Rhabdovirus - Classification, Family, Genus, Morphology, Genome, Habitat, WHO

Classification of Rhabdovirus

The classification of Rhabdovirus is done by:

Realm: Riboviria

Kingdom: Orthornavirae

Phylum: Negarnaviricota

Class: Monjiviricetes

Order: Mononegavirales

Family: Rhabdoviridae

Family, Genera of Rhabdovirus

The family Rhabdoviridae has several subfamilies which in turn contain numerous genera. It includes 150 viruses that infect mammals, reptiles, birds, fish, insects, and plants.

Some of the genera which are medically important include:

• Ephemerovirus - viral fever in cattle

• Perhabdovirus, Sprivivirus - infects fish

• Sigmavirus - infects dipterans

• Tibrovirus - usually infects cattle, and humans (Bas-Congo virus)

• Tupavirus - infects birds

• Vesiculovirus - infects humans, insects, cattle, horses, and pigs

• Lyssavirus - an important human pathogen

Lyssavirus

The Lyssavirus contains important pathogens including:

• Rabies lyssavirus - Rabies virus (RABV)

• Australian bat lyssavirus (ABLV)

• Bokeloh bat lyssavirus (BBLV)

• Duvenhage lyssavirus (DUVV)

• European bat lyssavirus 1 (EBLV-1) and European bat lyssavirus 2 (EBLV-2)

• Lagos bat virus (LBV)

• Mokola virus (MOKV)

• Shimoni bat virus (SHIBV)

• West Caucasian bat lyssavirus (WCBV)

Characteristics of Rhabdovirus

Rhabdovirus belongs to the family Rhadboviridae. It contains non-segmented, singe stranded negative sense RNA as its genome

Among the above genus, both Lyssaviruses, Tibrovirus, and Vesiculoviruses are recognized as viral antigens and are able to infect both humans and animals and cause clinical disease.

Rabies virus may be typed as fixed or street virus

• Fixed:

  One whose virulence and incubation period has been stabilized by serial passage and remained fixed during further transmission

  Rabies virus that has undergone serial passage through rabbits, thus stabilizing its virulence and I.P are called a fixed virus

• Street:

  Virus from a naturally infected animal, as opposed to a lab-adapted strain of the virus.

  The virulent rabies virus from a rabid domestic animal that has contracted the disease from a bite or scratch of another animal, is called the street virus

Morphology of Rhabdovirus

Rabies virion is ‘bullet-shaped’- one end conical, another end flat. Morphologically, it is approximately 75nm in diameter and its length is 180nm (130-200nm). Rhabdovirus RNA is encapsidated by nucleoprotein N to form a helical nucleocapsid.

The nucleocapsid is associated with a significant amount of phosphoprotein P, some of which carry copies of RNS-dependent RNA polymerase (L for large protein). The RNS plus N, P, and L form the ribonucleoprotein (RNP), which is the component that is active in transcription and replication.

The RNP is enwrapped in a lipid bilayer derived from the host cell plasma membrane during the budding process. The matrix protein M and the glycoprotein G are membrane-associated proteins. The M protein is located beneath the viral membrane and bridges the nucleocapsid and the lipid bilayer. The G protein is an integral transmembrane protein that is involved in viral entry.

Genome of Rhabdovirus

The genome size of Rhabdovirus is approximately 12,000 nucleotides (12kb). It encodes the five viral proteins in the order of 3’-N-P-M-G-L-5’.

• N = nucleoprotein

• P = Phosphoprotein

• G = glycoprotein

• L = Large polymerase proteins

The viral RNP core contains viral RNA encapsidated by N proteins and associated with P and L proteins. The viral RNP functions in viral replication i.e. is a replicative unit, M is a structural protein, and G is involved in attachment to cellular receptors.

The intrinsic region (G-L) is 450 nucleotides in length and does not encode any polypeptides. Each gene is composed of an internal coding region flanked by non-coding regions (NCRs) that are bordered by transcription initiation signals (TISs) and transcription termination polyadenylation (TTP) signals.

The genes are usually separated by conserved intergenic regions (IFRs).

• The five genes are flanked by 2 short NCRs at the 3’ and 5’ ends

• The sequences of the 3’ and 5’ ends of the genome are inversely complementary

Rabies viruses are sensitive to common chemicals

• The virus is sensitive to

  Ethanol

  Iodine

  Soap/detergents

  ether, choloroform, acetone

• Destroyed at:

  50°C in 1 hour

  60°C in 5 minutes

Habitat of Rhabdovirus

Rabies habitats widely in Asia and Africa and are widely distributed across the globe. More than 55,000 people die of rabies each year. About 95% of these deaths occur in Asia and Africa.

Most human deaths follow a bite from an infected dog and 30-60% of victims are children under 15 years. Recently, rabies cases in the US is caused by the rabies virus from bats. Awareness about bats can help people protect themselves their families and their pets

Categories of rabies exposure by WHO