A seven-day ban on poultry slaughter and transport imposed by the government to prevent and control H5N6 avian influenza expired on Feb. 24. Does this mean the crisis caused by bird flu outbreaks should be considered as over? Reflecting on the nation’s overall disease-control measures, what aspects still need to be improved?
Three disease-control measures adopted by Taiwan since the nationwide outbreaks of avian influenza in 2003 and 2004 have made a strong impression overseas. First, Taiwan handled that first wave of H5N2 low pathogenic avian influenza (LPAI) outbreaks in poultry by a massive culling of all affected flocks.
This prompt action prevented the quick occurrence of highly pathogenic avian influenza (HPAI) viruses mutated from LPAI viruses within one year, as was observed in Philadelphia and Mexico.
Second, after severe acute respiratory syndrome (SARS) broke out in several countries in 2003, the Centers for Disease Control provided workers in poultry and livestock farms and markets with free vaccinations against human influenza, thereby reducing the likelihood of viral genetic reassortment taking place.
Although not many people had these vaccinations during the first few years, vaccination coverage has grown to a record high in the 2016-2017 flu season.
Third, after cases of human infection with H7N9 occurred in China in 2013, Taiwan imposed a complete ban on the slaughter of live poultry at markets before the Ghost Festival.
However, problems might arise if the surveillance system is not sensitive enough and if central government officials do not have a professional mindset about infectious diseases or lack solid frontline field experiences in prevention and control.
This, combined with outdated methods of operating and managing poultry farms, has made it possible for poultry farmers to circumvent government policies, and that in turn makes it easy for avian influenza viruses (AIVs) to spread.
Consequently, the rate of positive results in serological tests for anti-H5 AIV antibodies on layer chickens has risen annually, showing that these weaknesses have allowed the virus to become more prevalent. It also shows that policymakers have overlooked the potential threat of genetic reassortment in segmented influenza viruses.
In early January 2015, Taiwan for the first time experienced large-scale outbreaks of HPAI viruses. These outbreaks involved an unprecedented number of virus subtypes and affected a wide variety of poultry species.
While the genetic sequences of the initial AIV isolates of different H5 subtypes had relatively high identity percentages to those found in wild birds, it should be noted that infections spread from south to north, which does not match the north-to-south direction and timing of migratory wild birds’ arrival in Taiwan.
If an infectious disease reaches a high prevalence and covers a wide area, it indicates a failure in the initial surveillance system (eg, insensitive surveillance system for early detection of AIVs). That is unlike South Korea, Japan and the US, where H5 viruses have been detected in wild birds.
Since then, Taiwan has striven to detect AIVs of different subtypes co-circulating in the same county or on the same farm. This is very important for subsequent disease prevention and it also affects local residential (non-migratory) birds.
Unfortunately, Taiwanese authorities have been more willing to provide viral sequences of AIVs that have close identity percentages to those from wild birds, particularly those that fly to Taiwan from foreign countries.
This causes Taiwan to miss the opportunity to make better judgements while higher-priority information on viral sequences isolated from domestic AIVs has not been available for integrated comparison.
Taiwanese officials lack the objectivity needed in evidence-based disease prevention with more scientific approaches to monitoring the dynamics of viral changes, and they fail to quickly publicize viral sequences for those AIVs of different subtypes co-circulating on the same farms or in the same county with epidemiological significance.
They forget that epidemiology emphasizes timely data analysis and grasping future trends. All major policy decisions should be supported by data and discussed through interdisciplinary collaboration, maintaining an open-minded and unselfish attitude to take prudent precautions.
The agricultural sector has never paid sufficient heed to infectious disease epidemiological expertise. As a consequence, there is a complete lack of academic freedom for avian influenza research in Taiwan and it is hard to cultivate new talent in the field.
For many years there has been a lack of novel thinking with regard to disease-control methods, and this outdated mindset and approach is the most important barrier to the successful prevention and control of avian influenza in Taiwan.
By the time this year’s H5N6 outbreak was detected, it had already affected several locations and various avian species. Central government decisionmakers listened to various opinions and banned the slaughter and transport of poultry for seven days starting from Feb. 17.
That illegal slaughter was detected on a silkie chicken farm in Chiayi County shows that there are local officials who engage in active disease prevention instead of sitting on their hands and watching as the disease spreads, and that in itself is a considerable advance.
The disease prevention measures that have been taken emphasize certain points. First, to avoid subsequent problems, a virus cannot be allowed to stay and become endemic.
Second, Taiwan has international responsibilities. It must not allow a repeat of what happened in 1957 and 1968, such that genetic reassortment would take place in Taiwan, creating novel influenza viruses with pandemic potential.
Third, Taiwan should reattain the admirable situation that prevailed before 2004, when there were no incidents of bird flu and ducks could be exported.
As of Feb. 23, H5N6 outbreaks had been reported in six cities and counties. Laboratory tests confirmed outbreaks in nine farms: seven chicken farms, one duck farm and one goose farm.
There were at least nine other cases that did not happen on poultry farms, but were found in slaughtering sites and private slaughtering and disposal areas, including the following: In northern Taiwan there was one non-farm case in Hsinchu County, while in eastern Taiwan there were two non-farm cases in Yilan County, and one poultry farm and one non-farm case in Hualien County. In central Taiwan there were two poultry farm cases in Yunlin County and four poultry farm and three non-farm cases in Chiayi County. Southern Taiwan saw two poultry farm and two non-farm cases in Tainan.
These clade 2.3.4.4 H5 AIVs are highly pathogenic to chickens and geese, but they cause milder symptoms in ducks. Notably, duck influenza viruses and wild bird influenza viruses often correlate in the gene pool.
In view of this, after Taiwan had its first case of H5N6 AIV in a duck, the authorities intervened decisively at the pre-slaughter stage by carrying out more comprehensive surveillance of AIVs in ducks and imposing a complete ban on their slaughter and transport. The measures were essential and unavoidable, and the authorities deserve support for their resolute action.
The important thing is for the authorities to instill and upgrade biosafety on poultry farms. When sick birds are dumped, released into the wild or illicitly slaughtered, it shows that there is not enough safety and hygiene education with regard to avian influenza.
As of Feb. 23, the three largest international gene banks of AIVs had not had any viral gene sequences for AIVs detected from domestic poultry in Taiwan between September and December last year, and this makes it difficult to forecast future trends.
This shows the urgent need for improved surveillance of AIVs. Taiwan needs to foster talent in the field of epidemiology, improve the sensitivity, specificity, reproducibility and, most importantly, the timeliness of bird flu surveillance in migratory and residential birds, as well as domestic fowl. Such a system must be strengthened and streamlined for early detection of AIVs.
King Chwan-Chuen is a professor at National Taiwan University’s Institute of Epidemiology and Preventive Medicine.
Translated by Julian Clegg
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