Pandemic (H1N1) 2009 Influenza and its Potential Implications for Animal Health

At present, the overall impact of the H1N1 virus for the health of the EU pig population is considered minimal and the current epidemiological situation of the virus in pigs does not justify their vaccination with pH1N1 vaccine, according the European Food Safety Authority (EFSA).
calendar icon 12 October 2010
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Following a request from The European Commission, the Panel on Animal Health and Welfare was asked to deliver a scientific opinion on the pandemic (H1N1) 2009 influenza and its potential implications for animal health and thus:

  1. To assess the significance for the health of animals of different species (specially pigs and different poultry species) of the occurrence of pandemic (H1N1) 2009 influenza virus in the EU and elsewhere
  2. To assess the implications and consequences of the possible evolution of the pandemic (H1N1) 2009 influenza virus on animal health
  3. To assess the effectiveness and efficiency of disease control options such as establishing animal movement restrictions in protection and surveillance zones, culling of infected pig herds and contact herds for pandemic (H1N1) 2009 influenza virus, as it is common practice for notifiable diseases, e.g. CSF, AI, FMD
  4. To assess the risk that animals from a herd/ flock which was infected with pandemic (H1N1) 2009 influenza virus spread the virus after the last clinical signs of disease have been observed
  5. To assess the possibility, efficacy and efficiency of vaccination, using existing vaccines or newly developed vaccines against pandemic (H1N1) 2009 influenza virus, in pig and poultry populations also in relation with possible evolution of variants of influenza viruses posing a serious risk to public and animal health, and
  6. To assess the role of wildlife, in particular wild boar and wild birds in the epidemiology of pandemic (H1N1) 2009 influenza virus, if any.

Analysis of the recent pandemic (H1N1) 2009 (pH1N1) virus shows that it contains gene segments from pig, bird and human influenza viruses in a combination that has never been observed before. It appears probable that the pH1N1 virus originates from pigs, however, the pH1N1 virus has not been detected in pigs prior to its emergence in humans.

In addition to human infections, several cases of pH1N1 virus infections in animals have been reported worldwide, predominantly in pigs but also in other animals including turkeys and cats.

Occasionally, pigs in the field have been infected following exposure to pH1N1 virus infected humans. Virus spread between and within herds has been observed, but the prevalence of pH1N1 in the swine populations worldwide is not known as no comprehensive epidemiological surveillance has been performed except in Norway.

In field infections, a sub-clinical course was very common and when clinical signs were seen (coughing, fever), they were generally mild, the morbidity was low, and there was no mortality.

Pig-to-pig transmission passages with the pH1N1 virus have occurred but no increase in virulence of the virus has been observed, even in herds with naïve pigs.

At present, the overall impact of pH1N1 virus for the health of the EU pig population is considered minimal, and there is no indication that the situation is different elsewhere.

Pathogenic features of pH1N1 virus in experimentally inoculated pigs indicate that the infection is purely of a respiratory nature and shows a course similar to that of the endemic swine influenza viruses (SIVs) currently circulating in the swine populations worldwide. Thus, clinical signs, in experimentally infected pigs, are variable but relatively mild with fever, coughing and inappetence.

In poultry, outbreaks of pH1N1 have been reported only in turkeys specifically in breeder flocks. The most likely cause of outbreaks in turkey breeder flocks is transmission of pH1N1 virus from infected poultry workers carrying out artificial insemination. Currently, there is no evidence that pH1N1 virus is able to spread horizontally among turkeys within a flock. A drop in egg production and decreased shell quality are the main clinical signs of pH1N1 virus infection of turkeys.

Turkeys, chickens and ducks are refractory to experimental infections with pH1N1 virus via the respiratory tract. However, turkeys can be infected experimentally with pH1N1 virus by the intrauterine and intracloacal route.

From the animal health point of view, no specific control measures against pH1N1 are considered necessary.

The use of clinical signs as temporal proxy for termination of virus excretion within an infected epidemiological unit is of little value in either pigs or poultry. In these species, the duration of virus excretion is not sufficiently associated with the appearance of clinical signs to allow epidemiological decision making based on their temporal order of occurrence. In consequence, using the time of cessation of clinical signs and a preset time interval at the level of epidemiological units to establish clearance from infectiousness (virus shedding) is lacking any scientific basis.

Immunity resulting from vaccination of pigs with SIV vaccines existing on the European market will provide some extent of cross-protection against infection with the pH1N1 influenza virus but specific pH1N1 vaccines will offer superior protection. Such vaccines will significantly reduce or even completely prevent pH1N1 replication and disease in the individual animal.

At present, from the available data, the epidemiological situation of pH1N1 in pigs does not justify their vaccination with pH1N1 vaccine. Vaccination on a voluntary basis will likely protect the vaccinated animals but it will not prevent the spread of the pandemic H1N1 virus in swine populations, unless sufficient proportion of farms coverage is reached.

Currently, no vaccines against H1 viruses for poultry are available.

Wild boar may be susceptible to pH1N1 but, if so, they are not expected to play any significant epidemiological role. No pH1N1 virus infections have been reported in wild boar or in wild birds despite the extensive surveillance programmes for influenza viruses conducted since the start of the H5N1 epidemic in poultry in 2004.


  • Place strong emphasis on information to (a) increase disease awareness and (b) ensure that biosecurity is implemented to contribute to the reduction of potential spread of pH1N1 within and between animal units and also from humans to animals and back.

  • Awareness should be raised about the risk of infecting breeder turkeys with pH1N1 virus during artificial insemination. Specific guidelines should be developed to lower the risk of transmission of pH1N1 during AI.

  • Clinical signs are not reliable as a basis to decide on the end of an infection with pH1N1 virus in an infected herd/flock because pH1N1 induced signs are variable, non-specific or absent. Therefore, when the health status in regard to excretion of pH1N1 virus from a farm/flock needs to be known, it is recommended to test a number of nasal/oro-pharyngeal swabs (swine) or oropharyngeal and cloacal swabs (poultry) according to the expected within herd/flock prevalence for pH1N1 virus by a specific pH1N1 PCR. Testing should start 14 days after the diagnosis is established and continue at two-week intervals until no excretion of virus can be demonstrated. In pigs, the focus should be on animals of eight to 12 weeks of age.

  • Inclusion of diagnostic procedures for the detection of pH1N1 might be considered in the event of the detection of non-notifiable influenza A viruses in existing syndromic surveillance programmes for H5/H7 in poultry to provide some baseline data should the virus change its tropism and pathogenicity for poultry.

  • There is no urgency for vaccination of pigs against pH1N1 virus. It could be useful, however, to have a specific vaccine, based on the pH1N1 virus, in case of change of the epidemiological situation of the virus in the pig population.

  • At present, there is no need to vaccinate poultry against pH1N1 virus.

  • Monitoring of circulating influenza viruses in swine and poultry populations should be instigated to obtain data to characterize the circulating influenza viruses for further evolution of the pH1N1 virus including changes in virulence etc can be assessed. This information should be shared and analyzed together with similar information from the human health area.

Recommendations for Future Research

Available/stored swine influenza viruses detected in surveillance programmes in a variety of countries in the 10 years prior to the pandemic should be sequenced as far as possible to provide valuable scientific data that may improve understanding of the factors involved and led to the emergence of pH1N1.

Further Reading

- You can view the Opinion by clicking here.

Further Reading

- Find out more information on influenza in pigs by clicking here.

October 2010
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