Antigenic drift of H1N1 influenza A virus in pigs with and without passive immunity.
BACKGROUND
The genetic and antigenic characteristics of influenza A viruses (IAV) within and between species change over time due to antigenic shift and drift. Although pigs are known to play a key role in the epidemiology of IAV between species, little is known about the molecular evolution of IAV hemagglutinin (HA) in pigs.


OBJECTIVE
The aim of this study was to evaluate the HA drift of an H1N1 IAV after infecting weaned pigs with or without maternally derived passive immunity.


METHODS
Three- to four-week-old piglets born either to vaccinated or unvaccinated sows were contact-infected upon exposure with an IAV-infected pig. Nasal swabs were collected daily from each pig and tested for IAV by RRT-PCR. Full-length HA sequences were obtained directly from positive nasal swabs and compared between groups.


RESULTS
Synonymous and non-synonymous mutations were detected in pigs with and without passive immunity. Most of the non-synonymous mutations occurred within the HA1 region of the HA. Changes within HA1 region were only identified in antigenic site B in pigs without passive immunity and in antigenic sites A, B, and D in pigs with passive immunity. However, there was no association between the immune status of the pig and the amino acid substitutions observed.


CONCLUSIONS
Overall, we demonstrated that amino acid substitutions within antigenic sites can happen in weaned pigs with or without passive immunity shortly after infection.
Department of Veterinary Population Medicine, College of Veterinary Medicine, University of Minnesota, St. Paul, MN, USA.
Andres
A
Diaz
Matthew
M
Allerson
Marie
M
Culhane
Srinand
S
Sreevatsan
Montserrat
M
Torremorell
D056704:Adaptive Immunity; D000818:Animals; D000940:Antigenic Variation; D040961:Genetic Drift; D019267:Hemagglutinin Glycoproteins, Influenza Virus / Q000235:genetics* / Q000276:immunology; D053118:Influenza A Virus, H1N1 Subtype / Q000145:classification / Q000235:genetics* / Q000276:immunology / Q000302:isolation & purification; D009980:Influenza A virus / Q000235:genetics / Q000276:immunology; D009154:Mutation; D009976:Orthomyxoviridae Infections / Q000276:immunology / Q000662:veterinary* / Q000821:virology; D010802:Phylogeny; D013552:Swine; D013553:Swine Diseases / Q000276:immunology / Q000821:virology*
D019267:Hemagglutinin Glycoproteins, Influenza Virus
Antigenic drift; Swine influenza; passive immunity