The rabies virus is a neurotropic pathogen that leads to rabies in both animals and humans. Globally, rabies causes an estimated 59,000 deaths annually. While present on all continents except Antarctica, most human cases are reported in Asia and Africa. The virus is transmitted through the saliva of infected animals, most often via bites.
Defining the Rabies Virus Shape
The rabies virus is known for its distinctive bullet-shaped or cylindrical morphology. This unique appearance is a defining characteristic of the Rhabdoviridae family. This shape helps distinguish it from many other viruses.
The virus measures approximately 180 nanometers in length and 75 nanometers in width. This bullet-like form is maintained by its internal components, which are organized to support this specific structure.
The Protective Outer Layer and Its Spikes
The outermost layer of the rabies virus is an envelope, a lipid bilayer derived from the host cell’s membrane during the budding process. This envelope provides a protective covering for the viral components within. Embedded within this lipid envelope are numerous glycoprotein (G protein) spikes that protrude from the surface of the virus.
These G protein spikes are important for the virus’s ability to cause infection. They serve as the primary means by which the rabies virus attaches to and enters host cells. The G protein is also significant because it induces the host’s immune response, making it a target for vaccine development.
Unpacking the Inner Core and Genetic Blueprint
Beneath the outer envelope lies the matrix protein (M protein), which forms a layer that helps maintain the bullet shape of the virus and facilitates the assembly of new viral particles. This protein acts as a bridge, connecting the outer envelope to the inner nucleocapsid. The nucleocapsid is a helical structure that contains the virus’s genetic material.
The genetic blueprint of the rabies virus is a single-stranded, negative-sense RNA molecule. This RNA genome is tightly bound by the nucleoprotein (N protein), forming a ribonucleoprotein complex. Also associated with this complex are two viral enzymes: the phosphoprotein (P protein) and the large protein (L protein), which is an RNA polymerase. These proteins are essential for the virus to replicate its RNA and transcribe its genes once it has entered a host cell.