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A presentation at the 21st International Pig Veterinary Society (IPVS) Congress held last July in Vancouver, Canada is making a bit of a stir in the farm trade magazines over the past week or so.
It details the discovery of a higher-than-expected rate of influenza infection among pigs in the UK.
The original abstract appears on page 269 the 1229 page Proceedings of the 21s IPVS PDF, which may be downloaded from the IPVS2010 website.
Towards risk-based surveillance for swine influenza virus
Barbara Wieland, Alexander Mastin, Dirk U. Pfeifer, The COSI Consortium
Farm publications covering the story include:
Swine 'flu more widespread in England than previously realised – Vetsonline
Swine Influenza Widespread in England, France - Thepigsite
Swine influenza widespread in England – FarmingUk
The researchers enrolled 146 farrow-to-finish farms representing roughly 17% of the English swine herd, and the conducted surveillance by taking serum samples from 20 animals from each farm.
Using Hemagglutination Inhibition (HI) assays, they tested for H1N1, H1N2, and H3N2 flu viruses.
They also collected supplementary information on herd management, health, reproduction, and farm environment to help with their analysis.
The results showed that 59% of the farms tested turned up at least 1 (out of 20 pigs tested) with an HI titer of 1:40 or 2 pigs with lower titers.
The most commonly detected virus was an avian-like H1N1, followed by H1N2, and with just one with H3N2. 18% of farms tested positive for two strains – H1N1 and H1N2 – which the authors state could either represent a cross-reaction or infection with both strains.
According to the Vetsonline article, the incidence of swine influenza detected in France in 2009 was far higher, with 97% of the 29 farms tested positive for at least one strain of the virus.
These strains are consistent with what is normally detected in pig herds, although the prevalence is higher than many had expected in the UK. This from the CDC Factsheet on swine influenza.
Key Facts about Swine Influenza (Swine Flu)
Over the years, different variations of swine flu viruses have emerged. At this time, there are four main influenza type A virus subtypes that have been isolated in pigs: H1N1, H1N2, H3N2, and H3N1. However, most of the recently isolated influenza viruses from pigs have been H1N1 viruses.
H1N2 is assumed to be a reassortment between the H1N1 and H3N2 virus. It has occasionally been detected in humans, and appears to be no more virulent that its parents.
Since its hemagglutinin and neuraminidase proteins are similar to the contributions from H1N1 and H3N2, the seasonal flu vaccine is believed to provide adequate protection.
While swine flu infections are often mild or subclinical in pig herds, and may not appear to have much impact, they can adversely affect productivity. Infection can result in abortion, still born piglets, and decreased lactation in sows.
Beyond the economics of farm production, there is an even greater reason to try to control swine influenza: the potential of seeing newly emerging viruses from the farm.
While influenza viruses normally mutate and change slowly over time time due to antigenic drift, bigger, more abrupt changes come about through a process known as antigenic shift.
Shift can occur when a novel virus makes a direct jump from another species to humans or (more likely) a reassortment of two flu viruses occurs in a host animal resulting in a new hybrid virus.
While rare, as any virologist will tell you. Shift Happens.
Although any susceptible host has the potential to serve as a `mixing vessel’ for influenza viruses, pigs appear particularly well adapted for this role. They are capable of being infected by a wide range of human, swine, and avian viruses.
Increasingly we are seeing research and surveillance showing how influenza viruses mutate and adapt within the pig host. A few examples include:
When Pigs Flu
EID Journal: Swine Flu Reassortants In Pigs
If You’ve Seen One Triple Reassortant Swine Flu Virus . . .
Hong Kong: Swine Flu Reassortment
H3N2 Swine Flu
Although avian influenzas had captured the headlines up until a couple of years ago, since the outbreak of pandemic H1N1 in 2009 - which circulated under-the-radar in pigs for about 10 years – scientists are looking at pigs, and swine influenzas with keener interest today.
Source: FAO
With global pig production growing rapidly to meet the demands of a hungry world, each year we add millions more `mixing vessels’ to natures laboratory.
The prevalence of influenza in UK pigs in the above report is obviously a concern, but it is the lack of surveillance and reporting on swine influenzas from around the world that is particularly worrisome.
A blind spot that could allow another novel influenza virus to emerge with virtually no warning, and spark another global pandemic.
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