Australian bat lyssavirus

Species of virus

Australian bat lyssavirus (ABLV), originally named Pteropid lyssavirus (PLV), is a 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 categorized to the Phylogroup I of the Lyssaviruses.

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

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. 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. 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 of 1998. She came in with symptoms of fever, vomiting, pain in her shoulder, 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 hospitalized, 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. Postmortem tests were all strongly positive for ABLV.

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 recognizes 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 recognized the G protein of lyssaviruses in phylogroup I (including ABLV) and completely neutralized 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.

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 euthanized 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 generalized neurological disease.