New West Nile Virus Strain May Worsen Epidemic

Reuters reports on Thursday that that a new strain of the West Nile Virus is spreading better and earlier across the country. This new strain may thrive on hot American Summers.

According to a second team of researchers, a new strain has already completely overtaken the original strain. This new West Nile Virus strain is reportedly better suited to hotter weather. This means that outbreaks may worsen up north.

According to Lyle Petersen who helps lead the West Nile surveillance at the CDC, this also means that the outbreak will be worse in North America Compared to any part of the world.

The West Nile Virus was first introduced to the U.S. in 1999. It was during a particularly hot summer in New York City.

Compared to the rest of the world, the pattern of the outbreak in the U.S. is quite unusual. In a phone interview, Petersen said "In Europe, Africa and West Asia, where the virus was previously endemic, you’d see these big outbreaks and then they’d kind of disappear and then not come back for years on end. What we have seen in the United States, we’ve had repeated outbreaks every single year since 2002 — in fact, big outbreaks. This is an unusual pattern that not been seen before."

Petersen and Marm Kilpatrick of the Consortium for Conservation Medicine and the University of California Santa Cruz may have found the culprit – Hot American Summers.

The New West Nile Virus Strain

In their writing in the Public Library of Science journal PLoS Pathogens earlier this week, Kilpatrick and colleagues said they showed the new strain, first seen in 2002, replicates faster inside the bodies of mosquitoes when it’s warm.

In a phone interview, Kilpatrick said "The warmer the temperature, the faster it replicates in mosquitoes and the faster the mosquito can transmit the virus. "It also indicates that increases in temperatures due to global climate change would have major effects on transmission of the virus."

Petersen and Kilpatrick said it is known that mosquitoes transmit other diseases faster when it’s warm. And in their lab work, Kilpatrick and his colleagues showed that the 2002 strain of the West Nile Virus, does particularly well in warmer temperatures.

"The new strain appears to have evolved naturally," said Petersen. "We can no longer find the 1999 strain. It’s pretty dramatic," he said.

He also added that Kilpatrick’s findings fit in with what the CDC has seen. "What we observed is, at least in temperate climates, these big West Nile Virus outbreaks tend to occur in heat waves" said Petersen. However, he admits that it’s to soon to tell if there are any links between climate change and West Nile Virus.

Kilpatrick shares his findings, "If it gets too warm, mosquitoes die sooner, before they can spread the infection". He believes that in southern states, the new strain may not have an advantage since the temperatures would be too high. But in northern states and Canada, hot summers could make a big difference.

"It is probably going to push the northern boundary farther north," Kilpatrick predicts.

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