Antibodies to West Nile virus in feral swine from Florida, Georgia, and Texas, USA.

West Nile virus (WNV) exposure has not yet been reported in feral swine (Sus scrofa) despite the broad geographic range and population density of this species. The objectives of this study were to determine the prevalence of antibodies to WNV in feral pigs, and to evaluate serologic diagnostics as applied to this species. Feral pig serum from three states was evaluated for antibodies to WNV. The overall WNV seroprevalence rate for 222 samples collected in 2001-2004 was 22.5%. Seroprevalence rates in Florida, Georgia, and Texas were 17.2%, 26.3%, and 20.5%, respectively. The results of this study demonstrate that feral pigs could represent useful mammalian sentinels of WNV.

Dynamics of maternal antibodies to hemorrhagic disease viruses (Reoviridae: Orbivirus) in white-tailed deer.

Enzootic stability, potentially associated with acquired resistance and subsequent transfer of maternal antibodies, innate resistance, or both, has been hypothesized to explain the lack of reports of hemorrhagic disease (HD) in white-tailed deer (Odocoileus virginianus) from Texas. The objectives of this research were to determine the following: how long maternal antibodies to epizootic hemorrhagic disease (EHD) and bluetongue (BT) viruses persist; whether fawns from an enzootic site are naturally exposed to EHD and BT viruses while maternal antibodies are present; and whether field-challenged fawns develop clinical disease. Twelve of 52 fawns from Texas were moved to an indoor facility. All 12 (100%) were positive for maternal antibodies to EHD or BT viruses by agar gel immunodiffusion (AGID) and serum neutralization (SN) tests. Weekly monitoring demonstrated that precipitating antibodies disappeared by 23 wk of age and serum neutralizing antibodies disappeared by 17-18 wk of age. Fawns that remained outdoors in Texas were not observed with signs of HD. At 14-21 wk of age (October), 39 of 40 (98%) fawns that had remained outdoors were positive for EHD and/or BT virus antibodies by AGID and 32 (80%) had SN antibody titers to one or more of five viruses (EHDV-1, EHDV-2, BTV-10, BTV-11, BTV-17). Antibody titers to EHDV-1, EHDV-2, and BTV-11 all exceeded titers of same-age indoor fawns, suggesting recent exposure. Epizootic hemorrhagic disease viruses were isolated from seven (18%) of the outdoor fawns and all 40 remained clinically normal. Natural exposure of deer to EHD and BT viruses occurred at this site in the presence of maternal antibodies without causing disease. This may be due to acquired immunity and the subsequent transfer of maternal antibodies, but it does not exclude innate resistance as a possible factor in the enzootic stability of EHD and BT viruses at this location.

A new flavor-coated sachet bait for delivering oral rabies vaccine to raccoons and coyotes.

Research was conducted during 1996-2000 to develop baits for delivering an oral rabies vaccine to raccoons (Procyon lotor) and coyotes (Canis latrans). A bait was sought that: (1) was attractive to the target species, (2) could be distributed by aircraft, (3) was as effective (or more so) than the currently used fish meal polymer bait, and (4) could be produced in large numbers by automated procedures and could be purchased by user groups at substantially lower cost. Ten field trials were conducted to document raccoons' bait flavor preferences, evaluate a new vaccine sachet bait coated with various attractants, and determine if the sachet bait would effectively deliver Raboral V-RG oral rabies vaccine (Merial Limited, Athens, Georgia, USA) to this species. Raccoons preferred fish and crustacean-based flavors over those derived from plant materials. Raccoon visits to tracking stations, frequency of bait removals, and percent of sachets discarded by this species that were emptied of placebo vaccine indicated efficacy of the new bait was equal or superior to the currently used fish meal polymer bait. A field trial conducted in fall 1998 compared aerially distributed vaccine-laden sachet and polymer baits and showed there was no difference between the percent of raccoons from the test and reference areas subsequently found positive for rabies antibody. Four bait trials to determine coyote response to sachet baits were conducted in 1997-98. The propensity for canids to gulp or bolt smaller food items is well known. Thus, a first trial involved offering fish-flavored sachet baits of different sizes to 30 captive coyotes to determine if smaller size baits were more frequently swallowed intact. Two field trials were also conducted in fall 1997 to determine if free-ranging coyotes discriminated among sachet baits coated with different attractants. Finally, Raboral V-RG-laden poultry-flavored sachet baits were aerially dropped and the percent of seropositive coyotes was compared with coyotes from surrounding areas where fish meal polymer vaccine baits had been distributed. Captive coyotes did not swallow sachet baits intact, regardless of size. Bait preference field trials indicated that coyotes preferred poultry, cheese/beef tallow, and fish-flavored sachet baits and that such baits were taken at the same rate as polymer baits. A sample of coyotes from the area baited with vaccine-laden sachet baits had a markedly higher (P = 0.01) seropositivity rate than coyotes from areas where vaccine was distributed in polymer baits. Sachet bait production could be facilitated by automated technology and sachet baits used either as an alternative vaccine delivery device or in combination with the fish meal polymer bait.