What shape capsid is influenza?

By electron microscopy, influenza A and B viruses are virtually indistinguishable. They are spherical or filamentous in shape, with the spherical forms on the order of 100 nm in diameter and the filamentous forms often in excess of 300 nm in length.

What is the basic structure of an influenza virus?

The influenza particle, or virion, is typically spherical, but sometimes filamentous. It has an outer lipid membrane layer called an envelope derived from the host cell that it replicated in. The envelope is covered with glycoproteins HA and NA which form structures like spikes.

Is influenza helical or icosahedral?

In fact, most plant viruses are helical, and it is very uncommon that a helical plant virus is enveloped. In contrast, all helical animal viruses are enveloped. These include well-known viruses such as influenza virus, measles virus, mumps virus, rabies virus, and Ebola virus (Fig. 2.5 ).

What is unique about the influenza virus?

Despite 50 years in intense research, influenza remains unique as the only truly pandemic viral infection of humans. In addition, although vaccines against this disease have been developed and used for the past four decades, they remain less effective than those used against other viral infections.

What is the capsid of a virus?

Viral capsids are the protein cage derived from the protein shell of a virus, and can have different shapes, sizes, and protein subunits, depending on the virus type [101].

Does the influenza virus have an envelope?

The influenza virion is an enveloped virus that derives its lipid bilayer from the plasma membrane of a host cell. Two different varieties of glycoprotein spike are embedded in the envelope.

How many subtypes of flu are there?

There are 18 different HA subtypes and 11 different NA subtypes. Subtypes are named by combining the H and N numbers – e.g., A(H1N1), A(H3N2). Click on the image to enlarge the picture. There are four types of influenza viruses: A, B, C and D.

Are capsids infectious?

The capsid enclosing nucleic acid is referred to as nucleocapsid, which can be considered as an infectious and functional virus. Envelope—In some viruses, the nucleocapsid is covered with another layer of proteins and fats called as glycoproteins.