Treatment and eradication of murine fur mites: III. Treatment of a large mouse colony with ivermectin-compounded feed.

We determined the efficacy of ivermectin-compounded feed against fur mites in mice and describe its use to eradicate mites in vivaria holding approximately 30,000 cages. C57BL/6NCrl mice infested with Myobia musculi and Myocoptes musculinus were treated with ivermectin-compounded feed (approximate ingested dose, 1.3 mg/kg) for 1, 4, or 8 consecutive weeks. Regardless of treatment duration, all treated mice, as well as contact sentinels, remained free of fur mites for as long as 21 wk after treatment. No adverse effects were observed. Subsequently, facility-wide treatment was implemented in an attempt to eradicate fur mites from 3 vivaria housing approximately 120,000 mice. Medicated feed was provided for 8 wk to ensure that all cages and mice were treated. A single investigative group reported adverse effects in their colony 4 wk after treatment was initiated; mortality was attributed to ivermectin toxicity after an intracranial injection at 1 d of age. Naïve pups were unaffected. No other adverse effects were noted. Approximately 14,500 skin scrape samples were evaluated during the 12-mo posttreatment surveillance period. All samples were negative for mites. To our knowledge, this is the first report of successful eradication of fur mites from a mouse colony of this large size.