Ha ha ha virus

Full Sized Infographic and Text Version. Genome sequencing reveals the sequence of the nucleotides in a gene, like alphabet letters in words. Comparing the composition of nucleotides in one virus gene with the order of nucleotides in a different virus gene can reveal variations between the two viruses. Proteins are made of sequences of amino acids. The substitution of one amino acid for another can affect properties of a virus, such as how well a virus transmits between people, and how susceptible the virus is to antiviral drugs or current vaccines.

CDC and other public health laboratories around the world have been sequencing the gene segments of influenza viruses since the s. The sequences deposited into these databases allow CDC and other researchers to compare the genes of currently circulating influenza viruses with the genes of older influenza viruses and those used in vaccines.

This process of comparing genetic sequences is called genetic characterization. CDC uses genetic characterization for several reasons:. Each sequence from a specific influenza virus has its own branch on the tree. Viruses are grouped by comparing changes in nucleotides within the gene. Viruses which share a common ancestor can also be described as belonging to the same clade.

The degree of genetic difference number of nucleotide differences between viruses is represented by the length of the horizontal lines branches in the phylogenetic tree.

The further apart viruses are on the horizontal axis of a phylogenetic tree, the more genetically different the viruses are to one another. The changes associated with antigenic drift happen continually over time as flu viruses replicate i. The small changes that occur from antigenic drift usually produce viruses that are closely related to one another, which can be illustrated by their location close together on a phylogenetic tree. Flu viruses that are closely related to each other usually have similar antigenic properties.

However, the small changes associated with antigenic drift can accumulate over time and result in viruses that are antigenically different further away on the phylogenetic tree. It also is possible for a single change in a particularly important location on the HA to result in antigenic drift. Antigenic drift is an important reason why people can get flu more than one time. Drift is also a primary reason why the composition of flu vaccines for use in the Northern and Southern Hemispheres is reviewed annually and updated as needed to keep up with evolving flu viruses.

Avian influenza viruses rarely infect people. The most frequently identified subtypes of avian influenza that have caused human infections are H5, H7 and H9 viruses. H7 virus infection in humans is uncommon. The most frequently identified H7 viruses associated with human infection are Asian lineage avian influenza A H7N9 viruses, which were first detected in China in While human infections are rare, these have commonly resulted in severe respiratory illness and death.

Rare, sporadic H9N2 virus infections in people have been reported to generally cause mild upper respiratory tract illness; one infection has results in death. Skip directly to site content Skip directly to page options Skip directly to A-Z link. Influenza Flu. Section Navigation. Most antibody responses against HA are strain-specific. However, antibodies that have neutralizing activities against multiple strains or even subtypes have now been discovered and characterized.

These broadly neutralizing antibodies bnAbs target conserved regions on HA, such as the receptor-binding site and the stem domain.