Descriptive clinical and epidemiological characteristics of influenza A H1N1 2009 virus infections in pigs in England

Abstract

Infection of pigs with influenza A H1N1 2009 virus (A(H1N1)pdm09) was first detected in England in November 2009 following global spread of the virus in the human population. This paper describes clinical and epidemiological findings in the first English pig farms in which A(H1N1)pdm09 influenza virus was detected. These farms showed differences in disease presentation, spread and duration of infection. The factors likely to influence these features are described and relate to whether pigs were housed or outdoors, the age of the pigs, inter-current disease and the management system of the unit. Infection could be mild or clinically inapparent in breeding pigs with more typical respiratory disease being identified later in their progeny. Mortality was low where disease was uncomplicated by environmental stresses or concurrent infections. Where deaths occurred in pigs infected with A(H1N1)pdm09 influenza, they were mainly due to other infections, including streptococcal disease due to Streptococcus suis infection. This paper demonstrates the ease with which A(H1N1)pdm09 virus was transmitted horizontally and maintained in a pig population.

Increased risk of A(H1N1)pdm09 influenza infection in UK pig industry workers compared to a general population cohort

“…The increased risk of A(H1N1)pdm09 in pig industry workers is compatible with the concurrent emergence of infection with A(H1N1)pdm09 in pigs in England, which was first observed in November 20096 and confirmed by the serological results in our study. As there was minimal trade of live pigs between North America and Europe during the period of the study and no reports of the pandemic strain in European pigs prior to human cases,37 it is likely that pigs were initially infected by humans during the early stages of the 2009 pandemic, and infection then transmitted efficiently within and between pig herds but also through reverse zoonoses events following contact of pigs with infected humans.…”

“…Between 1998 and 2009, an avian‐like H1N1 strain most commonly and an H1N2 strain were regularly detected in UK pigs 4, 5. The A(H1N1)pdm09 virus was detected in pig herds from autumn 2009,6 although it may have been first transmitted to pigs from humans several months earlier 7…”

Influenza A virus infection of healthy piglets in an abattoir in Brazil: animal-human interface and risk for interspecies transmission

“…2010, Song et al 2010, Forgie et al 2011, CDC 2012, Gray et al 2012, Williamson et al 2012). Swine workers and their family members are at increased risk of contracting swine influenza virus infections ( Olsen et al 2002, Myers et al 2006, Gray et al 2007, Robinson et al 2007, Yassine et al 2009, Beaudoin et al 2012, CDC 2012, Wong et al 2012).…”

“…Coughing, nasal discharge, fever, lethargy, difficulty in breathing, depressed appetite and reproductive disorders have been associated with different influenza A virus subtype infections throughout the world (Kuntz-Simon & Madec 2009). Close contact between pigs, stress, meteorological and environmental factors have been shown to contribute to influenza virus spread (Brown 2000, Williamson et al 2012). …”

“…Swine viruses bind equally well to both NeuAcα2,6Gal and NeuAcα2,3Gal (with a slightly higher binding affinity for NeuAcα2,6Gal), therefore they are able to infect both human and avian cells [for review see Ma et al (2009) ]. Evidence exists demonstrating transmission of influenza viruses from humans to pigs (Howden et al 2009, Adeola et al 2010, Song et al 2010, Forgie et al 2011, Gray et al 2012, Williamson et al 2012) as well as from pigs to humans (Robinson et al 2007, Yassine et al 2009, CDC 2012). Influenza A virus transmission between humans and swine often results in the emergence of new strains with the potential of spreading among both populations (Myers et al.…”