Aiming At Swine Influenza Virus

Livestock Trends

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In the last decade, influenza A virus in swine (IAV-S) has become an increasingly difficult disease challenge for hog producers to control. In part, this is due to shifting strains that make IAV-S – like it’s human influenza counterpart – difficult to vaccinate against.

The damage
Pigs infected with IAV-S can suffer from slow growth and poor feed conversion. The economic hit can be coupled with secondary infections that can result in mortalities.

“A lot of the cost of the disease is in the growing pigs,” says Montse Torremorell, DVM, Ph.D., associate professor at the University of Minnesota College of Veterinary Medicine. “Although prior to weaning is when the piglets are at greatest risk of infection.”

Typically, piglets become infected with IAV-S around the second week of life, Torremorell says. Even though not all farms manage pigs in the same way, the virus is a challenge across the United States and globally.

IAV-S also is a concern for farm workers. Influenza in hogs can infect humans, as the fast-spreading strain, H1N1 – or as the mainstream media called it, “swine flu” – in 2009 demonstrates, says Micah Jansen, DVM, Pork Technical Services, Zoetis. Likewise, influenza in humans can infect pigs. Therefore, pig caregivers who are sick should stay home.

The costs for IAV-S adds up even when looking at production alone.

“The financial impact is around $3 to up to $10 per head, depending on if the case is paired with PRRS or Mycoplasma hyopneumoniae,” Jansen says. “The swine influenza virus complicates things by damaging lung tissue and allowing opportunistic pathogens to set up shop. Even if a herd does pretty well with vaccinating for M. hyo, for example, influenza can come in and cause infection because the immune system is not fighting other challenges as effectively.”

Prevention: The best treatment
Antibiotics can help battle secondary bacterial infections, but animals must mount an effective immune response to fight off the virus. The best IAV-S treatment is ensuring animals continue to eat and drink. Some veterinarians may prescribe medication to help reduce fever, Torremorell notes.

Preventing IAV-S through good biosecurity protocols helps limit animals’ exposure to disease. Researchers are working to understand more about how the virus is transmitted to develop more precise guidelines.

Currently, one of the most effective methods for disease prevention is vaccination. Typical protocols include vaccinating sows to help provide subsequent piglets with maternal antibodies or vaccinating piglets 10 weeks after birth.

“There is interference between passive immunity and vaccination if you use the vaccine when the pigs have a lot of maternal immunity in their system,” Torremorell says.

Strain change
Immunity from vaccines is typically limited to the specific strain included in the product. However, newer IAV-S vaccines may provide some cross protection against multiple strains.

“It is hard to predict which strain you will have on a farm,” Torremorell says.

Strains currently circulating in U.S. herds include H1N1, H1N2 and H3N2, but the virus is rapidly changing within the U.S. and abroad, Jansen notes.

“Up until 1998, we really only had H1N1 circulating in pigs,” Jansen says. “H1N1 was actually a pretty stable virus that would circulate, but – in general – we were able to control it pretty well. Then, we started seeing the emergence of different types and that’s when influenza became more challenging.”

Herd veterinarians typically identify IAV-S by the tell-tale signs of lethargic animals with a hard, barking cough. An initial PCR test determines the presence of pathogen, and a subsequent test can identify the specific strain.

This information helps DVMs make recommendations about herd movements. For instance, being able to understand what IAV-S strain is present in a group of gilts testing positive for IAV-S can help understand what restrictions, if any, should be placed on movements into the sow farm, Jansen says.

“Understanding gilt status before entering the farm is important,” Jansen says. “We want to avoid adding ‘fuel’ to the fire and compromising piglet health.”

Vaccination choices
Jansen recommends considering a multivalent vaccine to help protect against IAV-S. Products should include the most recent strains identified to provide relevant protection to the herd.

“We can’t predict what strain the animals are going to be exposed to,” Jansen says. “You want to choose a vaccine that has several strains and demonstrated cross protection.”

In outbreak situations, producers should vaccinate the whole sow herd to remove the disease’s opportunity to replicate and cause further damage, Jansen advises.

“If a new virus is entering a herd – or if influenza has been there a long time and producers have been unable to get rid of it – they can use the vaccine as a way to stimulate the immune system and clear the virus from the herd,” she says. “Producers should administer the vaccine to all adult pigs at the same time – two doses at three weeks apart. If they can implement this along with using good management practices in the farrowing house, the virus doesn’t have anywhere to go because they have helped eliminate it and pigs that are susceptible.”

Key Points:

  • Formerly known as simply “swine influenza virus” or “SIV,” industry experts are now using the more specific name: influenza A virus in swine (IAV-S).
  • IAV-S is a respiratory disease of swine caused by multiple subtypes of type A influenza viruses.
  • The virus is endemic in swine populations in North and South America, Asia, and Europe.
  • Classic swine influenza infection was caused by the H1N1 subtype and remained relatively unchanged for 75 years.
  • Since 1998, swine influenza infections in the United States have evolved from a seasonal disease caused by a single, relatively stable H1N1 genotype to an endemic year-round respiratory disease caused by multiple genetically unstable subtypes (H1N1, H1N2, and H3N2).
  • The USDA conducts voluntary surveillance for swine influenza to identify viruses that may be circulating in swine and contribute to improved diagnostics and vaccines.

Courtesy of USDA Swine Influenza Surveillance Update. July 31, 2015.