快猫短视频

A DNA vaccine that protects horses against a deadly virus has been developed
by a team of researchers in Colorado. The work could pave the way for a human
vaccine.

Two years ago, a wave of West Nile virus infection took New York City by
surprise, killing seven people and making dozens of others sick. Many wild birds
succumbed to the virus, as did dozens of horses. And last year, an outbreak in
southern France killed about twenty horses.

Because there has been no vaccine against the virus, public health efforts
have focused on controlling mosquitoes, which spread the disease. But Jeffrey
Chang of the Centers for Disease Control and Prevention in Fort Collins,
Colorado, says that while the West Nile outbreak was unexpected, the virus
itself looks familiar. West Nile is part of a family that includes Japanese
encephalitis, and Chang鈥檚 team was already designing vaccines against that
virus.

Chang works on DNA vaccines, which contain viral genes. When the DNA is
injected into animals, some of it gets into cells, which then churn out viral
proteins that trigger an immune response. Chang鈥檚 team quickly adapted its
Japanese encephalitis vaccine by adding two West Nile genes for proteins that
assemble themselves into an empty viral shell. 鈥淚t looks like the virus to the
immune system,鈥� says Chang. 鈥淏ut it is completely harmless.鈥�

Within three months, the researchers had showed the vaccine could protect
mice from infection, so they moved on to a more relevant species. Four horses
were given a single injection of the DNA. Thirty-nine days later, mosquitoes
carrying West Nile virus were allowed to bite them. None of the horses developed
any signs of viral replication, fever, infection or sickness. In contrast, the
virus replicated rapidly in seven out of eight unvaccinated horses.

鈥淎nyone can protect a mouse, but the horse result is quite promising,鈥� says
Tom Monath of Acambis, a vaccine company based in Massachusetts. 鈥淢any vaccine
approaches don鈥檛 work in animals of that scale.鈥� Monath鈥檚 company is also
developing a human vaccine based on weakened yellow fever virus containing West
Nile genes. But it hasn鈥檛 reported any results yet.

Chang thinks his vaccine might also protect people and is looking for funding
to test it on monkeys. But it isn鈥檛 yet clear if the risk to human health
warrants spending millions of dollars on clinical trials, he points out.
Meanwhile, next month Chang plans to test his vaccine on American crows to see
if it is versatile enough to protect birds as well.