Communicable disease factsheets

Rabies - Information for Health Professionals

Rabies is an ancient viral disease which exists in a carrier state in certain wild animal populations. This fact sheet covers: background; occurrence; vaccination requirements for travel; treatment; avoidance; quarantine measures.

Version 1.0
This fact sheet was last updated on 19 February 2009

Infectious agent

Rabies is a preventable viral disease of mammals most often transmitted through the bite of a rabid animal. It is still a significant public health problem in many countries of Asia and Africa, even though safe, effective vaccines for both human and veterinary use exist.

The first symptoms of rabies may be non-specific flu-like signs – malaise, fever, or headache, which may last for days. There may be discomfort or paresthesia at the site of exposure (bite or scratch), progressing within days to symptoms of cerebral dysfunction, anxiety, confusion and agitation, progressing to delirium, abnormal behavior, hallucinations and insomnia.

The acute period of disease typically ends after two to 10 days. Once clinical signs of rabies appear, the disease is nearly always fatal, and treatment is typically supportive. After exposure to rabies virus, the administration of a course of both passive rabies antibody (immune globulin) and active vaccine is required to prevent death from the disease.

After cleaning and flushing the wound area immediately with soap or detergent and water, a viricidal antiseptic should be applied. Specific immunological protection in humans should be provided by administration of human rabies immunoglobulin (see the Australian Immunisation Handbook for details) at the site of the bite as soon as possible after exposure, to neutralise the virus. Further, the patient should be given specific vaccine at a different site to elicit active immunity.

Post-exposure treatment of a patient presenting after possible rabies exposure should be commenced as soon as possible; treatment should not be withheld even if there has been a considerable delay in recognising the exposure.

To date, fewer than ten documented cases of human survival from clinical rabies have been reported, and most have had a history of partial pre- or post-exposure prophylaxis.
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Identification

Clinical features

Rabies virus infects the central nervous system, causing encephalopathy and, ultimately, death. Early symptoms of rabies in humans are non-specific, consisting of fever, headache, and general malaise. As the disease progresses, neurological symptoms appear and may include insomnia, anxiety, confusion, slight or partial paralysis, excitation, hallucinations, agitation, hypersalivation, difficulty swallowing, and hydrophobia (fear of water). Death usually occurs within days of the onset of symptoms.

Laboratory confirmation

Several tests are necessary to diagnose rabies ante-mortem in humans; no single test is sufficient. Tests are performed on samples of saliva, serum, spinal fluid, and skin biopsies of hair follicles at the nape of the neck. Saliva can be tested by virus isolation or reverse transcription followed by polymerase chain reaction (RT-PCR). Serum and spinal fluid are tested for antibodies to rabies virus. Skin biopsy specimens are examined for rabies antigen in the cutaneous nerves at the base of hair follicles.

The standard test for rabies is direct fluorescent antibody (dFA). This test has been thoroughly evaluated for more than 40 years, and is recognized as the most rapid and reliable of all the tests available for routine use.

Other tests for diagnosis and research, such as electron microscopy (EM), histologic examination immunohistochemistry (IHC), RT-PCR, and isolation in cell culture are useful tools for studying the virus structure, histopathology, molecular typing, and virulence of rabies viruses.

Pathology of rabies infection is typically defined by encephalitis and myelitis. Perivascular infiltration with lymphocytes, polymorphonuclear leukocytes, and plasma cells can occur throughout the entire central nervous system (CNS). Rabies infection frequently causes cytoplasmic eosinophilic inclusion bodies (Negri) in neuronal cells, especially pyramidal cells of the hippocampus and Purkinje cells of the cerebellum. These inclusions have been identified as areas of active viral replication by the identification of rabies viral antigen.

Several factors may affect the outcome of rabies exposure. These include the virus variant, the dose of virus inoculum, the route and location of exposure, as well as individual host factors, such as age and host immune defenses.
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Public health significance and occurrence

Most of the estimated 55 000 deaths from rabies annually around the world occur in rural Asia and Africa, and most of the victims are children: 30 to 50 per cent of the reported cases of rabies—and therefore deaths—occur in children under 15 years of age. The majority of the cases result from bites by rabid dogs.

The vast majority of animal rabies cases reported to the USA Centers for Disease Control and Prevention (CDC) each year occur in wild animals like raccoons, skunks, bats, and foxes. Domestic animals account for less than 10 per cent of the reported rabies cases, with cats, cattle and dogs most often reported rabid.

Mode of transmission

Transmission of rabies virus usually begins when infected saliva of a host is passed to a susceptible animal. Various routes of transmission have been documented and include contamination of mucous membranes (i.e., eyes, nose, mouth), aerosol transmission, and corneal transplantations. The most common mode of rabies virus transmission is through the bite and virus-containing saliva of an infected host.

Communicability

Human to human transmission is theoretically possible, but rare. Airborne spread has been demonstrated in the laboratory setting, but this occurs very rarely.
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Control measures

Preventive measures

Rabies is currently not a problem in Australia but, to prevent human exposure to Australian bat lyssavirus (ABL) and/or rabies, it is recommended that humans avoid all contact with suspected or confirmed infected animals and all bats, both flying foxes and insectivorous bats.

Control of case

Pre-exposure prophylaxis with rabies vaccine is recommended for people in Australia liable to receive bites or scratches from bats (this includes bat handlers, veterinarians, wildlife officers and others who come into direct contact with bats).

Pre-exposure prophylaxis is recommended for expatriates and travellers who will be spending prolonged periods (i.e. more than a month) in rabies endemic areas.

Booster doses of rabies vaccine are recommended for immunised people who have ongoing exposure to either ABL or rabies. People who work with live lyssaviruses in research laboratories are at risk of unapparent exposures, and should have rabies antibody titres measured every 6 months with a booster dose of vaccine given if necessary.

Disclaimer

While every care has been taken in preparing this fact sheet, the Australian Government does not accept liability for any injury or loss or damage arising from the use of or reliance upon the content of the fact sheet.