Part 1: Census and survey
Poultry husbandry and production is a ubiquitous and heterogeneous activity in Purbalingga District. Small-scale poultry keeping is common (approximately 60% of households kept small numbers of birds, nearly half of which contributed towards supplementary household income). Although 30% of households reported having had sick or dead poultry in the previous 12-month period, these mortalities were not reported to any surveillance system. The distribution of backyard poultry density (highest in higher-populated areas), collector yards (correlated with backyard poultry density), live bird markets (in urban centres and in proximity to roads) and commercial farms (somewhat removed from human population dense areas) was much as would be expected. Nomadic duck flocks consisted of relatively large flocks which were grazed on rice paddy fields post-harvest, often on contract basis (consistent with the description of Henning et al., 2010). Approximately 20 flocks were found to move from village to village per 2 week period, within Purbalingga but also to and from neighbouring Districts. Although biosecurity was not consistently practised, H5N1 vaccination was carried out. However, the type of vaccination and vaccine schedules could not be ascertained.
Commercial production units mostly consisted of Sector 3 layer and broiler chickens, with a smaller number of duck farms, and a small number of Sector 2 and Sector 1 farms. AI vaccination was most commonly performed in the layer sector, and to intents and purposes not at all in the backyard sector. Nomadic duck farmers reported using vaccine, but the type of vaccine and vaccination schedule could not be reliably recorded.
It was common practice for live birds at collector yards to be taken to other villages (by buyers) after sale. Traders at LBMs often did not sell all of their birds (collected from different sources); surplus birds were taken back to their homes. These traders reported attending multiple markets to sell their birds. Although the commercial sector was not entirely closed, there were less opportunities for transmission of infection than between backyard poultry and ducks. Moreover, transmission between these smallholder populations was likely to be driven more strongly by the value chain and by the husbandry system than by direct or indirect contacts in the source populations. As a consequence, clinical outbreaks are more likely to manifest as ‘jumps’ between villages or locations than showing a pattern of local spread.