Deadliness Of West Nile Virus Explained

New Scientist ^ | 8-22-2007

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Deadliness of West Nile virus explained

22 August 2007
NewScientist.com news service

A single genetic mutation might explain why West Nile virus has, within a decade, switched from causing relatively mild infections in humans to outbreaks of deadly encephalitis.

The virus, which can pass to humans via mosquitoes that feed on infected birds, didn't pose a serious threat until the mid-1990s, when outbreaks of deadly infection sprang up in Israel, Romania, Russia and eventually North America. Aaron Brault and colleagues at the University of California, Davis, discovered that these new strains have in common a mutation in the gene for helicase - a protein involved in viral replication. The mutation arose independently in each strain, suggesting that it gives the virus a selective advantage.

To confirm their suspicion, the researchers injected American crows with a weak strain of virus engineered to have the helicase mutation. This boosted the death rate from 25 per cent to nearly 100 per cent. The virus also replicated faster, increasing the amount of circulating viral particles by a factor of at least 10,000 (Nature Genetics, DOI: 10.1038/ng2097).

"Mosquitoes feeding on these birds would take in more than 1 million viral particles in a meal," says Brault. This would greatly enhance the efficiency of infection.

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I've read that 90+% of people who get WNV never know it.

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West Nile Virus Decimates Suburban Birds

[Cacique]

btt

[WestSylvanian]

My 62 year old cousin was bitten by a mosquito and developed encephalitis this April. She was dead three days later.

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"My 62 year old cousin was bitten by a mosquito and developed encephalitis this April. She was dead three days later."

That's terrible.

The horses around here have trouble with EEE.

[Pining_4_TX]

I hope I already had it and didn’t know it, consdiering that I have to go out in the back yard almost every evening and chase my daughter’s big, nutty dog back in the house. Sheesh.

[Popocatapetl]

I wonder how it compares to the other prominent encephalitis’, such as equine and St. Louis?

In the desert southwest, we were starting to have a serious problem with encephalitis and dengue fever carrying mosquitoes, until either naturally or artificially, we got a population explosion of dragonflies.

The mosquitoes vanished. I like dragonflies.

[tommix2]

I am taking precautions, using mosquito repellent and sleeping inside a mosquito net, as I am over eighty years old. I was bittten a few weeks ago and had no ill effects so I know that not every mosquito carries the virus.