A targeted investigation to demonstrate the freedom of West Timor from HPAI H5N1
Received 16 May 2017, Revised 1 December 2017, Accepted 1 December 2017, Available online 5 December 2017, Version of Record 22 December 2017.
https://doi.org/10.1016/j.prevetmed.2017.12.002
Introduction
The first outbreak of the disease in humans caused by H5N1 occurred in Hong Kong in 1997, with six of 18 infected individuals dying (Chan, 2002). Subsequently in 2004 the virus caused major outbreaks of disease in poultry in Indonesia (Smith et al., 2006), Vietnam (Hien et al., 2004), Thailand (Chotpitayasunondh et al., 2005, Grose, 2004), Republic of Korea, Japan, Cambodia, and Lao People’s Democratic Republic (WHO, 2005b). The outbreaks were associated with high levels of mortality, up to 100%, in poultry (WHO, 2014), as well as high case fatality rates (CFR) in humans (>50%) (WHO, 2005a).
In Indonesia, HPAI H5N1 virus was first detected in domestic poultry in 2003 (Sedyaningsih et al., 2007) and by the end of June 2006, the virus had been detected in 27 provinces (Indonesia Ministry of Agriculture, unpublished data, cited by Sedyaningsih et al., 2007). The virus was reported to be endemic in poultry in several provinces by 2009, with frequent outbreaks being reported on the islands of Java and Sumatera (Sumiarto and Arifin, 2008). In Indonesia HPAI not only resulted in the restriction of international trade of live birds and poultry meat products, but also affected tourism (Rushton et al., 2005) and public health. Until 2015 there had been 199 confirmed human cases with a CFR of 83.9% (WHO, 2016). Most human cases in Indonesia (76%) have been associated with contact with poultry or poultry products (Sedyaningsih et al., 2007). However recent studies have demonstrated person to person transmission, with clusters of epidemiologically linked H5N1 cases occurring among families (Kandun et al., 2008).
In West Timor, HPAI (H5N1) caused the death of approximately one hundred chickens from both commercial and backyard farms between 2004 and 2006. It was first diagnosed in 2004 when five samples from chickens from two different farms tested positive on the haemagglutination inhibition (HI) test (unpublished data from Provincial Livestock Services, Nusa Tenggara Timur (NTT). Smith et al. (2006) suggested that the virus originated from West Indonesia (Java) through two separate introductions via the movement of poultry and/or poultry products.
Active surveillance for H5N1 in West Timor was first implemented in 2005, and was aimed primarily at the sector 4 poultry industry (household/backyard level) (Azhar et al., 2010). Passive surveillance is also conducted through the reports of farmers to field veterinarians of dead chickens and the first diagnosis of the disease in 2004 resulted from farmers reporting deaths in their chickens to the Livestock Services (Personal communication, Drh. Cahyo Sunarno, Coordinator of the Participatory Disease Surveillance and Response (PDSR) program of NTT).
The results of serological surveys conducted by the Provincial Livestock Services in West Timor demonstrated a seroprevalence to HPAI in the years 2004, 2005 and 2006 of 72.2% (95%CI: 66.2, 77.6), 13.2% (95%CI: 9.7, 17.4), and 18.0% (95%CI:10.1, 28.5) respectively. However, no evidence of the presence of disease has been reported since 2007. No evidence of disease or infection has also been reported in the neighbouring country, Republic of Democratic Timor Leste, since 2005 (Amaral, 2011). Disease freedom in Timor Leste is important because of the potential for cross-border movements of poultry between the two countries.
In response to the H5N1 outbreak in West Timor in 2004–2006 vaccination was not implemented, instead slaughter/stamping out was undertaken based on the Government’s control strategic plan and regulation in 2004 (Decision of Directorate General of Livestock No:17/Kpts/PD.640/F/02.04 Guidelines of prevention, control and eradication of zoonotic disease of AI) (Directorate of Animal Health Indonesia, 2012). Since these initial cases no other clinical cases have been reported in the Province (unpublished data of the Provincial Livestock Services, NTT). Besides slaughter, the Government implemented movement controls of chickens and the importation of chickens was prohibited from infected areas, with importation of day old chickens (DOCs) only permitted from high biosecurity level, HPAI test-negative flocks approved and inspected by the Provincial Government. No day old ducks (DODs) are imported into West Timor.
According to the Terrestrial Animal Health Code, (OIE, 2015) a country, zone or compartment can be considered free from infection in poultry when: infection with HPAI viruses in poultry have not been present in the country, zone or compartment for the preceding 12 months, although the LPAI virus status may be unknown; or based on surveillance, any virus detected has not been identified as HPAI virus; or if infection has occurred in poultry in a previously free country, zone or compartment, free status can be regained three months after a stamping-out and disinfection policy has been applied, providing that surveillance has also been carried out during that period.
Analysis of the results of structured representative surveys can be used to demonstrate a zone or country is free from disease (Martin et al., 2007). To support freedom from HPAI, a surveillance program targeting all susceptible species is required in a country/zone/region. This surveillance program can be carried out using appropriately designed randomised sampling techniques or by using targeted surveillance of high risk species in specific locations or birds/farms undertaking high-risk practices (OIE, 2010). In order to provide evidence that HPAI H5N1 was absent from West Timor, targeted surveillance was undertaken in high-risk areas comprising live bird markets (100 samples) and villages and commercial farms (200 samples). The results of this surveillance are reported and discussed in this study.
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Section snippets
Study area
West Timor is situated on the island of Timor, between Australia and the Democratic Republic of Timor Leste, and its economy is predominantly agricultural. Based on the animal census in 2013, poultry represented 90% of the total livestock population in West Timor (Central Bureau of Statistics of Nusa Tenggara Timur, 2013). Village/backyard reared chickens, commercial chickens (broilers and layers), and ducks are the most common types of poultry raised by households in West Timor. Commercial
Results
All swab samples were negative on testing with the Anigen® Rapid test (0%; 95% CI: 0.0–1.2%). One sample in Naitimu gave an invalid result and therefore was retested. On retesting the result was negative.
The probability of detecting 0 positive samples in a sample of 300 from an infected population with a prevalence of 20% in a population of 10,000 was 0.0000 (95%CI: 0.0000–0.0122). Consequently it can be concluded with a high level of confidence (1.0, 95%CI: 0.9878, 1.0) that this population is
Discussion
Targeted surveillance is defined as a sampling approach where samples (animals or sites) are specifically selected for testing (Williams et al., 2009). This form of surveillance increases the probability of detecting infection, if present. In this study, the high-risk areas included markets and backyard and commercial poultry farms. Backyard farms (village chickens) have been shown to play an important role in the transmission of HPAI H5N1 in Thailand (Tiensin et al., 2005) and LBM have also
Acknowledgements
The authors would like to thank the poultry farmers in the surveyed districts of West Timor for their involvement in the study; the Provincial Animal Health Department of NTT for their help and support during the field data collection; and the Directorate of Higher Education of Indonesia for providing a Post Graduate Scholarship to the lead author. This paper represents part of a thesis submitted by the lead author for award of a doctorate degree at Murdoch University.
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