Social network analysis for the assessment of pig, cattle and buffalo movement in Xayabouli, Lao PDR

The aim of this study is to understand the role that the movement patterns of pigs, cattle and buffalo play in the spread of foot-and-mouth disease (FMD). A cross-sectional survey consisting of a questionnaire was used in a hotspot area for FMD: Xayabouli Province, Lao People’s Democratic Republic. A total of 189 respondents were interviewed. We found that the key players in this network were people who were involved with more than one species of animal or occupation (multipurpose occupational node), which represents the highest number of activities of animals moved off the holding (shown with the highest out-degree centrality) and a high likelihood of being an intermediary between others (shown with the highest betweenness centrality). Moreover, the results show that the animals moved to and away from each node had few connections. Some nodes (such as traders) always received animals from the same group of cattle owners at different times. The subgroup connection within this network has many weak components, which means a connection in this network shows that some people can be reached by others, but most people were not. In this way, the number of connections present in the network was low when we defined the proportion of observed connections with all possible connections (density). These findings indicate that the network might not be busy; only one type of node is dominant which enables increased control of disease spread. We recommend that the relevant authorities implement control measures regarding the key players, which is the best way to effectively control the spread of infectious diseases

Patterns and Risks of <i>Trichinella</i> Infection in Humans and Pigs in Northern Laos

<div><p>Several outbreaks of trichinellosis associated with the consumption of raw pork have occurred in Laos since 2004. This cross-sectional study was conducted in four provinces of northern Laos to investigate the seroepidemiology of trichinellosis in the human population and determine the prevalence and species of <i>Trichinella</i> infection in the domestic pig population. Serum samples and questionnaire data were obtained from 1419 individuals. Serum samples were tested for <i>Trichinella</i> antibodies by ELISA using larval excretory–secretory (ES) antigens and a subset of 68 positive samples were tested by western blot. The seroprevalence of <i>Trichinella</i> antibodies was 19.1% (95% confidence interval (CI) = 17.1–21.1%). The risk of having antibodies detected by ELISA using ES antigens increased with age, being of Lao-Tai ethnicity, living in Oudomxay province and being male. Tongue and diaphragm muscle samples were collected from 728 pigs and tested for <i>Trichinella</i> larvae by the artificial digestion method. <i>Trichinella</i> larvae were isolated from 15 pigs (2.1%) of which 13 were identified as <i>T. spiralis</i> by molecular typing; the species of the two remaining isolates could not be determined due to DNA degradation. <i>Trichinella</i> spp. are endemic in the domestic environment of northern Laos and targeted preventative health measures should be initiated to reduce the risk of further outbreaks occurring.</p></div

Survey population structure, stratified by province, ethnicity, wealth status, age and gender.

<p>Survey population structure, stratified by province, ethnicity, wealth status, age and gender.</p

<i>Trichinella</i> spp. western blot positivity verses ES ELISA positivity for diagnostic cut-off equal to standardised ratios of ≥1.0, ≥1.2 and ≥1.4 for 68 human samples.

<p><i>Trichinella</i> spp. western blot positivity verses ES ELISA positivity for diagnostic cut-off equal to standardised ratios of ≥1.0, ≥1.2 and ≥1.4 for 68 human samples.</p

Adjusted odds ratio (AOR) of population characteristics associated with <i>Trichinella</i> ES ELISA reactivity, as determined by random effects multiple logistic regression modeling controlling for household clustering.

<p>All models adjusted for gender, province, wealth, ethnicity, age, frequency of raw pork consumption, raw beef consumption and fermented pork sausage consumption. Model 1; Diagnostic cut-off in <i>Trichinella</i> ES ELISA  =  standardised ratio ≥1.0; Model 2, Diagnostic cut-off in <i>Trichinella</i> ES ELISA  =  standardised ratio ≥1.2; Model 3, Diagnostic cut-off in <i>Trichinella</i> ES ELISA  =  standardised ratio ≥1.4. In descending order population characteristics are: Gender; female (referent), male. Province; Oudomxay (referent), Luangprabang, Huaphan, Xiengkhuang. Wealth status; most poor (referent), very poor, poor, less poor, least poor. Ethnicity; Lao-Tai (referent), Mon-Khmer, Hmong-Mien. Age category; 6–11 years (referent), 12–19 years, 20–34 years, 35–49 years, ≥50 years. Raw pork consumption; does not eat (referent), weekly, monthly, every few months, infrequent. Raw beef consumption; does not eat (referent), weekly, monthly, every few months, infrequent. Raw fermented pork consumption; does not eat (referent), weekly, monthly, every few months, infrequent (refer to data in <a href="http://www.plosntds.org/article/info:doi/10.1371/journal.pntd.0003034#pntd.0003034.s003" target="_blank">Table S1</a>).</p

Prevalence of <i>Trichinella</i> spp. larvae isolated by artificial digestion from the tongue and diaphragm of pigs slaughtered at official slaughter points in four provinces of northern Laos.

¶<p>Indigenous and cross-breed pig breeds were from small backyard farms, even if from a penned system. The pig production system in northern Laos is quite complex and pigs raised in penned systems before going to slaughter may have been raised to weaner age in a free range system. The information on the production systems for the life of the pigs sampled could not be ascertained. Some of the exotic breeds were possibly produced in small intensive systems and at the time of the study, there were no large intensive piggeries in the provinces surveyed.</p

Unadjusted prevalence of <i>Trichinella</i> ES ELISA positivity (95% CI) for diagnostic cut-off equal to standardised ratios of ≥1.0, ≥1.2 and ≥1.4.

<p>Unadjusted prevalence of <i>Trichinella</i> ES ELISA positivity (95% CI) for diagnostic cut-off equal to standardised ratios of ≥1.0, ≥1.2 and ≥1.4.</p

The economic impact of pig-associated parasitic zoonosis in northern Lao PDR

The parasitic zoonoses human cysticercosis (Taenia solium), taeniasis (other Taenia species) and trichinellosis (Trichinella species) are endemic in the Lao People's Democratic Republic (Lao PDR). This study was designed to quantify the economic burden pig-associated zoonotic disease pose in Lao PDR. In particular, the analysis included estimation of the losses in the pork industry as well as losses due to human illness and lost productivity. A Markov-probability based decision-tree model was chosen to form the basis of the calculations to estimate the economic and public health impacts of taeniasis, trichinellosis and cysticercosis. Two different decision trees were run simultaneously on the model's human cohort. A third decision tree simulated the potential impacts on pig production. The human capital method was used to estimate productivity loss. The results found varied significantly depending on the rate of hospitalisation due to neurocysticerosis. This study is the first systematic estimate of the economic impact of pig-associated zoonotic diseases in Lao PDR that demonstrates the significance of the diseases in that country