Pathology of Brucellosis in Bison From Yellowstone National Park

Abstract

Between February 1995 and June 1999, specimens from seven aborted bison (Bison bison) fetuses or stillborn calves and their placentas, two additional placentas, three dead neonates, one 2-wk-old calf, and 35 juvenile and adult female bison from Yellowstone National Park (USA) were submitted for bacteriologic and histopathologic examination. One adult animal with a retained placenta had recently aborted. Serum samples from the 35 juvenile and adult bison were tested for Brucella spp. antibodies. Twenty-six bison, including the cow with the retained placenta, were seropositive, one was suspect, and eight were seronegative. Brucella abortus biovar 1 was isolated from three aborted fetuses and associated placentas, an additional placenta, the 2-wk-old calf, and 11 of the seropositive female bison including the animal that had recently aborted. Brucella abortus biovar 2 was isolated from one additional seropositive adult female bison. Brucella abortus was recovered from numerous tissue sites from the aborted fetuses, placentas and 2-wk-old calf. In the juvenile and adult bison, the organism was more frequently isolated from supramammary (83%), retropharyngeal (67%), and iliac (58%) lymph nodes than from other tissues cultured. Cultures from the seronegative and suspect bison were negative for B. abortus. Lesions in the B. abortus-infected, aborted placentas and fetuses consisted of necropurulent placentitis and mild bronchointerstitial pneumonia. The infected 2-wk-old calf had bronchointerstitial pneumonia, focal splenic infarction, and purulent nephritis. The recently-aborting bison cow had purulent endometritis and necropurulent placentitis. Immunohistochemical staining of tissues from the culture-positive aborted fetuses, placentas, 2-wk-old calf, and recently-aborting cow disclosed large numbers of B. abortus in placental trophoblasts and exudate, and fetal and calf lung. A similar study with the same tissue collection and culture protocol was done using six seropositive cattle from a B. abortus-infected herd in July and August, 1997. Results of the bison and cattle studies were similar.

Safety of Revaccination of Pregnant Bison With Brucella Abortus Strain Rb51

“…However, as compared to the study of bison infected under field conditions (Rhyan et al, 2001), the supramammary and internal iliac lymph nodes were not as predictive of culture status after calfhood vaccination. After calfhood vaccination, SRB51 was recovered from the supramammary lymph node of 50% and 75% of bison at 14 and 18 wk, respectively, whereas B. abortus was recovered from the supramammary lymph node of 83% of bison culture-positive for field strains of B. abortus (Rhyan et al, 2001). In addition, SRB51 was not recovered at either sampling time from the internal iliac lymph node of any calfhood vaccinated bison; whereas this lymph node was culture-positive in 58% of naturally infected bison.…”

“…In bison calves vaccinated once with 10 10 CFU, SRB51 was recovered from multiple lymphatic tissues of all bison (nϭ4 vaccinates/time) sampled at 14 and 18 wk after vaccination (Roffe et al, 1999). However, as compared to the study of bison infected under field conditions (Rhyan et al, 2001), the supramammary and internal iliac lymph nodes were not as predictive of culture status after calfhood vaccination. After calfhood vaccination, SRB51 was recovered from the supramammary lymph node of 50% and 75% of bison at 14 and 18 wk, respectively, whereas B. abortus was recovered from the supramammary lymph node of 83% of bison culture-positive for field strains of B. abortus (Rhyan et al, 2001).…”

“…Although tissue sampling was limited in the current study, the SRB51 vaccine strain was recovered from only 17% of pregnant bison at 10 wk after booster vaccination. The tissues sampled in the present study were based on a previous study of bison naturally infected with virulent B. abortus in which Brucella was recovered from the supramammary and internal iliac lymph nodes of 83% and 58%, respectively, of culture-positive bison (Rhyan et al, 2001). It is apparent from our data that SRB51 is cleared more rapidly during anamnestic responses of adult bison as compared to clearance of SRB51 after calfhood vaccination.…”

“…In pregnant animals, samples of fetal liver, fetal spleen, and gastric contents were also obtained. Tissues selected for bacteriologic sampling were based on availability during abattoir processing and tissue localization data from a previous study of a bison herd chronically infected with B. abortus (Rhyan et al, 2001).…”

“…The prevalence of brucellosis in freeranging bison (Bison bison) and elk (Cervus elaphus nelsoni) in Yellowstone National Park (Wyoming, Montana, and Idaho, USA) and surrounding areas has been well documented (Thorne et al, 1978;Pac et al, 1991;Rhyan et al, 2001). Following completion of the brucellosis eradication program for cattle, bison and elk in the Greater Yellowstone Area will be the sole remaining reservoirs of Brucella abortus in the U.S.…”