An integrated disease management strategy for the control of rabies in Ethiopian wolves
Section snippets
General introduction
Empirical evidence and population viability analyses indicate that diseases pose an important extinction risk for a number of carnivore and canid populations (Thorne and Williams, 1988, Macdonald, 1993, Ginsberg et al., 1995, Murray et al., 1999, Vucetich and Creel, 1999, Haydon et al., 2002b). Furthermore, as the global populations of humans and domestic animals grow, the threat of spill-over infections from domestic reservoir hosts to wild and often threatened carnivore populations is
Ethiopian wolves – a rare highland canid
Ethiopian wolves are medium-sized canids (13–20 kg) specialized to prey upon the abundant rodent fauna of the highlands of Ethiopia (Sillero-Zubiri et al., 2004b). Despite their solitary foraging habits, competition for limited habitat fosters delayed dispersal of males, which tend to remain in the natal pack leading to the formation of close-kin groups of up to 13 adults. All pack members cooperate in raising the offspring, typically from a litter of two to seven pups born annually to the
Rabies in Ethiopian wolves
At least two, possibly three, separate rabies epidemics have resulted in dramatic declines in the Bale Mountains wolf population since the early 1990s (Sillero-Zubiri et al., 1996b, Randall et al., 2004). In 1990, 12 out of 23 (52%) known wolves in three study packs died or disappeared on the Sanetti Plateau within three months (Sillero-Zubiri et al., 1996b). Although no samples were obtained for diagnosis, the level and pattern of mortality suggested rabies was responsible for the sudden
Long-term dynamics under the effect of epidemics
The close monitoring of packs in the Web Valley has resulted in a unique dataset for a population of endangered carnivores, particularly because it includes a period before and after the 1991–1992 epidemic (Marino et al., 2006), and the more recent die-off in 2003–2004 (Fig. 2). Total count data come from observations of neighbouring packs in an area of around 50 km2 in the Web Valley, over 18 years of monitoring. This study population contained between 13 and 52 adult and yearling wolves (>1
The domestic dog reservoir population
Spill-over from domestic dogs living in wolf habitat and surrounding areas is the accepted source of pathogen transmission to Ethiopian wolves (Sillero-Zubiri et al., 1996b, Laurenson et al., 1997, Laurenson et al., 1998, Randall et al., 2004). Rabies is endemic in Ethiopia and is widespread in domestic dog populations throughout the country (Fekadu, 1982, Mebatsion et al., 1992, Tefera et al., 2002) and in neighbouring regions (Johnson et al., 2004). Dogs are by far the most abundant carnivore
Vaccination of domestic dogs
Since 1996, with increased effort from 1998 to present, parenteral vaccination of dogs in and adjacent to the BMNP has been undertaken by the EWCP to reduce the incidence of disease, particularly rabies, in the reservoir population. The overall goal of the dog vaccination campaign is to reduce the number of susceptible hosts for the pathogen and thus rabies incidence, and therefore reduce the chance of dog-to-wolf transmission. To date over 30,000 vaccinations have taken place in the BMNP and
Emergency parenteral vaccination of Ethiopian wolves
In response to the epidemic in the Bale Mountains in August 2003, advice was sought from a range of individuals and institutions including the IUCN/SSC Canid and Veterinary Specialist Groups and rabies experts from the UK, USA, France and South Africa on management options. Based on this, the EWCP sought permission from the Ethiopian government for a trial emergency Ethiopian wolf vaccination campaign to control the spread of the outbreak (Randall et al., 2004). Once granted, the campaign was
Modelling disease to guide management of Ethiopian wolves
When supported by detailed and accurate empirical data, predictive models can add substantially to the evaluation of disease risk and the development of disease management strategies (Ferguson et al., 2001, Ferguson et al., 2003, Keeling et al., 2001, Keeling et al., 2003, Anderson et al., 2004). Advanced modelling techniques can be used to predict the impact of disease outbreaks on threatened populations and the ecological and demographic conditions under which vaccination is a reliable, or
A case for oral vaccination of Ethiopian wolves
With models suggesting that vaccination of 20–40% of wolves substantially reduce extinction risks, vaccination of wolves as a preventative measure might provide a feasible and cost-effective means of achieving an adequate level of disease control regardless of disease incidence in the reservoir population or the risk of dog-to-wolf transmission. Whilst the intervention during the 2003 outbreak shows that parenteral vaccination is possible and effective, we do not advocate this approach except
Future recommendations
The disease management strategy for Ethiopian wolves has been both multi-disciplinary and adaptive over time. Of critical importance is the long-term population monitoring in the Bale Mountains and other wolf ranges. In addition to enabling the collection of detailed wolf demographic and spatial data, continuous population monitoring ensures the rapid detection of outbreaks by observation of clinical signs and/or the discovery of carcasses. The rapid diagnosis of putative disease agents by
Conclusions
Although difficult to collect, the amount and breadth of data and analyses presented here have substantially improved our understanding of the overall threat of disease to the persistence of remnant Ethiopian wolf populations and options for control. In fact, data on the demography, spatial structure, and dynamics of the wolf population coupled with the monitoring of disease incidence, screening and diagnosis of pathogens, and disease control in both the reservoir and target population make
Acknowledgements
We thank the Ethiopian Wildlife Conservation Department, the Oromia and Amhara Regional Governments, and the Bale Mountains National Park for permission to undertake this research and conservation work. We are grateful to the EWCP, especially Stuart Williams and Zelealem Tefera for management and guidance and the staff for their dedication and commitment in the field; the WCD vets Drs Fekadu Shiferaw and Kifle Argaw; Dada Gottelli and the IoZ-ZSL, UK; Charles Rupprecht and his staff at CDC,
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