Kansas State University
The strains have led to the culling of
millions of commercial chickens and turkeys as well as the death of hundreds of
people.
The
new vaccine development method is expected to help researchers make vaccines
for emerging strains of avian influenza more quickly. This could reduce the
number and intensity of large-scale outbreaks at poultry farms as well as curb
human transmission.
It
also may lead to new influenza vaccines for pigs, and novel vaccines for sheep
and other livestock, said Jürgen Richt, Regents distinguished professor of
veterinary medicine and director of the U.S. Department of Homeland Security's
Center of Excellence for Emerging and Zoonotic Animal Diseases.
"H5N1
is a zoonotic pathogen, which means that it is transmitted from chickens to
humans," Richt said. "So far it has infected more than 700 people
worldwide and has killed about 60 percent of them. Unfortunately, it has a
pretty high mortality rate."
Researchers
developed a vaccine for H5N1 by combining two viruses. A vaccine strain of the
Newcastle disease virus, a virus that naturally affects poultry, was cloned and
a small section of the H5N1 virus was transplanted into the Newcastle disease
virus vaccine, creating a recombinant virus.
Tests
showed that the new recombinant virus vaccinated chickens against both
Newcastle disease virus and H5N1.
Researchers
also looked at the avian flu subtype H7N9, an emerging zoonotic strain that has
been circulating in China since 2013. China has reported about 650 cases in
humans and Canada has reported two cases in people returning from China. About
230 people have died from H7N9.
"In
Southeast Asia there are a lot of markets that sell live birds that people can
buy and prepare at home," Richt said. "In contrast to the H5N1 virus
that kills the majority of chickens in three to five days, chickens infected
with the H7N9 virus do not show clinical signs of sickness. That means you
could buy a bird that looks perfectly healthy but could be infected. If an
infected bird is prepared for consumption, there is a high chance you could get
sick, and about 1 in 3 infected people die."
Using
the same method for developing the H5N1 vaccine, researchers inserted a small
section of the H7N9 virus into the Newcastle disease virus vaccine. Chickens
given this recombinant vaccine were protected against the Newcastle disease
virus and H7N9.
"We
believe this Newcastle disease virus concept works very well for poultry
because you kill two birds with one stone, metaphorically speaking," Richt
said. "You use only one vector to vaccinate and protect against a selected
virus strain of avian influenza."
Using
the Newcastle disease virus for vaccine development may extend beyond poultry
to pigs, cattle and sheep, Richt said.
Researchers
found they were able to protect pigs against an H3 influenza strain by using
the Newcastle disease virus to develop a recombinant virus vaccine. Wenjun Ma,
Kansas State University assistant professor of diagnostic medicine and
pathobiology, is building on this finding and using the Newcastle disease virus
to make a vaccine for porcine epidemic diarrhea virus, a disease that has
killed an estimated 6 million pigs.
Richt
conducted the avian influenza study with Ma, Adolfo Garcia-Sastre at the Icahn
School of Medicine at Mount Sinai in New York, and several other colleagues.
They published their findings in the Journal of
Virology study,
"Newcastle disease virus-vectored H7 and H5 live vaccines protect chickens
from challenge with H7N9 or H5N1 avian influenza viruses." It is the first
study to look at an H7N9 vaccine in chickens, the animals the disease
originates in.