Adaptive selection of a prion strain conformer corresponding to established North American CWD during propagation of novel emergent Norwegian strains in mice expressing elk or deer prion protein.

Prions are infectious proteins causing fatal, transmissible neurodegenerative diseases of animals and humans. Replication involves template-directed refolding of host encoded prion protein, PrPC, by its infectious conformation, PrPSc. Following its discovery in captive Colorado deer in 1967, uncontrollable contagious transmission of chronic wasting disease (CWD) led to an expanded geographic range in increasing numbers of free-ranging and captive North American (NA) cervids. Some five decades later, detection of PrPSc in free-ranging Norwegian (NO) reindeer and moose marked the first indication of CWD in Europe. To assess the properties of these emergent NO prions and compare them with NA CWD we used transgenic (Tg) and gene targeted (Gt) mice expressing PrP with glutamine (Q) or glutamate (E) at residue 226, a variation in wild type cervid PrP which influences prion strain selection in NA deer and elk. Transmissions of NO moose and reindeer prions to Tg and Gt mice recapitulated the characteristic features of CWD in natural hosts, revealing novel prion strains with disease kinetics, neuropathological profiles, and capacities to infect lymphoid tissues and cultured cells that were distinct from those causing NA CWD. In support of strain variation, PrPSc conformers comprising emergent NO moose and reindeer CWD were subject to selective effects imposed by variation at residue 226 that were different from those controlling established NA CWD. Transmission of particular NO moose CWD prions in mice expressing E at 226 resulted in selection of a kinetically optimized conformer, subsequent transmission of which revealed properties consistent with NA CWD. These findings illustrate the potential for adaptive selection of strain conformers with improved fitness during propagation of unstable NO prions. Their potential for contagious transmission has implications for risk analyses and management of emergent European CWD. Finally, we found that Gt mice expressing physiologically controlled PrP levels recapitulated the lymphotropic properties of naturally occurring CWD strains resulting in improved susceptibilities to emergent NO reindeer prions compared with over-expressing Tg counterparts. These findings underscore the refined advantages of Gt models for exploring the mechanisms and impacts of strain selection in peripheral compartments during natural prion transmission.

CATTLE ( BOS TAURUS) RESIST CHRONIC WASTING DISEASE FOLLOWING ORAL INOCULATION CHALLENGE OR TEN YEARS' NATURAL EXPOSURE IN CONTAMINATED ENVIRONMENTS.

We conducted a 10-yr study to establish whether chronic wasting disease (CWD) was readily transmissible to domestic cattle ( Bos taurus) following oral inoculation or by cohousing cattle with captive cervids in outdoor research facilities where CWD was enzootic. Calves ( n=12) were challenged orally on one occasion using brain homogenate derived from CWD-infected mule deer ( Odocoileus hemionus). Five uninoculated cattle served as unchallenged controls. Two other groups of cattle ( n=10-11/group) were housed outdoors for 10 yr in captive cervid research facilities. The environmentally challenged cattle were exposed to CWD-associated prions through common paddocks, feed, and water and via direct daily contact with known and potentially infected mule deer or wapiti ( Cervus canadensis) throughout the decade-long study period. None of the exposed cattle developed neurologic disease during the study. We euthanized cattle surviving to 10 yr postchallenge and examined all for lesions or disease-associated prion protein (PrPd) by histopathology, immunohistochemistry, and western immunoblot analysis of central nervous system and lymphoid tissue. None had evidence of PrPd accumulation. We conclude that the risks of CWD transmission to cattle following oral inoculation or after prolonged exposure to contaminated environments are low.

Endemic chronic wasting disease causes mule deer population decline in Wyoming.

Chronic wasting disease (CWD) is a fatal transmissible spongiform encephalopathy affecting white-tailed deer (Odocoileus virginianus), mule deer (Odocoileus hemionus), Rocky Mountain elk (Cervus elaphus nelsoni), and moose (Alces alces shirasi) in North America. In southeastern Wyoming average annual CWD prevalence in mule deer exceeds 20% and appears to contribute to regional population declines. We determined the effect of CWD on mule deer demography using age-specific, female-only, CWD transition matrix models to estimate the population growth rate (λ). Mule deer were captured from 2010-2014 in southern Converse County Wyoming, USA. Captured adult (≥ 1.5 years old) deer were tested ante-mortem for CWD using tonsil biopsies and monitored using radio telemetry. Mean annual survival rates of CWD-negative and CWD-positive deer were 0.76 and 0.32, respectively. Pregnancy and fawn recruitment were not observed to be influenced by CWD. We estimated λ = 0.79, indicating an annual population decline of 21% under current CWD prevalence levels. A model derived from the demography of only CWD-negative individuals yielded; λ = 1.00, indicating a stable population if CWD were absent. These findings support CWD as a significant contributor to mule deer population decline. Chronic wasting disease is difficult or impossible to eradicate with current tools, given significant environmental contamination, and at present our best recommendation for control of this disease is to minimize spread to new areas and naïve cervid populations.

Chronic Wasting Disease Drives Population Decline of White-Tailed Deer.

Chronic wasting disease (CWD) is an invariably fatal transmissible spongiform encephalopathy of white-tailed deer, mule deer, elk, and moose. Despite a 100% fatality rate, areas of high prevalence, and increasingly expanding geographic endemic areas, little is known about the population-level effects of CWD in deer. To investigate these effects, we tested the null hypothesis that high prevalence CWD did not negatively impact white-tailed deer population sustainability. The specific objectives of the study were to monitor CWD-positive and CWD-negative white-tailed deer in a high-prevalence CWD area longitudinally via radio-telemetry and global positioning system (GPS) collars. For the two populations, we determined the following: a) demographic and disease indices, b) annual survival, and c) finite rate of population growth (λ). The CWD prevalence was higher in females (42%) than males (28.8%) and hunter harvest and clinical CWD were the most frequent causes of mortality, with CWD-positive deer over-represented in harvest and total mortalities. Survival was significantly lower for CWD-positive deer and separately by sex; CWD-positive deer were 4.5 times more likely to die annually than CWD-negative deer while bucks were 1.7 times more likely to die than does. Population λ was 0.896 (0.859-0.980), which indicated a 10.4% annual decline. We show that a chronic disease that becomes endemic in wildlife populations has the potential to be population-limiting and the strong population-level effects of CWD suggest affected populations are not sustainable at high disease prevalence under current harvest levels.

Immobilization of Wyoming bears using carfentanil and xylazine.

Seven grizzly (Ursus arctos; four male, three female) and three black (Ursus americanus; two male, one female) bears caught in culvert traps or leg snares were immobilized in northwestern Wyoming with carfentanil and xylazine at doses, respectively, of 0.011 ± 0.001 and 0.12 ± 0.01 mg/kg for grizzly bears and 0.014 ± 0.002 and 0.15 ± 0.04 mg/kg for black bears. These drugs were antagonized with 1 mg/kg naltrexone and 2 mg/kg tolazoline. Induction and recovery times, respectively, were 4.3 ± 0.5 and 7.1 ± 0.8 min for grizzly bears and 5.2 ± 0.4 and 9.1 ± 2.2 min for black bears. Inductions were smooth and uneventful. Recoveries were characterized initially by increased respiration followed by raising of the head, which quickly led to a full recovery, with the bears recognizing and avoiding humans and moving away, maneuvering around obstacles. All bears experienced respiratory depression, which did not significantly improve with supplemental oxygen on the basis of pulse oximetry (P=0.56). Rectal temperatures were normothermic. Carfentanil-xylazine immobilization of bears provided significant advantages over other drug regimens, including small drug volumes, predictable inductions, quick and complete recoveries, and lower costs. On the basis of these data, both grizzly and black bears can be immobilized effectively with 0.01 mg/kg carfentanil and 0.1 mg/kg xylazine.

Sufentanil citrate immobilization of Alaskan moose calves.

Free-ranging Alaskan moose calves (Alces alces gigas) were immobilized with 0.12 mg/kg sufentanil (S; n=16), 0.12 mg/kg sufentanil plus 0.27 mg/kg xylazine (SX; n=11), or 0.007 mg/kg carfentanil plus 0.36 mg/kg xylazine (CX; n=13). Immobilants were antagonized with 1.2 mg/kg naltrexone (S) or 1.2 mg/kg naltrexone plus 2.4 mg/kg tolazoline (SX, CX). There were no differences in induction (P ≥ 0.29) or processing (P ≥ 0.44) times between groups. Moose given either S or SX had significantly shorter recovery times than moose given CX (P=0.001) and recovery times from S were shorter than from SX (P=0.02). Oxygen saturation values for all groups averaged 85 ± 8%, but were significantly higher (P=0.048) for CX (89 ± 7%) than for S (82 ± 8%). Based on these data, sufentanil at 0.1 mg/kg or sufentanil at 0.1 mg/kg plus xylazine at 0.25 mg/kg could provide effective remote immobilization for Alaskan moose calves and could be substituted for carfentanil or thiafentanil should the need arise.

Sufentanil and xylazine immobilization of Rocky Mountain elk.

From October 2009 through July 2010, five captive, 3-yr-old, female Rocky Mountain elk (Cervus elaphus) and nine free-ranging elk (one male, eight female) were immobilized with 0.1 mg/kg sufentanil plus 0.5 mg/kg xylazine which was antagonized with 1 mg/kg naltrexone and 2 mg/kg tolazoline. Induction and recovery times averaged 4.9 ± 0.3 min and 3.9 ± 0.4 min, respectively. Physiologic and blood gas parameters as well as bispectral index (BIS) were measured on the captive elk every 10 min for 30 min. Immobilization induced profound hypoxemia via hypoventilation and ventilation-perfusion mismatching as demonstrated by depressed partial pressure of arterial oxygen (P(a)O(2)) and increased partial pressure of arterial carbon dioxide (P(a)CO(2)). The only values to significantly (P<0.05) change over time were base excess (BE), bicarbonate (HCO(3)), and lactate. Bispectral index is a measure of anesthetic depth. The average BIS value over the 30 min period (59.1 ± 2.4) was higher than the BIS value at the approximate point where elk lose consciousness, which indicated that this drug combination produced neuroleptanalgesia but not general anesthesia. Sufentanil and xylazine provided effective remote immobilization in elk and could be substituted for carfentanil or thiafentanil and xylazine should the need arise.

Observations on the use of GonaCon in captive female elk (Cervus elaphus).

Overabundant populations of elk (Cervus elaphus) are a significant concern in some areas of the western United States because of potential ecologic damage and spread of brucellosis to domestic livestock. Brucella abortus is transmitted among elk through direct contact with aborted fetuses, placentas and associated fluids, or postpartum discharge of infected animals. Because transmission of brucellosis is dependent on pregnancy, contraception of cows could be used for both disease and population management. The objective of this study was to evaluate the contraceptive efficacy of a gonadotropin-releasing hormone vaccine (GonaCon) in female elk. In September 2004, cows were given a single immunization of either 1,000 microg (n = 12) or 2,000 microg (n = 10) of GonaCon and compared with a group of adjuvant-treated controls (n = 15). In November 2004, 2005, and 2006, cows were grouped with bulls for the breeding season. Blood samples were taken in February 2005 and March 2006 and 2007 for pregnancy testing, progesterone assays, and antibody titers. For cows given 1,000 microg GonaCon the percentages that were infertile for 2005, 2006, and 2007 were 86%, 90%, and 100%, respectively, compared with 90%, 100%, and 100% for cows given 2,000 microg GonaCon. Rates of infertility for control cows were 23%, 28%, and 0% (P<0.0001). The results indicated that either dose of GonaCon prevented pregnancy of elk cows for at least 3 yr. We concluded that GonaCon use for population management of elk warrants consideration as part of a strategy to control brucellosis.

Paresis and death in elk (Cervus elaphus) due to lichen intoxication in Wyoming.

During February-April 2004, an estimated 400-500 free-ranging elk (Cervus elaphus) developed paresis, became recumbent, and died or were euthanized in the Red Rim Wildlife Habitat Management Area (RRWHMA), Wyoming, USA. Elk were found in sternal recumbency, alert and responsive, but unable to rise. Their condition progressed to lateral recumbency followed by dehydration, obtundation, and death. Gross lesions were limited to degenerative myopathy, with pallor and streaking in skeletal muscles. Microscopically, affected muscles had degenerative lesions of varying duration, severity, and distribution, some with early mineralization and attempts at regeneration. Diagnostic testing ruled out common infectious, inflammatory, toxic, and traumatic causes. Tumbleweed shield lichen (Xanthoparmelia chlorochroa) was found in the area and in the rumen of several elk. This lichen was collected and fed to three captive elk. Two of these elk exhibited signs of ataxia, which rapidly progressed to weakness and recumbency after 7 and 10 days on this diet, respectively, and a degenerative myopathy, consistent with lesions observed in the elk affected at RRWHMA, was observed. All remaining elk migrated from the RRWHMA during the spring and no subsequent losses have been documented.

Oral transmission of chronic wasting disease in captive Shira's moose.

Three captive Shira's moose (Alces alces shirasi) were orally inoculated with a single dose (5 g) of whole-brain homogenate prepared from chronic wasting disease (CWD)-affected mule deer (Odocoileus hemionus). All moose died of causes thought to be other than CWD. Histologic examination of one female moose dying 465 days postinoculation revealed spongiform change in the neuropil, typical of transmissible spongiform encephalopathy. Immunohistochemistry staining for the proteinase-resistant isoform of the prion protein was observed in multiple lymphoid and nervous tissues. Western blot and enzyme-linked immunosorbent assays provided additional confirmation of CWD. These results represent the first report of experimental CWD in moose.

Brucellosis in captive Rocky Mountain bighorn sheep (Ovis canadensis) caused by Brucella abortus biovar 4.

Nine (four female, five male) captive adult Rocky Mountain bighorn sheep (Ovis canadensis) contracted brucellosis caused by Brucella abortus biovar 4 as a result of natural exposure to an aborted elk (Cervus elaphus) fetus. Clinical signs of infection were orchitis and epididymitis in males and lymphadenitis and placentitis with abortion in females. Gross pathologic findings included enlargement of the testes or epididymides, or both, and yellow caseous abscesses and pyogranulomas of the same. Brucella abortus biovar 4 was cultured in all bighorn sheep from a variety of tissues, including testes/epididymides, mammary gland, and lymph nodes. All bighorn sheep tested were positive on a variety of standard Brucella serologic tests. This is the first report of brucellosis caused by B. abortus in Rocky Mountain bighorn sheep. It also provides evidence that bighorn sheep develop many of the manifestations ascribed to this disease and that infection can occur from natural exposure to an aborted fetus from another species. Wildlife managers responsible for bighorn sheep populations sympatric with Brucella-infected elk or bison (Bison bison) should be cognizant of the possibility of this disease in bighorn sheep.

Validation of a Brucella abortus competitive enzyme-linked immunosorbent assay for use in Rocky Mountain elk (Cervus elaphus nelsoni).

Brucellosis caused by infection with Brucella abortus is present in some elk (Cervus elaphus nelsoni) of the Greater Yellowstone Area (parts of Wyoming, Montana, and Idaho, USA). Since 1985, the Wyoming Game and Fish Department has vaccinated elk on elk feedgrounds in northwestern Wyoming during the winter months using B. abortus strain 19 (strain 19). Analysis of this vaccination program is hampered by the inability of standard serologic tests to differentiate between strain 19 vaccinated elk and those exposed to field strain B. abortus. In 1993, a competitive enzyme-linked immunosorbent assay (cELISA) was licensed to serologically differentiate between strain 19 vaccinated cattle and cattle exposed to field strain B. abortus. Seven groups of elk sera representing various B. abortus exposure histories were used to validate the cELISA test for elk. The cELISA test differentiated strain 19 vaccinated elk from elk that were challenged with B. abortus strain 2308, a pathogenic laboratory strain. The specificity of the cELISA was 96.8% for elk vaccinated with strain 19 only and sampled between 6 mo and 2 yr post vaccination, or with no B. abortus exposure. The sensitivity of the cELISA was 100%. The cELISA test will be useful in evaluating sera collected from elk in vaccinated, brucellosis endemic herds in the Greater Yellowstone Area.

Safety of Brucella abortus strain RB51 vaccine in non-target ungulates and coyotes.

Brucellosis is endemic in free-ranging elk (Cervus elaphus) and bison (Bison bison) in the Greater Yellowstone Area (GYA; USA). It is possible that an oral brucellosis vaccine could be developed and disseminated in the GYA to reduce disease transmission. Should this occur, non-target species other than elk and bison may come in contact with the vaccine resulting in morbidity or mortality. To assess biosafety, bighorn sheep (Ovis canadensis; n = 10), pronghorn (Antilocapra americana; n = 9), mule deer (Odocoileus hemionus; n = 11), moose (Alces alces shirasi; n = 10), and coyotes (Canis latrans; n = 24) were given a single oral dose of at least 1.0 x 10(10) colony-forming units of Brucella abortus strain RB51 vaccine (RB51). Animals were randomly divided into vaccinated and control groups. Ungulates were captured, blood sampled, and swabs taken from the nares, rectum, and vagina for bacterial culture on day 0, 42, and 84 post-inoculation (PI). On day 42, the vaccinated group became a control group and vice versa in a crossover design. Blood and swab samples were taken from coyotes on days 0, 14, 28, and 42 PI. There was no crossover for the coyote study. Two coyotes from each group were also euthanized and cultured for RB51 on days 42, 84, 168, and 336 PI. Blood samples were analyzed for hematologic changes and antibodies to RB51 using a modified dot-blot assay. No morbidity or mortality as a result of vaccination was observed in any animal. There were no differences in hematologic parameters at any time for ungulate species; vaccinated coyotes had higher hematocrit, hemoglobin, and eosinophil counts (P < or = 0.006). All individuals, except some moose, seroconverted to RB51. Strain RB51 was cultured from oropharyngeal lymph nodes from one coyote 42 days PI and from a moose 117 days PI. This study suggested that a single oral dose of RB51 was safe in these species.

Brucella abortus strain RB51 vaccination in elk. I. Efficacy of reduced dosage.

Bovine brucellosis is a serious zoonotic disease affecting some populations of Rocky Mountain elk (Cervus elaphus nelsoni) and bison (Bison bison) in the Greater Yellowstone Area, USA. The fear that elk and/or bison may spread Brucella abortus to livestock has prompted efforts to reduce or eliminate the disease in wildlife. Brucella abortus strain RB51 (RB51) vaccine has recently been approved for use in cattle. Unlike strain 19 vaccine, RB51 does not cause false positive reactions on standard brucellosis serologic tests. If effective, it may become the vaccine of choice for wildlife. In February 1995, 45 serologically negative female elk calves were trapped and taken to the Sybille Wildlife Research and Conservation Education Unit near Wheatland, Wyoming, USA. In May 1995, 16 of these elk calves were hand-vaccinated with 1 x 10(9) colony forming units (CFU) of RB51, 16 were vaccinated with 1 x 10(8) CFU RB51 by biobullet, and 13 were given a saline placebo. The elk were bred in fall of 1996 and they were challenged with 1 x 10(7) CFU of B. abortus strain 2308 by intraconjunctival inoculation in March 1997. Thirteen (100%) control elk aborted, 14 (88%) hand-vaccinated elk aborted, and 12 (75%) biobullet vaccinated elk aborted or produced nonviable calves. These results suggest that a single dose of 1 x 10(8) to 1 x 10(9) CFU RB51 does not provide significant protection against B. abortus induced abortion in elk. However, the vaccine appears to be safe at this dose and additional study may reveal a more effective RB51 vaccine regimen for elk.

Brucella abortus strain RB51 vaccination in elk. II. Failure of high dosage to prevent abortion.

Brucella abortus strain RB51 is used as a vaccine because it induces antibodies that do not react on standard serologic tests for brucellosis allowing differentiation between vaccination and infection. Strain RB51 was evaluated in captive elk (Cervus elaphus) to determine if vaccination protected against abortion following experimental challenge. Thirty elk were vaccinated intramuscularly with 1.0 x 10(10) colony-forming units (CFU) of strain RB51 in March 1998. Fourteen of these were given a booster dose of 1.13 x 10(10) CFU exactly 1 yr later. All vaccinated elk seroconverted via a modified dot blot assay to strain RB51 with the booster group having higher titers (P < or = 0.001). Seventeen other elk served as unvaccinated controls. All elk were bred and determined pregnant using pregnancy-specific protein B analysis. Elk were challenged in March 2000 with 1.1 x 10(7) CFU of B. abortus strain 2308 administered intraconjunctivally and all elk seroconverted to strain 2308. Fifteen of 17 control elk aborted; 16 of 16 elk given a single vaccination aborted (P = 0.44); and 13 of 14 elk given a booster aborted (P = 0.86). There were two viable calves in the control group and one in the booster group. Strain 2308 was recovered from fetuses and nonviable calves in all groups. Based on the results of this and other studies, the use of strain RB51 to prevent abortion in elk cannot be recommended.

Immune responses of bison to ballistic or hand vaccination with Brucella abortus strain RB51.

From January through July of 2000, a study was conducted to evaluate clearance, immunologic responses, and potential shedding of Brucella abortus strain RB51 (SRB51) following ballistic or subcutaneous (SQ) vaccination of 7 mo old bison (Bison bison) calves. Ten bison calves were vaccinated SQ with 1.4 x 10(10) colony-forming units (CFU) of SRB51 and five calves were inoculated SQ with sterile 0.15 M sodium chloride. An additional 10 bison calves were ballistically inoculated in the rear leg musculature with 1 x 10(10) CFU of SRB51 and five calves were ballistically inoculated with an empty Biobullet. Serologic responses were monitored at 0, 2, 4, 6, 8, 12, 18, and 24 wk using the standard tube agglutination test and a dot-blot assay. Swabs from rectal, vaginal, nasal, and ocular mucosal surfaces, and blood were obtained for culture from all bison at 2, 4, 6, and 8 weeks post-inoculation to evaluate potential shedding by vaccinated bison or persistent septicemia. The superficial cervical lymph node was biopsied in eight ballistic and eight hand vaccinated bison at 6 or 12 wk to evaluate clearance of the vaccine strain from lymphatic tissues. Lymphocyte proliferative responses to irradiated SRB51 bacteria were evaluated in peripheral blood mononuclear cells (PBMC) at 4, 6, 8, 12, 18, and 24 wk after inoculation. Serum obtained from hand or ballistically vaccinated bison demonstrated antibody responses on the dot-blot assay that were greater than control bison (saline or empty Biobullet) at 2, 4, 6, and 8 wk after vaccination. Antibody titers of ballistically vaccinated bison did not differ (P > 0.05) from hand vaccinated bison at any sampling time. Blood samples obtained from all bison at 2, 4, 6 and 8 wk after vaccination were negative for SRB51. One colony of SRB51 was recovered from the vaginal swab of one ballistically vaccinated bison at 2 wk after vaccination. All other ocular, vaginal, nasal, and rectal swabs were culture negative for SRB51. Strain RB51 was recovered from superficial cervical lymph nodes of hand and ballistic vaccinated bison at 6 (two of four and two of four bison, respectively) and 12 wk (three of four and one of four bison, respectively). Serologic tests and bacterial culture techniques failed to demonstrate infection of nonvaccinated bison. Peripheral blood mononuclear cells obtained from hand vaccinated bison had greater (P < 0.05) proliferative responses to strain RB51 bacteria when compared to PBMC from nonvaccinated and ballistically vaccinated bison. Proliferative responses of PBMC from ballistically vaccinated bison did not differ (P > 0.05) at any sampling time from proliferative responses of PBMC from control bison. Serum alpha 1-acid glycoprotein concentrations, plasma fibrinogen, and total protein concentrations were not influenced by treatments. Ballistic delivery of SRB51 did not induce adverse effects or influence clearance of the vaccine strain. There were no proliferative responses of PBMC to SRB51 in bison ballistically vaccinated with SRB51; whereas bison inoculated with SRB51 by hand injection had greater proliferative responses than control or ballistically vaccinated bison. Our study suggests that ballistic delivery may require a greater dose of SRB51 to induce cell-mediated immune responses in bison that are comparable to those induced by hand injection, and that ballistic or hand delivery of 1 x 10(10) CFU of SRB51 is safe in bison calves.

Immune responses of elk to vaccination with Brucella abortus strain RB51.

In a study conducted from January to August 2000, elk (Cervus elaphus) were vaccinated with Brucella abortus strain RB51 (SRB51, n = 6) or injected with 0.15 M NaCl solution (n = 3) at approximately 6 mo of age. Beginning at 2 wk and continuing to 25 wk after vaccination, SRB51-vaccinated elk had greater antibody responses (P < 0.05) to SRB51 when compared to nonvaccinated elk. Peripheral blood mononuclear cells (PBMC) from SRB51-vaccinated elk had greater (P < 0.05) proliferative responses to SRB51 at 18 wk after vaccination when compared to responses of nonvaccinated elk. Strain RB51 was recovered from blood samples of all vaccinates at 2 wk, and three of six vaccinates at 4 wk after vaccination. The SRB51 vaccine strain was recovered from the superficial cervical lymph node of all vaccinates sampled at 6 wk after vaccination. but not from lymph node samples obtained from vaccinates at 12 or 18 wk after vaccination. At 34 wk after vaccination, SRB51 was recovered from the bronchial lymph node of one of five vaccinates but not from other tissues. Strain RB51 was not recovered at any time from samples obtained from nonvaccinated elk. This study suggests that following vaccination with SRB51, elk remain bacteremic for a prolonged period of time, rapidly develop high antibody titers, and are slower to develop detectable proliferative responses in PBMC when compared to responses of cattle or bison (Bison bison).