Researchers have produced the strongest evidence yet to suggest that a targeted reactive vaccination programme, rather than blanket vaccination, can control infectious diseases like rabies in threatened wild canid populations (wild dogs, wolves and foxes. (Low-coverage vaccination strategies for the conservation of endangered species’, D.T.Haydon et al Nature 443, 692-695 -12 October 2006)
The research team from Oxford University, Edinburgh University and Glasgow University demonstrated that by vaccinating just thirty per cent of the Ethiopian wolf population, the spread of rabies during an outbreak can be reduced.. Their study, published in the journal Nature, suggests that by vaccinating wolf packs living in the connecting mountain valleys close to the outbreak, they can contain disease outbreaks with unexpectedly low overall levels of vaccine coverage.
For nearly twenty years Oxford University’s Wildlife Conservation Research Unit (WildCRU) have been studying these animals and in 1995 established the Ethiopian Wolf Conservation Programme (EWCP) to address the most urgent threats to wolf survival. The population of just 500 can only be found in remote mountain enclaves in the Ethiopian Highlands. There are six subpopulations of between 10 and 50, with the largest group of 350 living in the Bale Mountains in the southeast. Canid diseases, such as rabies and distemper, are the major killers with domestic dogs being the main disease-carriers. The EWCP continues to vaccinate domestic dogs in wolf habitat in an attempt to protect the wolves.
After rabies outbreaks in the Bale Mountains in the early 1990s, which wiped out two thirds of the Ethiopian wolf population in this area, an emergency vaccination programme was introduced in 2003 in response to yet another outbreak that year. The study, an analysis and modelling of data collected by the EWCP, suggests that a preventative strategy to capture and vaccinate the whole population is impractical as the wolves live in remote, inaccessible mountain enclaves. The alternative strategy adopted by the EWCP is an effective reactive response to outbreaks, whereby Ethiopian wolves living in the mountain valleys close to infected packs are targeted. The researchers have shown through modelling that even if outbreaks became more frequent, fewer wolves would need to be vaccinated under this targeted scenario, than under a wholesale vaccination programme, in order to virtually eliminate the extinction threat posed by such outbreaks.
The researchers suggest that routine monitoring of the population enables the early detection of disease and a rapid response to deal with it. In the event of a single suspected case, they suggest that monitoring should be intensified and once two rabid carcass are found, vaccination teams should be dispatched to target subpopulations living in connecting valleys. Additional measures, such as vaccinating between 10 and 40 per cent of wolves in affected packs, if targeting the particularly large and highly connected packs, can further reduce overall mortality due to these outbreaks.
Dr Claudio Sillero-Zubiri, from Oxford’s WildCRU, said: ’Ethiopian wolves are the rarest carnivore in the world, restricted to a few montane enclaves in the Ethiopian Highlands. Canid diseases, such as rabies and distemper, transmitted from domestic dogs pose the most immediate threat to their persistence, and targeted reactive vaccination intervention presents a useful tool to protect the remaining small wolf populations from extinction.’
Lead author Dr Dan Haydon, from the University of Glasgow, said: ‘Theoreticians have devoted a lot of effort to working out how to vaccinate populations in ways that prevent epidemics getting started, but this requires coverage that is impractical in wild populations.
We’ve looked at vaccination studies that don’t prevent all outbreaks, but do reduce the chances of really big outbreaks – ones that could push an endangered population over the extinction threshold. These strategies turn out to be effective and a lot more practical.’
Dr Karen Laurenson, the University of Edinburgh, who has led the disease work Ethiopian wolves said: ‘We have shown that the vaccination of Ethiopian wolves, when appropriately and strategically used, is a safe, direct and effective method of reducing extinction threats. With the advent of new generations of oral vaccines, such methods are becoming ever more feasible and cost-effective.’
Professor David Macdonald, Director of the WildCRU, said ‘The WildCRU's aim is to put innovative science to practical use. These discoveries would have been impossible without long-term field-studies, and they show how cutting-edge science can have down-to-earth practical significance both for the protection of a very rare, and spectacular, wild species, and also for human well-being.’