- Chinese scientists claim to have developed a vaccine
to prevent the spread of the killer bird flu. The Ministry of Agriculture
says its new vaccine can effectively "cut a key link in the transmission
chain of highly pathogenic avian influenza among water fowl."
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- Using a technique called reverse genetics, scientists
at the Key Laboratory of Animal Influenza, affiliated with Harbin Veterinary
Research Institute, altered the genome sequence of the virus to construct
a vaccine that is believed to be safe for both poultry and mammals. The
vaccine will be administered to fowl in the country's key water areas,
including rivers and lakes, a ministry statement released yesterday [6
Feb 2005] said.
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- Laboratory tests show the vaccine enabled ducks and geese
to fight H5N1, the highly lethal strain of bird flu, 3 weeks after the
flocks were vaccinated, the statement claimed. The new vaccine also provides
at least 10 months of protection for chickens, 4 months longer than the
existing bird flu preventive drugs.
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- "China has developed and mass-produced shots targeting
H9 and H5N2, the less dangerous subtypes of avian influenza," Xu Shixin,
a division director of the Veterinary Bureau of the Ministry of Agriculture,
said yesterday [6 Feb 2005]. The bureau has released a certificate for
the new vaccine as a registered veterinary drug.
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- Ministry sources said the new vaccine had overcome the
bottleneck in the technology of developing a remedy for preventing "highly
pathogenic bird flu."
-
- Apart from the encouraging laboratory test results, field
tests also indicate that upon receiving 2 shots of the vaccine, ducks and
geese can each produce antibodies effective for 10 months and 3 months,
respectively. The birds could then fight the H5N1 strain of the virus.
"The vaccination thus makes it impossible for ducks and geese to become
the load of H5 subgroup bird flu virus. Therefore, it can cut a key link
for the highly pathogenic avian influenza to spread," said the ministry
statement.
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- China developed advanced bird flu virus test technology
(RT-PCR reagent kit) last April 2004. This can detect H5, H7 and H9 subgroups
of the bird flu simultaneously in several hours.
-
- Vaccination is a must for water fowl and poultry farms
in Chinese regions at high risk, according to a national teleconference
in bird flu prevention on 28 Jan 2005 in Beijing.
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- Elsewhere in Asia, the Cambodian Ministry of Health and
the World Health Organization (WHO) confirmed on Saturday [5 Feb 2005]
that a 25-year-old woman from Kampot Province, who died of respiratory
illness in Viet Nam on 30 Jan 2005, was infected with avian influenza.
This is the 1st human case of avian influenza in Cambodia, according [to]
media reports.
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- Hundreds of wild birds have died of avian influenza in
central Thailand in the past 2 weeks.
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- http://www.chinadaily.com.cn/english/doc/2005-02/07/content_415649.htm
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- Article submitted by:
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- Mark Schipp Agriculture Counsellor Australian Embassy,
Beijing Mark.Schipp@dfat.gov.au
-
- ProMed Mail
-
- Mass-application techniques for live vaccines are preferred
by today's large poultry operations, worldwide. The goal for mass vaccination
is to deliver a minimum of one dose of live vaccine to each bird. Live
virus vaccines may be administered to birds by incorporation in the drinking
water, delivered as a coarse spray, or by intranasal or conjunctival instillation.
-
- Application in drinking water offers the advantages of
lower labor costs, minimal bird stress and -- generally -- stimulation
of good immunity. This administration technique is applied for various
commercial poultry vaccines, against Newcastle disease, Infectious Bronchitis,
Avian Encephalomyelitis, Infectious Bursal Disease and Infectious Laryngotracheitis.
-
- The efficacy of such vaccines depends, besides the immunogenicity
of the vaccines themselves, upon their stability in the drinking water
(i.e. in the presence of certain chemicals or in adverse pH or temperatures),
the water intake of the birds (sometimes requiring initial water withdrawal)
and other factors.
-
- Though administration by drinking water or by aerosols
could have been extremely helpful for mass vaccination of mammals as well,
especially small ruminants in extensive husbandry systems, such mode has
been rarely applied so far. An exception is the Brucella suis S2 live vaccine,
developed in China since 1952 and widely used there since the beginning
of the 1970s to vaccinate sheep and goats. The vaccine is administered
through drinking water.
-
- Regarding the published data on the new, genetically
modified Chinese AI vaccine, its application by drinking water for farmed
poultry might be perfectly feasible, and its use in the field might be
a true and much needed achievement, provided the vaccine's safety for animal
and man and its efficacy have been satisfactorily secured and tested. However,
putting the vaccine into "rivers and lakes" is another story;
it will be interesting to get more information on the research and tests
which will enable such an application.
-
- The above news-wire has been sent also by Mary Marshall,
who is kindly acknowledged. - Mod.AS
-
- The influenza viruses are negative-strand RNA viruses,
and, as such, lack the ability to interact by intermolecular recombination.
As a consequence, the controlled modification of the genetic properties
of such viruses by the introduction of specific mutations into the viral
genome has been difficult to achieve by classical genetic techniques. (The
production of the standard human influenza vaccines depends on the fact
that the influenza virus genome exists in the form of a complement of subunits,
and intact whole genes can be exchanged between viruses multiplying in
the same cell substrate, thereby allowing the rapid selection of progeny
virus with different combinations of antigens, a process known as reassortment.
The final product is used as an inactivated vaccine). The technique of
reverse genetics depends on the synthesis of an infectious DNA copy of
the negative-stranded RNA virus genome, which enables the standard genetic
methodologies of directed mutagenesis and manipulation of DNA genomes to
be applied to an RNA virus. At first, it proved difficult to obtain infectious
DNA clones of negative strand RNA viruses, but the technical break-through
was achieved by Schnell et al. in 1994 with rabies virus, and infectious
DNA clones of most types of negative-strand RNA viruses are now available.
Early progress in the design of an H5N1 vaccine for use in the human population
has been documented previously in ProMED-mail: see, Avian influenza A (H5N1)
virus, human vaccine pros... 20040125.0300 to Avian influenza A (H5N1)
virus, human vaccine (06) 20040410.0975. The scientists at the Harbin Institute
have clearly mastered the technology of reverse genetics and produced a
candidate live attenuated vaccine virus. It remains to be seen whether
they have modified the virus sufficiently to allow it to be administered
to different species and to obtain protective immune responses without
exacerbation of disease. - Mod.CP
-
-
- Patricia A. Doyle, PhD
- Please visit my "Emerging Diseases" message
board at:
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