Modeling the transmission and vaccination strategy for porcine reproductive and respiratory syndrome virus

Abstract

14 15 In the monitoring of porcine reproductive and respiratory syndrome virus (PRRSv), 16 knowledge about between-farm transmission dynamics is still lacking. Our objective was 17 to assess the relative contribution of between-farm PRRSv transmission routes through a 18 mechanistic epidemiological model calibrated with PRRSv occurrence, identify risk 19 areas, and estimate the impact of immunization strategies in the disease spread. We 20 developed a mathematical model of PRRSv transmission accounting for spatial 21 proximity, pig movements, and re-breaks in sow farms, parametrized on data collected 22 routinely by commercial pig farms. We then used the model to simulate the weekly 23 frequency of cases and built risk maps, and compared with the observed cases. We 24 simulated the implementation of two immunization strategies (preventive and reactive) to 25 mitigate the between-farm transmission. Our results indicated for sow and GDU farms' 26 local spread on average was above 60%, while for nurseries between-farm movements 27 represented 83% of transmissions and in finisher farms it was distributed almost 50% 28 local and 50% between-farm movement, the model allowed reproduce the weekly 29 frequency of observed cases and the risk maps built allowed the identification of 30 observed cases in the space. The increase in vaccine efficacy was the most important 31 parameter to mitigate between-farm transmission. Also, the implementation of 32 immunization by a preventive and reactive strategy combined had the better result to 33 mitigate between-farm transmission than implement these strategies individually. These 34 immunization strategies had a better performance with the use of rigorous protocols, such 35

Modeling the Spread of Porcine Reproductive and Respiratory Syndrome Among Pig Farms in Lira District of Northern Uganda

“…As expected, an increase in vaccination coverage resulted in a greater reduction of infectious herds at the end of 52 weeks, with the best results observed at 60 and 80% vaccine coverage. This trend was observed in other studies in Vietnam (21) and the United States of America (38). Due to the high contact rates from large farms to other farms, vaccination of large and medium farms resulted in a high reduction of infectious herds at the end of 52 weeks.…”

“…The model included the spread of PRRS virus via scavenging, sharing breeding boars, and sharing equipment which are very common practices in East African pig farms, including Uganda (10,37). Scavenging was not considered in PRRS simulation models in other countries, making this model unique (21,23,38). Other studies suggested that boar sharing was a critical contributor to the spread of swine diseases where other forms of direct contact (pig trade) have been halted, which was observed in our study (11,14).…”

The between‐farm transmission dynamics of porcine epidemic diarrhoea virus: A short‐term forecast modelling comparison and the effectiveness of control strategies

“…Porcine epidemic diarrhoea virus (PEDV) remains endemic in North America (Stevenson, Hoang, et al., 2013; USDA, 2017; Weng et al., 2016); however, based on the data from the Morrison's Swine Health Monitoring Project (MSHMP), the PEDV incidence in the United States has been in decline (Goede et al., 2015; Machado et al., 2019; Perez et al., 2019). Similar to porcine reproductive and respiratory syndrome virus (PRRSV), PEDV epidemic seasonal with most outbreaks occur during colder months (Galvis et al., 2020; Goede & Morrison, 2016; USDA, 2017). The most important clinical signs are vomiting, watery diarrhoea and dehydration in suckling piglets during the weeks of life that lead to a high morbi‐mortality (Annamalai et al., 2015; Madson et al., 2016; Niederwerder & Hesse, 2018).…”

“…Other studies indicated that limited biosecurity practices and/or the introduction of unexposed gilts increases the risk of virus persisting in farrowing units (Niederwerder & Hesse, 2018). In addition, between‐farm pig movements have been described as the main route of different pathogens including PEDV (Galvis et al., 2020; Lee et al., 2017; Machado et al., 2019; O’Dea et al., 2016; Widgren et al., 2018), with farrowing units being the most likely superspreaders (Lee et al., 2017; Passafaro et al., 2020). In areas of high hog production density, the proximity among farms has been suggested to play an important role in PEDV spread through indirect pathways such as airborne, people, tools, insects or other animals (Alonso et al., 2014; Alvarez et al., 2016).…”

Porcine reproductive and respiratory syndrome virus dissemination across pig production systems in the United States

“…While our analyses were not aimed to explore the route of transmission events or how viral lineages first entered a population (Rasmussen et al, 2018), they reinforce the importance of PRRSV collateral spread and open the question of how this dissemination is happening. Indeed, a recent work (Galvis, Prada, Jones, & Machado, 2020) showed that for sow farms, more than 50% of the between-farm transmission occurred by proximity among infected TA B L E 3 Number of transmission events that have been originated in farms that belong to the same pig system (local) compared to the events coming from farms integrated into another pig system (external)…”