Continuing growth in cases of the H1N1 Flu Outbreak Virus (just renamed by the U.S. Department of Agriculture) has raised many questions about the severity and control of the virus and the future implications for the swine industry, according to Iowa State University (ISU) veterinary diagnostician Greg Stevenson, who spoke at a World Pork Expo seminar sponsored by Fort Dodge Animal Health.

Interestingly, the proportion of swine respiratory cases in which influenza virus is detected at the ISU Veterinary Diagnostic Laboratory (VDL) has been declining since 2003 (see Figure 1). “That steady decrease has likely been due to changes in management as well as increased vaccine pressure,” Stevenson says.

Changing Flu Viruses

It's important to remember that H1N1 flu viruses are not new to swine, he points out. Historically, the original or “classic” swine flu was type H1N1. Only in recent years (1998) have both H3N2 and H1N2 viruses (called triple reassortants because they contain gene segments of avian, human and swine viruses) evolved from a mixing of that original classic swine influenza virus (SIV) with human and avian flu viruses.

Figure 2 depicts the proportion of cases of all three types of SIV identified at the Iowa State VDL since 1999.

Most times when reassortment of flu viruses occurs, the impact is minimal because the new virus does not survive and spread, he says.

“But once in a while one of the new reassortant viruses becomes established in a population, and that is what is happening with this new H1N1 Flu Outbreak Virus infecting people,” Stevenson explains.

The federal Centers for Disease Control and Prevention became concerned because of the apparent establishment of the H1N1 virus in the human population and its transmission among people, unusual events for H1N1 viruses.

To be clear, the H1N1 flu viruses that are currently most common in pigs are different in their makeup from the H1N1 strain recently discovered in humans — but they are also different from the classic H1N1 flu virus that exclusively circulated in swine prior to 1990, Stevenson explains.

“We do still find this classic strain in our swine population, but not very commonly. The viruses that we have today in our pigs are mostly triple reassortant H1N1 strains, comprised of genes from the classic swine H1N1 virus and also genes from human and avian viruses,” he states.

Key Questions

Stevenson provided answers to several key questions:

  • Where did this novel H1N1 flu virus infecting humans come from?

    The virus is a quadruple reassortant and contains mostly genes from the triple reassortant H1N1 viruses found in swine in North America as well as two genes from flu viruses found only in swine in Europe and Asia. It was originally assumed that this novel virus must have originated from pigs in Mexico, but pig herds in close proximity to humans that were first infected have been negative, he asserts.

  • Is the novel virus present in Iowa swine?

    Stevenson says ISU diagnostic lab virologist K-J Yoon, DVM, compared 125 H1N1 swine isolates to sequences obtained from the new H1N1 Flu Outbreak Virus. “Absolutely none of this flu outbreak virus was detected in our testing of samples,” Stevenson reports.

  • Will the Iowa State standard diagnostic test for influenza viruses in swine detect the H1N1 Flu Outbreak Virus?

    The standard influenza tests will identify all flu viruses, but it will take further testing to identify the novel H1N1 virus; Iowa State has developed a rapid test with that capability, he says. It is expected that other state diagnostic labs will also have access to a rapid diagnostic test, which will only test positive for the H1N1 Flu Outbreak Virus and negative for all known North American swine influenza viruses.

Next Page: Surveillance Program

Previous Page: Changing Flu Viruses

Surveillance Program

Each state will be cooperating in USDA's surveillance program for flu viruses in swine, Stevenson says. The program, to be rolled out at a date to be determined, contains three surveillance streams:

  • Swine that are linked to a human case of the new H1N1 flu virus will be tested.

  • Swine observed with influenza-like illness at first points of concentration (shows, fairs, sale barns) will be tested.

  • Submissions to veterinary diagnostic laboratories; however, the Iowa State Veterinary Diagnostic Laboratory will be testing for the novel H1N1 Flu Outbreak Virus on a voluntary basis only. “We will not be running this test on any samples that come into our laboratory unless we have written permission to run it from the person submitting the samples,” Stevenson stresses.

However, any positive test results must be reported to the state veterinarian's office and to USDA, he adds.

The decision by state officials in Iowa to keep testing of samples for this virus strictly voluntary is a wise move, Stevenson believes. Part of the reason that flu sample submissions from swine have slowed this year has been due to producer fears their herd might be infected with the novel strain and the unknown consequences that could result. The Alberta, Canada hog farmer whose herd was quarantined due to infection with the novel flu strain has voluntarily culled his entire herd because meat processors were reluctant to buy his hogs.

Vaccine Research, Development

The National Animal Disease Center in Ames, IA, is evaluating whether current swine flu vaccines will protect against this novel strain of the flu virus, according to Stevenson.

Comparison of the complete sequencing of the novel flu strain to swine viruses sequenced at Iowa State indicates there is a lot of similarity, meaning most U.S. pigs vaccinated with available influenza vaccines should have some protection from the hybrid strain.

“Should this virus be transmitted from infected people to pigs, we don't expect it to be any different from existing influenza viruses in the swine industry from a health standpoint,” Stevenson declares.

USDA's Animal and Plant Health Inspection Service has announced that the genetic material for the H1N1 Flu Outbreak Virus is being shipped to veterinary biologics manufacturers and is expected to be available in ample supply by early to mid July.

The genetic material of the novel virus is being derived from a sample acquired from the federal Centers for Disease Control and Prevention through collaboration with the National Animal Disease Center and USDA's Animal and Plant Health Inspection Service's (APHIS) Center for Veterinary Biologics (CVB).

In providing the same H1N1 genetic material to all interested manufacturers, APHIS eliminates the need for each manufacturer to develop its own master seed that would then require confirmatory testing by CVB.

Instead, while the global master seed virus is undergoing tests at CVB, each interested manufacturer can start work on vaccine development and production.