Australian bat lyssavirus

Australian bat lyssavirus (ABLV) is an enzootic virus closely related to the rabies virus. It was first identified in a 5-month-old juvenile black flying fox (Pteropus alecto) collected near Ballina in northern New South Wales, Australia, in January 1995 during a national surveillance program for the recently identified Hendra virus. ABLV is the seventh member of the genus Lyssavirus (which includes rabies virus) and the only Lyssavirus member present in Australia. ABLV has been categorised to the Phylogroup I of the Lyssaviruses.

Virology

Molecular structure

The Australian bat lyssavirus (ABLV) shares many structural characteristics with the other Lyssaviruses, despite being genetically and serologically distinct from the others.

Viral entry mechanism and intracellular trafficking

ABLV has a similar entry mechanism to other rabies viruses, utilizing receptor-mediated endocytosis by the host cells. The glycoprotein (G) is a trimeric spike protein that extends through the virus's envelope and can interact with surface receptors of host cells. While the specific receptors remain mostly unknown at this time, it is thought that ABLV enters the nervous system of host through the neuromuscular junction of the peripheral nervous system. Additionally, it is believed that the spike protein either binds to a highly specific host receptor or uses a co-receptor in lipid rafts.

thumb|280x280px|Viral entry pathway of lyssavirus

After attaching to the host cell surface, ABLV uses a clathrin-dynamin-dependent pathway to invaginate the host membrane and pinch off a vesicle. Actin polymerization at the site of invagination is also required for successful viral entry. The virus is endocytosed fully, unenveloped. The vesicle fuses with a lysosome, causing the pH within the infected vesicle to drop. The lowering of pH in the early-endosome causes a conformational change in the spike protein G. This allows the viral envelope to fuse with the endosome, releasing the nucleocapsid into the cytoplasm of the host cell. It is estimated that less than 1% of healthy bats are ABLV carriers. As for sick or injured bats, it is estimated that 5–10% have been infected, detected with fluorescent antibody testing. She reported to the hospital four to five weeks later for shoulder pain, dizziness, vomiting, headache, fever, and chills. While hospitalised, her condition rapidly deteriorated, with slurred speech, diplopia (double-vision), dysphagia (difficulty swallowing), and progressive weakness in her limbs. From cerebrospinal fluid samples, no organisms were found with microscopy or culturing, despite elevated white blood cell levels. She was treated with several broad spectrum antibiotics with no improvement. An electroencephalogram was performed and found diffuse encephalitis. She eventually fell into a depressed conscious state, with a single incidence of extreme agitation. By her 11th day of hospitalization, she was fully ventilation dependent, nonresponsive, and hyperthermic. She died 20 days after her initial admittance. ABLV was identified from brain tissue by polymerase chain reaction and immunohistochemistry.

The second case began in August 1996; 37-year-old Monique Todhunter from Mackay was bitten on the finger by a flying fox at a birthday party while attempting to remove it from a child on whom it had landed. Six months later, following heightened public attention from the first ABLV death, she consulted a general practitioner regarding testing for the virus. Post-exposure prophylaxis was advised, but for an unknown reason she declined the treatment. After a 27-month incubation, a rabies-like illness developed in November 1998. She came in with symptoms of fever, vomiting, shoulder pain, dysphagia, and muscle spasms. Her condition worsened after hospital admission, as her dysphagia increased, her muscle spasms became more pronounced and frequent, and she became increasingly agitated. She became ventilation-dependent and unable to communicate due to full paralysis. On the day the woman was hospitalised, cerebrospinal fluid, serum, and saliva were submitted for testing. On the fourth day of her hospital admission, these tests were returned with results of probable ABLV infection. ABLV infection was confirmed by PCR on the 8th day of hospitalization. She died 19 days after the onset of illness in Mackay. Postmortem tests were all strongly positive for ABLV.

The fourth case was reported by the NSW Health department on 2 July 2025. In northern New South Wales, a man in his 50s was in critical condition with ABLV after being bitten by a bat several months earlier. The man had received treatment for the bat bite following the incident. The man died on 3 July.

Pathology and pathogenesis of ABLV in humans

ABLV (and the other Lyssaviruses) present similarly to the traditional encephalitic rabies virus (RABV) in humans. The symptoms first are flu-like with fevers, headaches, and fatigue. The symptoms progress with paralysis, delirium, convulsions, and death. Currently, there are two effective variations of RIGs used in PEP protocol, human RIG (HRIG) and equine RIG (ERIG). Drawbacks for HRIG are that there are limited supplies and the cost of production is high. HRIG is overall inaccessible for the general population. Drawbacks for ERIG are potential immunogenicity, which is when the immune system recognises the RIG as foreign and causes an immune reaction. In a 2021 study performed by Weir, Coggins, et.al., a new treatment method was proposed that used human monoclonal antibodies over RIGs. They identified two (A6 and F11) that recognised the G protein of lyssaviruses in phylogroup I (including ABLV) and completely neutralised the virus. They also proposed it as a potential diagnostic tool, in which there are only limited methods with PCR and are late into the symptomatic phase to positively identify ABLV.

Non-human health

ABLV has also been reported to have the ability to transfer to horses. Currently, this is the only other known susceptible species.

ABLV was confirmed in two horses on Queensland's Darling Downs in May 2013. Both horses were euthanised when their condition deteriorated despite treatment and the attending veterinarian performed a post mortem examination obtaining samples that allowed for the laboratory diagnosis. The property was then quarantined. Three dogs and the four horses in closest contact received post exposure prophylaxis, as did all nine in-contact people. The virus was isolated and identified as the insectivorous bat strain. These cases have prompted reconsideration of the potential spillover of ABLV into domestic animal species. Veterinarians are urged to consider ABLV as a differential diagnosis in cases of progressive generalised neurological disease.

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Additional reading

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