Pigs infected with influenza virus typically shed virus for a limited period of time, 7-10 days.However, less is known about influenza virus transmission in swine populations such as swine breeding farms. An understanding of within herd transmission of influenza virus in swine populations may guide control and management practices for influenza. This study was conducted to describe the disease ecology of influenza virus in infected swine breeding farms.
Swine breeding farms confirmed to be infected with influenza virus were selected for enrollment in this study. To determine the subpopulation responsible for maintaining influenza virus infections in breeding farms over time, cross-sectional nasal swab samplings of all subpopulations within selected breeding farms were conducted. Sixty nasal swabs were collected from the following four subpopulations within breeding farms: sows, gilts, neonatal pigs of 3-10 days of age, and neonatal pigs of 11 days of age. All nasal swabs were tested for influenza virus by a Matrix gene RRT-PCR and a subset of samples were isolated and sequenced (HA).3 At the time of submission of this paper, two farms have been sampled.
Influenza virus was not detected in sows or gilt replacements at any point in time at farms enrolled in the study. However, virus was detected in neonatal pigs. On initial samplings, virus was detected in neonatal pigs at both farms. Sampling conducted 30 days following the initial sampling at both farms also revealed that virus was present in neonatal pigs of 11 days of age.
Influenza virus causes respiratory disease in pigs, reduces pig performance and production efficiencies, and has the ability to infect humans. Preliminary results of this study highlight the role of the neonatal pig in the circulation of influenza virus in swine breeding farms. It appears that this subpopulation may be important for the continued circulation of influenza virus in breeding farms as previously described.
M. Allerson, M. Gramer, M. Torremorell. The disease ecology of influenza virus in swine breeding farms. AASV Annual Meeting :37.