First case of highly pathogenic H5N2 avian influenza confirmed in Taiwan, China
↑This image is a screenshot from documentary director Lee Hui-jen's latest work, "The Secret That Cannot Be Stamped - The Case of the Missing Virus"
When the Director-General and Deputy Director-General of the Bureau of Animal and Plant Health Inspection and Quarantine (BAPHIQ) were asked by reporters from NewsMarket by phone last night (March 2) to verify whether an outbreak of highly pathogenic avian influenza had occurred, they did not directly deny it. It is understood that senior officials of the Council of Agriculture recently held closed-door meetings to conduct scenario planning and response measures regarding the potential impact on animal disease prevention, the poultry industry, and political effects if Taiwan were removed from the "highly pathogenic avian influenza-free zone" for East Asia. Especially at a time when the ractopamine issue is still raging, the highly pathogenic avian influenza outbreak that immediately followed is yet another test for the newly appointed Council of Agriculture Minister Chen Bao-ji.
According to the definition of the World Organisation for Animal Health (OIE), so-called highly pathogenic avian influenza (HPAI) is determined by two methods: the intravenous pathogenicity index (IVPI) of H5 or H7 virus strains, and analysis of the basic amino acid sequence at the HA cleavage site. When experimentally infected chickens inoculated intravenously show a mortality rate of 75% or more, or an IVPI greater than 1.2, it is designated as HPAI. If the intravenous inoculation mortality rate of chickens is less than 75% or the IVPI is below 1.2, the amino acid sequence at the HA protein cleavage site of the virus must be interpreted to determine whether the virus poses a potential threat.
BAPHIQ Director-General Hsu Tien-lai said last night (March 2) only that this case involved an epidemiological investigation team jointly formed at the end of December last year by the Changhua County Animal Disease Control Center, the Animal Health Research Institute, and avian disease experts, based on locations of abnormal chicken deaths reported by the public, conducting sampling at nearby suspect chicken farms and epidemiological investigation of surrounding poultry farms.
The member of the public referred to by Hsu Tien-lai was documentary director Lee Hui-jen, whose film "The Secret That Cannot Be Stamped" covered the chicken death incident discovered on December 25 last year at a laying hen farm in Fangyuan, Changhua. In his latest documentary, "The Secret That Cannot Be Stamped - The Case of the Missing Virus," Lee Hui-jen had sent specimens from the dead chickens he collected to the BAPHIQ of the Council of Agriculture.
According to a press release issued by BAPHIQ on January 2 this year, titled "Launching Epidemic Investigation of Poultry Farms in Changhua Area and All Counties and Cities, Strengthening Visits and Sampling Work, No Abnormal Deaths Found," the on-site epidemic investigation results at that time showed that the laying hens in the farm were normal, with no clinical symptoms of abnormal death or decreased egg production. However, when Hsu Tien-lai was interviewed by the media at that time, he admitted that some live chickens were found to have H5N2 virus antibodies in their bodies, indicating past infection with avian influenza, and based on clinical judgment considered it to be low pathogenicity, but for the sake of caution, still sent the collected specimens to the Animal Health Research Institute for virulence testing.
It is understood that the virulence test results have already been released. The Animal Health Research Institute inoculated the collected H5N2 virus antibodies into specific-pathogen-free (SPF) chicken embryonated eggs for propagation, and then inoculated the collected virus fluid into 10 specific-pathogen-free (SPF) chicks, observing and recording daily the number of normal, sick, and dead birds. It was found that the intravenous inoculation mortality rate of the experimental chickens exceeded 75%, and the virus strain pathogenicity index (IVPI) was also greater than 1.2, already meeting the OIE definition of highly pathogenic avian influenza (HPAI).
However, BAPHIQ Director-General Hsu Tien-lai stated that the Animal Health Research Institute's report still awaits interpretation and judgment by officials and experts at a meeting. He did not directly respond as to whether it was highly pathogenic avian influenza, saying only that for the sake of caution, it was still under judgment, and that the relevant information had been reported to the World Organisation for Animal Health in accordance with regulations.
The reporter then turned to BAPHIQ Deputy Director-General Huang Kuo-ching by phone for verification. Huang Kuo-ching hesitated for a few seconds on the phone, then in surprise asked the reporter where the information came from, said with embarrassment that he was not authorized to speak publicly on this matter, and immediately hung up the phone.
If this case is confirmed as highly pathogenic avian influenza, it will be Taiwan's first occurrence. However, the virus strain H5N2 differs from H5N1, which has broken out in other Asian countries such as China, Hong Kong and Japan, South Korea, and Southeast Asia. H5N1 highly pathogenic avian influenza is extremely virulent, not only causing high mortality rates in poultry and wild birds, but China, Hong Kong, and Vietnam have even experienced public health incidents of human infection and death from H5N1 avian influenza.
As of today (March 3), Council of Agriculture Deputy Minister Wang Cheng-teng, BAPHIQ Director-General Hsu Tien-lai, and Animal Health Research Institute Director Huang Chin-cheng jointly held a press conference at 10:30 AM, confirming that the H5N2 avian influenza virus strains found at the Changhua Fangyuan chicken farm and the Tainan Liujia broiler farm have a very high potential for highly pathogenic avian influenza. Among them, the three H5N2 specimens collected from the Changhua Fangyuan chicken farm showed pathogenicity index (IVPI) values of 2.69, 2.01, and 0.16 respectively in laboratory tests, with two exceeding the OIE standard of pathogenicity index (IVPI) 1.2 for determining highly pathogenic virus strains; hemagglutinin HO cleavage site nucleic acid sequence analysis showed 4 basic amino acids, consistent with highly pathogenic characteristics. Although on-site clinical investigation showed normal egg production and mortality rates in the chickens, a comprehensive judgment by an expert meeting determined it to be highly pathogenic, and on the morning of March 3, an order was issued to cull all 53,000 laying hens at the farm.
As for the H5N2 avian influenza virus found at the Tainan Liujia chicken farm, it was traced back after a local disease control agency discovered it on February 7 at a poultry slaughterhouse in Yunlin. On February 9, local disease control agencies found increased chicken mortality in clinical investigation, and the next day carried out preventive culling and clearing, culling a total of 4,500 broiler chickens. Analysis of the two specimens collected from that farm showed pathogenicity index (IVPI) values of 2.60 and 2.53 respectively, exceeding the OIE standard of pathogenicity index (IVPI) 1.2 for determining highly pathogenic virus strains. After comprehensive discussion by an expert meeting, it was determined to be highly pathogenic.
↑(From left to right) BAPHIQ Director-General Hsu Tien-lai, Council of Agriculture Deputy Minister Wang Cheng-teng, and Animal Health Research Institute Director Huang Chin-cheng hold a press conference with grave expressions.
While Taiwan's previous monitoring of migratory bird droppings and poultry farm epidemics did not find highly pathogenic H5N1 avian influenza virus, after the first case of H5N2 low pathogenic avian influenza was discovered at a laying hen farm in Changhua County at the end of December 2003, the epidemic continued until February 2004, with a total of 21 farms testing positive for the virus. Experiments by the Animal Health Research Institute showed that the H5N2 virus strain isolated during that outbreak had an IVPI value close to 0.0, with almost no pathogenicity to chickens, but subsequently in 2008, the H5N2 virus strain isolated from Kaohsiung had an IVPI value that increased to 0.89, clearly showing that the virus already existed in Taiwan's environment and continued to mutate as chickens reproduced over generations, causing the IVPI value to continuously increase.
Unlike other Asian countries where poultry outbreaks of H5N1 highly pathogenic avian influenza are mostly transmitted through migratory bird migration, the pathogenic pathway of the H5N2 low pathogenic avian influenza outbreak in Taiwan in 2003 is inferred to have very likely been caused by the administration of inferior vaccines. Domestic research has pointed out that the gene composition of the H5N2 low pathogenic avian influenza virus strain isolated in Taiwan in 2003 is a reassortant virus with surface antigens of the American virus group and internal structures of the Eurasian virus group. Based on evidence of viral evolution and the virus's major antigens, it is believed to have high similarity and identical characteristics with the virus strains currently used internationally for vaccine production, indicating that the H5N2 low pathogenic avian influenza virus strain isolated in Taiwan in 2003 was not a naturally occurring virus strain.
According to data from the Animal Health Research Institute, the clinical symptoms of poultry infected with avian influenza vary greatly, ranging from asymptomatic, mild respiratory symptoms and decreased egg production to severe clinical symptoms and even death. Based on the disease type presented, avian influenza can be classified into low pathogenic avian influenza (LPAI) and highly pathogenic avian influenza (HPAI).
Avian influenza viruses are classified into 16 different HA subtypes (H1-H16), of which only H5 and H7 subtypes are associated with highly pathogenic avian influenza. In recent years, many outbreak cases have confirmed that after H5 and H7 subtype low pathogenic avian influenza (LPAI) viruses enter poultry farms, they can mutate into highly pathogenic avian influenza (HPAI) viruses, such as the H5N2 outbreak in Pennsylvania, USA, the H5N2 outbreak in Mexico, and the H7N1 outbreak in Italy. The evolution of the H5N2 virus in Taiwan is similar to the cases in Pennsylvania, USA, and Mexico.
Further Reading
Lee Hui-jen: The Latest "The Secret That Cannot Be Stamped" - The Case of the Missing Virus