Samuel B. Linhart

A modified bait for oral delivery of biological agents to raccoons and feral swine.

A field study was conducted on Ossabaw Island (Georgia, USA) in March 1994 to evaluate four different types of bait for delivering orally effective biological agents to raccoons (Procyon lotor) and feral swine (Sus scrofa). A deep-fried corndog batter bait, which was previously shown to be ingested by both captive and free-ranging raccoons, and a polymer fishmeal bait which had been shown effective for both raccoons and feral swine were compared with a grain-based dog food meal polymer bait topically coated with corn oil and cornmeal or with fish oil and fishmeal. Tracking stations were used to determine the number of each bait type visited and removed by animals visiting stations. We found no significant differences in the numbers of different baits removed by either species. These data support the results of earlier studies which also indicated that an inexpensive grain-based matrix bait surface-coated with attractive flavors can be used to deliver oral biologics to problem species.

FORMULATION AND EVALUATION OF BAITS FOR ORAL RABIES VACCINATION OF RACCOONS (PROCYON LOTOR)

Captive raccoons were offered a variety of vaccine containers and bait components in a series of three-choice tests. Paraffin wax ampules were the most readily accepted vaccine container. Preferred bait components included corn and shellfish oils, deep fried corn meal batter, and egg, apple and buttermilk flavorings. These results, together with factors including ease of bait formulation, cost, and suitability for field use, were used to develop an experimental delivery system for an oral rabies vaccine. The developed system was composed of a polyurethane sleeve (1.5 × 5.5 cm) dipped in a commercial food batter mix together with corn meal, milk and egg. The sleeve was deep fried in corn oil and a 2.0 ml ampule containing a recombinant rabies vaccine was then inserted into the sleeve bait. These baits were presented to 10 captive raccoons. Nine of the 10 animals developed high levels of rabies virus neutralizing antibodies. Field tests are needed to determine if the delivery system developed also is effective for wild raccoons.

A FIELD EVALUATION OF BAITS FOR DELIVERING ORAL RABIES VACCINES TO RACCOONS (PROCYON LOTOR)

Eight field trials were conducted in 1989 and 1990 in Georgia (USA) and Maryland (USA) to evaluate baits and baiting strategies for delivering oral rabies vaccines to raccoons (Procyon lotor). Bait packets consisting of corn meal and egg batter-based baits enclosed in plastic bags were placed at 1.0-m diameter, raked tracking stations and checked daily. Packets were well accepted by raccoons; they visited 31 to 44% of the tracking stations where they removed 69 to 90% of the packets within 4 to 5 days. All or nearly all baits were removed from plastic bags and less than 1% of the baits were found only partially eaten. No rejection of water-filled paraffin ampules in baits was observed. The use of an odor attractant on bait packets did not appear to enhance bait discovery when packets were placed on raccoon travel routes. An attractant did enhance discovery when baits were placed off-road in a simulated aerial baiting test. Nontarget species comprised 31 to 53% of all visits to the stations; they took 28 to 55% of the baits but did not appear to adversely affect bait availability for raccoons. A total of 2,300 baits, each containing a wax ampule holding 10 mg of a physiological marker (iophenoxic acid), were distributed at a rate of 82 baits/km2 on 2,800 ha of Sapelo Island, Georgia. Thirty-five (65%) of 54 raccoons collected following bait placement had eaten one or more baits as indicated by elevated levels of iodine in the blood serum.