Estimation of a within-herd transmission rate for African swine fever in Vietnam

Abstract

We describe results from a panel study in which pigs from a 17-sow African swine fever (ASF) positive herd in Thái Bình province, Vietnam were followed over time to record the date of onset of ASF signs and the date of death from ASF. Our objectives were to: (1) fit a susceptible-exposed-infectious-removed disease model to the data with transmission coefficients estimated using Approximate Bayesian Computation; and (2) provide commentary on how a model of this type might be used to provide decision support for disease control authorities For the outbreak in this herd the median of the average latent period was 10 days (95% HPD [highest posterior density interval]: 2 to 19 days) and the median of the average duration of infectiousness was 3 days (95% HPD: 2 to 4 days). The estimated median for the transmission coefficient was 3.3 (95% HPD: 0.4 to 8.9) infectious contacts per ASF-infectious pig per day. The estimated median for the basic reproductive number, R 0 , was 10 (95% HPD: 1.1 to 30). Our estimates of the basic reproductive number R 0 were greater than estimates of R 0 for ASF reported previously. The results presented in this study may be used to estimate the number of pigs expected to be showing clinical signs at a given number of days following an estimated incursion date. This will allow sample size calculations, with or without adjustment to account for less than perfect sensitivity of clinical examination, to be used to determine the appropriate number of pigs to examine to detect at least one with disease. A second use of the results of this study would be to inform the equation-based within-herd spread components of stochastic agent based and hybrid simulation models of ASF.

Leptospira infection among human-close-contact animals in different geographical areas in Vietnam

“…8,9 In 2019, Vietnam livestock had suffered from an African swine fever outbreak that led to the death and culling of approximately 5.9 million pigs, accounting for approximately 22% of the total swine population. 36,37 Consequently, new swine herds have been raised after the outbreak, which may have affected our findings. Nevertheless, serovars Castellonis and Patoc were the most frequently detected in our swine serum, unlike previous studies in Vietnam, suggesting a diversity of Leptospira serovars circulating in this species.…”

Food Safety in Low and Middle Income Countries

“…These results were expected as following the 2019 ASF outbreak in Vietnam more than 5.9 million pigs were either culled or died from the disease despite significant government efforts to control the disease (Ngoc Que, 2020). Furthermore, during this time, the demand for live pig export from Vietnam to China increased (Bui and Gilleski, 2020). The higher demand and lack of pigs in the supply chain led to a substantial price increase for pork, and this is reflected by 90.4% of consumers in this survey reporting high prices as the main reason for difficulty with the purchase of pork.…”