As we enter influenza season in humans and swine, it is important to remember the importance of vaccination and other control measures (such as frequent hand washing) to minimize the risk of viral spread. Since influenza viruses can spread both ways between swine and people, vaccination of employees is important as is encouraging farm employees to stay home if sick with influenza-like symptoms. Likewise, swine vaccination may help prevent clinical signs and minimize viral spread within the herd. It is also important to remind consumers that flu viruses are not found in pork. Consumption of pork is safe.

Continued participation in the influenza surveillance program instituted last year is also important to provide animal health and public health officials with a source of isolates to further vaccine development and diagnostic improvements. Tissues or nasal swabs from clinically sick animals submitted to the veterinary diagnostic lab are automatically entered anonymously into the surveillance program. Unique or novel isolates are submitted to the National Veterinary Services Laboratory for further analysis and inclusion in GenBank to allow access to researchers in human and animal health.

There have been a number of recent reports involving the circulation of H3N2 viruses within the human population. This strain of H3N2 has acquired the Matrix gene from the pandemic H1N1 virus prominent in 2009. This most likely occurred in a pig co-infected with both the swine H3N2 and 2009 H1N1 viruses.

To date, approximately 10 human cases have been identified in Indiana, Iowa, Maine and Pennsylvania. These cases have resulted in relatively mild illnesses with all patients fully recovering. Nine of the recent cases have involved children and many had direct or indirect contact with pigs. Human to human transmission appears uncommon or very limited at this point.

H3N2 viruses commonly circulate in the human population each winter and, according to the Centers for Disease Control and Prevention (CDC), this virus appears most closely related to human H3N2 viruses circulating in the early 1990s. CDC speculates that many people born before 1990 would likely have some level of protection against this virus. This specific strain is not included in the human seasonal flu vaccine currently available. CDC, however, has developed a vaccine seed strain for distribution to human vaccine manufacturers.

The key points to keep in mind are:

  1. Get vaccinated and vaccinate at-risk swine
  2. Farm employees experiencing influenza-like symptoms should stay away from pigs
  3. Frequent hand washing helps prevent the spread of disease
  4. Continue to submit diagnostic samples from clinically sick pigs to the diagnostic lab for inclusion in the influenza surveillance program
  5. Do not transport clinically sick swine
  6. Report vaccine failures to the manufacturer and USDA Center for Veterinary Biologics (online or call 800-752-6255)

Source: American Association of Swine Veterinarians