Advisory Council on Food and Environmental Hygiene
Report on Recent Avian Influenza Incidents
This paper reports four recent avian influenza incidents that occurred in December 2002 and early January 2003 and the measures taken by the Administration to prevent the spread of the disease.
(a) Penfold Park
2. On 3 December 2002, the Hong Kong Jockey Club (HKJC) reported to the Agriculture, Fisheries and Conservation Department (AFCD) that there was unusual mortality in the waterfowl kept in Penfold Park and submitted three dead birds for testing on 4 December 2002. It was confirmed on 9 December 2002 that two of the three dead birds were infected with H5 influenza virus.
3. During on-site investigation on 10 December 2002, park attendants reported that 31 waterfowls died between 30 November 2002 and 9 December 2002. They had also observed deaths in some of the wild population of little egrets that roosted in the Penfold Park each evening. Upon AFCD's recommendations, HKJC agreed to depopulate the remaining 63 waterfowl in Penfold Park on 10 December 2002 and close the park for one month for cleaning and disinfection.
4. Gene sequencing analysis of the H5 viruses isolated from the dead birds showed that the viruses were H5N1 virus but were not the same as the H5N1 virus that affected humans in 1997.
5. The Penfold Park reopened on 16 January 2003 after thorough cleaning and disinfection. No more dead egrets were found since 10 December 2002 and tests confirmed that the caged birds were not infected by H5 virus. HKJC does not intend to re-stock the waterfowl in the near future.
(b) Kowloon Park
6. On 17 December 2002, the Leisure and Cultural Services Department reported to AFCD that three ducks in Kowloon Park were found dead on 14 - 17 December 2002 and submitted samples for diagnostic testing on 18 December 2002. One of the dead ducks was suspected of being infected with H5 virus after initial screening on 19 December 2002. Later on 20 December 2002, one swan and one duck found dead were also suspected of being infected with H5 virus.
7. As a result of the findings, the Chinese Garden Pond and the Bird Lake in Kowloon Park were cordoned off, drained, and thoroughly disinfected. All the 200 ducks, geese and swans were isolated, sampled and vaccinated against H5 avian influenza on 20 December 2002. No new cases occurred after 2 January 2003 but some convalescing ducks died on 4 January 2003. A total of 106 birds (89 waterfowl, 16 flamingos and 1 pigeon) died out of the 480 birds collection at Kowloon Park during the period from 17 December 2002 to 4 January 2003.
8. Gene sequencing analysis of the H5 viruses isolated from some of the dead birds showed that the viruses were H5N1 virus but were not the same as the H5N1 virus that affected humans in 1997. Tests also confirmed that no H5 virus was isolated from the dead pigeon.
(c) Chicken Farm in Ta Kwu Ling
9. Surveillance testings of dead chickens from the Cheung Sha Wan Temporary Wholesale Poultry Market (CSWTWPM) on 26 December 2002 gave suspicious reaction on rapid tests for H5 virus infection. Monitoring of those local farms that had supplied the market with chickens in the previous evening revealed that a farm in the Ta Kwu Ling area had experienced high mortality on 27 December 2002. Rapid tests confirmed H5 virus in dead chickens in the farm in late evening of 27 December 2002. The farm owner undertook in writing to surrender his chickens to the Administration for proper disposal on the same day.
10. On 28 December 2002, AFCD staff depopulated the remaining 13,500 chickens in the farm. By the time of killing, some 2,500 chickens were already dead in the farm.
11. To prevent the spreading of the highly pathogenic avian influenza virus, the Administration decided to implement ring vaccination, that is to have all chickens 8 - 55 days of age vaccinated against H5 avian influenza in the Ta Kwu Ling area immediately. AFCD would inspect the farms involved daily for dead or sick chickens. Dead chickens and cloacal swabs from sick chickens would be submitted to the Tai Lung Veterinary Laboratory for testing. Sale of chickens would not be allowed unless AFCD staff are satisfied after a farm inspection with head count, visual inspection for sick chickens, blood test from 14 chickens and faecal swab test from 60 chickens in the market batch five days before sale, and a second inspection for head count and close visual inspection for sick chickens one to two days before sale.
12. As the concerned farm has supplied chickens to the CSWTWPM on both 24 and 25 December 2002, the Administration decided to have CSWTWPM and retail markets thoroughly cleaned and disinfected to prevent possible spreading of the virus. CSWTWPM stopped sale in the early morning of 30 December 2002 to enable CSWTWPM to be emptied for cleaning and disinfection on 30 and 31 December 2002 and the retail markets be cleansed and disinfected on 1 January 2003. Sale of chickens in retail markets resumed on 2 January 2003.
13. Gene sequencing analysis of the H5 viruses isolated from some of the samples from the Ta Kwu Ling farm showed that the viruses were H5N1 virus but were not the same as the H5N1 virus that affected humans in 1997.
(d) Chicken Farm in Pat Heung
14. On 6 January 2003, a farm owner at Pat Heung reported to the AFCD that there were chicken deaths in his farm. AFCD Staff immediately went to the farm to investigate and found 158 dead chickens in three chicken sheds. Samples were taken from the dead chickens for testing and the birds in the farm were quarantined at once. After further investigation, it was confirmed that the three chicken sheds (involving 10,000 chickens) were infected with H5 virus while other sheds holding some 40,000 chickens remained uninfected.
15. The Administration immediately arranged for ring vaccination to the eight farms nearby and the other 40,000 chickens in the concerned farm to contain the infection. On 10 January 2003, the farm owner culled all the remaining suspected infected chickens in the three sheds.
16. Sale of chickens from the eight farms with ring vaccination will follow the procedure described in paragraph 11. Sale of chickens from the concerned farm will only be considered 21 days after the last clinical case and subject to no H5 virus isolated from the farm. The trail of the sold chickens from this farm will be monitored closely.
17. AFCD is investigating these four incidents with a view to establishing the causes leading to the outbreaks and recommending measures to reduce the likelihood of such incidents recurring in future.
18. Avian influenza is endemic in Hong Kong and the risk of H5 avian influenza will remain as long as live poultry are consumed in Hong Kong. Depopulation is no longer the only course of action to take in the event of an outbreak. Out strategy is to adopt a mult-pronged approach to minimize the risk of outbreak occurrence. We have implemented a comprehensive and sensitive surveillance system to detect avian influenza viruses at all levels. In enhancing our preventive capability, we will continue to seek the trades' cooperation in upgrading farm biosecurity, introducing stricter hygiene measures and additional rest days as necessary in markets, and piloting and evaluating vaccination as a complementary control measure. In addition, we will also provide the public with a choice of chilled and fresh chickens.
Agriculture, Fisheries and Conservation Department
Health, Welfare and Food Bureau