科研之友
微信
新浪微博
Facebook
分享链接
摘要
It is believed that so-called 'S' strains of Mycobacterium avium subsp. paratuberculosis, the causative agent of ovine paratuberculosis, were introduced into Australia in Merino sheep from New Zealand in the 1960s. The disease was first diagnosed in Australia in the central tablelands of New South Wales in the early 1980s, but caused few problems until the mid 1990s, when the current epidemic of the disease emerged to become one of the most important endemic diseases in Australia. Paratuberculosis continues to spread well beyond the original infected region in New South Wales, with prevalence rising in all states of the country, except South Australia and Queensland. A research project on Gudair (TM) vaccine, which led to the licensing of the product in 2002, identified that numbers of vaccinated sheep that died of the disease, or shed the causative agent declined by 90% in the first generation of vaccinated sheep. Vaccination and a risk-based trading scheme known as the ABC scheme (Assurance Based Credit points accrued for evidence suggestive of disease absence, currently including points for paratuberculosis vaccination) that uses a national sheep vendor declaration for sale of sheep, are now the main tools used for the control of the disease in most Australian states. However, vaccination for paratuberculosis remains controversial in some parts of the world, largely based on concerns relating to the efficacy of the vaccine in decreasing the risk of infection and transmission of the organism. The Australian experience has shown that vaccination against paratuberculosis quickly eliminates the significant mortalities in infected, high prevalence flocks. However, our applied research has shown that shedding of M. avium subsp. paratuberculosis from vaccinated sheep may persist for many years after commencing of vaccination programmes. In a longitudinal study of 11 flocks over 6 years, where 3- and 4-year-old animals were monitored every 2 years, we observed a substantial reduction in the prevalence of microbial shedding of >75% following vaccination, although in four flocks such a reduction was not evident. Further, in a study of 41 flocks where vaccination of lambs had been applied for 6 years, shedding persisted in the majority of flocks (81) and risk factor studies in these flocks indicated a number of management factors may be important in persistence of the disease. Stray sheep, failure to vaccinate wethers, introduction of unvaccinated sheep into the flock and use of commercial 'contractors' to do the vaccinations were associated with increased prevalence of paratuberculosis in vaccinated flocks. Improvement of farm biosecurity and correct vaccination schedules of all sheep in a flock are suggested as important management interventions to optimize the protection offered by Gudair (TM). A recent study on Kangaroo Island has confirmed that where a majority of these practices are rigorously applied, eradication of the disease is potentially possible. Despite the persistence of shedding in vaccinates in many parts of the country, vaccination to control paratuberculosis in Australia has been of enormous benefit to the sheep industry and rural communities and this needs to be recognized internationally.
- 出版日期2013-3
