Page content: Victorian statutory requirement | Infectious agent | Identification | Incubation period | Public health significance & occurrence | Reservoir | Mode of transmission | Period of communicability | Susceptibility & resistance | Control measures | Outbreak measures | Additional sources of information

Victorian statutory requirement

Rabies (Group A disease) must be notified immediately by telephone or fax followed by written notification within five days.

Australian bat lyssavirus (Group B disease) must be notified in writing within five days of diagnosis.

Rabies is subject to Australian quarantine.

Infectious agents

Rabies virus and Australian bat lyssavirus (ABL) are closely related members of the genus Lyssavirus.

Identification

Clinical features
Rabies is an acute viral disease of the central nervous system (CNS). CNS symptoms are preceded by a non-specific prodrome of fever, headache, malaise, anorexia, nausea and vomiting lasting one to four days. This is followed by signs of encephalitis manifested by periods of excitation and agitation leading to delirium, confusion, hallucinations and convulsions. Signs of brain stem dysfunction begin shortly after with excessive salivation and difficulty in swallowing. This produces the classical picture of ‘foaming at the mouth’.

Even with medical intervention the disease is almost invariably fatal. Death from respiratory paralysis generally occurs within two to six days of the onset of symptoms.

The criterion for a suspect rabies case is progressive encephalitis with a past history of exposure in a rabies endemic area.

The criteria for a confirmed case are a clinically compatible neurological illness and one or more positive results from the three laboratory tests described below.

Symptoms of encephalitis due to ABL include numbness, muscle weakness, collapse and coma. A confirmed case requires laboratory definitive evidence only.

Method of diagnosis
The Australian Animal Health Laboratory at Geelong is the reference laboratory for the diagnosis of rabies and ABL. The State Chief Quarantine Medical Officer at the Department of Human Services should also be advised at the time of submitting any specimen. Transfer of human and animal specimens is coordinated by the State Chief Quarantine Medical Officer in consultation with the chief veterinary officer.

Rabies and ABL can be diagnosed by:

• detection of virus antigen by direct fluorescent antibody of a clinical specimen such as neural tissue (preferred), skin snips from the nape of the neck, saliva or CSF
• isolation in cell culture or laboratory animal of the virus from saliva, CSF or CNS tissue
• identification of rabies-neutralising antibody in the serum or CSF of unvaccinated persons.
  Confirmation by all the above methods is recommended.

Incubation period

The incubation period for rabies is usually three to eight weeks. It is rarely as short as nine days or as long as seven years. It tends to be shorter for wounds in areas of the body with rich nerve supply and close to the head.

The incubation period for ABL is not well characterised but it is assumed to be similar to rabies. The first case, reported in 1996, is believed to have had an incubation period of at least several weeks. In the second patient the incubation period was greater than two years.

Public health significance & occurrence

Rabies is endemic in Asia, India, Africa, North and South America and parts of Europe. High rates of rabies are reported from the Philippines, Thailand and Indonesia.

Australia is currently rabies-free. Rabies is a very rare infection of travellers to endemic areas outside of Australia. Only two imported human cases were reported between 1900 and 1995 (1987 and 1990).

Two human cases of ABL infection have been reported. One of these was from Northern New South Wales (1996) and the other from Rockhampton in Queensland (1998). Both patients had a history of bites and scratches from a bat and both died from their infections.

Rabies is subject to human quarantine controls under the Commonwealth Quarantine Act 1908. Rabies is a quarantinable disease because of Australia’s freedom from this disease. It is also reportable to the World Health Organization.

The primary quarantine concern is the prevention of the introduction of rabies virus to local dog and wildlife populations.

ABL is an emerging infectious disease which has much in common with rabies. The risk of human exposure increases with increasing human contact with Australian bat environments. This risk would increase significantly if ABL became established in terrestrial animal populations, particularly dogs.

Reservoir

Rabies is a disease primarily of animals. Most wild and domesticated dog-species (including foxes, coyotes, wolves and jackals) are susceptible to infection. Infected dogs remain the highest risk source for human transmission. Other species include skunks, racoons and bats.

In developed countries rabies is mainly found in wild animal hosts. Disease is spread from wild hosts to domestic animals and humans. In contrast dogs continue to be the main hosts in most African, Asian and Latin American countries, and are responsible for most of the rabies deaths that occur worldwide.

Australia is one of a growing number of countries in the world where the animal population is free of rabies.

ABL is known to infect all four Megachiroptera (fruit bats and flying foxes) species in Australia and at least three species of Microchiroptera (insectivorous bats). Ongoing serological testing and virus studies suggest that this lyssavirus is widely distributed in Australia. It is therefore assumed that all Australian bats have the potential to carry and transmit ABL.

There is no evidence that lyssaviruses in bats can establish and spread amongst terrestrial animals, although isolated cases in humans may occur on rare occasions.

Mode of transmission

Rabies virus and other lyssaviruses are usually transmitted to humans via bites or scratches which provide direct access of the virus in saliva to exposed tissue and nerve endings. It can also occur where mucous membrane exposure to bat saliva has occurred such as eyes, nose or mouth.

The most frequent way that humans become infected with rabies is through the bite of infected dogs, cats, wild carnivorous species like foxes, raccoons, skunks, jackals and wolves, and insectivorous and vampire bats. Cattle, horses, deer and other herbivores can become infected with rabies but rarely transmit the virus to other animals, although they may transmit the disease to humans.

People are not exposed to ABL through tactile contact with bats where parenteral or mucous membrane exposure does not occur. Contact such as patting bats or exposure to urine and faeces does not constitute a likely exposure to ABL, although bat urine and faeces may carry other human pathogens.

Transmission from person to person is theoretically possible but it has only ever been documented through corneal transplantation.

Period of communicability

In dogs and cats rabies is usually communicable three to seven days before onset of clinical signs and throughout the course of the illness. Viral excretion up to 14 days prior to clinical signs has been observed in some animal species. Similar communicability can be assumed for human cases.

Communicability for ABL is not known but assumed to be similar to rabies.

Susceptibility & resistance

All mammals are susceptible to varying degrees. In one case series, only 40% of children bitten by known rabid dogs developed the disease.

Control measures

Preventive measures
Pre-exposure vaccination is recommended for people whose occupation or recreational activities place them at increased risk of being bitten or scratched by a bat. It is also recommended for travellers who will be spending prolonged periods (i.e. more than one month) in rural parts of rabies endemic areas (see rabies/ABL vaccination information sheet below).

The World Health Organization maintains data on rabies infected countries – see www.who.int/csr

Control of case
There is no specific treatment available. Intensive supportive treatment is required.

The patient should be placed in a private room with standard isolation precautions implemented for respiratory secretions for the duration of the illness. There should be concurrent disinfection of all saliva-contaminated articles. Although transmission from a patient to attending carers has not been documented, health care workers should be advised to wear gowns, gloves and masks while attending patients. Blood and urine are not considered infectious.

Control of contacts
Other individuals exposed to the source animal are identified and offered post-exposure prophylaxis. Contacts that have open wound or mucous membrane exposure to a patient’s saliva should be offered full post-exposure prophylaxis.

Post-exposure treatment
Proper cleansing of the wound is the single most effective measure for reducing the transmission of rabies virus and this is likely to be also true for ABL.

When a person has been injured by a potentially infected animal overseas, or any Australian bat, the wound should be washed thoroughly for approximately five minutes as soon as possible with soap and water. If available, a virucidal antiseptic such as povidone-iodine, iodine tincture, aqueous iodine solution or alcohol (ethanol) should be applied after washing. Exposed mucous membranes such as eyes, nose or mouth should be flushed well with water.

The decision to offer post-exposure prophylaxis (rabies vaccine and rabies immunoglobulin) to a potentially exposed person should be made in consultation with the Communicable Diseases Section of the Department of Human Services (see rabies/ABL vaccination information sheet below).

Control of environment
See Outbreak measures, below.

Outbreak measures

If the source of the ABL infection is likely to be in Australia, a search should be made for the infected animal in collaboration with animal health authorities. Where possible, without placing other persons at risk of exposure, the bat should be kept and the Department of Human Services consulted about arranging testing of the bat for virus carriage.

If a rabies case, human or animal, is believed to have been locally acquired, the AUSVETPLAN rabies control procedures should be implemented. In designated areas animal owners may be required to have susceptible animals vaccinated with rabies vaccine. Animal movements are restricted and stray animals destroyed.

ABL is unique to Australia and currently it is only found in Australian bat species. If a human case of ABL is diagnosed in Victoria or ABL is found in another animal species such as a dog or cat, investigation and control measures similar to those for a rabies case, should be instigated.

Additional sources of information

• Animal Health Australia 1996, AUSVETPLAN
• Communicable Diseases Network of Australia 2001, Australian bat lyssavirus – Information for medical practitioners.