U.S. Department of Agriculture: Animal and Plant Health Inspection Service


Date of this Version

Fall 2010


Published in Human–Wildlife Interactions 4(2):275–282, Fall 2010
This is a US Government work, not subject to copyright in the United States.


The USDA/APHIS/Wildlife Services (WS) oral rabies vaccination program uses tetracycline, a broad-spectrum antibiotic and relatively reliable biomarker, to quantify vaccinebait uptake by raccoons (Procyon lotor). However, obtaining samples (e.g., bone or teeth) to assess tetracycline uptake is highly invasive, and sample preparation can be expensive. By contrast, rhodamine B, a commercially available dye, is absorbed systemically in growing tissues, including hair and whiskers, and can be observed under ultraviolet (UV) light as fluorescent orange bands. Our goal was to evaluate whether rhodamine B can be used as a biomarker to monitor bait uptake by raccoons. We began by orally administering a solution containing 100 mg, 150 mg, or 200 mg of rhodamine B to captive raccoons. We monitored whisker and hair samples for fluorescence using a hand-held UV lamp and a fluorescent microscope for 13-weeks post-treatment. All raccoons that were administered rhodamine B exhibited fluorescence in their whisker and hair samples during the course of the study. Our ability to detect fluorescing whiskers varied based on the method of detection and time interval, but not with rhodamine B dosage level. We detected rhodamine B in 81% of marked individuals using the fluorescent microscope and 58% of marked subjects using the UV lamp. We were able to detect rhodamine B when doses as low as 1 mg/kg were given. Raccoons did not exhibit a taste aversion to baits containing ≤3% rhodamine B. We believe that rhodamine B can be a useful biomarker for raccoons and has potential as an application to monitor the uptake of oral rabies vaccine.