Former Council of Agriculture (COA) minister Chen Wu-hsiung (陳武雄) recently said at a press conference that the high pathogenicity of H5N2 avian flu is determined by the number of infected chickens that die. He also questioned the significance to chicken farmers and the public of Intravenous Pathogenicity Index (IVPI) data and data on the number of DNA basic amino acids. Chen seems to have gotten his facts wrong, because the World Organisation for Animal Health (OIE) offers clear regulations in the form of two indicators for determining the presence of highly pathogenic H5N2. The first indicator is that the IVPI is greater than 1.2, and the second is that the number of basic amino acids between the H and N genes in the avian flu virus is greater than two.
The number of clinically dead chickens is only provided as a reference. This is because if there is no previous resistance against H5N2 among the chicken population, the death rate among those infected by the highly pathogenic H5N2 virus will be very high.
If, however, the chicken population has been previously infected by H5N2, the chickens will be carrying H5N2-resistant antibodies and the death rate will not be very high even in the case of a highly pathogenic strain of the virus. Furthermore, egg production will not drop by much. This is why it is incorrect to use the death rate to determine pathogenicity.
Low-pathogenicity H5N2 was detected at a Taiwanese chicken farm for the first time in 2004, but although 380,000 chickens were killed, the virus was not wiped out. In 2008, another 200,000 were killed. Since the virus has been spreading for several years, many chickens should have developed H5N2 antibodies. This means that when a highly pathogenic strain of H5N2 breaks out, the death rate will not be very high.
The IVPI for chickens is arrived at by testing for infection in chickens that do not have antibodies. If the value is greater than 1.2, it means more than 75 percent of the chickens will die, which of course would constitute highly pathogenic H5N2. These examples all meet the requirements of highly pathogenic avian flu. In a recent meeting, some experts reportedly said that the latest H5N2 infections were highly pathogenic, but after the meeting, the COA disregarded expert opinion and ignored OIE regulations, instead saying that pathogenicity was low because so few chickens died.
Avian flu is a zoonosis — an infectious disease that can be transmitted from animals to humans — that the international community is paying great attention to. Because the avian flu virus is highly variable, any mutation means that people could potentially be infected. In 2006, it was demonstrated in Japan that the H5N2 virus can infect people, and a similar report appeared in Taiwan in 2008. If the avian flu virus mutates and becomes transmissible between humans, there is a risk that a highly pathogenic strain could appear and spread across the globe.
The H1N1 influenza that broke out in Mexico in 2009 infected tens of millions of people around the world in less than six months. The H1N1 flu that started in Spain in 1918 — the “Spanish flu” — caused more than 40 million deaths. Most of the virus’ genes came from the avian flu virus.
If the COA covered up the epidemic, it would have allowed a highly pathogenic avian flu virus to spread across the country. We still cannot tell if this will bring serious harm to chicken farmers or the general public, but we do know that irreparable damage has been done to Taiwan’s international image.
Lai Shiow-suey is an honorary professor in the Department of Veterinary Medicine at National Taiwan University.
Translated by Perry Svensson
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