Australian Bat Lyssavirus Infection

A rare but invariably fatal rabies like encephalomyelitis caused by Australian bat lyssavirus, a lyssavirus closely related to classical rabies virus.

It is transmitted through the bite or scratch of an infected bat. All Australian bat species are considered potential reservoirs, and the virus is not known to be transmitted by any other animal species.

It represents the Australian specific equivalent consideration to classical rabies given the historical absence of terrestrial rabies within Australia.

Management follows essentially identical principles to rabies given the closely related virology, shared clinical presentation, and shared uniformly fatal outcome once clinical symptoms develop.

Pathophysiology

• Following inoculation through a bat bite or scratch (or, theoretically, mucous membrane exposure to bat saliva), the virus travels retrogradely along peripheral nerves to the central nervous system, following the same fundamental pathophysiological process as classical rabies virus.
• It produces a progressive, fatal encephalomyelitis once established.
• The incubation period is variable and, as with classical rabies, potentially prolonged, extending from days to, in rare cases, more than a year following the initial exposure.

• The clinical presentation is essentially indistinguishable from classical rabies. It begins with an initial non specific prodrome (fever, headache, malaise, and, characteristically, localised pain or paraesthesia at the site of the original bat bite or scratch).
• The prodrome is followed by progression to either the encephalitic (furious) form with agitation, hydrophobia and fluctuating consciousness, or the less common paralytic form with ascending flaccid weakness.
• Disease progresses to coma and death in essentially all cases once clinical symptoms have developed, mirroring the uniformly fatal natural history of established classical rabies.
• A relevant history of bat exposure (bite, scratch, or direct handling of a bat) should be specifically sought in any patient presenting with a compatible progressive neurological illness in a relevant geographical context.
• Bat bites and scratches can be very minor and easily overlooked or forgotten, in contrast to the frequently more obvious nature of exposure with larger mammalian rabies vectors.

• Diagnostic approach mirrors that detailed under rabies. Antemortem confirmation is supported by reverse transcriptase polymerase chain reaction testing on saliva, skin biopsy from the nape of the neck, or cerebrospinal fluid, together with serum and cerebrospinal fluid antibody testing.
• The diagnosis is frequently established clinically in the appropriate exposure context, given the characteristic and highly specific clinical presentation once overt symptoms have developed.
• The most critical diagnostic and management focus in practice, exactly as for classical rabies, is not confirmation of established fatal disease but rather immediate, careful risk assessment and appropriate post exposure prophylaxis following any reported bat exposure.
• Post exposure prophylaxis is the only genuinely effective intervention, and must be pursued before the window of opportunity for effective prevention closes with the onset of viral central nervous system invasion.

• Post exposure management follows essentially the same principles detailed under rabies:
  • immediate, thorough wound washing with soap and water for a minimum of fifteen minutes
  • administration of human rabies immunoglobulin infiltrated around the wound site (with any remaining volume given intramuscularly at a distant site)
  • a full course of rabies vaccine
• Standard rabies biologicals have demonstrated cross protective efficacy against Australian bat lyssavirus, reflecting the close antigenic relationship between these two lyssaviruses.
• Any bat bite, scratch, or mucous membrane exposure to bat saliva occurring within Australia should be managed with the same urgency and post exposure prophylaxis approach as a potential rabies exposure elsewhere in the world.
• This reflects the equivalent risk and identical, uniformly fatal natural history of established disease should appropriate prophylaxis not be administered.
• Pre exposure prophylaxis, following the same vaccine schedule detailed under rabies, is recommended for individuals with occupational or regular exposure risk to bats, including wildlife carers, veterinarians and researchers working with Australian bat species, given the ongoing, recurrent nature of their exposure risk.
• Once clinical symptoms of established infection have developed, management is exclusively palliative and supportive, given the essentially universal fatality of established disease, following the same approach and rationale detailed under classical rabies.
• Communication with the patient's family regarding the invariably fatal prognosis at this stage of illness should be open and compassionate.
• Public health notification of any confirmed case, together with clear public education regarding the risk associated with handling bats, represents an important preventive strategy.
  • Only vaccinated, trained individuals should handle bats.
  • Any member of the public who has been bitten or scratched by a bat should seek immediate medical assessment regardless of how minor the injury may appear.
• This reflects the entirely preventable nature of this otherwise uniformly fatal disease with prompt, correctly administered post exposure prophylaxis.