Impact of farm management on expression of early mortality syndrome/acute hepatopancreatic necrosis disease (EMS/AHPND) on penaeid shrimp farms in Thailand.

Asian shrimp farming industry has experienced massive production losses due to a disease caused by toxins of Vibrio bacteria, known as early mortality syndrome/acute hepatopancreatic necrosis disease (EMS/AHPND) for the last 5 years. The disease can cause up to 100% cumulative pond mortality within a week. The objective of this study was to identify factors associated with AHPND occurrence on shrimp farms. A case-control study was carried out on shrimp farms in four provinces of Thailand. Factors related to farm characteristics, farm management, pond and water preparation, feed management, post-larvae (PL) shrimp and stock management were evaluated. Multivariable logistic regression analysis identified factors affecting AHPND occurrence at the pond level. Chlorine treatment, reservoir availability, use of predator fish in the water preparation, culture of multiple shrimp species in one farm and increased PL stocking density contributed to an increased risk of AHPND infection, while delayed first day of feeding, polyculture and water ageing were likely to promote outbreak protection. Additionally, the source of PL was found to be associated with AHPND occurrence in shrimp ponds, which requires further study at the hatchery level. Identification of these factors will facilitate the development of effective control strategies for AHPND on shrimp farms.

Social network analysis of cattle movement in Kampong Cham, Kampong Speu and Takeo, Cambodia.

The aim of this study is to provide insight the network of cattle movement in Kampong Cham, Kampong Speu and Takeo, Cambodia. A cross-sectional study was carried out from July 2014 to August 2014, using questionnaires. It was implemented with 435 interviewees (24.4%, 24.6% and 51.0% from Kampong Cham, Kampong Speu and Takeo, respectively) using one-step snowball sampling. The findings suggest that the key players in all three provinces are producers who raise their cattle as backyard animals. In all three provinces the key players in spreading disease are probably the middlemen, collectors, brokers or traders. The network of cattle movement is presented as a strong component of varying size in each location. In this network we found three cut-points in both Kampong Cham and Kampong Speu. The network in each province indicates a random pattern of node distribution. The results of our study are useful to relevant authorities and researchers to understand the spread of infectious diseases into different areas. The middlemen, collectors, brokers and traders need to be controlled as first priority in order to reduce the magnitude of the spread of disease.

Social network analysis for assessment of avian influenza spread and trading patterns of backyard chickens in Nakhon Pathom, Suphan Buri and Ratchaburi, Thailand.

The aim of this study is to explain the social networks of the backyard chicken in Ratchaburi, Suphan Buri and Nakhon Pathom Provinces. In this study, we designed the nodes as groups of persons or places involved in activities relating to backyard chickens. The ties are all activities related to the nodes. The study applied a partial network approach to assess the spreading pattern of avian influenza. From 557 questionnaires collected from the nodes, the researchers found that the degree (the numbers of ties that a node has) and closeness (the distance from one node to the others) centralities of Nakhon Pathom were significantly higher than those of the others (P<0.001). The results show that compared with the remaining areas, this area is more quickly connected to many links. If the avian influenza virus subtype H5N1 was released into the network, the disease would spread throughout this province more rapidly than in Ratchaburi and Suphan Buri. The betweenness centrality in each of these provinces showed no differences (P>0.05). In this study, the nodes that play an important role in all networks are farmers who raise consumable chicken, farmers who raise both consumable chicken and fighting cocks, farmers' households that connect with dominant nodes, and the owners and observers of fighting cocks at arenas and training fields. In this study, we did not find cut points or blocks in the network. Moreover, we detected a random network in all provinces. Thus, connectivity between the nodes covers long or short distances, with less predictable behaviour. Finally, this study suggests that activities between the important nodes must receive special attention for disease control during future disease outbreaks.

Estimating spatial and temporal variations of the reproduction number for highly pathogenic avian influenza H5N1 epidemic in Thailand.

Since 2003, highly pathogenic avian influenza (HPAI) H5N1 virus has spread, causing a pandemic with serious economic consequences and public health implications. Quantitative estimates of the spread of HPAI H5N1 are needed to adapt control measures. This study aimed to estimate the variations of the reproduction number R in space and time for the HPAI H5N1 epidemic in Thailand. Transmission between sub-districts was analyzed using three different and complementary methods. Transmission of HPAI H5N1 was intense (R(t)>1) before October 2004, at which point the epidemic started to progressively fade out (R(t)<1). The spread was mainly local, with 75% of the putative distances of transmission less than 32km. The map of the mean standardized ratio of transmitting the infection (sr) showed sub-districts with a high risk of transmitting infection. Findings from this study can contribute to discussions regarding the efficacy of control measures and help target surveillance programs.