|
Study: Vaccine can stop poultry from spreading bird flu to each other
(AP)
Updated: 2005-11-29 11:07
Vaccines can keep chickens from dying of bird flu, but can immunized birds
still silently spread infection?
It's an important question, as China and Vietnam vaccinate millions of
chickens in an effort to stamp out a worrisome strain of bird flu called H5N1.
Scientists in the Netherlands put the question to a test _ using vaccines
against a different strain _ and concluded that vaccinating poultry indeed can
block viral spread between birds.
"Vaccination can be an attractive tool to prevent outbreaks of highly
pathogenic AI (avian influenza) viruses in poultry, thereby achieving the aim of
eliminating the source of human infections," concludes lead researcher J.A. van
der Groot of the Netherlands' Central Institute for Animal Disease Control.
Birds catch numerous strains of influenza, but only a few types are
particularly deadly to both fowl and people. Today, the H5N1 strain is the
worst. At least 68 people so far have died from H5N1 in Asia since 2003, almost
all linked to contact with sick birds _ and millions of birds have died or been
slaughtered in an effort to contain the virus. Health experts fear that the bird
flu one day could mutate into a virus that is easily passed from person to
person, sparking a global epidemic.
Hence the interest in chicken vaccines.
Previous research found that vaccination could protect individual chickens
from falling ill with various flu strains. But there have been reports of
asymptomatic chickens shedding virus after vaccination, raising concern.
So van der Groot and colleagues tested two vaccines against the H7N7 bird-flu
strain, by housing infected chickens together with healthy vaccinated ones.
Two weeks after inoculation, both vaccines completely blocked H7N7 spread
between chickens, they reported Monday in Proceedings of the National Academy of
Sciences.
Some transmission occurred one week after vaccination, but the virus'
reproduction rate already had dropped enough that the researchers predict only a
small number of new infections that soon after the shots.
There were marginal differences in effectiveness between the two vaccines,
however, leading the researchers to conclude that poultry vaccines' ability to
stop viral spread should be tested before health authorities choose which one to
use.
The research backs guidelines from the United Nations' Food and Agriculture
Organization, which recommends targeted vaccination of poultry as one measure to
control outbreaks of bird flu _ along with other steps such as culling infected
flocks _ and already warns that it can take two weeks for full protection.
So far, the H5N1 virus has not been found in U.S. birds. If a bird outbreak
did occur here, the Agriculture Department stockpiles poultry vaccine that would
be used to help contain it.
|
