Longitudinal field studies reveal early infection and persistence of influenza A virus in piglets despite the presence of maternally derived antibodies

Abstract

A longitudinal study was performed in three Danish farrow to grower (30 kilos) herds over a 4-month period to investigate the dynamics and clinical impacts of influenza A virus (IAV) infections. In each herd, four batches consisting of four sows each with five ear-tagged piglets were included. Nasal swabs and/or blood were sampled from the sows and/or the piglets prior to farrowing and at weeks 1, 3, and 5 and at the end of the nursery period. Clinical examinations were performed at each sampling time. The sows and piglets were tested for IAV and IAV antibodies in nasal swabs and blood samples, respectively. The results revealed three enzootically infected herds, where the majority of the pigs were infected during the first 5 weeks after birth. Infected piglets of only 3 days of age were detected in the farrowing unit, where the sows were also shedding virus. In all herds, low to moderate numbers of infected pigs (ranging from 3.6 to 20.7%) were found to be virus positive in nasal swabs at two consecutive sampling times. Furthermore, clinical signs of respiratory disease were associated with IAV detection. The findings of this study documented that IAV can persist in herds and that piglets as young as 3 days can be infected despite the presence of maternally derived antibodies. Electronic supplementary material The online version of this article (10.1186/s13567-019-0655-x) contains supplementary material, which is available to authorized users.

Co-circulation of multiple influenza A variants in swine harboring genes from seasonal human and swine influenza viruses

“…IAV infections in swine has been considered a disease of late autumn and early winter [30][31][32][33] , but the results reported here reveal that while the percentage of samples testing positive for swIAV fluctuate between months, no significant differences are observed between the different seasons. This supports the recent studies describing the enzootic persistence of swIAV [34][35][36][37] , most likely as a consequence of the herd-sizes and management procedures under the current conditions of commercial swine herds. A similar lack of seasonality was found in other countries with comparable management structures 16,33,38 .…”

A Systematic Review Analyzing the Prevalence and Circulation of Influenza Viruses in Swine Population Worldwide

“…Interestingly, a study in Denmark observed a piglet as young as just three days was infected with IAV despite having maternally derived IAV antibodies [183], suggesting that the infection might have occurred from the infected sow which was shedding the virus [183]. However, the symptoms of the influenza-like illness in swine may last only for one week but the virus shedding may still persist until 41 days after appearance of the influenza-like symptoms [183,296]. This phenomenon may have serious implications in influenza virus spill over to the non-infected swine as well as to the exposed farm workers due to prolonged virus shedding.…”

“…A large number of investigations have reported sub-clinical influenza virus infections in asymptomatic (apparently healthy) swine [78,103,150,161,171,278,300], indicating that influenza infections can go undetected while the swine may be shedding virus and hence may infect other swine and farm workers in contact [183]. Intriguingly, most of the swine samples processed in Australia, Europe, and North America were obtained from the symptomatic swine whi Egypt is recognized as a "hot spot" for the influenza virus reassortment due to its geographical location [345].…”

“…Europe Belgium H1N1, H1N2, H3N2 None [179][180][181] Denmark H1N1, H1N2, H3N2 None [182][183][184] United Kingdom H1N1, H1N2, H3N2, A(H1N1)pdm09, H1N7 IBV, ICV [185][186][187][188][189][190][191][192] Finland H1N1, H1N2, H3N2, A(H1N1)pdm09 None [193,194] France H1N1, H1N2, H3N2, A(H1N1)pdm09 None [195][196][197][198][199] Germany H1N1, H1N2, H3N2, A(H1N1)pdm09 None [200][201][202][203] Greece H1N1, H1N2, H3N2, A(H1N1)pdm09 None [204] Italy H1N1, H1N2, H3N2, A(H1N1)pdm09 IDV [205][206][207][208][209][210][211][212][213][214][215][216][217] Spain H1N1, H1N2, H3N2 None [218][219][220][221] Netherlands H1N1, H1N2, H3N2 None [222] Norway A(H1N1)pdm09 None [223][224]…”

“…This study observed that most of the swine were shedding IAV right before achieving six weeks of age. Surprisingly, a piglet as young as just three days was found infected with IAV [183]. Two H3N2 isolates having H3 genes from seasonal human influenza along with internal genes that originated from A(H1N1)pdm09 virus and NA genes from contemporary N2 swine influenza viruses that have been in circulation in Denmark were retrieved from young piglets at two locations during 2011-2014 [184].…”