Simulation of control scenarios of porcine reproductive and respiratory syndrome in Nghe An Province in Vietnam

Abstract

The main objective of this study was to develop various models using North American Animal Disease Spread Model (NAADSM) to simulate the transmission of Porcine reproductive and respiratory syndrome (PRRS) virus between farms in Nghe An Province in Vietnam in order to inform the prevention and control of this important disease. Using real data from the household survey, credible parameters for direct/indirect mean contact rates between different farms were estimated. A total of eleven models were developed, including immunization scenarios. In addition, we conducted sensitive analysis on how the mean contact rates influenced the results. The immunization scenarios showed that a high proportion of pigs in medium size farms needs to be vaccinated in order to reduce the transmission to pigs in small farms under the Vietnamese pig production system. In order to promote the use of vaccinations, incentives (such as a vaccine subsidy) for medium size farms may be needed. It could be the most cost‐effective control and prevention strategy for pig diseases in Vietnam. Our study provides insights on how pig diseases can be spread between pig farms via direct and indirect contact in Nghe An under the various hypothetical scenarios. Our results suggest that medium/large farms may play an important role in the transmission of pig diseases.

A stochastic simulation model of African swine fever transmission in domestic pig farms in the Red River Delta region in Vietnam

“…The NAADSM requires three key parameters: (a) transmission probability (TP) related to each contact (it is a probability between 0 and 1, and representing the likelihood of the contact herd will become infected given the exposure to an infected herd); (b) distance distribution associated with contact between farms; and (c) mean contact rates (estimated number of contacts per week) (Harvey et al., 2007). These parameters were estimated based on previous studies (Guinat et al., 2016; Lee et al., 2019) and assumptions (expert opinions) (Table 1). Transmission of ASF in Vietnam is mainly through indirect contact (e.g.…”

“…A PERT distribution was defined for contact distances between farms, with a minimum of 0.5 km, a most likely value of 30 km and a maximum of 300 km (Table 1). The weekly mean contact rates (following a Poisson distribution) between different farm types were obtained from a previous study and plugged into simulation models (Lee et al., 2019) (Table 2).…”

“…In Vietnam, the first study using NAADSM explored porcine reproductive and respiratory syndrome (PRRS) transmission via direct and indirect contacts across different farm types (Lee et al., 2019). With the ongoing outbreak and impact of ASF on the pig sector, the main objectives of this study were to model various scenarios of ASF virus transmission among farms and to evaluate the impact of control strategies using NAADSM.…”

A stochastic network-based model to simulate farm-level transmission of African swine fever virus in Vietnam

“…The indirect contact TP for large farms was estimated based on previous studies and assumptions (expert opinions). The mean contact rates per farm type combination were used from the study used to simulate the between farm spread of porcine reproductive and respisratory syndrome virus in Vietnam [ 23 ]. In addition, we had to create the new mean contact rate per week between farms as the network model we used was not able to distinguish between direct and indirect contacts ( Table 2 ).…”

“…In Vietnam, recent studies on pig movement structures provided better insights into which farm production systems were likely to play an important role in the spread of infectious diseases in pigs [ 11 , 22 , 23 ]. However, to our knowledge, no studies have been conducted to simulate the spread of ASF among farms using their contact network structure in Vietnam.…”