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. 2015 Jun 15;10(6):e0129213.
doi: 10.1371/journal.pone.0129213. eCollection 2015.

Association between Influenza A Virus Infection and Pigs Subpopulations in Endemically Infected Breeding Herds

Andres Diaz  1 , Andres Perez  1 , Srinand Sreevatsan  1 , Peter Davies  1 , Marie Culhane  1 , Montserrat Torremorell  1
Affiliations

Association between Influenza A Virus Infection and Pigs Subpopulations in Endemically Infected Breeding Herds

Andres Diaz et al. PLoS One. .

Abstract

Influenza A viruses (IAVs) are distributed worldwide in birds, pigs and humans, and cause important endemic disease affecting hosts in all countries. Although pigs play a key role in the ecology of IAVs, the epidemiology of IAVs within swine herds is poorly understood. In this longitudinal study we describe the prevalence of IAVs infection in three subpopulations of pigs in 5 breeding herds in the Midwestern USA. Each herd was sampled monthly for a year and, at each visit, 30 individual nasal swabs were collected from the three subpopulations, namely, a) replacement females, resident on-farm for less than 4 weeks (new gilts), b) replacement females, resident on-farm for more than 4 weeks (gilts), and c) neonatal pigs less than 21 days of age (piglets). Real time reverse transcriptase polymerase chain reaction (RRT-PCR) was used to detect IAVs, and the association between IAVs infection and pig subpopulation was measured using a mixed logistic regression model. Nasal swabs (n = 4,190) were collected from 141 groups of pigs. At least, one IAV-positive nasal swab was found in 19.9% (n = 28) of the sampled groups, and 7.7% (n = 324) of all nasal swabs tested positive. After adjusting by annual quarter and sampling event, the odds of testing IAV positive were 7.9 (95% CI 1.4, 43.9) and 4.4 (95% CI 1.1, 17.1) times higher in groups of new gilts and piglets compared to groups of gilts, respectively. Results indicate that new gilts and piglets had higher odds of testing IAV positive than gilts in swine breeding herds and that season influences IAV infection in pigs. Based on these findings, we recommend that IAV control strategies be aimed at preventing infection before gilts are introduced into the farm, and in pigs prior to weaning.

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Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.

Figures

Fig 1
Fig 1. Study design.
Five swine-breeding herds (largest rectangles, 1 to 5) in the Midwest were sampled between November 2011 (month 1) and December 2012 (month 14). White rectangles represent sampling visits (12 per farm), and the smallest rectangles (n = 141) indicate the groups of pigs sampled. Groups are colored based on pig subpopulation: yellow (new gilts, n = 21), green (gilts, n = 60), and purple (piglets, n = 60). Missing group-rectangles indicate that there were no new gilts on that visit. Groups were assumed nested within sampling events, and sampling events were assumed nested within farms.
Fig 2
Fig 2. Percentage of influenza A virus positive samples distributed by farm, subpopulation and month.
See this image and copyright information in PMC

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