A new scientific article from the Torremorell lab, about the influence of maternal antibodies on influenza dynamics was published in PLoS ONE.
The study followed 10 cohorts of nursery piglets form a single influenza-positive sow farm and compared influenza dynamics based on the vaccination status of the dam.
Methods
Around 300 piglets from one single influenza-positive sow farm were followed during their time at the nursery. The data was collected from 10 cohorts of 30 piglets placed into 2 nurseries over 6 months. During the time of the study, the sows received their biannual PRRS vaccine and 2 commercial influenza vaccines. The piglets originating from that time were cohorts 3a, 3b, 4a and 4b.
Nasal swabs were taken at weaning and then every week in the nursery. They were then tested for influenza by RT-PCR. Each week, for each cohort, the sample with the lowest Ct-value were selected for virus isolation and then submitted for Whole Genome Sequencing. Based on this information, Hemagglutinin gene sequences were translated into amino acid sequences and compared to the sow farm, between cohorts and with the commercial vaccines data.
Blood samples were collected at weaning, and 3 and 6 weeks post weaning. They were tested by hemagglutination inhibition (HI) assay. 15 piglets were selected based on their HI titers at weaning and their serum samples were tested by ELISA.
Results
Overall, 28% of serum samples had a reciprocal HI titer of 40 or higher. 16% of the nasal swabs were RT-PCR positive for influenza A virus. 62% of the pigs tested PCR positive for influenza A virus at least once during the study.
Cohorts with high seroprevalence at weaning showed low influenza prevalence (% PCR positive) whereas cohorts with a low seroprevalence showed a high virus prevalence. Levels of seroprevelence measured by HI titers were high in cohorts issued from vaccinated sows.
Some cohorts showed a second peak of infection during their time in the nursery.
Almost all pigs at weaning tested ELISA positive. However, the percentage of positive pigs declined over time or increased slightly after the second peak of infection, similar to the HI titers dynamics observed in most of the cohorts.
20 Hemagglutinin gene sequences were collected throughout the study.
The sequencing approach demonstrated the circulation of one predominant strain (H1 delta 2) in the 10 cohorts and in the sow farm. There was no difference in the H1 antigenic sites between the viruses detected in the study and the vaccine strains.
Conclusions
High levels of strain-specific hemagglutination inhibition antibodies at weaning:
- decreased IAV infection at weaning,
- delayed time to become influenza-positive,
- decreased the number of weeks that pigs tested influenza-positive during the nursery stage,
- decreased the overall estimated virus quantity during the infection period.
- IAV infection and circulation in nursery pigs may be decreased by using adequate influenza sow vaccination protocols.
Influenza infection and circulation in nursery pigs may be decreased by using adequate influenza sow vaccination protocols.
Abstract
Reducing the number of influenza A virus (IAV) infected pigs at weaning is critical to minimize IAV spread to other farms. Sow vaccination is a common measure to reduce influenza levels at weaning. However, the impact of maternally-derived antibodies on IAV infection dynamics in growing pigs is poorly understood. We evaluated the effect of maternally-derived antibodies at weaning on IAV prevalence at weaning, time of influenza infection, number of weeks that pigs tested IAV positive, and estimated quantity of IAV in nursery pigs. We evaluated 301 pigs within 10 cohorts for their influenza serological (seroprevalence estimated by hemagglutination inhibition (HI) test) and virological (prevalence) status. Nasal swabs were collected weekly and pigs were bled 3 times throughout the nursery period. There was significant variability in influenza seroprevalence, HI titers and influenza prevalence after weaning. Increase in influenza seroprevalence at weaning was associated with low influenza prevalence at weaning and delayed time to IAV infection throughout the nursery. Piglets with IAV HI titers of 40 or higher at weaning were also less likely to test IAV positive at weaning, took longer to become infected, tested IAV RT-PCR positive for fewer weeks, and had higher IAV RT-PCR cycle threshold values compared to piglets with HI titers less than 40. Our findings suggest that sow vaccination or infection status that results in high levels of IAV strain-specific maternally-derived antibodies may help to reduce IAV circulation in both suckling and nursery pigs.