A systematic review of influenza A virus prevalence and transmission dynamics in backyard swine populations globally

Abstract

Background: Backyard swine farming is critical to generating subsistence and food security in rural and peri-urban households in several developing countries. The objective of this systematic review was to analyze the molecular and serological prevalence of influenza A virus (IAV) in backyard swine populations globally.

Results: We identified 34 full-text research articles in NCBI-PubMed and Google Scholar databases that have reported IAV sero- and/or virological prevalence in backyard swine up to 11 July 2021. The highest number of studies were reported from Asia (n = 11) followed by North America (n = 10), South America (n = 6), Africa (n = 6), and Europe (n = 1). While the maximum number of studies (44.12%) reported human-to-swine transmission of IAV, swine-to-human (5.88%), poultry-to-swine (5.88%), and wild birds-to-swine (2.94%) transmissions were also reported. An overall higher IAV seroprevalence (18.28%) in backyard swine was detected compared to the virological prevalence (1.32%). The human-origin pandemic A(H1N1)pdm09 virus clade 1A.3.3.2 was the more frequently detected IAV subtype in virological studies (27.27%) than serological studies (18.92%). In addition, the avian-origin highly pathogenic H5N1 and H5N8 viruses were also detected, which further substantiated the evidence of avian-swine interactions in the backyards.

Conclusion: Human-swine and avian-swine interactions in backyards may transmit IAV between species. Monitoring the circulation and evolution of IAV in backyard swine would help stakeholders make informed decisions to ensure sustainable backyard swine farming and public safety.

Keywords: Avian influenza; Backyard swine farming; Biosecurity; IAV outbreak; IAV pandemic; Influenza A virus; Interspecies IAV transmission.

Fig. 1

A schematic representation of IAV transmission within the backyard farms. a Birds may disseminate IAV strain(s) to the poultry and/or swine. A high probability remains for the zoonotic and reverse-zoonotic transmission of IAV between swine and household members, which may also trigger human-to-human transmission. b A schematic representation of IAV transmission in backyard swine kept within the pens. Birds may disseminate IAV to the swine confined in the pens, resulting in swine-to-swine transmission. Occupational exposure may facilitate zoonotic or reverse zoonotic IAV transmission between swine and household members. The IAV transmission may occur in both production types through contaminated feed, water, or bird faeces. c Humans, swine, chickens, ducks, geese, and birds may frequently interact within the backyard which increases the risk of IAV transmission among them

Fig. 2

PRISMA chart illustrating the search strategy for identifying the relevant full-text research articles available in NCBI-PubMed and Google Scholar databases up to 11 July 2021 for inclusion in the study. Full-text original research articles which investigated molecular and/or serological prevalence of IAV exclusively in backyard swine populations were included in systematic review

Fig. 3

The trend of IAV investigations in backyard swine populations globally

Fig. 4

Serological and virological prevalence of IAV in a asymptomatic (clinically healthy) and b symptomatic (sick) backyard swine populations globally

Fig. 5

a Serological and b Virological prevalence of IAV in African backyard swine populations

Fig. 6

a Serological and b Virological prevalence of IAV in Asian backyard swine populations

Fig. 7

Serological (a) and virological (b) prevalence of IAV in North American backyard swine populations. The highest seroprevalence was reported in the Mexican backyard swine. The highest virological prevalence was identified in the backyard swine in Guatemala

Fig. 8

Serological (a) and virological (b) prevalence of IAV in South American backyard swine populations

Fig. 9

a Serological and b Virological prevalence of IAV in backyard swine populations globally c Serological and d Virological prevalence of IAV in backyard swine populations in various countries. It should be noted that the objectives of IAV surveillance may vary among countries; hence the data presented here may only be used as an indicator of IAV sero- and virological prevalence in the backyard swine populations

Fig. 10

The global status of backyard swine farming along with transmission dynamics of IAV. a Several studies reported the presence of various animal species in swine backyard farms. b The number of studies that reported the interactions between backyard swine and other animal species in the backyards. c The number of studies that reported IAV interspecies transmission in the backyards. d The number of studies that investigated symptomatic and clinically healthy backyard swine. e Many molecular studies identified and characterized various IAV subtypes in backyard swine swabs and tissue samples. f The number of serological studies that identified and characterized different IAV subtypes in backyard swine sera samples.