Advocacy in action: National Swine Influenza Surveillance Program update

Harry Snelson, DVM
AASV Director of Communications

In May 2009, the US Department of Agriculture (USDA) Animal and Plant Health Inspection Service Veterinary Services implemented the National Swine Influenza Virus Surveillance Program following the emergence of the pandemic H1N1 (pH1N1) virus in the human population. Swine veterinarians, pork producers, and the USDA collaborated with the Centers for Disease Control and Prevention to establish this surveillance program to facilitate access to swine influenza virus (SIV) isolates to human- and animal-health researchers for further analysis. This program is seen as a model for future comprehensive and integrated surveillance programs in animal agriculture. The following is an update on the progress of this program.

The objectives of the SIV Surveillance Program are the following:

1. To monitor endemic and emerging influenza viruses in the US swine herd,

2. To facilitate the collection of influenza isolates for animal and human research, and

3. To provide isolates for development of diagnostic reagents and vaccines.

The surveillance program focuses on the collection of isolates representative of those present in the US swine herd. The program targets three swine populations:

1. Case-compatible diagnostic samples submitted to veterinary diagnostic laboratories,

2. Swine exhibiting clinical signs of influenza-like illness at points of concentration, and

3. Swine herds associated with human illness.

In fiscal year 2010 (FY2010), the first complete year of surveillance collection data, 1537 swine (423 herds) were tested as part of the surveillance program. One hundred one (101) herds were influenza-positive and virus was isolated from 59 herds. Samples tested in FY2010 identified pH1N1, H1N1, H1N2, and H3N2 viral subtypes. The predominant subtype was H1N2.

Concerns associated with possible restrictions on market access resulted in decreased numbers of samples submitted to veterinary diagnostic laboratories during late 2009 and early 2010. In late 2010, an anonymous submission protocol was adopted as the default submission standard to encourage more participation from veterinarians and producers. This modification appears to have resulted in significant increases in sample submissions. Producers retain the option to participate in a traceable submission protocol if they agree to provide additional contact information.

According to data recently released by USDA covering influenza surveillance submissions from October 2010 through July 2011, 4630 swine have been tested representing 1500 herds. Samples analyzed by one of the 26 participating National Animal Health Laboratory Network veterinary diagnostic laboratories represented the vast majority of the surveillance submissions (4602 swine and 1495 herds). The remaining samples were collected in association with public-health investigations (28 pigs and five herds). To date, there have been no submissions from swine exhibiting influenza-like illness at points of concentration (such as markets, fairs, and livestock shows). The anonymous submission protocol accounted for 1404 of the 1500 herds participating in the surveillance program.

Of the 1500 herds tested, 658 were matrix-assay positive and 332 were virus-isolation positive. Of note, the pandemic N1 assay detected 110 positive herds. The influenza surveillance program has shifted its focus from concentrating on pH1N1, given the declining human-health concerns and the relatively endemic nature of the pandemic subtype within the US swine population.

— Harry Snelson, DVM
AASV Director of Communications