There are between 60 to 70 of them. They include yellow fever, St. Louis encephalitis, dengue, Japanese encephalitis, tick-borne encephalitis, and a lot of others you’ve probably never heard of.

The mouse allele that bestows resistance to flaviviruses was originally discovered in the 1920s, but it wasn’t until late in the 1960s that it was appreciated that those viruses to which this gene gave resistance were related and were all flaviviruses. Although any of a number of flaviviruses could have been used for these studies, I used West Nile virus because it was considered a relatively safe flavivirus as compared with the others. Most people with normal immune systems don’t develop disease after infection. The other reason I used West Nile virus was because it grew efficiently in mice and in cell cultures.

The ultimate goal is to find out how the product of the resistance allele confers resistance to flaviviruses. This is a naturally occurring mutation in a cell protein that reduces the replication efficiency of a particular type of virus. This suggests that the interaction of cell proteins and viral products is important in determining the amount of virus that is made by an infected cell. In animals, the production of lower levels of virus results in a slower spread of the infection and gives the host immune response time to develop and clear the virus before it overwhelms the host. Since techniques were not available to clone the resistance gene until recently, early studies were aimed at trying to identify the gene product by its presumed association with viral components. Since the effect of the gene product seemed to be at the level of viral RNA replication, initial studies investigated the increased production of defective interfering viral RNAs by resistant cells. We next tried to identify cell proteins that might be associated with purified viral replication complexes to see if they differed in resistant and susceptible cells. Because of the difficulties encountered in purifying intact viral replication complexes from cell membranes, the focus of the study was changed to identifying cell proteins that interacted with the 3’ promoter regions of the viral RNAs. The initial results of these studies were published in the 1995 highly cited paper.

That was the first report of the detection of cell proteins that were interacting specifically with a flavivirus 3’ RNA. A subsequent paper reported the identification of one of these proteins as a cell translation factor, elongation factor 1 alpha. However, the demonstration of an interaction doesn’t tell you how the particular cell protein is being used by the virus during its replication cycle. We are in the process of addressing this question now.

Our recent data shows that the interaction between flavivirus genomic RNA and this cell protein is definitely relevant for the virus replication, but we do not yet understand what functions it provides for the virus.

I have actually worked on a number of different projects as well as other viruses over the years, but have continued to study West Nile host-virus interactions and genetic resistance to flaviviruses. Sometimes it is necessary to wait until new techniques become available before you can move forward with a project. In my lab, Dr. Andrey Perelygin recently cloned the flavivirus resistance gene. This discovery has opened the door for many new avenues of study. Although we now know the identity of the gene, we do not yet understand how it specifically reduces flavivirus genomic RNA levels in infected cells.

Dramatically. The number of invitations to write reviews and to give talks has definitely increased and I now get large numbers of e-mail requests for West Nile virus information. This is also partly due to the fact that I wrote an article on West Nile for Annual Review of Microbiology this year. Interestingly, many people think that I suddenly have gotten a lot of grant money because I’ve been working on West Nile for so long. The truth is most of the available funding for West Nile virus in the U.S. has so far gone to support epidemiology, vaccine development, and setting up health departments for surveillance and testing. Very little has yet trickled down to basic research, but I think that in the next year or two that will probably begin to change.

As for me personally, the first thing that happened when West Nile virus arrived in Georgia was that I got called at six in the morning by a news radio station. They wanted to know what kind of mosquito spray people should be using.

Oh yes, there are many new areas for research on West Nile virus and flavivirus genetic resistance that we are perusing. We hope that our studies will eventually lead us to an understanding of the connection between the resistance gene product and viral RNA transcription. We are also analyzing mechanisms used by West Nile virus for regulating transcription and translation.

Well, I was surprised, but not greatly. West Nile virus was first isolated in the 1930s in Africa where it has been endemic for a very long time. Infected birds have periodically carried it across the Mediterranean to Southern Europe and Turkey where local transmission occurred for a single season. So the idea that this virus could initiate a local transmission cycle after being brought to a new geographic region was not surprising. Although it will never be known for sure, it is possible that West Nile virus was brought to the United States on a plane in an infected mosquito or bird. What was surprising was that the virus successfully over-wintered in the United States in 1999. Once the virus had survived that first winter, we all knew it would spread across the United States and into Canada as well as Central and South America because there are no natural barriers.

I really think that understanding the intracellular interactions between a virus and its host cells at the molecular level will help in the development of effective new therapies for flavivirus infections.

Margo A. Brinton, Ph.D.
Department of Biology
Georgia State University
Atlanta, GA, USA