Memories of the Novel H1N1 influenza outbreak that rocked the pork industry last year are something you would rather forget. While many questions remain, such as the pig’s role in how the virus evolves, it’s worth reviewing your on-farm influenza prevention and control practices to stay ahead of this constantly evolving virus challenge.

Pig-to-pig transmission is the primary route of influenza infection in a herd. However, on farms last fall and winter, human-to-pig transmission of the Novel H1N1 virus was suspected in some flu outbreaks in pigs. That’s why it’s important to take precautions to fortify your line of defense to block this transmission route, as well as review your herd biosecurity and vaccination practices.

A good place to start is with your employees. Make sure all your employees and family members, even if they don’t come in direct contact with pigs, receive a flu shot. “We recommend that swine workers receive the seasonal flu shot, especially if they work within hog facilities,” says Lisa Becton, DVM, director of swine health information, National Pork Board.

Review your farm’s sick-leave policy. It should be designed so that workers aren’t penalized for taking a sick day. If workers feel ill and suspect influenza, they should stay home until symptoms subside. Adults may be able to infect others beginning one day before symptoms develop and up to seven days after becoming sick.

“One method to entice ill employees to stay (home) is to provide compensation for lost hours due to illness,” says Matt Allerson, DVM, University of Minnesota. Allerson polled Minnesota and Iowa hog farms and discovered that “many systems (five out of eight) combine personal and sick-leave hours that are available to employees.” But that can be a disincentive because people would rather take time for personal use versus calling in sick. So, the point is to be careful how you package sick-leave options. 

His survey found that most systems require or recommend that employees stay home if they have respiratory illness symptoms. Allerson also found that five out of eight systems hold flu vaccination clinics for employees.

“It is vitally important that farm workers do not come to work if they are showing signs of influenza-like illness and are running a fever,” says Michael Kuhn, DVM, Pfizer Animal Health’s manager of veterinary operations. Having sick employees stay home will help prevent exposing coworkers, as well as transmitting viruses to swine.

General biosecurity practices that limit pathogens from entering your hog facilities also assist in influenza prevention. These include limiting visitors, preventing bird and pest entry, boot washing and frequent hand washing. Becton recommends that you monitor herd health daily, especially during influenza season, and contact your veterinarian if an influenza-like illness is suspected.

“It’s hard to predict what will happen for the remainder of the flu season, as influenza virus is normally found in many U.S. herds,” Becton says. “Influenza surveillance can help the industry better understand what strains are circulating by state and help match vaccine needs and improve diagnostic testing reagents.”

Tracking Influenza

Due to influenza viruses’ reassortment capabilities, national surveillance has become increasingly important for the pork industry. Launched in April 2009, USDA’s national surveillance plan for influenza virus tracks genetic changes in endemic and emerging virus isolates from pigs showing influenza symptoms.

The information generated is then used to make timely and scientific decisions about disease control and prevention measures, as well as help researchers develop effective vaccines.

Becton says surveillance also benefits the industry by identifying circulating influenza viruses and improving the reliability of diagnostic testing. “Having this surveillance information for influenza also can help mitigate potential international trade issues,” she adds.

Pork producer participation in the national influenza surveillance program has been limited and so far focused on identifying the Novel H1N1 virus. However, looking to the future, all influenza strains — including avian and human — will be included in the surveillance efforts.

Teamwork Required

“Swine influenza virus is alive and well in our swine population, and producers are seeing seasonal increases in SIV related to changes in weather and ventilation,” Kuhn says.

Every producer should discuss influenza vaccination strategies with the herd veterinarian. “The decision to vaccinate and which vaccines to use is best done between the producer and his/her veterinarian who can tailor herd-health plans to best fit the farm’s needs,” Becton says.

While influenza vaccination strategies vary widely, most producers routinely vaccinate sow herds, Kuhn says. This can be done in a seasonal, whole-farm strategy with all breeding animals vaccinated in the fall (September to November) and again in winter (January to February) or in a pre-farrowing program during every gestation period, he notes. “Vaccinating incoming gilts is important so you don’t introduce a new, naïve population to the sow herd,” Kuhn adds.

All swine influenza-virus vaccines are made from killed virus and require an initial two-dose protocol.

Maternally derived antibodies, which can linger through the nursery period, make vaccinating piglets a challenge. “Some producers vaccinate piglets in the mid- and late-nursery phase to reduce problems in finishing,” Kuhn says. Again, it’s best to consult with your herd veterinarian for a specific plan. 

One thing is certain — preventing the occurrence and spread of influenza viruses within your herd is the best option. Planning and implementing effective employee sick-leave policies, system biosecurity and herd vaccination protocols will set you on the right path.

Two Options for Influenza Surveillance

Developing a better understanding of influenza viruses is beneficial to the U.S. pork industry. USDA rolled out a national influenza surveillance program in April 2009 and wants pork producers to submit samples for analysis from pigs showing influenza symptoms.

“Producers were initially reluctant to participate in surveillance efforts, as they feared being singled out or having their market chain disrupted,” admits Lisa Becton, DVM, National Pork Board. That was certainly true during the Novel H1N1 influenza virus outbreak, but with the virus less prominent today, producers should reconsider participating in the program.

There are two participation options — anonymous and traceable.

“The default participation method is anonymous, where no information can be traced to the sample except date and state,” Becton says. “No other information will be  available on that sample.”

According to USDA’s Influenza Surveillance in Swine Procedures Manual, “Anonymous data entry removes all owner and submitting personnel information and limits geographical detail to the sample collection’s state.”

The second option is traceable, where producers can provide farm information to USDA to further aid in disease evaluation and analysis. This will occur only with the producer’s signature allowing permission.  Producers who authorize the traceable option receive information from USDA on their sample submissions that would be in addition to the information already gained from the primary diagnostic laboratory. “The farm information provided can be useful in developing more detailed epidemiological analysis of influenza patterns and detail on potential virus change and movement,” Becton says.

“It’s important that veterinarians and producers understand that the samples submitted to the surveillance program are anonymous unless the producer specifically requests in writing to participate in a traceable system,” points out Harry Snelson, DVM, American Association of Swine Veterinarians.

If you suspect influenza in your herd, your veterinarian can advise you on recommended sampling methods and submit the samples to an appropriate diagnostic laboratory. Once samples are collected and submitted, USDA will cover all costs for the surveillance program and associated testing.

Samples submitted to veterinary diagnostic labs are eligible to be entered into USDA’s influenza surveillance program. Toward that effort, the diagnostic lab may run additional tests, including virus sequencing, to further characterize the influenza strain.

“These sequences would then be made available to animal-health and public-health researchers for further study,” Snelson says. “There is no cost to the producer for this additional testing, but the producer and veterinarian will not receive any results of those tests unless the producer requests to participate in the traceable system.”

“It’s our hope that with more samples collected for the surveillance program, future vaccines and herd-health protocols can be improved,” Becton says.