Endogenous gamma interferon and interleukin-10 in Brucella abortus 2308 infection in mice

Abstract CD-1 mice intravenously infected with the virulent Brucella abortus 2308 strain simultaneously produce significant levels of gamma interferon (IFN-γ) and interleukin-10 (IL-10) in their spleens between the second and eighth day post-infection with no production of interleukin-4 (IL-4). Endogenous synthesis of IL-10 does not affect the production of IFN-γ in this organ, while the production of both cytokines during this period of time is accompanied by a statistically significant increase ( P < 0.001) in the number of colony forming units (cfu) of B. abortus 2308 present in the organ. These findings suggest that although the endogenous synthesis of IL-10 apparently does not affect IFN-γ production, it may affect the effector functions of macrophages to control intracellular brucellae. Production of the Th1 cytokine IFN-γ during B. abortus 2308 infection is also associated with a specific IgG3 and IgG2a response against the B. abortus 2308 lipopolysaccharide (S-LPS) antigen.     

Environmental persistence of Brucella abortus in the Greater Yellowstone Area

Bison (Bison bison) and elk (Cervus elaphus) of the Greater Yellowstone Area (GYA) are the last remaining reservoirs of bovine brucellosis (Brucella abortus) in the United States. An important factor in evaluating the risk of transmission to cattle is the persistence of bacteria and infectious birth materials shed on pastures where cattle graze. We selected 2 study areas near the northern and western boundaries of Yellowstone National Park (YNP) to determine the persistence of bacteria on fetal tissue, soil, and vegetation, and scavenging on infectious materials from birth and abortion sites. We performed 3 independent field experiments to determine: 1) persistence of Brucella abortus (RB51) purposely applied to fetal tissues, 2) scavenging of fetuses by native scavengers, and 3) natural contamination of birth or abortion sites in the GYA. Results from these field experiments established that Brucella bacteria can persist on fetal tissues and soil or vegetation for 21–81 days depending on month, temperature, and exposure to sunlight. Bacteria purposely applied to fetal tissues persisted longer in February than May and did not survive on tissues beyond 10 June regardless of when they were set out. Brucella abortus field strain persisted up to 43 days on soil and vegetation at naturally contaminated bison birth or abortion sites. Fetuses were scavenged by a variety of birds and mammals in areas near YNP and more rapidly inside YNP than outside the Park boundary. Models derived from our data determined a 0.05% chance of bacterial survival beyond 26 days (95% Credible Interval of 18–30 days) for a contamination event in May. May 15 is the final date for hazing all bison into Yellowstone National Park under the current interagency bison management plan. With these data managers can predict when it is safe to graze cattle onto pastures previously occupied by bison. © 2011 The Wildlife Society.     

Survival of Brucella abortus Strain RB51 Lyophilized and as Liquid Vaccine under Different Storage Conditions

Brucella abortus strain RB51 (SRB51) is a new cattle vaccine that is approved for use in the U.S. for prevention of brucellosis. At the present time, other countries are implementing or considering the use of SRB51 vaccine in their brucellosis control programs. In the current study, the effect of three stabilizing media, two fill volumes (1 and 3 ml), and three storage temperatures (−25, 4 and 25°C) on the viability of lyophilized SRB51 over a 52 week period was determined. The effects of three concentrations of bacteria (5×10⁸, 1×10⁹, or 5×10⁹ cfu/ml) and two storage temperatures (4 or 25°C) on viability of liquid SRB51 vaccine were also determined. For lyophilized strain RB51 vaccine, fill volume did not influence viability (P> 0·05) during lyophilization. Although fill volume did not influence viability during storage in World Health Organization (WHO) media or media containing both WHO and Lactose Salt (LS) media, 1 ml fill volumes of SRB51 in LS media had greater (P< 0·05) viability when compared to 3 ml fill volumes. Lyophilized SRB51 vaccine stored at 25°C had a more rapid decline in viability (P< 0·05) when compared to vaccine stored at −25 or 4°C. With the exception of the 3-ml fill volumes of LS media, all three stabilizing media were similar in maintaining viability of SRB51 at −25°C storage temperatures. However, when compared to WHO or WHO/LS media, stabilization in LS media was associated with a more rapid decline in viability during storage at 4 or 25°C (P< 0·05). Initial SRB51 concentration in liquid vaccine did not influence (P> 0·05) viability during storage at 4 or 25°C. When compared to liquid SRB51 vaccine stored at 25°C, storage at 4°C was associated with a slower decline in viability (P< 0·05) during 12 weeks of storage. Biochemical and morphological characteristics of SRB51 were stable under the storage conditions utilized in the present study. This study suggests that viability of SRB51 can be readily maintained during storage as a lyophilized or liquid brucellosis vaccine.     

Variations in elk aggregation patterns across a range of elk population sizes at Wall Creek,Montana

In the Greater Yellowstone Ecosystem, growing concern over increasing rates of brucellosis seroprevalence in wildlife has challenged wildlife managers to develop strategies for minimizing the potential for pathogen exchange within and between wildlife populations. Recent evidence suggests that increases in elk seroprevalence may be associated with increasing elk densities and/or increasing size of elk aggregations. However, the interactions between elk population density, landscape factors, and elk aggregation patterns are not well-understood, making appropriate management responses challenging. Using a unique, long-term elk aggregation dataset collected across a wide range of elk population sizes, we investigated relationships between elk population size, landscape factors, and elk aggregation responses (group size and group density) with goals of clarifying how changes in elk population size may affect elk aggregation patterns. Overall, landscape attributes and weather had a stronger influence on elk aggregation patterns than factors such as elk population size that are within management control. We found little evidence that elk population size affected mean elk group sizes, but we did find evidence that the size and density of the largest elk aggregations increased as elk population size increased. We also found some evidence that group densities increased following the establishment of wolves. However, across the relatively wide range of elk population sizes observed in this study, only modest changes in elk group density were observed, suggesting that dramatic reductions in population sizes would be necessary to produce measureable reductions in elk group density to affect frequency-dependent transmission. Management actions designed to lower disease transmission are likely to negatively affect other objectives related to elk management and conservation. We therefore suggest that a first step in managing disease transmission risk is agreement among stakeholders interested in elk management of all objectives related to elk management, including acknowledgment that disease transmission is undesirable. © 2011 The Wildlife Society.