Lyssaviruses: special emphasis on rabies virus and other members of the lyssavirus genus

Why we can prevent, control and possibly treat – but will not eradicate – rabies

ABSTRACT 

Rabies is an acute, progressive viral encephalitis. Despite historical recognition, millions still remain exposed annually. Most fatalities are of children, although this zoonosis is a vaccine-preventable disease. All developed countries interrupted canine transmission and increasingly, Asian and African communities recognize what Latin Americans demonstrated – dog rabies can be eliminated – by mass application of veterinary vaccines. Realistically, rabies is not a candidate for eradication. Management is lacking for major reservoirs, such as bats. Increasing pre-exposure immunization of individuals at risk, simplification of postexposure schedules, enhancing vaccine delivery by alternative routes, development of less expensive biologics and antiviral drugs, may lessen its impact if applied strategically in a One Health context.

A two-step lyssavirus real-time polymerase chain reaction using degenerate primers with superior sensitivity to the fluorescent antigen test

A generic two-step lyssavirus real-time reverse transcriptase polymerase chain reaction (qRT-PCR), based on a nested PCR strategy, was validated for the detection of different lyssavirus species. Primers with 17 to 30% of degenerate bases were used in both consecutive steps. The assay could accurately detect RABV, LBV, MOKV, DUVV, EBLV-1, EBLV-2, and ABLV. In silico sequence alignment showed a functional match with the remaining lyssavirus species. The diagnostic specificity was 100% and the sensitivity proved to be superior to that of the fluorescent antigen test. The limit of detection was ≤ 1 50% tissue culture infectious dose. The related vesicular stomatitis virus was not recognized, confirming the selectivity for lyssaviruses. The assay was applied to follow the evolution of rabies virus infection in the brain of mice from 0 to 10 days after intranasal inoculation. The obtained RNA curve corresponded well with the curves obtained by a one-step monospecific RABV-qRT-PCR, the fluorescent antigen test, and virus titration. Despite the presence of degenerate bases, the assay proved to be highly sensitive, specific, and reproducible.

A perspective on lyssavirus emergence and perpetuation

Rabies is propagated globally by viruses in the Family Rhabdoviridae, Genus Lyssavirus. These RNA viruses utilize the mammalian central nervous system as their ultimate niche, and exploit routine social mechanisms, as well as host behavioral alterations, to facilitate transmission by neural transport and innervations of the salivary glands, and ultimately excretion via the saliva, towards circulation thereafter in host populations. All mammals are susceptible to infection, but lyssavirus reservoirs are represented by several species of Carnivora, with viral global diversity and distribution in toto driven by a wide variety of the Chiroptera. Pathogen diversity is maintained by multiple faunas, and facilitated by pronounced host vagility, as exemplified by the ease of routine daily and seasonal movements by bats. Viral 'ensembles', or subpopulations associated with productive transmission events, emerge locally in vivo through a combination of naive host infections in some individuals versus acquired immunity by others, using complex metapopulation dynamics. Enhanced surveillance, improved diagnostics, increased pathogen detection, and an integrated One Health approach, targeting human, domestic animal and wildlife interfaces, provide modern insights to the ecology of bat lyssaviruses to augment future prevention and control.