Occurrence and distribution of AI in South and Southeast Asian countries: December 2003-June 2004

Geographic distribution and disease notification in Southeast Asia

Since December 2003, HPAI has been reported to have progressively occurred in different countries in Southeast and South Asia. HPAI type A, subtype H5N1, has been reported in Cambodia, China, Indonesia, Japan, the Lao People’s Democratic Republic, the Republic of Korea, Thailand and Viet Nam. HPAI type A, H7 and H9 strains, were reported in Pakistan in January 2004. The countries officially declared confirmation of the disease to appropriate international organizations including FAO, the World Organisation for Animal Health (OIE) and the World Health Organization (WHO).

The crisis rapidly gained an international dimension and developed beyond Southeast Asian countries to threaten the whole region, if not the world. Declarations of new outbreaks culminated at the end of January, and new cases were reported on a daily basis through mid-February, when the number of outbreaks decreased. As of June 2004 outbreaks had been reported in Cambodia (9 May 2004) and in Indonesia and Thailand (end-May). As opposed to China, which has reported limited outbreaks only in smallholder operations over a wide geographic area, Japan and the Republic of Korea have reported limited outbreaks that are geographically confined.

Data from official and non-official sources on AI outbreaks in the Asian countries have been regularly entered in the EMPRES Global Animal Disease Information System (EMPRES-i) for processing and analysis. This reporting system has made it possible to identify the geographic locations of HPAI outbreak sites using geographic information systems (GIS) to produce maps with the distribution of outbreaks reported and subsequently to carry out further analytical epidemiology. In this context, collaborating centres have been assigned to work with FAO for disease surveillance analysis. Different parameters, such as localities affected, poultry density, human density, pig density, elevation, rivers, markets and distance from the roads, will be taken into consideration in order to produce risk maps to focus better on surveillance in these areas and to be able to predict the occurrence of the disease in the future.

· Cambodia: 12 confirmed avian influenza H5N1 positive outbreaks were identified. Eight of the confirmed positives were in the south of the country (Takeo, Kandal and Phnom Penh), three were in the northwest (Siem Reap) and one in the east (Kampong Cham). The two latest cases occurred in the northeastern Kampong Cham and southern Takeo Provinces, both of which border Viet Nam, in April 2004. The first case of H5N1 was detected in Phnom Penh on 24 January 2004. Nevertheless, retrospective investigations have established that HPAI may have been present there in early- to mid-December.

The epidemic increased through January and had all but died out by mid-February. Evidence suggests that HPAI may not become established in Cambodia to the extent that it did in Viet Nam and Thailand. This could be attributable in large part to the primarily extensive nature of the poultry industry; poultry density in Cambodia is much lower than in Thailand or Viet Nam. Indeed, as a result of the crisis in neighbouring countries, the consumption of chicken dropped drastically as did its price, and commercial broiler operations could not be restocked from Thailand because of the importation ban imposed. As a consequence of the lack of operational funds, less than 15 percent of the reported cases were investigated, and the confirmatory diagnoses were supported by the Pasteur Institute, France. There was no epidemiological tracing conducted from confirmed premises, and no systematic list of contiguous or related properties was prepared. It is therefore difficult to identify the origin of the infection in the country. Current prevalence of the disease is also difficult to estimate, as few data are available to enable investigators to define zones and determine the status of different areas.

· China: The first outbreak of the current epidemic was confirmed on 27 January 2004 in Guangxi, a province in the south of China bordering Viet Nam. There were subsequently 49 outbreaks confirmed in 16 provinces across China. No new outbreaks have been reported since 16 February 2004. The cases involved a wide range of poultry, including chickens, ducks, geese, “rock pigeons” and birds in a zoological collection. On 22 February 2004, quarantine on the last two affected areas was lifted. As a result of low biosecurity standards in smallholder production systems, domestic poultry are highly susceptible to the introduction of avian influenza via a wide range of sources (if the virus is present in the area). Wild birds are one potential route of exposure but should not necessarily be considered the only or main source of the disease. The virus could also be spread through contact with contaminated objects used in the poultry industry, via farmers or visitors inadvertently carrying the virus on to farms or by direct contact with infected poultry, such as domestic waterfowl.

· Indonesia: 14 provinces and 95 districts have been affected. The island of Java is the epicentre of the outbreak, the first recorded case having been in the Tangerang Regency of Banten Province of Java in August 2003. The disease then spread south and east, and subsequently to Bali, Kalimantan and Sumatra.

· Japan: Since January 2004 HPAI has occurred in five prefectures. The first outbreak of HPAI caused by H5N1 virus was detected in mid-January 2004 in a commercial flock in Yamaguchi Prefecture. The second outbreak occurred in mid-February in a non-commercial flock (i.e. backyard flock) in Oita Prefecture. The three other outbreaks occurred in the Kansai area (around Kyoto Prefecture) in different commercial flocks.

· Lao People’s Democratic Republic: HPAI has been reported in three provinces: Vientiane Prefecture, Champasak and Savannakhet. The first suspected cases, in Nonsavang, District of Xaysetha, Vientiane Prefecture, were confirmed on 14 January 2004. By the first week in March, there had been confirmed outbreaks in 45 different locations, of which 42 were commercial enterprises and 3 villages. There were 38 outbreaks in 5 districts within Vientiane Prefecture, 5 in Savannakhet and 2 in Champasak. These outbreaks resulted in 50 670 poultry deaths and the slaughter and disposal (“stamping out”) of 100 250 birds. The last case reported was on 4 March 2004. In Vientiane Prefecture a total of 35 commercial farms were affected; 24 were commercial layer farms, 6 broilers and 2 quail. Of the remainder, one produced native chickens and quail, one produced quail and broilers and one produced eggs and mixed meat varieties. The three affected villages raised native chickens and ducks. Four of the five reports from Savannakhet were from one village in Khanthabouly District, and the fifth in a neighbouring village. Both reports from Champasak were from villages in the District of Paksé. HPAI was only reported in areas of high poultry concentration, and the outbreaks occurred mainly in egg producing facilities, broiler units and quail farms close to areas of high human population (Vientiane City, Paksé and Savannakhet).

· Pakistan: Outbreaks of HPAI serotype H7N3 occurred in layers in and around Karachi until the end of January 2004. Since then, no outbreaks have been reported, and no signals of AI outbreaks have been recorded. The Karachi area is a particular place of great concern because many risk factors for continuous virus circulation and major outbreaks are present. Communications about the presence of AI viruses in Pakistan have led to a general loss of public confidence in food safety of poultry products. This loss of confidence has had dramatic economic consequences, especially on individual small-scale farmers.

· Republic of Korea: Since December a total of 19 farms have been confirmed with HPAI. They span seven provinces. The last case of the disease was confirmed on 21 March 2004. All 19 farms were restocked with sentinel animals. None of the sentinel birds showed clinical signs of avian influenza. The final serological testing of the sentinel birds was conducted on 13 July 2004. All results were favourable.

· Thailand: Avian influenza was isolated and confirmed in Thailand for the first time in January 2004. HPAI was first detected in a layer farm in Bangplama District, Suphanburi Province, central region of Thailand. H5N1 was isolated in different species. Similar to Viet Nam, Thailand was a country with human fatalities. Among 190 confirmed HPAI cases, the most affected population was village chicken (58.5 percent), followed by layers (12.4 percent). The viruses from Thailand were genetically very similar to each other and to the virus isolates from humans in Viet Nam. The virus isolated from native birds was similar to the viruses isolated from domestic poultry. The N1 gene showed two sublineages; those associated with the recent outbreak in Viet Nam and Thailand had a 20-amino acid deletion in the stalk region of the neuraminidase gene, and a separate sublineage associated with the human cases in China, Hong Kong Special Administrative Region in 2003 had no such deletion in the neuraminidase. Antigenic analysis also confirmed that the Thailand viruses seemed similar to each other and to the Viet Nam human viruses. However, they were genetically different from the H5N1 viruses isolated in China, Hong Kong Special Administrative Region in 1997 and 2001-2002.

· Viet Nam: Avian influenza was first officially declared in Viet Nam on 8 January 2004, after heavy losses had been experienced on 25 December in two southern provinces (Tien Giang and Long An) and on 27 December in the Ha Tay Province close to Hanoi. Of all the countries in the region, Viet Nam has been the most severely affected by the avian influenza epidemic. The poultry sector was devastated, and human lives were tragically lost to the disease. The earliest recorded cases in Viet Nam were those that occurred on 25 December 2003. These were subsequently confirmed as HPAI by laboratory diagnosis on 6 January 2004 and reported to OIE on 8 January. Two of these cases were in Long An Province and one in Tien Giang Province. The disease then spread rapidly throughout the country, affecting 22 provinces (13 in the south and 9 in the north of Viet Nam) by the end of January. The incidence of HPAI had reached a peak by mid-February, when up to 57 out of the 64 provinces had reported known cases (about 3 000 communes out of 8 970). The rapidity and intensity of the spread of the disease overwhelmed the capacity of the veterinary service and its disease surveillance systems to contain the epidemic.

Asian countries and regions that have experienced infection in 2004, as of June 2004
(see “Stop the press - September 2004” for latest information)

¹ Official (OIE) and non-official information (ProMED, press agencies, FAO tracking systems, etc.).

² GPHIN: Global Public Health Intelligence Network (Health Canada).

³ FAO; government: FAO representative in concurrence with government sources.

⁴ LP: low pathogenic strain.