Australian Bat Lyssavirus

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Monday, 18 February, 2013

Sadly, a young 8 year old Queensland boy was critically ill on 16 February 2013 from the rabies-like virus, Australian bat lyassavirus (ABLV). This virus has caused two deaths, both in Queensland. The first was a woman in 1996 in Rockhampton (Samaratunga et al 1998) and the second a Mackay woman in 1998 (Hanna et al 2000).

ABLV causes a disease similar to that caused by classical rabies virus. The incubation period varies with the site of the bite and the amount of virus inoculated. It can be a month or more (eg, 4.5 weeks for the Rockhampton case), and even very long as in the Mackay case, 27 months after a bat bite (Hanna et al 2000). During this time the virus that was inoculated in the skin travels up the motor nerves to the brain. Symptoms begin to appear when the lyssavirus reaches the brain, starts to multiply and then migrates out through motor and sensory nerves to all organs. Initially there is a non-specific prodromal period of a day or so (fever, malaise) which may be followed by strange sensations (pain, itchiness, tingling) at the site of the infecting bite. This progresses rapidly into the encephalitic phase with various neurological signs and other abnormalities due to autonomic instability in multiple systems (eg, marked fluctuations in body temperature and blood pressure as in the Mackay case). Lyssavirus infection is a multi-system disease not just an encephalitis as virus is found in nervous tissue in all organs. The Mackay case had a pancarditis and mononuclear cells infiltrating nerves in salivary glands (Hanna et al 2000). The final phase is progressive loss of consciousness, ending in coma and death. The full-blown clinical phase typically lasts 5-15 days.

Fortunately, the ABLV antigens are close to those of classical rabies virus; so rabies immunoglobulin and vaccine are protective (Hooper et al 1997). Although experimental studies have shown that classical rabies vaccine is not 100% protective for mice challenged with ABLV (Brookes et al 2005), no person who has received the recommended rabies post-exposure prophylactic regime has died from ABLV.

There are two strains of ABLV: the most common strain (pteropid ABLV) is found in the flying foxes, Pteropus spp. while an insectivorous bat, the yellow bellied sheath tailed bat (Saccholamus flaviventris) is the only known host of this strain (insectivorous ABLV) (Gould et al 2002).

ABLV is not common in wild bats. The oldest record is in a wild black flying fox (P. alecto) in Townsville in 1995 (Speare et al 1997) although obviously the virus has been endemic in Australian bats for quite some time. However, ABLV is relatively common in sick and injured bats that come into contact with humans. In surveys before 2005 the prevalence of ABLV was 5% or less in the four pteropid species, the little red flying fox (P. scapulatus), the black flying fox (P. alecto), the grey headed flying fox (P. poliocephalus) and the spectacled flying fox (P. conspicillatus). However, in recent years the prevalence of ABLV in sick and injured bats has declined to low levels. The June 2012 report of ABLV stats reports only one ABLV positive bat (see http://www.wildlifehealth.org.au/ProgramsProjects/BatHealthFocusGroup.aspx)

Key points for prevention:
1. People who have not been vaccinated for rabies must not handle Australian bats in any Australian state or territory.
2. If bitten or scratched by a bat, wash the wound.
3. Ask for post-exposure rabies prophylaxis from the state or territory health service. This is free in Australia and can be arranged through general practitioners and hospitals.

For additional information on ABLV see the Australian Wildlife Health Network’s Fact Sheet on ABLV.

References

Brookes SM, Parsons G, Johnson N, McElhinney LM, Fooks AR. Rabies human diploid cell vaccine elicits cross-neutralising and cross-protecting immune responses against European and Australian bat lyssaviruses. Vaccine 2005;23:4101-4109.
Gould AR, Kattenbelet JA, Gumley SG, Lunt RA. Characterisation of an Australian bat lyssavirus variant isolated from an insectivorous bat. Virus Research 2002;89:1-28.
Hanna JN, Carney IK, Smith GA, Deverill JE, Botha JA, Serafin IL, Harrower BJ, Fitzpatrick PF, Searle JW. Australian bat lyssavirus infection: a second human case, with a long incubation period. Medical Journal of Australia 2000;172(12):597-599.
Hooper PT, Lunt RA, Gould AR, Samarantunga H, Hyatt AD, Gleeson LJ, et al. A new lyssavirus - the first endemic rabies-related virus recognized in Australia. Bull Inst Pasteur 1997;95:209-218.
Samaratunga H, Searle J W; Hudson N. Non-rabies Lyssavirus Human Encephalitis from Fruit Bats: Australian Bat Lyssavirus (Pteropid Lyssavirus) Infection. Neuropathology and Applied Neurobiology 1998;24 (4):331–335.
Speare R, Skerratt L, Foster R, Berger L, Hooper P, Lunt R, Blair D, Hansman D, Goulet M, Cooper. Australian Bat Lyssavirus Infection in three Fruit Bats from north Queensland. Communicable Disease Intelligence 1997;21(9):117–120.

Image is Fig 2 from Hanna et al (2000)
Posted by Rick Speare