Department of Energy Argonne National Laboratory Office of Science NEWTON's Homepage NEWTON's Homepage
NEWTON, Ask A Scientist!
NEWTON Home Page NEWTON Teachers Visit Our Archives Ask A Question How To Ask A Question Question of the Week Our Expert Scientists Volunteer at NEWTON! Frequently Asked Questions Referencing NEWTON About NEWTON About Ask A Scientist Education At Argonne Flu codes
Name: Richard
Status: Educator
Grade:  Other
Location: N/A
Country: United States
Date: February 2006

My students have asked "What to the letters and numbers mean in the bird flu H5N1? Are they just a code or do they means anything? If they are a code how are viruses numbered?"

The numbers refer to the types of antigens/proteins that are found on their surface. These are proteins that allow the virus to attach and enter the host cell. Because there is variety in all proteins and they mutate over time, there are different versions of each protein. The N stands for neuraminidase and the H stands for hemaglutinin. So H5N1 is a virus that has the "5th" type of H gene and the "1st" type of N gene. I don't know if they are named in the order in which they were discovered. What scientists worry about is that more than one of these viruses can inhabit a host cell at the same time. If one is the H5N1 version that so far only infects birds and can't spread from human to human, and another is say H3N2, which is able to spread between humans are inhabiting the same cell and exchange parts, the bird flu would be able to spread from person to person. Viruses mutate very rapidly and there is nothing that says it WILL do this-it may never happen. But it COULD happen, and it is good that the CDC and the WHO are monitoring the situation and trying to be prepared in case it does. Here is a link to a good animation that shows how this process could take place:


Click here to return to the Molecular Biology Archives

NEWTON is an electronic community for Science, Math, and Computer Science K-12 Educators, sponsored and operated by Argonne National Laboratory's Educational Programs, Andrew Skipor, Ph.D., Head of Educational Programs.

For assistance with NEWTON contact a System Operator (, or at Argonne's Educational Programs

Educational Programs
Building 360
9700 S. Cass Ave.
Argonne, Illinois
60439-4845, USA
Update: June 2012
Weclome To Newton

Argonne National Laboratory