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Treatment and eradication of murine fur mites: I. Toxicologic evaluation of ivermectin-compounded feed
Rodolfo J Ricart Arbona1, Neil S Lipman, Elyn R Riedel
1Tri-Institutional Training Program in Laboratory Animal Medicine and Science, Memorial Sloan-Kettering Cancer Center, Weill Cornell Medical College and The Rockefeller University, New York, New York, USA. ricartr@pi.cpmc.columbia.edu
Abstract:
Fur mite outbreaks remain a persistent problem in laboratory mouse colonies. All currently published treatment methods are labor-intensive, expensive, or unreliable. During a recent outbreak with Myobia musculi and Myocoptes musculinus in a large colony (approximately 30,000 cages), we developed a feed-based treatment regime in which ivermectin was the active ingredient. Rodent feed was compounded with 3 different concentrations of ivermectin (12, 24, and 48 ppm) and γ-irradiated. Postcompounding analysis revealed loss of ivermectin during manufacturing, but the remaining drug was stable for at least 6 mo. In an 8-wk toxicity study in a C57BL/6NTac mouse breeding colony, ad-libitum feeding of the 3 diets yielded estimated doses of 1.3, 2.7, and 5.4 mg/kg. Adult mice lacked adverse clinical effects, except that 1 of the 144 mice in the 48-ppm group developed tremors and ataxia and was euthanized. No significant differences between doses were revealed by CBC, serum chemistry, body weight, or gross necropsy. Plasma drug concentrations plateaued at a dose-dependent level 7 to 10 d after initiation of treatment and decreased to undetectable levels 6 to 9 d after its discontinuation. Fertility of the P0 generation was unaffected. Pup mortality was higher in the 24- and 48-ppm groups, reaching 100% at the higher dose. Animals exposed to ivermectin as neonates had normal weaning weights, but mice receiving 24-ppm feed had lower adult weights. Our results indicate that using feed containing 12 ppm ivermectin (estimated ingested dose, 1.3 mg/kg) was safe in a C57BL/6NTac breeding colony.
Insights
A new feed-based ivermectin treatment effectively controlled fur mites in laboratory mice. The 12 ppm ivermectin feed was safe for breeding colonies, offering a reliable solution for mite outbreaks.
Area of Science:
- Veterinary Parasitology
- Laboratory Animal Science
- Drug Efficacy Studies
Background:
- Fur mites (*Myobia musculi*, *Myocoptes musculinus*) are a persistent issue in laboratory mouse colonies.
- Current treatments are often labor-intensive, costly, or ineffective.
- A novel, feed-based approach using ivermectin was investigated.
Purpose of the Study:
- To develop and evaluate a feed-based ivermectin treatment for fur mites in laboratory mice.
- To assess the safety and efficacy of different ivermectin concentrations in a mouse breeding colony.
Main Methods:
- Rodent feed was compounded with 12, 24, or 48 ppm ivermectin and γ-irradiated.
- An 8-week toxicity study was conducted on a C57BL/6NTac mouse breeding colony.
- Evaluated clinical effects, hematology, serum chemistry, body weight, necropsy, drug pharmacokinetics, fertility, and pup mortality.
Main Results:
- Ivermectin concentrations decreased during manufacturing but remained stable for at least 6 months.
- Estimated doses of 1.3, 2.7, and 5.4 mg/kg were well-tolerated by adult mice, with minimal adverse effects at the highest dose.
- Plasma ivermectin concentrations reached dose-dependent plateau levels and became undetectable after treatment cessation.
- Fertility was unaffected, but pup mortality increased at 24 and 48 ppm, reaching 100% at 48 ppm.
- Neonatal exposure to 12 ppm ivermectin resulted in normal weaning weights and adult weights comparable to controls.
Conclusions:
- Feed containing 12 ppm ivermectin (estimated dose 1.3 mg/kg) is safe for C57BL/6NTac breeding colonies.
- This feed-based treatment offers a potentially reliable and less labor-intensive method for controlling fur mites.
- Higher ivermectin concentrations (24 and 48 ppm) negatively impacted pup survival and development.
