5. Possum Biocontrol Category
5.1 PBC 258
| Programme Title: | Improved diagnostic tests and vaccines for control of bovine tuberculosis |
| Programme Leader: | Bryce Buddle |
| Institution: | AgResearch |
Summary
Develop and evaluate improved diagnostic tests and vaccines for control of bovine tuberculosis in cattle and possums. Develop vaccine delivery systems for possum biocontrol vaccines.Approach & Outcomes
With the aim of improving the specificity and the sensitivity of our current tests to diagnose tuberculosis in cattle, we have initiated and completed a range of studies to assess the potential of novel approaches for the diagnosis of tuberculosis in cattle. Our data, at the molecular and immunological level, indicates that a variety of mediators are recruited during the delayed type hypersensitivity (DTH) response in cattle. Notably, cytokines of both the Th1 and Th2 subtypes were expressed at DTH sites in challenged cattle, when gene expression was assessed. Similarly, when the release of immune mediators was measured in the supernatants of peripheral blood mononuclear cells (PBMCs) of infected animals stimulated with purified protein derivative (PPD), we found that molecules associated with both Th1 subtypes (IL-12, IFN-γ, TNF-α) and Th2 subtypes (IL-10) were released at high levels. These studies of immunological mediators released during tuberculosis provide potential new diagnostic approaches and offer important clues in the pathogenesis of the disease. Indeed, our data suggest that the cytokines of the Th2 type (IL-4, IL-13, IL-10) are also released in tuberculosis. The importance of these mediators has been generally overlooked in previous studies, and our data suggest that we have generated assays that will allow us, for the first time, to assess the potential of these molecules to act as diagnostic tools, as well as allow us to truly appreciate the importance of these molecules in naturally and experimentally infected cattle.
An IFN-γ (BOVIGAM™) test with increased specificity has recently been developed by AgResearch Wallaceville using specific Mycobacterium bovis antigens (ESAT-6 and CFP10). This test is now being used for the re-testing of skin test reactor cattle from tuberculosis-free regions of New Zealand and has resulted in a marked reduction in the number of false positive reactors which need to be slaughtered. Due to problems with the supply of the individual proteins, a trial was undertaken to compare fusion proteins of ESAT-6/CFP10 with the individual proteins. The sensitivity and specificity of the test using the different forms of the proteins was shown to be identical. A fusion protein of ESAT-6/CFP10 has now replaced the individual proteins in the Specific Antigen IFN-g test for the New Zealand Bovine Tuberculosis Control Programme and results from the field over the past two months have been very encouraging.
Tuberculosis vaccine for possums
The human tuberculosis vaccine, BCG has been shown to induce considerable protection in possums against infection with M. bovis and when encapsulated in a lipid matrix, can be formulated into an effective oral bait tuberculosis vaccine for wildlife. A number of studies have been undertaken in the past year to optimise levels of protection, develop improved vaccines and determine vaccine efficacy in the field. A strain of BCG (Danish) more suited for commercial vaccine manufacture was shown to induce equivalent protection in possums to that induced by the standard Pasteur BCG strain. Oral administration of 10 doses of BCG vaccine to possums induced a similar effect to a single dose and administration of killed BCG prior to live BCG did not have a detrimental effect on protection. Four new attenuated M. bovis vaccines were administered orally to possums and two of these vaccines induced levels of protection against M. bovis infection which was at least equivalent to BCG vaccine. Studies in which BCG vaccine was administered orally to possums at various intervals prior to challenge have shown that high levels of protection were achieved when vaccines were administered at 8 and 29 weeks prior to challenge, while protection appeared to wane when the vaccine was administered 54 weeks prior to challenge. Two field trials have been initiated in the Orongorongo Valley, Wellington to determine the efficacy of orally administered BCG vaccine for wild possums. These trials are in collaboration with Landcare Research and Frank Aldwell (Otago University). In the first trial, a total of 86 possums have now been vaccinated with BCG, with an equal number of matched non-vaccinated possums. Protection against natural exposure to M. bovis infection will be monitored by clinical examination of possums at 2-monthly intervals and killing and necropsy of all possums at the end of the two year study. The second trial is a mortality study which will determine whether orally vaccinated possums have increased resistance to an experimental infection with M. bovis compared to matched, non-vaccinated possums. Progress has been made in the development of a rapid trap-side serological test for the diagnosis of tuberculosis in possums which could be particularly useful for determining whether possum control programmes have successfully eradicated tuberculosis from possum populations. An understanding of possible reasons for the high susceptibility of possums to M. bovis infection has been obtained from studying the interactions between possum lymphocytes, macrophages and M. bovis bacilli.
Biological control of brushtail possums
Using a highly sensitive transgenic mouse model, we have identified some promising novel molecules which exert strong adjuvant activities when administered by the mucosal route. These molecules will form ideal adjuvant components for immunosterilising vaccines aimed at biological control of brushtail possums. We are currently planning experiments that will test the potential of these molecules to induce mucosal immune responses in possums. In addition, we have devised novel in vitro systems to rapidly screen for the ability of various molecules to show adjuvant properties.
Contact for Enquiries
Farm Monitoring Programme Manager
Monitoring and Evaluation
MAF Policy
PO Box 2526
Wellington
NEW ZEALAND
Phone: +64 4 894 0623
Fax: +64 4 894 0741
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