CASE NOTES


Rabies Preparedness and Response in Northern Australia

Professor Michael Ward, Sydney School of Veterinary Science, The University of Sydney, 425 Werombi Road, Camden NSW 2570

Posted Flock & Herd April 2017

Introduction

The first written record of rabies appeared in the Mesopotamian Codex of Eshnunna ca. 1930 BC.1 This disease has plagued societies in Africa, the Middle East and Europe from ancient times. More recently, it has spread to most areas of the world, via the process of colonisation. Caused by a lyssavirus, dog-associated rabies remains a major public health issue in Asia and Africa. In humans it is almost inevitably fatal, following a severe illness that can include hydrophobia, paranoia, hallucinations and terror.

The rabies virus vaccine was one of the first vaccines developed in the 19th century. However, after 125 years or more of vaccination, rabies is still a neglected disease: it remains a threat to public health in developing and transitioning countries,2 an indigenous threat (from wildlife reservoirs) in developed countries,3−5 and it also threatens wildlife and ecosystems.6 Globally, there are an estimated 59,000 human deaths each year.7,8 Rabies is the 3rd ranked neglected tropical disease by life-years lost, and is still the number one disease ranked by deaths.8 The global financial burden is about 2.921.5 billion USD p.a., and has an impact of 1.610.4 million disability-adjusted life years.8 Dog-associated rabies endemicity is maintained in areas with a high dog density.9,10

Rabies likely was introduced to Indonesia during the 1880s, probably via importation of dogs from Europe.11 Despite quarantine laws and attempts to control the disease, rabies spread within two to three decades throughout the Greater Sunda islands (Java, Sumatra, Borneo, and Sulawesi). Within the past two to three decades, more and more islands have reported rabies outbreaks, particularly in eastern Indonesia: Ambon, Flores and Bali have recently been affected by rabies incursions and rabies currently threatens Lombok. Rabies was recently (2006−2007) reported from Maluku.11 In 2010, rabies was reported from Larat Island in West Maluku Tenggara, <500km north of the Tiwi Islands and the Australian mainland (west Arnhem). Unless this spread is controlled, it is likely that rabies will enter Irian Jaya and then Papua New Guinea, or Timor. Regional spread via fishermen’s dogs is suspected,11 although movement via the trade in dogs as pets, for hunting and for food is likely another driver of rabies spread in this region.

There has been one reported outbreak of rabies in Australia (Tasmania, 1867) since European settlement.12 Despite the discovery of Australian bat lyssavirus, Australia has never experienced endemic dog-associated rabies. A rabies incursion would be very difficult, perhaps impossible, to eradicate if rabies were introduced into northern Australia due to free-roaming dog populations and indigenous fauna.13 Wild dogs pose a risk of maintaining and spreading dog rabies were it to be introduced to Australia.14,15

A large scale rabies epidemic could occur in an area of low human population, probably along the northern coast, and would involve wild and feral dogs.13 At the high densities of wild dogs and dingoes found in northern Australia, dog rabies would likely persist were it introduced.15 Interaction between free-roaming dogs and feral dogs and dingoes would be the most likely avenue for dog rabies transmission to humans.

An emergency plan for rabies is incorporated into the Australian Veterinary Emergency Plan (AUSVETPLAN). The Australian default policy is to quickly eradicate rabies through a combination of quarantine, movement controls, destruction of infected animals, and vaccination. Part of the response would include vaccination of domesticated carnivores, other selected species and targeted animal groups in declared areas. Wild animals would be monitored and if disease establishes, implementing a vaccination program would be considered. In the case of wild and unmanaged dog populations, this would require knowledge of population demographics and networks. Population control would be problematic.14,16

To inform preparedness and response plans, a research program was commenced in 2012 that integrated field observational studies with disease spread simulation.

Studies in Indigenous communities to estimate dog contact rates

To estimate the rate at which dogs contact each other within and between indigenous communities in northern Australia, GPS tracking devices have been used. Detailed methodology has been presented by Dürr and Ward.17 Compact GPS units were attached to regular nylon dog collars (Figure 1), and have been deployed over periods ranging from days to months, in communities in East Arnhem (NT), the Katherine region (NT), the Northern Peninsula Area (QLD) and the Torres Strait.

GPS data recovered from these GPS units (Figure 2) have been used to estimate the dogs’ home ranges. This process is performed using a Biased Random Bridge method, which provides information on where and for what periods each dog utilises the landscape (i.e. its 50% and 95% isopleth utilisation distribution). These are referred to as core and extended home ranges, respectively.

Figure 1. A community dog with a GPS collar deployed.
Figure 2. GPS data recorded from 10 community dogs in Bamaga QLD.

Most dogs have been found to have compact home ranges, in the order of <1 ha core home range. However, some dogs have been found to roam widely, 10 ha or more. Also, human-mediated transport has been recorded, for example between communities and for the purpose of hunting. Predictors of roaming have also been investigated; it has been found that home ranges can be greater in the dry season, and for male intact dogs.

Most importantly for planning for a rabies incursion, this data has been used to estimate how frequently dogs come into contact within these remote, indigenous communities in northern Australia.

Disease modelling of the potential spread of rabies, should an incursion occur

A state-transition disease spread model has been developed and parameterized.18 Individual dogs are the unit of interest; at any point in time they can exist in only one of four mutually exclusive states: susceptible (S) to rabies infection; latently-infected (E); infectious (I); and removed (R). A novel component of this SEIR model is the representation of dog behaviour to define likelihoods of infection.

Preliminary modelling suggests that vaccination is the most efficient approach to controlling a rabies incursion in these communities. Importantly, reactive vaccination (in response to an outbreak, once detected) is as efficient as pre-emptive vaccination (ahead of an anticipated incursion). Culling of dogs and movement bans in general do not have a major impact on the outcome of an incursion.

Conclusions

The rabies spread model being developed is informed by how dogs come into contact with each other in remote indigenous communities. It is a tool to assist decision making, in preparation of a potential incursion of rabies in this region. Additional research has been undertaken using risk assessment methodology in Papua New Guinea, the Torres Strain and the Northern Peninsula area,19 and the issue of rabies infection in wild dog populations is also actively being pursued.20

References

  1. Adamson PB. The spread of rabies into Europe and the probable origin of this disease in antiquity. J R Asiatic Soc Great Britain Ireland 1977;2:140–4
  2. Wandeler AI. Global perspective of rabies. Global Conference on Rabies Control. Incheon, 7−9 September 2011. www.oie.int
  3. Bellwood P. The Great Pacific Migration. In: Yearbook of Science and the Future 1984. Encyclopaedia Britannica, Washington, 1984: 80–93
  4. Bourhy H, Dautry-Varsat A, Hotez PJ et al. Rabies, still neglected after 125 years of vaccination. PLoS Negl Trop Dis 2010;4: e839
  5. Jackson AC. Rabies. Neurol Clin 2008;26:717−26
  6. Karesh WB. Other relevant international standard. Global Conference on Rabies Control. Incheon, 7−9 September 2011. www.oie.int
  7. Knobel DL, Cleaveland S, Coleman PG et al. Re-evaluating the burden of rabies in Africa and Asia. Bull World Health Organ 2005;83:360−8
  8. Hampson K, Coudeville L, Lembo T et al. Estimating the Global Burden of Endemic Canine Rabies. PLoS Negl Trop Dis 2015;9:e0003709
  9. Cleaveland S, Dye C. Maintenance of a microparasite infecting several host species: rabies in the Serengeti. Parasitol 1995;111: S33−S47
  10. Lembo T, Hampson K, Haydon DT et al. Exploring reservoir dynamics: a case study of rabies in the Serengeti ecosystem. J Appl Ecology 2008;45:1246−57
  11. Ward MP. Rabies in the Dutch East Indies a centuary ago – a case study in disease emergence. Prev Vet Med 2014;114: 11−20
  12. O'Brien P. Introduction: rabies in wildlife. In: O'Brien P, Berry G, editors, Wildlife Rabies Contingency Planning in Australia. BRS Proc. No. 11, AGPS, Canberra, 1992: 3-5
  13. Forman AJ. The threat of rabies introduction and establishment in Australia. Aust Vet J 1993;70:81–83
  14. Fleming P, Corbett L, Harden R et al. Bomford M, editor. Managing the Impacts of Dingoes and Other Wild Dogs. BRS, Canberra, 2001
  15. Newsome A, Catling P. Host range and its implications for wildlife rabies in Australia. In: O'Brien P, Berry G, editors. Wildlife Rabies Contingency Planning in Australia. BRS Proc. No. 11, AGPS, Canberra, 1992:97–107
  16. Thomson PC, Marsack PR. Aerial baiting of dingoes in arid pastoral areas with reference to rabies control. In: O'Brien P, Berry G, editors. Wildlife Rabies Contingency Planning in Australia. BRS Proc. No. 11, AGPS, Canberra, 1992:125-134
  17. Dürr S, Ward MP. Roaming behaviour and home range estimation of domestic dogs in Aboriginal and Torres Strait Islander communities in northern Australia using three different methods. Prev Vet Med 2014;117:340−357
  18. Dürr S, Ward MP. Development of a novel rabies simulation model for application in a non-endemic environment. PLoS Negl Trop Dis 2015;9: e0003876
  19. Brookes VJ, Ward MP. Expert-opinion on the likely routes of entry of canine-rabies into Papua New Guinea. Zoon Public Health 2017;doi:10.1111/zph.12238
  20. Johnstone SP, Fleming PJ, Ward MP et al. Predicted spatial spread of canine rabies in Australia. PLoS Negl Trop Dis 2017;11:e0005312

 


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