Maternally Derived Immunity Extends Swine Influenza A Virus Persistence within Farrow-to-Finish Pig Farms: Insights from a Stochastic Event-Driven Metapopulation Model

Abstract

Swine Influenza A Viruses (swIAVs) have been shown to persist in farrow-to-finish pig herds with repeated outbreaks in successive batches, increasing the risk for respiratory disorders in affected animals and being a threat for public health. Although the general routes of swIAV transmission (i.e. direct contact and exposure to aerosols) were clearly identified, the transmission process between batches is still not fully understood. Maternally derived antibodies (MDAs) were stressed as a possible factor favoring within-herd swIAV persistence. However, the relationship between MDAs and the global spread among the different subpopulations in the herds is still lacking. The aim of this study was therefore to understand the mechanisms induced by MDAs in relation with swIAV spread and persistence in farrow-to-finish pig herds. A metapopulation model has been developed representing the population dynamics considering two subpopulations—breeding sows and growing pigs—managed according to batch-rearing system. This model was coupled with a swIAV-specific epidemiological model, accounting for partial passive immunity protection in neonatal piglets and an immunity boost in re-infected animals. Airborne transmission was included by a between-room transmission rate related to the current prevalence of shedding pigs. Maternally derived partial immunity in piglets was found to extend the duration of the epidemics within their batch, allowing for efficient between-batch transmission and resulting in longer swIAV persistence at the herd level. These results should be taken into account in the design of control programmes for the spread and persistence of swIAV in swine herds.

Substantial Antigenic Drift in the Hemagglutinin Protein of Swine Influenza A Viruses

“…This study documented IAV persistence within a swine herd over a one-year period, supporting the increasing number of studies that have shown that IAV may persists within the herd [38][39][40][41][42][43][44][45]. Furthermore, the study confirms previous studies documenting a lack of seasonality of swIAV infections [28,80].…”

“…Over the past ten years, the understanding of swIAV circulation in swine herds has changed and it is now recognized that an infection with swIAV is likely to result in an enzootic infected herd [38][39][40][41][42][43][44][45]. This is probably a consequence of increasing herd sizes, which provides a continuous flow of naïve piglets [46,47].…”

Examining the Effect of Host Recruitment Rates on the Transmission of Streptococcus suis in Nursery Swine Populations

“…Consequently, it is difficult to assess what impact neglecting a more complex herd structure would have on our model outputs. Previous studies have examined disease dynamics in smaller structured populations using a metapopulation approach [44]. Alternatively, models could also be stratified by age or level of risk to capture heterogeneity in host contacts.…”

The use of vaccines to control pathogen spread in pig populations

“…In the case of swine flu, it has been shown recently in a transmission experiment involving piglets born to vaccinated or non-vaccinated sows that the presence of maternally derived antibodies in piglets significantly decreased the virus transmission but not enough to block its propagation within the population. Moreover, the transmission intensity in this immunized population born to vaccinated sows was slowed down, increasing the total duration of the infectious process within the population and enhancing potentially the enzootic persistence of the virus in the farm [19, 20]. …”