Matt McCollum

Failure of Fallow Deer (Dama dama) to Develop Chronic Wasting Disease When Exposed to a Contaminated Environment and Infected Mule Deer (Odocoileus hemionus)

We monitored a herd of fallow deer (Dama dama) for evidence of prion infection for 7 yr by periodic postmortem examination of animals from the herd. The fallow deer were exposed to the chronic wasting disease (CWD) agent from mule deer by living in a paddock considered contaminated with infectivity from its history of housing CWD infected deer and, after the first year of the study, by comingling with infected mule deer (Odocoileus hemionus). At least 8 of 12 mule deer serving as sentinels for prion transmission and 25 additional mule deer serving as sources of infectivity developed clinical CWD or were otherwise confirmed to be infected with CWD via lymphoid tissue immunohistochemistry (IHC). In contrast, none of the 41 exposed fallow deer showed clinical signs suggestive of CWD, IHC staining of disease-associated prion in lymphoid or brain tissues, or evidence of spongiform degeneration in sections of brain stem at the level of the obex when sampled 18 mo to 7 yr after entering the mule deer paddock. The absence of clinical disease and negative IHC results in fallow deer housed in the same contaminated paddock for up to 7 yr and almost continuously exposed to CWD-infected mule deer for up to 6 yr suggests a species barrier or other form of resistance preventing fallow deer infection by the CWD agent or delaying progression of the disease in this species.

Immunization with a Synthetic Peptide Vaccine Fails to Protect Mule Deer (Odocoileus hemionus) from Chronic Wasting Disease

Chronic wasting disease (CWD) adversely affects both wild and captive cervid populations. A vaccine to prevent CWD would be a highly desirable tool to aid in disease management. To this end, we tested in mule deer a combination of CWD vaccines consisting of cervid prion peptide sequences 168-VDQYNNQNTFVHDC-182 and 145-NDYEDRYYRENMYRYPNQ-164 that had previously been shown to delay onset of clinical disease and increase survival in a mouse-adapted scrapie model. Thirteen captive mule deer (Odocoileus hemionus) were divided into vaccine (n=7) and control groups (n=6), and given prime and boost vaccinations intramuscularly 5 wk apart. Eight weeks postprime (3 wk postboost), all animals were challenged via natural exposure to an environment contaminated with infective CWD prions. Deer were monitored intermittently for prion infection by rectal and tonsil biopsies beginning 275 days postchallenge. All vaccinates responded to both peptide conjugates present in the combination vaccine as measured by enzyme-linked immunosorbent assay. However, all deer eventually became infected regardless of vaccine status.

The potential for transmission of BCG from orally vaccinated white-tailed deer (Odocoileus virginianus) to cattle (Bos taurus) through a contaminated environment: experimental findings.

White-tailed deer (Odocoileus virginianus) experimentally infected with a virulent strain of Mycobacterium bovis have been shown to transmit the bacterium to other deer and cattle (Bos taurus) by sharing of pen waste and feed. The risk of transmission of M. bovis bacille Calmette-Guerin (BCG) vaccine from orally vaccinated white-tailed deer to other deer and cattle, however, is not well understood. In order to evaluate this risk, we orally vaccinated 14 white-tailed deer with 1×109 colony forming units BCG in lipid-formulated baits and housed them with nine non-vaccinated deer. Each day we exposed the same seven naïve cattle to pen space utilized by the deer to look for transmission between the two species. Before vaccination and every 60 days until the end of the study, we performed tuberculin skin testing on deer and cattle, as well as interferon-gamma testing in cattle, to detect cellular immune response to BCG exposure. At approximately 27 weeks all cattle and deer were euthanized and necropsied. None of the cattle converted on either caudal fold, comparative cervical tests, or interferon-gamma assay. None of the cattle were culture positive for BCG. Although there was immunological evidence that BCG transmission occurred from deer to deer, we were unable to detect immunological or microbiological evidence of transmission to cattle. This study suggests that the risk is likely to be low that BCG-vaccinated white-tailed deer would cause domestic cattle to react to the tuberculin skin test or interferon-gamma test through exposure to a BCG-contaminated environment.

Feasibility of quarantine procedures for bison (Bison bison) calves from Yellowstone National Park for conservation of brucellosis-free bison.

OBJECTIVE--To determine the feasibility of qualifying individuals or groups of Yellowstone National Park bison as free from brucellosis. DESIGN--Cohort study. SAMPLE--Serum, blood, and various samples from live bison and tissues taken at necropsy from 214 bison over 7 years. PROCEDURES--Blood was collected from bison every 30 to 45 days for serologic tests and microbiological culture of blood for Brucella abortus. Seropositive bison were euthanized until all remaining bison had 2 consecutive negative test results. Half the seronegative bison were randomly euthanized, and tissues were collected for bacteriologic culture. The remaining seronegative bison were bred, and blood was tested at least twice per year. Cow-calf pairs were sampled immediately after calving and 6 months after calving for evidence of B abortus. RESULTS--Post-enrollment serial testing for B abortus antibodies revealed no bison that seroconverted after 205 days (first cohort) and 180 days (second cohort). During initial serial testing, 85% of bison seroconverted within 120 days after removal from the infected population. Brucella abortus was not cultured from any euthanized seronegative bison (0/88). After parturition, no cows or calves had a positive test result for B abortus antibodies, nor was B abortus cultured from any samples. CONCLUSIONS AND CLINICAL RELEVANCE--Results suggested it is feasible to qualify brucellosis-free bison from an infected herd following quarantine procedures as published in the USDA APHIS brucellosis eradication uniform methods and rules. Latent infection was not detected in this sample of bison when applying the USDA APHIS quarantine protocol.

CLINICAL, CULTURE, SEROLOGY, AND HISTOPATHOLOGY OUTCOMES OF BIGHORN SHEEP EXPERIMENTALLY INFECTED WITH BRUCELLA OVIS

Abstract Disease caused by Brucella ovis has not been previously reported in bighorn sheep (BHS; Ovis canadensis canadensis). Antibodies to B. ovis, however, are occasionally detected in free-ranging BHS, and this has been a concern for managers involved in translocation programs. To investigate the pathogenesis of B. ovis infection in this species, 20 BHS (10 male, 10 female) were inoculated intraconjunctivally (IC) with 5.4×108 colony forming units (cfu) B. ovis. Six BHS (three male, three female) received 1 mL phosphate-buffered saline IC and served as in-contact control animals, and eight BHS (one male, seven female) received 1 mL phosphate-buffered saline (PBS) IC and served as noncontact controls. In addition, 14 domestic sheep (Ovis aries, nine male, five female) were inoculated IC with 5.4×108 cfu B. ovis (positive controls), and five domestic sheep (three male, two female) received 1 mL PBS IC (contact controls). All domestic sheep were housed separately from BHS. Bighorn sheep experimentally infected with B. ovis became antibody and culture positive and developed clinical signs of B. ovis infection including abortion and epididymal and testicular swelling. Lesions in BHS were consistent with, and in some cases more severe, than those observed in domestic sheep. Antibodies against B. ovis were detected within 4 wk postinoculation and remained positive until the end of the study. These findings have important implications for BHS management.

Determining the persistence of Mycobacterium bovis bacille Calmette–Guerin Danish in select tissues of orally vaccinated feral swine (Sus scrofa ssp.)

Mycobacterium bovis bacille Calmette-Guerin (BCG) is being considered for vaccination of feral swine (Sus scrofa ssp.). Since BCG is a live bacterium, evaluation of its safety and persistence in tissues is important. Fifteen feral swine received approximately 4.5 × 10(6) colony forming units of BCG Danish via oral bait. Four animals received bait without BCG. At 1, 3, 6, and 9 months post-vaccination, four vaccinates were euthanized. Non-vaccinates were euthanized at 9 months. Clinical signs were not noted in vaccinated pigs at any time. Tissues from all 20 pigs were culture-negative for mycobacteria. Based on our data, BCG is safe and appears not to persist in feral swine tissues after one month post-oral vaccination. However, further work must be performed at higher doses, and on a larger number of animals representing the target population, and further evaluation of persistence in tissues within the first month post-vaccination is needed.

Evaluation of bison (Bison bison) semen from Yellowstone National Park, Montana, USA, bulls for Brucella abortus shedding.

To determine if bison (Bison bison) bulls from Yellowstone National Park (YNP), Montana, USA, shed an infective dose of Brucella abortus in semen, 50 YNP bulls were captured on public lands in Montana during the winter and early spring (April–May) of 2010 and 2011. The bulls were immobilized, and blood and semen samples were collected for serology and Brucella culture. Thirty-five bulls (70%) were antibody-positive, and B. abortus was cultured from semen in three (9%) of the 35 antibody-positive or suspect bulls, though not at concentrations considered an infective dose. Eight bulls (six antibody-positive, two negative) had palpable lesions of the testes, epididymides, or seminal vesicles consistent with B. abortus infection. Breeding soundness exams and semen analysis suggested that antibody-positive bulls were more likely to have nonviable ejaculate (8/35; 23%) than bulls without detectable antibody (2/15; 13%).

EVALUATION OF TRANSMISSION OF BRUCELLA ABORTUS STRAIN 19 IN BISON BY INTRAVAGINAL, INTRAUTERINE, AND INTRACONJUNCTIVAL INOCULATION

Bovine brucellosis, caused by the bacterium Brucella abortus, is endemic in bison (Bison bison) and elk (Cervus elaphus nelsoni) populations in the area of Yellowstone National Park, USA. Two strategies have been proposed to reduce the risk of transmission of disease in bison: remote vaccination with the vaccine RB51, and the use of immunocontraception of bison to decrease shedding of organisms from infected females. The frequent occurrence of venereal transmission in bison would complicate either of these strategies, requiring vaccination of males as well as females, and rendering immunocontraception less effective in reducing transmission of B. abortus. To address the question of venereal transmission, we inoculated each of 18 bison cows with 4.5 × 108 colony-forming units of B. abortus strain 19, as a surrogate of field strain, by three routes: intraconjunctival (IC), intravaginal (VI), and intracervical/intrauterine (AI). Bison semen was mixed with strain 19 inoculum for the latter route. Bison were monitored by serology and culture for 12 wk, at which time they were euthanized and specimens collected for culture. All IC-inoculated animals seroconverted on multiple tests and one was culture positive at 12 wk postexposure. Seven of eight VI bison developed suspect or positive serologic tests and four were positive at one or more time points. Weak transient serologic responses (suspect) were seen in four of five AI bison. Results showed that IC inoculation with strain 19 was a suitable surrogate for field strain to demonstrate exposure to the B. abortus. The seroconversion of four of eight VI bison indicated exposure of the immune system to the agent and the need for further studies on venereal transmission in bison.

Rabies in Two Bison from Colorado

Two adult female bison, housed in an outdoor research facility and observed daily, died suddenly three days apart. Minimal coordination and behavioral changes were observed in one animal the evening before being found in a moribund state. Malignant catarrhal fever was suspected in both bison due to a recent confirmed MCF case with similar course. The cause of death was not apparent from necropsy, but brains of both animals were strongly positive for rabies virus antigen by fluorescent antibody and/or immunohistochemical tests. Minimal to mild encephalitis with Negri bodies was observed on histopathology. The bison were located in an area that had not been endemic for skunk rabies; however, a case of rabies in a skunk had been discovered 1.6 km north of the bison paddock two months prior to the bison cases.