Vigilancia epidemiologica dels virus d'influença porcina en granges de porcs

Resumen

In the first study of the present thesis, we investigated outbreaks of respiratory disease (n=211) compatible with influenza A virus (IAV) as well as farms without overt respiratory disease (n=19) for the presence of IAV. In the outbreak investigations, nasal swabs were taken from animals with respiratory signs and fever (≥40°C) while in the farms with no evident respiratory disease, nasal swabs were randomly taken from suckling piglets, weaners and fatteners (20 animals per phase). Presence of IAV and lineage determination were assessed by RT-qPCR and isolation was attempted in selected samples using MDCK cells. Isolates were sequenced (full genome) by using Illumina Miseq technology. IAV participation was confirmed in 145 (68.7%) of the outbreaks, and in 15 (78.9%) of the farms without overt disease. The most commonly detected lineages were H1avN2hu (33.6%), H1avN1av (24.3%) and H1huN2hu (18.7%). Sixty IAV isolates were obtained and the genomes were fully sequenced. Genotypes D and A, H1avN2hu and H1avN1av, respectively, were predominant but up to 14 genotypes were identified, of which seven had not been previously reported. Four isolates containing a new H3hu lineage derived from a human seasonal virus were detected, and isolates containing genes from the pandemic virus represented a 31.7 % of the total. In the second study of the present thesis, the transmission dynamics of IAV in the nurseries from an endemic farm were assessed before and after the application of different vaccination schemes for sows. Three follow-up periods were examined: before vaccination, after vaccination with a commercial inactivated polyvalent H1N1-H1N2-H3N2 and after vaccination with a monovalent pandemic H1N1. Nasal swabs of piglets were taken weekly from 3-9 weeks of age and blood samples were taken at three, six and nine weeks of age. In the first follow-up before vaccination, the basal IAV circulation was assessed by sampling 50 piglets in 4 batches. In the second longitudinal study, sows were blanket vaccinated with the polyvalent vaccine (control group) and half of them received an extra dose 3 weeks pre-farrowing (treatment group). A random cohort of 10 sows in each group was selected and 5 piglets per sow were weekly followed. The trial was replicated in 4 consecutive batches. In the third follow-up period, the procedure was the same as in the second, but using a pandemic H1N1 inactivated vaccine. Nasal swabs were examined by RT-qPCR and serum samples were analysed using a commercial ELISA (Civtest-Suis Influenza). Incidences and beta values per week and pen were calculated after the RT-qPCR results. Before applying any vaccination scheme, the patterns of incidence were diverse in the examined pens but often viral circulation was detected as early as 4 weeks of age. At three weeks of age, most of the analysed animals were positive with high S/P ratios. In the second follow-up period after the application of the first vaccination scheme, the onset of infection was delayed by two weeks but there were no other significant differences between both groups, and in the third, the onset of infection shifted to the left for all groups, without significant differences among them. In all of the three studies, animals that shed virus in two and even three consecutive sampling times were detected, as well as some cases of re-infection. Interestingly, an H1avN1av virus was initially detected in the farm, but during the third study, a H3huN2hu was found circulating in the batches, carrying a new H3 human-like derived from human seasonal virus.