The impact of the prairie dog oral sylvatic plague vaccine on non-target small rodents in the grassland ecosystem

Wild rodent populations have been decimated by plague since it was introduced in the western US in the early 20th century. Insecticidal dusting of prairie dog burrows is the main tool used in grassland ecosystems to mitigate... [ view full abstract ]

Wild rodent populations have been decimated by plague since it was introduced in the western US in the early 20th century. Insecticidal dusting of prairie dog burrows is the main tool used in grassland ecosystems to mitigate this primarily flea-borne disease caused by the bacterium Yersinia pestis. In 2013-15, a field trial assessed the efficacy of a potential new plague management tool for prairie dogs, the sylvatic plague vaccine (SPV). Baits containing SPV or a placebo were distributed on pairs of prairie dog colonies. Our study assessed the impact of SPV on non-target small rodents on these study sites, e.g. deermice (Peromyscus spp), Northern grasshopper mice (Onychomys leucogaster) and kangaroo rats (Dipodomys Ordii). We hypothesized that non-target small rodents would consume the bait and could be impacted by vaccination directly and indirectly. Animals would be directly impacted if individuals were protected after vaccine consumption. Alternatively, they may be indirectly impacted due to changes in plague occurrence in prairie dogs and rodent community composition. To determine non-target species abundance and richness, small mammals were live-trapped for 3-5 consecutive nights on 12 SPV paired study sites; 6 on black-tailed prairie dog (C. ludovicianus) colonies (2 in South Dakota, 4 in Montana) and 6 on Utah prairie dog (C. parvidens) colonies in the summers of 2013, 2014 and 2015. Blood, hair and whiskers were collected to determine seroprevalence and presence of bait biomarker. Over 3100 unique animals were caught and most non-target small rodents consumed the bait (72% +/- 0.2%). Deermice were highly abundant (78.2%) and vaccine application had a positive effect on their abundance, however few deermice seroconverted. Thus, SPV likely has an indirect impact on deermice abundance, probably due to reduced plague activity on the colonies. Based on this short-term study, SPV application should not disrupt the short-lived rodent community.