What is a virus?

A virus is basically a nucleic acid (RNA or DNA) wrapped by a protein coat or capsid. Most biologists do not consider them to be alive. Here is a typical definition from Suite 101.com: "Viruses are acellular non-living particles...incapable of carrying out all life processes."

There is some disagreement, however, and it begins with the definition of life itself. The University of Cape Town (South Africa), in its on-line course on the Introduction to Virology, defines an organism as "the unit element of a continuous lineage with an individual evolutionary history." By this definition, viruses can be considered organisms because they do replicate and have a traceable evolutionary history.

Whether considered living or non-living, viruses are efficient parasites of plants and animals. The diagram above, taken from Wikipedia, shows a typical virus replication cycle. It begins with the virus attaching itself to a suitable cell, followed by the injection of the viral genetic material into the cell. Once inside, the virus comandeers the cell's machinery to assemble the building blocks needed to produce new virus particles.

The encoded hereditary information, or genome, inside a virus particle is incredibly diverse, a greater variety of structures than those found in plants, animals or bacteria. In addition, viruses may change their genetic code through mutation, or simple errors in copying the RNA or DNA that make up the virus. They may also "reassort" or swap genetic information with another virus strain to create a new, drug-resistant one. This is what scientists believe happened with the current flu bug affecting Mexico. It is actually a mixture of genetic information from swine, avian and human inluenza viruses.

Given this genetic complexity, the identity of a virus is diffiucult to nail down. Health authorities in Mexico have had to send samples from flu victims to Winnipeg, Manitoba or to the Center for Disease Control and Prevention in Atlanta, Georgia for confirmation. This is one of the reasons that it has been so difficult to get clear data about the number of people infected with the new virus or the mortality rate it has caused.

In today's press conference, Health Secretary José Angel Córdova announced that Mexico is in the process of establishing six new laboratories that will be able to speed up the identification process. Hopefully, these new resources will be able to give us a clearer picture of the status of the outbreak and the possiblities of resuming a more normal routine next week.