China's New Bird Flu Vaccine
Capable Of Prevention

From Patricia Doyle, PhD
By Zhao Huanxin China Daily
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."
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.
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.
"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.
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.
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.
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.
Hundreds of wild birds have died of avian influenza in central Thailand in the past 2 weeks.
Article submitted by:
Mark Schipp Agriculture Counsellor Australian Embassy, Beijing
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
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