Rabies is caused by negative strand RNA-viruses belonging to the genus Lyssavirus, family Rhabdoviridae of the order Mononegavirales. According to the International Committee on Taxonomy of Viruses (ICTV) the genus Lyssavirus is delineated into different virus species based on demarcation criteria such as genetic distance, immunological features and antigenic patterns in reactions with panels of antinucleocapsid monoclonal antibodies. This demarcation is further supported by geographic distribution and host range (see table).

Lyssavirus species segregate into two phylogroups. Phylogroup 1 includes Rabies lyssavirus, Duvenhage lyssavirus, European bat lyssaviruses, type 1 and 2, Bokeloh bat lyssavirus, and Australian bat lyssavirus. Also, Aravan lyssavirus, Khujand lyssavirus, and Irkut lyssavirus are members of phylogroup 1. Phylogroup 2 includes Lagos bat lyssavirus, Mokola lyssavirus, and Shimoni bat lyssavirus. West Caucasian bat lyssavirus, Ikoma lyssavirus and Lleida bat lyssavirus form independent phylogroup 3. Rabies virus (RABV), the prototype lyssavirus, is responsible for the vast majority of all human rabies cases. However, all lyssaviruses can cause indistinguishable fatal encephalitis both in humans and other mammals.

There is a significant serological neutralization within phylogroups, but very limited crossneutralization has been detected between phylogroups. Therefore, rabies virus vaccines however, may not provide adequate cross-protection against all genetically divergent lyssaviruses. Little or no cross-protection with pre-exposure vaccination and with conventional rabies post-exposure prophylaxis was observed against lyssaviruses of phylogroups 2 and 3.

Interestingly, bats are primary or sole reservoir hosts for all lyssaviruses except MOKV and IKOV (for which the reservoir species have not been clearly identified as of yet). Bat associated lyssaviruses appear to have more restricted geographical and host range, with with limited public and animal health implications.

Current diversity and taxonomy of lyssaviruses

 ^a ICTV = International Committee on Taxonomy of Viruses (www.ictvonline.org/)