Serological Responses of Raccoons and Striped Skunks to Ontario Rabies Vaccine Bait in West Virginia during 2012-2016

Abstract

Since the 1990s, oral rabies vaccination (ORV) has been used successfully to halt the westward spread of the raccoon rabies virus (RV) variant from the eastern continental USA. Elimination of raccoon RV from the eastern USA has proven challenging across targeted raccoon (Procyon lotor) and striped skunk (Mephitis mephitis) populations impacted by raccoon RV. Field trial evaluations of the Ontario Rabies Vaccine Bait (ONRAB) were initiated to expand ORV products available to meet the rabies management goal of raccoon RV elimination. This study describes the continuation of a 2011 trial in West Virginia. Our objective was to evaluate raccoon and skunk response to ORV occurring in West Virginia for an additional two years (2012-2013) at 75 baits/km² followed by three years (2014-2016) of evaluation at 300 baits/km². We measured the change in rabies virus-neutralizing antibody (RVNA) seroprevalence in targeted wildlife populations by comparing levels pre- and post-ORV during each year of study. The increase in bait density from 75/km² to 300/km² corresponded to an increase in average post-ORV seroprevalence for raccoon and skunk populations. Raccoon population RVNA levels increased from 53% (300/565, 95% CI: 50-57%) to 82.0% (596/727, 95% CI: 79-85%) during this study, and skunk population RVNA levels increased from 11% (8/72, 95% CI: 6-20%) to 39% (51/130, 95% CI: 31-48%). The RVNA seroprevalence pre-ORV demonstrated an increasing trend across study years for both bait densities and species, indicating that multiple years of ORV may be necessary to achieve and maintain RVNA seroprevalence in target wildlife populations for the control and elimination of raccoon RV in the eastern USA.

Keywords: ONRAB; bait density; oral rabies vaccination; rabies virus; raccoon; skunk; virus-neutralizing antibody.

Figure 1

Location of the cells sampled during the 2012–2016 oral rabies vaccination (ORV) field trials in West Virginia, USA. Four cells (CKB03, CKB04, CKB05, and CKB06) within the Ontario Rabies Vaccine Bait (ONRAB) field trial area were sampled during the period 2012–2013 when the area was baited at a target of 75 baits/km². Three cells (CKB03, CKB04, CKB05) continued to be sampled during the period 2014–2016 when the area was baited with ONRAB at a target of 300 baits/km².

Figure 2

Raccoon (a) and skunk (b) rabies virus-neutralizing antibody (RVNA) seroprevalence from oral rabies vaccination (ORV) field trials with Ontario Rabies Vaccine Baits (ONRAB) in West Virginia, USA in relationship to bait density, sampling period (pre- or post-ORV), and year. RVNA cutoff observed was 0.125 IU/mL for the period 2012–2016. * Information from 2011 was from Slate et. al. [32] and included for comparison with years 2012–2016.

Figure 3

Proportion of raccoons seropositive for rabies virus-neutralizing antibodies (RVNA) at a cutoff of 0.125 IU/mL by year of age and bait densities sampled pre- and post-oral rabies vaccination (ORV) in West Virginia, USA. Error bars represent 95% confidence intervals.

Figure 4

Proportion of raccoons seropositive for rabies virus-neutralizing antibodies (RVNA) at a cutoff of 0.125 IU/mL by sex and bait densities sampled pre- and post-oral rabies vaccination (ORV) in West Virginia, USA. Error bars represent 95% confidence intervals.