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Understanding Influenza A/H1N1 in Humans and Swine Influenza

INFORMATION IN THIS DOCUMENT WILL BE UPDATED ON A REGULAR BASIS AS NEW AND MORE INFORMATION BECOMES AVAILABLE

 

What is the currently on-going Influenza A/H1N1 crisis?


A new (re-assorted) type of H1N1 influenza virus is currently spreading in humans in at least a dozen countries, causing illness, mostly not severe; and as of 30 April 2009, deaths in two countries. Recent sequencing results made public from CDC Atlanta demonstrate that the Influenza A/H1N1 virus currently circulating among humans in the USA, Mexico and other parts of the world, contains genetic reassortment of three viruses which have been circulating in pigs in Europe, Asia and America since 1998. This new information suggests that the progenitor virus strain was a virus circulating in swine and has evolved in humans through gradual mutations over a 10-12 year span, and has components of avian and human origin.

 

On 2 May 2009, the Canadian Food Inspection Agency (CFIA) announced that it had found H1N1 flu virus in a swine herd in Alberta, and that it was highly probable that the pigs were exposed to the virus from a worker who had recently returned from Mexico and had been exhibiting flu-like symptoms. Signs of illness were subsequently observed in the pigs. The individual has recovered and all of the pigs are recovering. Further testing is underway to more fully characterise the virus.

 

Globally, investigations on the epidemiologic situation in pigs are still required to understand: i) if the virus is currently circulating widely in pigs; and ii) what other viruses are circulating in the pig population.


What is swine influenza?


Swine Influenza (SI) is a widespread and common disease in pig populations worldwide. In its severe form, it is characterized by an acute, febrile, respiratory disease of swine. It may be caused by a number of different type A influenza subtypes known to circulate in pig populations around the world. The most common types found in pigs belong to the H1N1, H1N2 and H3N2 subtypes. Once pigs become infected, and following a short incubation period of 1-3 days, they may develop clinical signs of a flu-like disease with high fever (40-41C°), ocular and nasal discharge and severe coughing. The animals appear lethargic and anorectic. Virus transmission among pigs occurs primarily through nasal discharges and the disease mostly spreads very rapidly. The disease is very common in industrial holdings. In individual pens, morbidity could be high, but mortality is usually very low.


Why are Influenza viruses changing all the time?

 

Influenza viruses have the peculiarity of possessing a genome made up of 8 distinct gene segments (coding for 11 viral proteins). If pigs or other animals (and also humans) become co-infected with two different strains of influenza viruses this may cause a partial mixing of the genetic material and a third, new virus may be generated with genes coming from both the original viruses. This mixing (called re-assortment) is largely due to the segmented nature of the genome. Reassortment may or may not change the antigenic characteristics. These reassortments may also bring changes to other virus characteristics, including virulence and host range. Re-assortments occur frequently, including when viruses from different animal species infect the same host. Swine influenza viruses do not infect humans frequently. When they do, such infections in humans are mostly associated with direct and close contacts with infected pigs. Human-to human transmission is usually not observed.

 

What is the difference between avian influenza, swine influenza and human influenza viruses?


Avian influenza viruses, swine influenza viruses, and human influenza viruses all belong to the same class of viruses known as Orthomyxoviruses.

Avian influenza viruses circulate in wild and sometimes also domestic birds populations. Certain sub-types, including the highly pathogenic H5N1, are occasionally transmitted to mammals, including humans. Swine influenza viruses circulate in swine populations and are occasionally, albeit infrequently, transmitted to birds and to humans. Human influenza viruses circulate in human populations and are transmitted from person to person. Human influenza viruses are also transmissible to animals, pigs in particular. Pigs can therefore harbor viruses from avian and human sources, and act as “mixing vessels” for these viruses. An example of humans infecting pigs is the recent case reported by the Canadian Food Inspection Agency (CFIA) on 2 May 2009, announcing that it had found H1N1 flu virus in a swine herd in Alberta, and that it was highly probable that the pigs were exposed to the virus from a worker who had recently returned from Mexico and had been exhibiting flu-like symptoms. Signs of illness were subsequently observed in the pigs, and further testing was being underatken to characterise the virus.


Is the Influenza A H1N1 virus infecting humans related to the highly pathogenic avian influenza (HPAI) H5N1 subtype that has resulted in the deaths of over 250 people and millions of poultry from 2003 - 2009?


Both H1N1 and H5N1 are subtypes of the Influenza type A virus. Both viruses contain the neuraminidase 1 (N1) protein helping virus to become released from an infected host cell after replication. While there is some similarity between the viruses, the emerging H1N1 virus in humans does not in any direct way relate to the HPAI H5N1 virus circulating in poultry.


It appears that the emerging H1N1 flu virus contains elements of avian influenza virus, in addition to swine and human influenza viruses. Are domestic poultry playing any role in the transmission and spread of this new virus ?


While it is true that the new H1N1 genome comprises two avian genes, this virus is spread among people, and does not circulate in poultry. This means that birds have no role in the transmission or spread of the novel H1N1 flu virus.


What should national authorities do if an influenza-like disease is suspected among animals?


National authorities are encouraged to carefully investigate possible occurrences of influenza-like events in domestic animals. Virus samples may be collected and sent to national labs and/or international reference centres. National authorities can always get in touch with FAO, and by contacting EMPRES-Shipping-Service@fao.org, avail of support for transporting samples for laboratory testing.

 

In order to reduce the risk for transmission of influenza A/H1N1 (humans-to-animals or animals-to-animals), FAO recommends the following:

 

  • Case definitions for suspect and probable cases should be developed in collaboration with animal health partners and disseminated widely. Outbreak investigation protocols and laboratory sampling procedures should also be developed and disseminated to all veterinary professionals.
  • Surveillance for porcine respiratory disease should be intensified and all cases of porcine respiratory syndrome should be immediately reported to the national veterinary authorities. The International Organizations -- OIE and FAO -- should be informed when presence of the new A/H1N1 Influenza virus is confirmed.
  • Movement restrictions should be implemented for all farms or holdings with swine showing signs of clinical respiratory illness until diagnosis of the illness have been made. Where influenza A/H1N1 is confirmed, these restrictions should be in force until seven days after the last animal has recovered. Animals suffering from swine influenza can be separated from healthy herd-mates and allowed to recover; there is no need to cull affected animals.
  • Animal handlers and veterinarians should wear protective gear to minimize risk of being infected by zoonotic agents, including influenza. Persons who work directly with swine should be urged not to go to work if they have any signs respiratory disease, fever or any influenza-like illness.
  • In high risk areas a swine influenza vaccine could be used in swine as long as it is considered effective against the circulating strain, and is permitted by relevant authorities.

 

Is it safe to handle or eat pork?


The risk of infection of H1N1 virus through ingestion has never been established. If at all present, influenza viruses are rapidly killed when meat is cooked, and there are no specific precautions other than the usual guidance of practicing good hygiene during preparation of meat or pork products.


Is it safe to handle or eat pork?


The risk of infection of H1N1 virus through ingestion has never been established. If at all present, influenza viruses are rapidly killed when meat is cooked, and there are no specific precautions other than the usual guidance of practicing good hygiene during preparation of meat or pork products.


What is FAO doing to address the current crisis?


The immediate actions to be taken are to ascertain whether the new H1N1 strain is circulating in pig populations, confirm that there are no direct linkages between animals and illnesses in the human population, and understand how this new virus has acquired genetic materials from human, avian and swine influenza strains. FAO is working in close coordination with the World Health Organisation (WHO), the World Organization for Animal Health (OIE), as well as other national and international actors, to clarify and interpret the evolution of this new disease, and advise member countries on how to best deal with this worrying turn of events, with maximum efficiency.


Where can more information be found on this issue?


This FAQ is to be considered a living document, and more information will be added on the FAO website over the coming days and weeks.

 

For up-to-date information on swine health, please contact your national veterinary authorities.

 

For information on human health related issues please contact your national health authorities.

 

The FAO, WHO and OIE websites provide additional information.

 

For up-to-date information on the novel influenza A virus subtype H1N1 circulation in humans, please refer to WHO Disease Outbreak News.