Test performance data demonstrates utility of a cattle DIVA skin test reagent (DST-F) compatible with BCG vaccination.

Bacillus Calmette-Guérin (BCG), an attenuated strain of Mycobacterium bovis (M. bovis), is the lead candidate vaccine for control of bovine tuberculosis (TB) in cattle. However, BCG vaccination sensitises cattle to bovine tuberculin, thus compromising the use of the current bovine TB surveillance tests. To address this, we have developed a diagnostic skin test that is not compromised by BCG vaccination and is able to detect BCG vaccinated animals that subsequently develop bovine TB following exposure to M. bovis. Building on previous work using 'in house' formulated protein cocktail reagents, we herein present test performance data for a single fusion protein (DST-F) containing the mycobacterial antigens ESAT-6, CFP-10 and Rv3615c formulated as a 'ready to use' reagent by a commercial manufacturer. Our results demonstrate that, unlike tuberculin reagents, a diagnostic skin test using DST-F maintained high specificity in BCG vaccinated animals. Furthermore, the DST-F skin test demonstrated a high relative sensitivity in identifying M. bovis infected animals, including those where BCG vaccination failed to prevent bovine TB pathology following experimental exposure to M. bovis. The DST-F is currently undergoing field trials in Great Britain to support its licensure and commercialisation.

Strategies to reduce methane emissions from farmed ruminants grazing on pasture.

Methane emissions from livestock are a significant contributor to greenhouse gas emissions and have become a focus of research activities, especially in countries where agriculture is a major economic sector. Understanding the complexity of the rumen microbiota, including methane-producing Archaea, is in its infancy. There are currently no robust, reproducible and economically viable methods for reducing methane emissions from ruminants grazing on pasture and novel innovative strategies to diminish methane output from livestock are required. In this review, current approaches towards mitigation of methane in pastoral farming are summarised. Research strategies based on vaccination, enzyme inhibitors, phage, homoacetogens, defaunation, feed supplements, and animal selection are reviewed. Many approaches are currently being investigated, and it is likely that more than one strategy will be required to enable pastoral farming to lower its emissions of methane significantly. Different strategies may be suitable for different farming practices and systems.

Vaccination of cattle with Mycobacterium bovis BCG by a combination of systemic and oral routes.

Mycobacterium bovis bacille Calmette-Guérin (BCG) vaccine delivered to calves by the subcutaneous (s.c.) or by the oral route in a formulated lipid matrix has been previously shown to induce similar levels of protection against bovine tuberculosis. The current study was aimed at determining whether a combination of delivering BCG by s.c. and oral routes would enhance levels of protection, compared to only one route of vaccination. Forty calves were randomly divided into four groups (10/group). Calves were vaccinated with 10(6)colony forming units (CFU) of BCG Pasteur by the s.c. route or orally with 10(9)CFU BCG incorporated into a lipid formulation. One group received a combination of BCG administered by both the s.c. and oral routes and a non-vaccinated group served as a control. The two groups of calves that received s.c. BCG produced strong IFN-gamma responses in whole blood cultures stimulated with bovine purified protein derivative (PPD) 3 weeks after vaccination. Cattle vaccinated just with oral BCG in a lipid matrix produced a strong IFN-gamma response 8 weeks after vaccination, and peaking at 11 weeks after vaccination. All calves were challenged by the intratracheal route with M. bovis 15 weeks after vaccination and were euthanized and necropsied to assess protection at 17 weeks following challenge. BCG given s.c. or orally induced significant and comparable levels of protection against the virulent challenge. Vaccination of cattle by a combination of s.c./oral routes did not enhance protection beyond that achieved by s.c. or oral vaccination alone. We conclude that vaccination of cattle with BCG by a combination of routes has no beneficial additive effects, compared to a single s.c. administration of BCG or BCG given orally in a lipid formulation.

Susceptibility of brushtail possums (Trichosurus vulpecula) infected with Mycobacterium bovis is associated with a transient macrophage activation profile.

The Australian brushtail possums are highly susceptible to Mycobacterium bovis and are the principal wildlife reservoir of M. bovis in New Zealand. To better understand the disease process in these animals, brushtail possums were infected by the aerosol route with a virulent strain of M. bovis, and immune parameters measured. M. bovis replicated actively in the lungs of infected animals. Animals began developing macroscopic lung lesions at 4 and 5 weeks following infection, with some lesions appearing in the livers and spleens. Infection determined the emergence of blood lymphocytes which proliferated in response to bovine purified protein derivative from M. bovis (PPD-b) at 3, 4 and 5 weeks. The response to a mitogen (Concanavalin A) waned progressively with time. Infection was associated with a modest increase in the numbers of free lung cells. Nitrite was detectable in the lavage fluids of infected animals at 3 weeks postinfection, but not at 4 and 5 weeks. Macrophage activation in the lungs was evident as alveolar macrophages produced more oxidants, significant levels of nitric oxide (NO), as well as tumor necrosis factor alpha (TNF-alpha) bioactivity at 3 weeks postinfection. However, macrophages from infected animals lost the ability to generate nitrite- and TNF-alpha generation was depressed at 4 and 5 weeks postinfection, the time at which macroscopic lesions in the lungs became apparent. Alveolar macrophages from animals at 3 weeks postinfection blocked the replication of M. bovis in part via a NO-dependent mechanism, and were more refractory for M. bovis growth than cells from naïve animals to bacterial replication. Alveolar macrophages from animals at 4 and 5 weeks postinfection allowed substantial replication of M. bovis, and no NO-dependent bacteriostatic activity was apparent. Introduction of autologous lymphocytes from the blood of infected animals in co-cultures rendered infected macrophages more resistant to M. bovis replication. We conclude that M. bovis infection in brushtail possums is associated with a transient activation of alveolar macrophages, although in vitro exposure to sensitized T cells can enhance this profile.