Rabies is transmitted in saliva, and is a zoonosis of great significance in global MPM.

" The ancient disease of rabies is a perennial component of any review of zoonotic diseases and a subject on which the veterinary practitioner is approached almost daily for advice. In the United States, the number of cases of human and domestic animal rabies has been dramatically reduced over the last three decades. In spite of the fact that there have been less than two cases of human rabies on average per year over the last 10 years [in the U.S.], the virtually inevitable fatal outcome following the development of clinical signs has ensured a high level of priority to the surveillance and control of this disease. "¹

We have used the quote above from North America for two reasons: first, it neatly explains why we need to consider this exotic disease here; and second, the paper is a fine review of how rabies works in a country where it has been endemic for a very long time.

The situation in Australia and New Zealand is somewhat different:

• risk of rabies

• Australian case studies

• many different types of rabies

• contingency plans

Australia and New Zealand do not have endemic rabies. Rabies, however, is present in most of the world except Oceania, Melanesia, Japan, Taiwan, UK, Ireland and Sweden. Most important to us, rabies is present in most of Indonesia apart from Irian Jaya. There is concern that if rabies becomes established in Irian Jaya, it can cross to PNG and then to Australia and New Zealand.

Three people have died of rabies in Australia: an unconfirmed case in 1867, and two recent cases in 1987 and 1990. Both recent cases were undiagnosed before death. This was not surprising since there was no history or recent travel outside Australia.

The first case was a 9-year-old boy who died in Brisbane. The likely source of the virus was a monkey bite in India 16 months before the illness. The second case was a 10-year-old girl who died in Sydney from encephalitis in 1990. This girl was a Vietnamese immigrant who had come from North Vietnam to Australia via Hong Kong. The presumed incubation period was very long, at least 6 years and 3 months.

The rabies virus is not one discrete disease organism as is commonly thought. Rather, there are different rabies-related viruses, different animal susceptibilities to rabies infection, and different rabies biotypes. All these factors affect where this virus fits into the scheme of things (phylogeny) and how it operates (its epidemiology).

There are at least six rabies-related viruses. Each is serologically different. Australian Bat Lyssavirus, which recently caused the death of a woman in Rockhampton, is one such virus. They all cause rabies-like diseases, but rabies itself is the pathogen of greatest significance to human health. It is designated serotype 1.

All warm-blooded animals are vulnerable to infection with rabies but there are variations in their relative susceptibilities. For a table of animal susceptibilities, see Geering et al.²

Analysis of the relative susceptibilities suggests that dingoes, dogs and their hybrids are the most important potential rabies hosts in northern Australia; red foxes are the most important potential hosts in the south of the continent. Native animals, cats, bats and rodents represent potential reservoir populations, depending on their local densities. In an urban environment, dogs and urban foxes are the most likely reservoirs but cats, and even brush-tailed possums, could be significant hosts.³

As well as victim animals varying in susceptibility to infection, the rabies virus itself comes in a range of different biotypes. These different biotypes are adapted to prefer specific types of host animals.

If an animal is infected by a non-compatible biotype, the virus will still kill, but it is unlikely to be passed on to other animals of the same type. For example, if a dog were bitten by a rabid dog infected with the dog biotype (urban rabies), both dogs would certainly die and, in the process, the bitten dog would most likely infect other dogs. On the other hand, if a cat were bitten by the same rabid dog, the cat would die from the infection, but would be most unlikely to pass the disease to other cats. In the case of the bitten dog, the biotype is matched while for the bitten cat, the biotype is mismatched. Different biotypes are of great significance in the epidemiology of rabies.

Biotype examples include biotypes adapted to skinks, red and Arctic foxes, raccoons, insectivorous and vampire bats, jackals, meerkats and mongooses, most of which are alien to Australia and New Zealand.

Most researchers believe that biotypes which have adapted to overseas wildlife species are unlikely to be introduced into Australia or New Zealand. The dog biotype (urban rabies) is a much greater risk here because dogs we have aplenty. If the dog biotype became established here, then there would be a further risk that the virus might mutate to adapt to native and feral species. This would be very serious, since this would create a reservoir of infection that would be very difficult to eradicate.³

In the event of a rabies-like case (human or animal) being reported to authorities in Australia or New Zealand, a series of questions have to be answered to decide what action needs to be taken:

1. Are the history and symptoms consistent with a rabies-like viral infection?

2. Is it likely (or possible) that the infection occurred from an animal in Australia or New Zealand?

3. Has a rabies-like causal organism been isolated?

4. If yes, which serotype is it?

5. If Serotype 1 (true rabies), which biotype is it?

Different answers will require different responses.

Plans to control and eradicate a number of animal diseases in Australia are contained in a series of manuals under the common title of AUSVETPLAN (Australian Veterinary Emergency Plan). ³ For most serious animal diseases, the manuals outline an immediate response. They are continuously updated so that they take account of the latest technology and information (See web site http//www.brs.gov.au.brs/aphb/aha/ausvet.htm). It was the responses outlined in AUSVETPLAN that were so successful in containing a recent outbreak of avian influenza at Bendigo.

Many diseases (apart from rabies) can cause aggression in domestic pets eg. canine distemper infections commonly cause encephalitis and rabies-like aggression. Inadequate socialisation, training and management are even more common causes of aggression. Aggression caused by rabies is a most unlikely scenario. But it is one that must always be in the back of PMOsí minds.

If an outbreak does occur, PMOs in local government together with veterinary and medical practitioners, will be in the frontline. They may be the people who sound the first alarm. Help is close to hand. In Australia PMOs can call the Exotic Diseases Hotline: ph1800 675 888.

But in an emergency, notifying the authorities may need to wait until the animal and the victims are dealt with. Just in case, every PMO needs to know what to do if they suspect they are facing a rabid dog. The following advice comes from Exotic Diseases in Animals: a field guide for Australian veterinarians:²

1. Perry BD. 1987. Rabies. In: August JR, Loar AS. (eds). Zoonotic diseases. The Veterinary Clinics of North America: Small Animal Practice 17(1): 73-89.

2. Geering WA, Forman AJ, Nunn MJ. 1995. Rabies. In: Exotic Diseases of Animals: a field guide for Australian veterinarians. Canberra: Australian Government Publishing Service: 203-217.

3. Banks DJD. 1992. Rabies: a forceful argument for urban animal management. In: Murray RW, editor. Urban Animal Management: proceedings of the First National Conference on Urban Animal Management in Australia (Brisbane, 1992). Mackay QLD: Chiron Media: 59-69.