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Over the past month we’ve been watching a small but growing number of human infections with a novel H3N2v influenza virus - most of which are associated with direct contact with pigs being displayed at county and state fairs.
Efficient and sustained human-to-human transmission has not been established by the CDC, and so their recommendations at this time revolve around preventing disease transmission from pigs to humans.
Earlier this week the CDC issued advice to Fair organizers, that included:
Animal Health Recommendations:
- Monitor animals daily for signs of illness, including discharge from nose and/or eyes, lethargy (sleepiness), no appetite, fever, or sometimes coughing. Ensure that a veterinarian, such as the fair vet or state vet, is notified of any ill animals.
- Ill pigs, animals suspected or known to be infected with influenza viruses, and animals from herds with a recent history of respiratory disease should not be exhibited. They should be immediately isolated or sent home.
Yesterday, a dispatch appearing in the CDC’s EID Journal illustrated just how difficult identifying and separating influenza-infected pigs from the rest can be.
It’s called:
Volume 18, Number 9—September 2012
Dispatch
Influenza A(H1N1)pdm09 Virus among Healthy Show Pigs, United States
Article Contents
Gregory C. Gray , Jeffrey B. Bender, Carolyn B. Bridges, Russell F. Daly, Whitney S. Krueger, Michael J. Male, Gary L. Heil, John A. Friary, Robin B. Derby, and Nancy J. Cox
Abstract
Within 5 months after the earliest detection of human influenza A(H1N1)pdm09 virus, we found molecular and culture evidence of the virus in healthy US show pigs. The mixing of humans and pigs at swine shows possibly could further the geographic and cross-species spread of influenza A viruses.
Asymptomatic carriage of viruses is not uncommon in humans, of course. A few examples we’ve looked at in the past include:
- During the 2009 pandemic I wrote They Walk Among Us, that looked at the difficulties of identifying those who might be infectious based on symptoms such as fever.
- Earlier this year, in The Very Common Cold, we looked at a study of rhinovirus among college students tested over an 8 week period – that found asymptomatic infections led symptomatic infections by a factor of 4 to 1.
- And last year, in EID Journal: Pre-Symptomatic Influenza Transmission, we saw evidence of presymptomatic spread of the H1N1 virus in three clusters in Japan, which also suggests that asymptomatic carriers ought to be able to spread the virus as well.
The idea that pigs might carry influenza viruses asymptomatically, therefore, is hardly surprising. But the amount of available scientific research has been limited.
Yesterday’s study found that nearly 1 in 5 healthy-looking pigs they tested were actually infected with a flu virus.
Last night Lisa Schnirring and Robert Roos of CIDRAP NEWS wrote extensively on this study, and so at this point, I’ll simply invite you to read their excellent report.
Study finds flu in healthy-looking pigs at state fairs
Lisa Schnirring and Robert Roos
Staff Writers
Aug 15, 2012 (CIDRAP News) – Testing of a sampling of pigs shown at the Minnesota State Fair during the 2009 H1N1 influenza pandemic revealed that 19% of them were infected with flu viruses, even though they looked healthy, according to a new study.
The findings highlight the challenges of preventing pigs and humans from passing flu viruses back and forth at fairs and swine shows, especially this summer when several states are tracking human illnesses from a novel H3N2 virus that has been detected in both pigs and people.
During the 2009 H1N1 pandemic Japan, India, and China were among the nations that attempted to identify, interdict, and isolate those who might be carrying the H1N1 virus when they entered their country.
While their efforts may have slowed the introduction of the virus, they certainly didn’t stop it. Earlier blogs on these attempts include:
Japan: Quarantine At Ports Ineffective Against Pandemic Flu
Experts: Extreme Measures Won’t Stop The Flu
Their failure was likely due to the large number of presymptomatic, and asymptomatic carriers of the virus that arrived without showing signs of illness.
And the same is likely true with pigs on display at county fairs this fall.
Removing symptomatic pigs certainly makes sense - and will certainly reduce the risks of spreading the virus - but it is unlikely to totally eliminate it.
Which means that additional human cases of H3N2v are likely, even with the enhanced biosecurity measures in place at county fairs.
Before anyone gets freaked out over the risks of going to the county fair, so far this summer there have been only about 200 confirmed cases of this H3N2v flu, involving 5 brief hospitalizations and no deaths.
During roughly the same time period, there have been nearly 700 West Nile Infections, involving hundreds of hospitalizations, and 26 deaths.
So if you are looking to lower your risks of illness when you go to the county fair this fall, it only makes sense to carry and use a hand sanitizer, and avoid eating or drinking around animal displays.
But to avoid serious illness, the better advice is to wear an insect repellant whenever you go outside, as your risks of contracting viral illness are greater right now from infected mosquitoes, than they are from sick pigs.
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