RHABDOVIRIDAE

Rhabdoviridae is a virus family within the Mononegavirales order, which also contains the Bornaviridae, Filoviridae, and Paramyxoviridae families. Rhabdoviridae contains six genera: vesiculovirus, lyssavirus, ephemerovirus, norvirhabdovirus, cytorhabdovirus, and nucleorabdovirus. The Rhabdoviridae family contains only two viruses that infect humans, however, which are rabies virus (RABV) and vesicular stomatitis virus (VSV.) These two viruses are in the lyssavirus and vesiculovirus genera respectively.

Morphology:

Rhabdoviruses are negative, ss, monopartite RNA viruses. They are noninfectious because their negative sense RNA genome cannot be immediately translated upon entry into the cell. They do not have a 5' cap or a polyA tail. Their capsid is roughly bullet shaped and about 75 nm wide and 180 nm long. These are enveloped viruses and the envelope contains large protein projections.

Protein Production:

Five sub-genomic transcripts are made and translated, which allows the virus to have differential gene expression. Each sub-genomic transcript makes a distinct amount the protein it encodes.

Replication:

Rhabdoviridae members replicate in the cytoplasm. They first transcribe a positive RNA template, then use that template to regenerate their negative RNA genome.

Rabies:

Rabies is the most notable human disease that is caused by this family of viruses. It is the most lethal human infectious disease known, with a fatality rate of nearly 100%. In addition to being deadly, rabies infection causes horrific symptoms. First, individuals who are infected with rabies experience 2-7 days of a non-specific, flu-like prodrome. The prodrome is followed by behavioral abnormalities such as anxiety, depression, hyperactivity, and aggression. Next, the unusual symptoms of intolerance of tactile, auditory, and visual stimuli begin. This is sometimes referred to as "hydrophobia" because patients are highly averse to the sensation of water in their mouths and on their skin. Insomnia and hallucinations eventually develop as well. The progression of rabies symptoms has been divided into two general tracts: 'furious rabies' and 'dumb rabies.' Symptoms of aggression and hyperactivity are generally more prominent in the case of furious rabies, while the symptom of paralysis is more prominent in the case of dumb rabies.

Rabies is transmitted to humans by bites or scratches from infected animals; most commonly skunks, raccoons, foxes, bats and dogs. The number of bites and the location of the bites affect the incubation period, with bites closer to the neck and head resulting in a shorter incubation period. Typically, it takes 30-90 days for the infection to become symptomatic, but incubation periods as short as 7 days have been known.

Pre-exposure and post-exposure immunizations are available and have a high success rate. Additionally, passive immunization is sometimes used. Once rabies virus has infected the CNS and disease symptoms have progressed, however, there is little that can be done.

Comments?

References:

Humans & Viruses class notes, Robert Siegel, 2004

http://www.vet.ksu.edu/depts/rabies/index.htm

http://www.cdc.gov/ncidod/dvrd/kidsrabies/TheVirus/rabvir.htm