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New research shows a second strain of West Nile virus has overtaken the original strain, and appears to be more virulent than the first, especially in hot weather.
In an interview with the Daily Herald, experts from the Centers for Disease Control said that while the second strain, first detected in 2001, now appears to spread "better and earlier," those results are based on laboratory research and may not reflect what happens in the real world.
More research is needed, said Dr. Marc Fischer of the CDC, and the public should not panic based on the research results.
New research on the second West Nile strain was recently published in a CDC-funded scientific journal called PLoS Pathogens and is available at www.plospathogens.org.
According to a summary of the research paper published by the journal, West Nile virus first appeared in the U.S in New York City in 1999. A new second strain was first detected in 2001 and has subsequently spread across North America. This second strain is "more efficient at infecting and being transmitted" by West Nile-carrying mosquitoes than the original strain.
According to the journal, "the advantage" of the new strain over the original strain "increased with both temperature and time. Thus, warmer temperatures would have facilitated the invasion of the [new] strain."
The results of the research show that both temperature and evolution over time of the second strain "influence the distribution and intensity of transmission of West Nile virus."
Both county and state health officials referred all questions about the second strain of West Nile to the Centers for Disease Control.
Fischer, of the CDC, called the PLoS Pathogens research "a very interesting study, but I think we need to be very careful about drawing conclusions about human health from this."
The research studied replication and transmission of the virus "in a laboratory and not in people in a field setting," he said.
And while the research shows the new strain of West Nile has replaced the original strain and the new strain replicates faster in the kind of hot weather that the West is known for during summer, "there is nothing in the article about the severity of human disease or increased human death."
On the contrary, the highest number of national West Nile infections was in 2003 and the number of serious neuro-invasive cases of the disease has been "relatively stabile," Fischer said. "No one should panic."
Infobox:
2007 West Nile facts (latest available data from the Centers for Disease Control)
• In 2007, West Nile expanded into 19 counties in the U.S. where it had not been previously reported, and recurred in 1,148 counties.
• A total of 1,227 neuro-invasive cases of West Nile and 117 deaths were reported nationally. The median age of neuro-invasive patients was 57 years old. The median age of those who died was 77.
• North Dakota had the most cases of West Nile in the nation. Utah did not rank in the top five.
• 2,182 dead West Nile-infected birds were reported from 315 counties in 35 states and Puerto Rico. |
