The impact was caused because of the media frenzy surrounding the outbreak and the name given to the strain of flu by the media - 'swine flu'.

The influenza A H1N1 virus was isolated in humans in Mexico in April and in the ensuing two months spread rapidly around the world to more than 70 countries, causing concern regarding a pandemic.

The composition of this virus is now known but its source remains unidentified, Greg Stevenson, DVM, MS, Iowa State University Veterinary Diagnostic Laboratory (ISU VDL) diagnostic pathologist told a seminar hosted by Fort Dodge at this year's World Pork Expo, in Des Moines. "H1N1 is the most common flu virus in swine herds. We see it every day," Dr Stevenson said.

"USDA is going to be referring to the virus found in humans as the H1N1 Flu Outbreak Virus (H1N1FOV) to try and distinguish it from the H1N1 that is in swine herds."

While the main make-up of the two viruses are similar – H1N1FOV is composed of six genes, which are similar to those in the most common endemic North American swine H1N1 virus – the remaining two genes are similar to those in endemic influenza viruses infecting European and Asian swine. They have never been seen in swine in the United States to date.

Dr Stevenson said that no swine herds in Iowa (or anywhere in the United States) at this time have been infected with the H1N1FOV virus. A retrospective study by the ISU VDL looked at 125 H1N1 viruses representing all regions of Iowa from November 2008 to April 2009. All viruses were typical of well-known endemic North American swine influenza viruses.

"Most of our standard tests detect H1N1FOV but they identify it as a regular influenza virus, and not as the outbreak virus," Dr Stevenson said.

"Instead, we developed a rapid test to detect the outbreak virus. We developed it because we knew USDA was working on a voluntary surveillance programme that will be implemented state by state."

He said there were major concerns that the virus would come back more strongly in the autumn to affect people and also that the virus could be transmitted from humans to pigs.

Dr Stevenson said that the USDA is launching a pilot surveillance programme in cooperation with officials in individual states for H1N1FOV in pigs in the United States.

Officials in Iowa are putting the final touches to their programme, including the involvement of the ISU VDL where samples will be tested. The programme will be composed of three surveillance streams: swine that are epidemiologically linked to a human case of the H1N1FOV; swine observed with influenza-like illness at first points of concentration, such as exhibitions, fairs and sale barns; and client-authorised (voluntary) influenza-like illness submissions to the ISU VDL.

In the first two surveillance areas, state officials will collect samples and deliver them to the ISU VDL for standard swine influenza testing, as well as for specific H1N1FOV testing. The third surveillance stream will be strictly voluntary.

"The specific H1N1FOV test will only be run on tissues from submissions in which the submitter has volunteered to participate by completing a written authorisation prior to testing," Dr Stevenson added.

"Any positive tests must be reported to the USDA and the state.

"But we will be running that test on submissions brought to us by the state veterinarians from the samples they are collecting. The samples coming to our laboratory will be strictly voluntary, and we won't be testing unless we have received permission."

However, he warned that any outbreaks in the pig population would not have a severe affect in the pigs but only an economic impact on the industry.