Immunization of Black-Tailed Prairie Dog Against Plague Through Consumption of Vaccine-Laden Baits

Abstract

ABSTRACT:Prairie dogs (Cynomys spp.) are highly susceptible to Yersinia pestis and, along with other wild rodents, are significant reservoirs of plague for other wildlife and humans in the western United States. A recombinant raccoon poxvirus, expressing the F1 antigen of Y. pestis, was incorporated into a palatable bait and offered to three groups (n518, 19, and 20) of black-tailed prairie dogs (Cynomys ludovicianus) for voluntary consumption, either one, two, or three times, at roughly 3-wk intervals. A control group (n519) received baits containing raccoon poxvirus without the inserted antigen. Mean antibody titers to Y. pestis F1 antigen increased significantly in all groups ingesting the vaccine-laden baits, whereas the control group remained negative. Upon challenge with virulent Y. pestis, immunized groups had higher survival rates (38%) than the unimmunized control group (11%). The mean survival time of groups ingesting vaccine-laden baits either two or three times was significantly higher than that of animals ingesting vaccine-laden baits just one time and of animals in the control group. These results show that oral immunization of prairie dogs against plague provides some protection against challenge at dosages that simulate simultaneous delivery of the plague bacterium by numerous (3-10) flea bites.

Oral vaccination reduces the incidence of tuberculosis in free-living brushtail possums

“…This high level of vaccine efficacy compares very favourably with other wildlife vaccines. For example, recent trials of the protection conferred by an orally delivered recombinant poxvirus against artificial plague challenge in prairie dogs have demonstrated an efficacy of only 40-50 per cent (Mencher et al 2004;Rocke et al 2008), while commercial oral rabies vaccine baits have 70-100 per cent efficacy across different species (Cliquet et al 2008). Furthermore, BCG vaccination of wild possums by intranasal and intraconjunctival routes only achieved 69 per cent efficacy of protection against natural Tb infection (Corner et al 2002a).…”

Population Differences in Host Immune Factors May Influence Survival of Gunnison’s Prairie Dogs (Cynomys gunnisoni) during Plague Outbreaks

“…Reports of apparent plague resistance in wild rodents exist, including black rats (Rattus rattus), grasshopper mice (Onychomys leucogaster), and rock squirrels (Spermophilus variegatus; Quan et al, 1985;Thomas et al, 1988;Tollenaere et al, 2008). In prairie dogs, this pathogen generally produces high mortality (Rocke et al, 2008) and, to our knowledge, resistance to plague has not been reported in any of the five prairie dog species. Therefore, it is surprising that the AV population has not experienced a die-off from plague in the last 40 yr. Possible explanations for the resilience of the AV population during epizootics that decimated other Arizona colonies include inefficient transmission by flea vectors or absence of this disease in the rodent community at AV.…”

Plague outbreaks in prairie dog populations explained by percolation thresholds of alternate host abundance

“…After infected with plague, prairie dogs die in approximately 6 d (12,34), and the fleas will subsequently search for new hosts. Dying prairie dogs infest a high proportion of their fleas with the plague bacterium: 18/22 (or 82%) O. hirsuta fleas found on dead prairie dogs were plague-positive, and fleas are likely to be infected only in the terminal stages of the host's Y. pestis infection (35,36).…”