbemycin is available only as an oral pill. For the study, the injectable form was created by crushing a tablet and suspending it in propylene glycol. The study used fifty-three turtles: red-eared sliders, gulf box turtles, and ornate box turtles. These turtles were proven to harbor nematode parasites and were administered either ivermectin (0.2 mg/kg orally), milbemycin (0.5 and 1.0 mg/kg orally or 0.25 and 0.5 mg/kg subcutaneously), or propylene glycol (0.2mg/kg orally). Fifty percent of the ten red-eared sliders showed either paresis or flaccid paralysis when given ivermectin orally. One eventually died, and the others slowly recovered. No injectable ivermectin was given. This phase illustrated the obvious toxicity of ivermectin in chelonians.
None of the ten red-eared sliders given oral milbemycin had a reaction. There were no reactions in the five red-eared sliders, the six gulf coast box turtles, or the four ornate box turtles given the drug subcutaneously. The nematode parasites were cleared after at least two doses.
No problems were noted in the five red-eared sliders that were given propylene glycol orally. This control group was important to illustrate that the carrier solution wasn’t responsible for any reactions.
In conclusion, the study proved that milbemycin, a drug very similar to ivermectin, is safe and effective against nematode parasites in red-eared sliders and box turtles. The drug has not been tested on tortoises, which are even more sensitive to the effects of ivermectin. However, if forced to administer the drug orally, then you might as well use fenbendazole, which we know is safe and effective. Milbemycin needs to be formulated to use as an injectable, which would be its main advantage. More studies on this versatile drug are warranted.
Excerpt from the book Understanding Reptile Parasites by Roger Klingenberg with permission from its publisher, Advanced Vivarium Systems, an imprint of BowTie Press. Purchase Understanding Reptile Parasites here.