Accelerated evolution of SARS-CoV-2 in free-ranging white-tailed deer.

The zoonotic origin of the COVID-19 pandemic virus highlights the need to fill the vast gaps in our knowledge of SARS-CoV-2 ecology and evolution in non-human hosts. Here, we detected that SARS-CoV-2 was introduced from humans into white-tailed deer more than 30 times in Ohio, USA during November 2021-March 2022. Subsequently, deer-to-deer transmission persisted for 2-8 months, disseminating across hundreds of kilometers. Newly developed Bayesian phylogenetic methods quantified how SARS-CoV-2 evolution is not only three-times faster in white-tailed deer compared to the rate observed in humans but also driven by different mutational biases and selection pressures. The long-term effect of this accelerated evolutionary rate remains to be seen as no critical phenotypic changes were observed in our animal models using white-tailed deer origin viruses. Still, SARS-CoV-2 has transmitted in white-tailed deer populations for a relatively short duration, and the risk of future changes may have serious consequences for humans and livestock.

Influence of oral rabies vaccine bait density on rabies seroprevalence in wild raccoons.

The effect of different oral rabies vaccine (ORV) bait densities (75, 150, and 300 baits/km(2)) on the seroprevalence of rabies virus neutralizing antibodies (RVNAs) in raccoons (Procyon lotor) was assessed at a 15% seroprevalence difference threshold in rural areas of northeast Ohio. Results (n=588 raccoons) indicated that seropositivity for RVNAs was associated with both bait density and bait campaign frequency. Associations were not detected for raccoon gender, age, or macro-habitat. The odds of being seropositive were greater for raccoons originating from 300 bait/km(2) treatment areas relative to those coming from the 75 bait/km(2) areas (odds ratio [OR]=4.4, probability [P]<0.001, 95% confidence interval [CI]=2.4-7.9), while accounting for cumulative ORV campaigns. No statistical advantage in seroprevalence was detected when comparing 150-75 baits/km(2). These results indicate that a relatively extreme bait density when evenly distributed may be necessary to obtain a significant increase in seroprevalence. Higher bait densities may be more appropriate and less costly to address focused outbreaks than labor intensive trap-vaccinate-release and local population reduction campaigns. Finally, dramatic increases in seroprevalence of RVNA were not observed in raccoons between sequential, semi-annual campaigns, yet cumulative ORV campaigns were associated with gradual increases in seroprevalence.

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.