Why the concern about avian influenza in pigs?
 

Avian Influenza and Swine

Influenza is a zoonotic disease, a disease that can be transmitted between animals, birds and humans. There are many different strains of influenza that circulate within pigs, birds, and humans. These strains usually affect a certain species, so that human influenzas only affect humans, swine influenzas only affect pigs, and avian influenzas only affect birds.

In general, human influenza circulates throughout the year, and regular outbreaks of seasonal influenza are expected during the fall and winter seasons. Throughout history, however, there have been several major outbreaks of pandemic influenza which cause significantly increased levels of illness and death across the world. A pandemic occurs when a new strain of influenza develops to which no one has been previously exposed. Pigs are a unique species because their lungs contain receptors that can attach both to human and avian influenzas. It is thought that if a human and avian influenza were to infect a pig at the same time, a new influenza strain could be developed to which no one would have immunity, and the result could be a human influenza pandemic.

• Why the concern about avian influenza in pigs?
• Can avian influenza be transmitted to pigs?
• What are the clinical signs of avian influenza in pigs?
• How do I protect my swine herd against infection by avian influenza?
• How will avian influenza infection in swine herds be monitored during the outbreak?
• references

Can avian influenza be transmitted to pigs?

Avian influenza can be transmitted to pigs but it appears that transmission does not occur easily. Several studies of pigs in Asian countries such as China, Korea, Thailand, and Vietnam following H5N1 avian influenza outbreaks have tried to look for the presence of antibodies which would suggest that infections with H5N1 avian influenza occurred. The number of positive samples for H5N1 avian influenza in pigs ranged from 0% to 9.9%, suggesting that the incidence of such infection is low. Avian influenzas of the subtypes H1N1, H3N3, and H4N6 have been found in swine herds in Canada although these are rare occurrences.
 

What are the clinical signs of avian influenza in pigs?

When a pig is infected with avian influenza, the clinical signs should be similar to that of swine influenza. These clinical signs include cough, fever, and decreased food consumption. One experiment that infected pigs with H5N1 avian influenza found that the cough was mild. 
 

How do I protect my swine herd against infection by avian influenza?

You can take measures to prevent the entry of avian influenza into your swine herd. The most important action is to implement good biosecurity practices around the barn, including:

• Barn entry
  Keep the barn doors closed and locked and only allow essential personnel inside. Separate clothing and footwear for inside the barn should be provided.
   
• Vehicles
  Only essential vehicles should be allowed near the barn. Trucks that enter the barnyard should be clean. Ensure that signs indicate where vehicles are allowed and where vehicles should park. Discuss biosecurity procedures with companies that send trucks to your farm.
   
• Equipment
  Equipment that enters the barn should be cleaned and disinfected.
   
• Other animals
  Establish a fly and rodent control program in and outside of the barn. Keep birds from entering the barn by placing and maintaining screens over air inlets. Other birds such as ducks and geese should never be allowed in a swine barn.
   
• Water supply
  A Canadian swine herd was infected by avian influenza presumably through a lake that provided water for the barn. Ensure that the incoming water supply from a dugout or other body of water is chlorinated, and that the chlorine level and pH is monitored regularly.
  

How will avian influenza infection in swine herds be monitored during an outbreak?

Avian influenza infection in pigs will be monitored through monitoring clinical signs in herds adjacent to the avian influenza outbreak. Surveillance by blood sampling of pigs may also be utilized but currently there is no reliable test for the detection of Avian Influenza by blood sampling in swine; and due to the low probability of infection, this method will likely not be used.

References

Choi YK et al. Studies of H5N1 influenza virus infection of pigs by using viruses isolated in Vietnam and Thailand in 2004. Journal of Virology. 2005; 79(16):10821-10825. 

Jung K et al. Serologic surveillance of swine H1 and H3 and avian H5 and H9 influenza A virus infections in swine population in Korea. Preventive Veterinary Medicine. 2007; 79:294-303. 

Karasin AI et al. Characterization of avian H3N3 and H1N1 influenza A viruses isolated from pigs in Canada. Journal of clinical Microbiology. 2004; 42(9):4349-4354. 

Ninomiya A et al. Seroepidemiological evidence of avian H4, H5, and H9 influenza A virus transmission to pigs in southeastern China. Veterinary Microbiology. 2002; 88:107-114. 

Olsen CW. The emergence of novel swine influenza viruses in North America. Virus Research. 2002; 85:199-210.