West Nile Virus: Structure and Function

Instructor: Wendy McDougal

Wendy has taught high school Biology and has a master's degree in education.

The West Nile virus is an illness transmitted by mosquitoes. Individuals infected with this virus may be completely asymptomatic, or end up with extreme complications.

A Virus-Transmitting Insect

There are many ways in which we can get sick. Viruses and bacteria are resourceful organisms, entering into our bodies by a variety of methods. If you get sneezed on, viruses can enter through your mouth or nose. Touch a toilet in the wrong place, and bacteria hitches a ride on your hand. Contact someone else's blood with your open cut, and a blood borne pathogen may have been transferred.

But did you know that insects can also make us sick? In fact, one in particular is known to carry within it a tiny virus, just waiting to enter our bodies.

A mosquito, transmitter of West Nile virus
Mosquito

The mosquito, infamous for its transmission of malaria, is a primary carrier of the West Nile virus. Originating in Africa, this exotic-sounding virus is harbored, carried, and transmitted by these pesky insects. Effects of this virus vary tremendously from person to person, and in a very small percentage are catastrophic. In this lesson, learn more about the structure and function of the West Nile virus, as well as its effects.

Characteristics of a Virus

Before we look at the specifics of the West Nile virus, let's take a look at some general characteristics of viruses. As you may know, viruses behave in some ways like living organisms, but it's a debate as to whether to consider them actually alive. Viruses are infectious agents often hosted by animals - they have their own genetic information, but can only reproduce by exploiting the bodies of other living hosts.

West Nile virus as seen under scanning electron microscope
West Nile Virus

Structure of a West Nile Virus

What does the West Nile virus actually look like? The composition of the virus has some surprising similarities to a peanut M&M. First we find the outer layer of the virus, which is a lipid bilayer known as an envelope. We can compare this to the chocolate layer in our M&M. However, instead of a smooth candy surface, on the virus we would see spiky glycoproteins projecting out from the envelope. These proteins will help the virus bind to the cells of its host.

General structure of West Nile virus
Virus structure

Like the prized peanut hidden in our M&M, tucked safely in the center of the virus is the core, which is called the nucleocapsid The nucleocapsid is made up of two parts.

  1. First is the protein shell, known as the capsid. Like a treasure chest, this structure protects the precious cargo inside.
  2. The second part of the nucleocapsid is genetic information in the form of single-stranded RNA.

Looking closer at the capsid, we see that it is not simply a round bubble which holds the RNA. This protein shell is quite an advanced structure, known as an icosahedron. For those of you who are not geometry buffs, an icosahedron is an object with twenty flat faces. Perhaps a unique structure, it serves to allow for plenty of room for the all-important RNA.

A twenty-faced icosahedron
icosahedron

Function of West Nile Virus

Virus's seems to have one purpose: to infect the cells of new hosts and replicate. The West Nile virus is no exception. Hosted in birds such as the American Robin, this virus is transferred to mosquitoes that bite infected birds. The virus then replicates within the mosquito, eventually congregating in the salivary glands of the insect. This is a smart move, because when the needle-like proboscis of the mosquito enters the skin of an animal or human's body, the virus is successfully injected.

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