Oral Bait Research Articles

Acceptance and palatability for domestic and wildlife hosts of baits designed to deliver a tuberculosis vaccine to wild boar piglets

Tuberculosis (TB) caused by Mycobacterium bovis, a member of the Mycobacterium tuberculosis complex, is an important health problem worldwide. The control of TB through vaccination of wildlife reservoirs may potentially have advantages over other management strategies. The most practical approach to deliver vaccines to wildlife is using oral baits that are stable under field conditions and effective in reaching the target species. Baits were developed in our laboratory to deliver oral vaccines to wild boar piglets. However, these baits were well accepted by other wild species. Therefore, bait consumption by different M. bovis hosts was evaluated herein. The results showed that the baits were well accepted by cattle, feral pigs, and adult red deer whereas small mammals like badgers and possums showed varying bait acceptance. Bait acceptance by different species has the advantage of targeting more than one wildlife reservoir when they coexist in the same area and need to be vaccinated for TB control. However, bait delivery methods such as the use of selective feeders to target the desired species should be developed to avoid bait consumption by other species.

Analysis by LC/ESI-MS of iophenoxic acid derivatives and evaluation as markers of oral baits to deliver pharmaceuticals to wildlife

Iophenoxic acid and its derivatives (methyl, ethyl, and propyl) are organic chemicals used as markers in baiting campaigns to deliver vaccines, pharmaceuticals, contraceptives or poisons to wildlife. In this study we develop a method of detection of IPA derivatives by LC/ESI-MS (using butyl-IPA as internal standard) obtaining a limit of detection and quantification in wild boar ( Sus scrofa) serum of 0.037 μg/ml and 0.123 μg/ml, respectively. The average recovery of IPA derivatives was 88% at levels >0.2 μg/ml, with coefficients of variation <15%. Wild boars in captivity were orally treated with 5 mg/kg b.w. (three adults) or 15 mg/kg b.w (two piglets and three adults) of methyl-, ethyl- and propyl-IPA and the serum levels of these were monitored during 18 months after dosing. Ethyl- and propyl-IPA were detected up to 18 months after a single oral dose in wild boar, especially at 15 mg/kg. Methyl-IPA was detected until 9 months after dosing. Half-lives of methyl-, ethyl- and propyl-IPA were (mean ± SD) 41 ± 5, 183 ± 85 and 165 ± 45 days, respectively. One control piglet not exposed to IPA, but housed in the same facility than treated animals showed detectable IPA levels in serum. Piglets born from mothers exposed to marked baits also showed detectable IPA levels in serum. The high persistence of Et- and Pr-IPA must be considered in the field trials, because the presence of the product at low levels in one animal may not reflect a real ingestion of the marked bait.

Escape of classical swine fever C-strain vaccine virus from detection by C-strain specific real-time RT-PCR caused by a point mutation in the primer-binding site

Classical swine fever (CSF) is one of the most important diseases of pigs. Vaccination in the European Union is limited to emergency situations. Currently, vaccination for the purpose of disease control is carried out in wild boar populations. Wild boar are in most cases vaccinated using an oral bait vaccine based on the live modified vaccine virus C-strain “Riems”. A real-time reverse transcription polymerase chain reaction (RT-PCR) protocol for differentiation of C-strain “Riems” vaccine virus from CSF virus (CSFV) field isolates was published previously. In this real-time RT-PCR system differentiation is based on two nucleotide difference one at the 3′ end of each of the primer-binding sites in the E RNS encoding genome region. During extensive diagnostic use of this protocol in an outbreak of CSF in wild boar in Germany, some C-strain positive field samples were found to give negative results in the C-strain “Riems” specific real-time RT-PCR, but positive results in a pan-CSFV real-time RT-PCR system. Moreover, sequencing of C-strain “Riems” vaccine batches for intramuscular use revealed differences in the E RNS encoding region. This led to the assumption that mutations in the corresponding primer-binding site of the C-strain specific system had appeared in the field, and possibly also during manufacturing of different vaccine batches. To test this hypothesis and restore sensitivity, a new primer set for detection of the possible C-strain virus quasi species was designed and tested.

Review of issues concerning the use of reproductive inhibitors, with particular emphasis on resolving human‐wildlife conflicts in North America

This manuscript provides an overview of past wildlife contraception efforts and discusses the current state of research. Two fertility control agents, an avian reproductive inhibitor containing the active ingredient nicarbazin and an immunocontraceptive vaccine, have received regulatory approval with the Environmental Protection Agency and are commercially available in the USA. OvoControl G Contraceptive Bait for Canada Geese and Ovo Control for pigeons are delivered as oral baits. An injectable immunocontraceptive vaccine (GonaCon Immunocontraceptive Vaccine) was registered with the Environmental Protection Agency for use in female white-tailed deer in September 2009. An injectable product (GonaCon Immunocontraceptive Vaccine) is registered for use in female white-tailed deer. Both products are labeled for use in urban/suburban areas where these species are overabundant. Several other compounds are currently being tested for use in wildlife in the USA, Europe, Australia and New Zealand that could have promise in the future. The development and use of reproductive inhibitors for resolving human-wildlife conflicts will depend on a number of factors, including meeting the requirements of regulatory agencies for use in the environment and on the biological and economical feasibility of their use. Use will also be dependent on health and safety issues and on public acceptance of the techniques.

Analysis of vaccine-virus-associated rabies cases in red foxes (Vulpes vulpes) after oral rabies vaccination campaigns in Germany and Austria

To eradicate rabies in foxes, almost 97 million oral rabies vaccine baits have been distributed in Germany and Austria since 1983 and 1986, respectively. Since 2007, no terrestrial cases have been reported in either country. The most widely used oral rabies vaccine viruses in these countries were SAD (Street Alabama Dufferin) strains, e.g. SAD B19 (53.2%) and SAD P5/88 (44.5%). In this paper, we describe six possible vaccine-virus-associated rabies cases in red foxes (Vulpes vulpes) detected during post-vaccination surveillance from 2001 to 2006, involving two different vaccines and different batches. Compared to prototypic vaccine strains, full-genome sequencing revealed between 1 and 5 single nucleotide alterations in the L gene in 5 of 6 SAD isolates, resulting in up to two amino acid substitutions. However, experimental infection of juvenile foxes showed that those mutations had no influence on pathogenicity. The cases described here, coming from geographically widely separated regions, do not represent a spatial cluster. More importantly, enhanced surveillance showed that the vaccine viruses involved did not become established in the red fox population. It seems that the number of reported vaccine virus-associated rabies cases is determined predominantly by the intensity of surveillance after the oral rabies vaccination campaign and not by the selection of strains.

Genetic stability (in vivo) of the attenuated oral rabies virus vaccine SAD B19

The distribution of oral rabies vaccine baits containing replication-competent live viruses poses certain environmental safety risks; among others, the possibility of reversion to or an increase in virulence. Hence, the genetic stability of the complete genome of the most widely used oral rabies vaccine virus, SAD B19, was examined after four and 10 serial i.c. passages in foxes and mice, respectively. It was shown that the consensus strain of SAD B19 was extremely stable in vivo. After 10 consecutive passages in mice not a single mutation was observed. In foxes, seven single nucleotide exchanges were found between the first and fourth passage, of which only one resulted in an amino acid exchange at position 9240 of the L-gene. This mutation was not observed during the first three passages and, furthermore, it was shown that this mutation was not linked to enhanced virulence.

Progress in the development of tuberculosis vaccines for wildlife.

Abstract Wildlife reservoirs of Mycobacterium bovis (bovine tuberculosis) serve as an important source of infection for domestic animals and impede attempts to eradicate the disease in many countries. In addition, wildlife reservoirs of bovine tuberculosis cause serious problems in game parks and hunting estates, where infection can spill over to iconic or endangered wildlife species. In the past decade, much progress has been accomplished towards designing vaccines aimed at wildlife species. Indeed, vaccination is emerging as a promising strategy for control of disease in wildlife, and M. bovis bacille Calmette Guérin (BCG) vaccine has been tested in a range of wildlife species, with very encouraging results. A crucial development has been the formulation of an oral bait delivery system, which provides a practical and cost-effective means of delivering a tuberculosis vaccine to wildlife. Major progress has been made in the development of the experimental challenge models in wildlife species, bait technology and the effectiveness of the vaccines against experimental challenge as well as to natural exposure to M. bovis . The aim of this review is to indicate the role for vaccines in control of bovine tuberculosis in wildlife and to provide an update on the development of these vaccines.

Effects of Natural Barriers and Habitat on the Western Spread of Raccoon Rabies in Alabama

Abstract: Although domestic animal transmission of rabies has largely been mitigated, the disease remains a concern in both Europe and North America where wildlife transmission has caused epizootics. Raccoon (Procyon lotor) rabies was established in Alabama, USA, in 1975, primarily in the southeastern corner of the state. However, with the exception of isolated events, rabies has not continued to spread westward across the Alabama River. We monitored movements of 100 radiocollared raccoons on 2 sites within hardwood and agriculture habitats in a rabies enzootic area east of the Alabama River, in managed pine habitat area west of the river where rabies sporadically occurs, and in a mixed pine hardwood area outside of the known rabies enzootic area to determine if raccoon movements and habitat use in certain habitat types and the presence of a river may serve as natural barriers preventing the western spread of rabies in Alabama. We also examined raccoon contact rates to determine if they influence disease transmission through static and dynamic interactions. Raccoons in mixed pine‐hardwood forest habitats had smaller home ranges and less overlap of ranges compared to the other 3 habitats. However, static interactions between habitats in the use of overlap areas did not differ (F11,129 = 1.63, P = 0.09). Rabies antibody titers were highest in the managed pine habitat (28%) even prior to oral vaccine bait distributions in spring of 2004 and 2005. Biomarker data from radiocollared and additional raccoons captured after the bait distribution west of the Alabama River demonstrated a low efficacy of the vaccine reaching the small southern raccoons. The combination of the river as a partial barrier, the high percentage of pine forested habitat west of the river, and limited spatial movements of raccoons within these forested habitats appears to have reduced the likelihood of rabies establishing west of the river. Understanding different host‐habitat‐ disease systems is important for successful management of diseases. Based on our results, we recommend that the oral vaccine program continue to use the Alabama River as a partial barrier and baiting be concentrated in the fragmented bottomland hardwood forests and around larger bodies of water where raccoon densities are highest. Success of baiting strategies designed to take advantage of northern raccoon dynamics and habitat use may not be applicable to southern populations.

Skunk Rabies in California (1992–2003)—Implications for Oral Rabies Vaccination

Skunk-variant rabies is endemic in California (United States), and the development of oral vaccines and baits to vaccinate skunks is in progress. In 2003, the California Department of Public Health (CDPH) began to quantify the impacts of skunk-variant rabies and to assess the feasibility of using oral rabies vaccination (ORV) as a containment measure. The CDPH rabies case data for skunks were spatially depicted and analyzed using a geographic information system. Statewide, rabid skunks (1992-2003) primarily occurred in seven physiographic regions: Central Coast, North Coast, North Sierra, Sacramento Valley, San Francisco Bay and Delta, San Joaquin Valley, and South Sierra. Detailed analysis of rabid skunks in San Luis Obispo (SLO) and Santa Barbara (SB) counties showed that skunk rabies was endemic in the coastal plain of SLO County between 1992 and 2000, but only became epizootic in SB County during 2002. Despite the widespread distribution of striped skunks (Mephitis mephitis) throughout most of California, the skunk rabies variant has not been found in Los Angeles County since 1979. Results imply that future ORV campaigns for skunk-variant rabies in the Pacific Coastal Plain could deter spread from SLO into SB County, as well as deterring the reintroduction of skunk-variant rabies into southern California.

Assessment of different formulations of oral Mycobacterium bovis Bacille Calmette-Guérin (BCG) vaccine in rodent models for immunogenicity and protection against aerosol challenge with M. bovis

Bovine tuberculosis (bTB) caused by infection with Mycobacterium bovis is causing considerable economic loss to farmers and Government in the United Kingdom as its incidence is increasing. Efforts to control bTB in the UK are hampered by the infection in Eurasian badgers ( Meles meles) that represent a wildlife reservoir and source of recurrent M. bovis exposure to cattle. Vaccination of badgers with the human TB vaccine, M. bovis Bacille Calmette-Guérin (BCG), in oral bait represents a possible disease control tool and holds the best prospect for reaching badger populations over a wide geographical area. Using mouse and guinea pig models, we evaluated the immunogenicity and protective efficacy, respectively, of candidate badger oral vaccines based on formulation of BCG in lipid matrix, alginate beads, or a novel microcapsular hybrid of both lipid and alginate. Two different oral doses of BCG were evaluated in each formulation for their protective efficacy in guinea pigs, while a single dose was evaluated in mice. In mice, significant immune responses (based on lymphocyte proliferation and expression of IFN-γ) were only seen with the lipid matrix and the lipid in alginate microcapsular formulation, corresponding to the isolation of viable BCG from alimentary tract lymph nodes. In guinea pigs, only BCG formulated in lipid matrix conferred protection to the spleen and lungs following aerosol route challenge with M. bovis. Protection was seen with delivery doses in the range 10 6–10 7 CFU, although this was more consistent in the spleen at the higher dose. No protection in terms of organ CFU was seen with BCG administered in alginate beads or in lipid in alginate microcapsules, although 10 7 in the latter formulation conferred protection in terms of increasing body weight after challenge and a smaller lung to body weight ratio at necropsy. These results highlight the potential for lipid, rather than alginate, -based vaccine formulations as suitable delivery vehicles for an oral BCG vaccine in badgers.

Oral Vaccination of Guinea Pigs with aMycobacterium bovisBacillus Calmette-Guérin Vaccine in a Lipid Matrix Protects against Aerosol Infection with VirulentM. bovis

Increased incidence of bovine tuberculosis (TB) in the United Kingdom caused by infection with Mycobacterium bovis is a cause of considerable economic loss to farmers and the government. The Eurasian badger (Meles meles) represents a wildlife source of recurrent M. bovis infections of cattle in the United Kingdom, and its vaccination against TB with M. bovis bacillus Calmette-Guérin (BCG) is an attractive disease control option. Delivery of BCG in oral bait holds the best prospect for vaccinating badgers over a wide geographical area. Using a guinea pig pulmonary challenge model, we evaluated the protective efficacy of candidate badger oral vaccines, based on broth-grown or ball-milled BCG, delivered either as aqueous suspensions or formulated in two lipids with differing fatty acid profiles (one being animal derived and the other being vegetable derived). Protection was determined in terms of increasing body weight after aerosol challenge with virulent M. bovis, reduced dissemination of M. bovis to the spleen, and, in the case of one oral formulation, restricted growth of M. bovis in the lungs. Only oral BCG formulated in lipid gave significant protection. These data point to the potential of the BCG-lipid formulation for further development as a tool for controlling tuberculosis in badgers.

EFFICACY OF ORAL AND PARENTERAL ROUTES OF MYCOBACTERIUM BOVIS BACILLE CALMETTE-GUERIN VACCINATION AGAINST EXPERIMENTAL BOVINE TUBERCULOSIS IN WHITE-TAILED DEER (ODOCOILEUS VIRGINIANUS): A FEASIBILITY STUDY

We investigated the efficacy of oral and parenteral Mycobacterium bovis bacille Calmette-Guerin Danish strain 1331 (BCG) in its ability to protect white-tailed deer (Odocoileus virginianus) against disease caused by M. bovis infection. Twenty-two white-tailed deer were divided into four groups. One group (n=5) received 10(9) colony-forming units (cfu) BCG via a lipid-formulated oral bait; one group (n=5) received 10(9) cfu BCG in culture directly to the oropharynx, one group (n=6) was vaccinated with 10(6) cfu BCG subcutaneously, and one group served as a control and received culture media directly to the oropharynx (n=6). All animals were challenged 3 mo after vaccination. Five months postchallenge the animals were examined for lesions. Results indicate that both oral forms of BCG and parenterally administered BCG offered significant protection against M. bovis challenge as compared to controls. This study suggests that oral BCG vaccination may be a feasible means of controlling bovine tuberculosis in wild white-tailed deer populations.

Recent Developments in Oral Bait Vaccines for Wildlife

The vaccination of wildlife reservoirs of infection is important for effective disease control programs and usually requires the use of oral vaccines. Current inventions in the field of oral baits for the immunization of wildlife cover effective vaccine compositions, vaccine containers to deliver the vaccine orally to target species, and baits that specifically attract the target species. Oral bait vaccine formulations need to provide an effective field performance, safety, cost-effectiveness, less waste, and improved environmental compliance. Herein, we review recent patents in oral bait vaccine formulations for the immunization of wildlife and particularly of terrestrial wild mammals. Recent progress in this field suggests that the application of oral bait vaccines to wildlife will impact disease control in the near future.

CP7_E2alf: A safe and efficient marker vaccine strain for oral immunisation of wild boar against Classical swine fever virus (CSFV)

Wild boar are an important reservoir of Classical swine fever virus (CSFV) in several European countries, where most of the primary outbreaks in domestic pigs are directly related to the endemic disease situation in the wild boar population. Oral immunisation has been introduced as an additional control measure to accelerate CSF eradication in wild boar in Germany since 1993. Immunisation with an oral bait vaccine based on the conventionally attenuated live vaccine strain “C” proved to be safe and effective, but does not allow differentiation between infected and vaccinated animals. Therefore, we examined the vaccine efficacy of the recently constructed chimeric pestivirus CP7_E2alf, whose coding sequences for the major envelope protein E2 of BVDV strain CP7 are replaced by E2 of the CSFV strain Alfort187 [Reimann I, Depner K, Trapp S, Beer M. An avirulent chimeric pestivirus with altered cell tropism protects pigs against lethal infection with classical swine fever virus. Virology 2004;322(1):143–57]. Following oral immunisation of wild boar, CP7_E2alf proved to be completely avirulent. Furthermore, all vaccinees were fully protected from clinical disease after a highly virulent CSFV challenge infection. The immunised animals seroconverted within 3 weeks after vaccination for CSFV E2-specific and CSFV neutralising antibodies, whereas prior to challenge infection no antibodies against CSFV E rns were detected with an appropriate CSFV-specific marker ELISA test. Thus, the BVDV backbone of CP7_E2alf enables serological and genetic differentiation from wild type CSFV infection. In conclusion, CP7_E2alf represents the first efficient and safe marker vaccine candidate for oral immunisation of wild boar against CSFV.

Elimination of Arctic Variant Rabies in Red Foxes, Metropolitan Toronto

To control the arctic variant of rabies virus in red foxes, 332,257 bait doses containing live, attenuated Evelyn-Rokitnicki-Abelseth rabies vaccine were distributed in greater metropolitan Toronto during 1989–1999. Human and pet contact with bait was minimal, and no adverse reactions to the vaccine were noted. Significantly fewer rabid foxes were found during the 17 years after fox baiting (5 cases during 1990–2006) than in the 17 years before (96 cases during 1973–1989). The last report of a rabid fox in metropolitan Toronto was in 1996 (reporting period through September 2006), which confirms that distributing oral rabies vaccine bait is a feasible tactic for the control of rabies in foxes in urban environments.

Suitability of canine herpesvirus as a vector for oral bait vaccination of foxes

Studies were conducted to evaluate the feasibility of using canine herpesvirus (CHV) as a vaccine vector for bait-delivered oral vaccination of wild foxes. To test the viability of CHV in baits, CHV was freeze-dried, incorporated into different baits, stored, and the remaining viral infectivity tested in cell culture after varying periods of time at different storage temperatures. Experimental baits (mouse carcasses) and commercial baits (FOXOFF and PROBAIT) were prepared with either liquid or freeze-dried CHV and tested in two fox trials for their capacity to induce CHV-specific antibodies following oral baiting. Freeze-drying and storage temperatures below 0 °C had a stabilizing effect to virus infectivity. When stored at −20 °C, freeze-dried CHV retained its full infectivity for up to 3 months in PROBAIT baits, the remaining infectivity in FOXOFF baits was 100-fold less. Oral baiting with CHV induced antiviral serum antibodies in all vaccinated foxes (20/20). None of the vaccinated foxes became ill or shed infectious virus into the environment although viral DNA was detected in body secretions as evaluated by PCR. The results indicate that CHV can be freeze-dried and stored over extended periods of time without loosing much of its infectivity. This is the first report of CHV being used for oral bait vaccination of foxes. It appears that CHV is well suited for use as a recombinant vector for wild canids.

Evaluation of Bait Matrices and Chemical Lure Attractants for Brown Tree Snakes

Author(s): Savarie, Peter J.; Clark, Larry | Abstract: Brown tree snake introduction to the snake-free island of Guam has severely impacted its native terrestrial vertebrates and economy. These nocturnal predators have extirpated forest birds, caused drastic reductions of lizards, and there is a major concern that snakes could be dispersed to other areas through Guam’s cargo transportation systems. Techniques to deter the spread of snakes include cargo inspection with detector dogs and live trapping using live mice as lures to reduce snake densities in cargo handling areas. Maintaining mice in traps is expensive, and an inanimate lure would be highly desirable. Oral baiting with dead neonatal mice (DNM) treated with acetaminophen is another technique being implemented for reducing snake populations. An objection to DNM is that they decompose and become putrid after 3-4 days. Consumption of 21 candidate bait matrices was compared to DNM in free-choice tests in individually caged snakes under laboratory conditions. Consumption of dead quail chicks and geckos was equivalent to DNM. Processed canned meat products, stew beef, and chicken were 30-50% as effective as DNM. Baits not consumed included dog blood, beef liver, and quail eggs. Under field conditions with live trapped snakes, consumption of 7 bait matrices was compared to DNM in 1-choice tests. DNM were preferred (55% consumption) over all other baits. Consumption of plastic lizards, chicken fat, and mealworms was 33%, 14%, and 13%, respectively. Odoriferous chemicals (n = 23), characteristic of decomposing animal flesh, were evaluated for their ability to attract snakes in the field. Chemicals were individually evaluated by placing them on tofu baits in PVC tubes (bait stations). Snake activity around the bait stations was monitored with infrared videography. Some of the 23 chemicals (i.e., L-methionine, 3-methyl-1-butanethiol) appeared to attract snakes to the tubes. However, no tofu baits treated with chemicals were consumed, whereas 100% of the snakes that visited tubes baited with DNM consumed the dead mice. These results, along with analysis of videos, indicate that chemicals may act as long distance lures but are insufficient for stimulating and initiating consumptive or appetitive search behaviors at close range.

Progress in the development of tuberculosis vaccines for cattle and wildlife

Vaccination against bovine tuberculosis is likely to become an important disease control strategy in developing countries, which cannot afford a test and slaughter control programme, or in countries which have a wildlife reservoir of Mycobacterium bovis infection. In the past decade, considerable progress has been made in the development and evaluation of tuberculosis vaccines for cattle and for a range of wildlife maintenance hosts including possums, badgers, deer and African buffaloes. Experimental challenge systems have been established for the different target species and the resulting disease process has mimicked that seen in the field. In cattle, neonatal vaccination with BCG appeared to be more effective than vaccination of 6-month-old calves and in most situations no other vaccine has been shown to be better than BCG. However, prime-boost strategies involving combinations of BCG with a protein or DNA vaccine, to improve on BCG vaccination alone, have produced very encouraging results. Differential diagnostic tests have been developed using mycobacterial antigens that are only present in virulent M. bovis to differentiate between BCG-vaccinated and M. bovis-infected cattle. BCG vaccine has been shown to reduce the spread of tuberculous lesions in a range of wildlife species and a prototype oral bait delivery system has been developed. Prospects for the development of improved vaccines against bovine tuberculosis are promising and vaccination approaches could become very valuable in the control and eradication of bovine tuberculosis.

Oral vaccine that breaks the transmission cycle of the Lyme disease spirochete can be delivered via bait

Borrelia burgdorferi causes Lyme disease, a potentially debilitating human disease for which no vaccine is currently available. We developed an oral bait delivery system for an anti- B. burgdorferi vaccine based in OspA. Mice were immunized orally via gavage and bait feeding. Challenge was performed via Ixodes scapularis field nymphs carrying multiple B. burgdorferi strains. Vaccination protected 89% of the mice and the systemic immune response was skewed toward IgG2a/2b production. Moreover, this oral vaccine reduced the pathogen in the tick vector by eight-fold. We conclude that this oral vaccine induces a protective systemic immune response against a variety of infectious B. burgdorferi strains found in nature and therefore it can eliminate this zoonotic pathogen from its major host reservoirs. Because we observed elimination of the spirochete from the tick vector, a broad delivery of this oral vaccine to wildlife reservoirs is likely to disrupt the transmission cycle of this pathogen.

Evaluation of oral rabies vaccination programs for control of rabies epizootics in coyotes and gray foxes: 1995–2003

To evaluate the effectiveness of intervention efforts to halt 2 wildlife rabies epizootics from 1995 through 2003, including 9 oral rabies vaccination campaigns for coyotes and 8 oral rabies vaccination campaigns for gray foxes. Retrospective study. 98 coyotes during prevaccination surveillance and 963 coyotes and 104 nontarget animals during postvaccination surveillance in south Texas, and 699 gray foxes and 561 nontarget animals during postvaccination surveillance in west-central Texas. A recombinant-virus oral rabies vaccine in edible baits was distributed by aircraft for consumption by coyotes and gray foxes. Bait acceptance was monitored by use of microscopic analysis of tetracycline biomarker in upper canine teeth and associated bone structures in animals collected for surveillance. Serologic responses were monitered by testing sera for rabies virus-neutralizing antibodies by use of the rapid fluorescent focus inhibition test. The incidence of rabies in the distribution area was recorded via active and passive surveillance activities; tracking of rabies virus variants in confirmed rabid animals was used to determine the number and type of rabies cases before and after distributions of the vaccine. The expansion of both epizootics was halted as a result of the vaccine bait program. The number of laboratory-confirmed rabid animals attributable to the domestic dog-coyote rabies virus variant in south Texas declined to 0, whereas the number of laboratory-confirmed rabid animals attributable to the Texas fox rabies virus variant in west-central Texas decreased. Data indicated that oral rabies vaccination resulted in protective immunity in a sufficient percentage of the target wildlife population to preclude propagation of the disease and provided an effective means of controlling rabies in these species.