|PANDEMIC H1N1 2009|
Questions and Answers
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What is the difference between pandemic H1N1 2009 and swine influenza?
“Classical” swine influenza is a well-known disease of pigs, caused by a distinct group of influenza A subtypes and strains. Different subtypes and variants are found in different parts of the world, but “classical” swine influenza is believed to occur worldwide. Infections with these “classical” swine influenza viruses, although capable of rapidly spreading within a herd, cause very low mortality or no mortality at all in infected herds, and are often of concern due to production losses, as pigs sick with influenza do not gain weight as quickly as unaffected pigs. Human infection with these known swine influenza viruses has occurred, but has been an uncommonly described event and usually associated with close contact with live pigs.
Have humans been infected with pandemic H1N1 2009 by animals?
Although it is likely that influenza viruses from animals are part of the history of the pandemic virus, the current influenza pandemic is predominantly a human disease. The virus rapidly emerged in human populations, and spread across the globe as infections were spread from one person to another.
How do we know that animals have not played a significant role in the spread of pandemic H1N1 2009?
Emergence of the pandemic influenza virus was first identified in humans in North America – epidemiologic investigations revealed that most infected humans, in this initial phase, had not been in contact with pigs. The virus rapidly spread among human populations in all regions of the world through human-to-human transmission. In investigations of animal illness, most cases reported to the OIE are believed to have resulted from animals being exposed to ill humans; reports of infection in animals have predominantly been associated with pigs, there have been a small number of reports in other animal species.
Why did the OIE insist to change the term “swine flu”?
The pandemic H1N1 2009 virus includes in its genetic characteristics human, avian and swine virus components. It is scientifically and factually not accurate to name this human disease “swine influenza” as this term refers to a well known disease, the “classical” swine influenza, and implies an ongoing role of pigs in the pandemic. The human and animal health global scientific community has agreed that the most appropriate way to refer to the disease is “pandemic H1N1 2009 influenza”.
What do we know about pandemic H1N1 2009 infections in pigs and birds?
An increasing number of pandemic H1N1 2009 outbreaks in pigs are being reported to the OIE; in most cases, human to pig transmission was the suspected cause of infection in pigs. Experimental studies demonstrate that pigs are susceptible to the pandemic H1N1 2009 virus isolated from people and that pigs can transmit virus among themselves. The susceptibility of pigs to the virus combined with the high prevalence of infection in people, suggests that it is possible that we will see increasing numbers of outbreaks in pigs. With this in mind there is potential for the pandemic H1N1 2009 virus to become established in some pig populations.
Does pandemic influenza H1N1 cause serious disease for pigs and birds?
Pandemic H1N1 2009 infection does not lead to serious disease in pigs; clinical signs are mild and similar to swine influenza. Infected pigs usually all recover.
Does OIE recommend vaccination of animals for pandemic H1N1 2009?
For swine influenza, vaccination may be recommended in certain cases, strictly for economic reasons. For pandemic H1N1 2009 in pigs, the disease does not have a significant impact on animal production and is not currently widespread in pig populations; vaccination is therefore unlikely to be worthwhile at present. There is currently no need to vaccinate any animals against pandemic H1N1 2009.
Why is culling of birds recommended for highly pathogenic avian influenza (HPAI), but it is not recommended for pigs and birds infected with pandemic influenza virus?
Highly pathogenic avian influenza (HPAI) is a severe threat to animal health – particularly in birds - and in the case of H5N1, a severe threat to human health as well. Classic control measures such as biosecurity and culling affected flocks aim to prevent spread of this serious disease to other birds and are proportionate to the risk. In the case of H5N1, culling also aims to control the public health risk in the animal source. When birds get infected with highly pathogenic avian influenza, they rapidly develop life threatening illness and many die in a few days. The farm and water sources on the farm can become contaminated with the avian influenza virus, because birds shed the virus in their faeces. Therefore culling is justified and is a critically important control measure to stop the spread of highly pathogenic avian influenza. When, for economic reasons culling is not possible - mainly in poor countries and in countries without early detection/ rapid response systems in their veterinary services - mass vaccination can be considered as an alternative option.
Does OIE recommend slaughtering of pigs infected with pandemic H1N1 2009?
If animals have recovered from illness and are not showing clinical signs they can be slaughtered for food production. However, it is not recommended to move live pigs from a currently infected farm to other farms.
What do we know about pandemic H1N1 2009 infections in animals other than pigs and birds?
We know that several species of animal will be susceptible to pandemic H1N1 2009. Experimental studies may further elaborate this. Certainly ferrets are used as a model for human influenza transmission and pathogenesis, and therefore it is not surprisingly that they are susceptible to the pandemic virus.
It is possible that pandemic virus will be detected in several species of animals, other than pigs, including companion animals; however sporadic occurrences in other species does not mean that the pandemic H1N1 2009 virus will become established in these animal populations or serve to provide additional risk to the human population.
Have other human influenzas become established in animal populations?
Yes. There is evidence that the H1N1 influenza virus that caused the 1918 pandemic (commonly known as the Spanish flu) was closely related to an influenza virus that caused disease in pigs in the following years; the virus was first isolated and identified in pigs in 1930. One hypothesis is that the H1N1 virus that caused the 1918 pandemic may have spread from humans to pigs and, over a period of time, became established in pig populations. An alternate hypothesis is that both humans and pigs were infected from an avian source around the same time, and these avian-origin viruses independently developed into the Spanish flu among humans and swine influenza among pigs. H3N2 viruses that were circulating in humans in the 1970s later became, over a period of time, established in pig populations.
There seems to be many subtypes and strains of influenza A viruses that have and are circulating in animals and humans?
Yes, there are many subtypes and strains of influenza A virus circulating in different animals. Individual strains of influenza A viruses generally only become established in one or a limited number of animal species. These strains are continuously spread within these animal populations, resulting in a limited number of circulating strains. Occasionally an influenza strain can cross over and infect another species of animal. Most of the time, this kind of cross-species infection does not spread well in the new population; however, in certain cases, the influenza virus may become established as new circulating strain in this new population.
What has happened to avian influenza?
H5N1 Highly pathogenic avian influenza (HPAI) remains a significant threat to human and animal health. The disease is currently endemic in poultry in Egypt and Indonesia, and during 2009 up until 1 November, limited outbreaks of H5N1 HPAI in animals have been reported to the OIE by 12 other member countries/territories.
Can cats and dogs be infected with influenza A viruses, and pandemic H1N1 2009?
Yes, like other animals, cats and dogs can be infected with influenza A viruses and it may be possible that there will be more reports of pandemic H1N1 2009 in cats and other pet animals, although these animals may not be as sensitive to the influenza virus infection as humans and pigs. Thanks to advances in veterinary care and diagnostic testing, nowadays it is more likely that influenza infections will be detected in pet animals. However reports of sporadic occurrences of infection in animals do not imply that the pandemic H1N1 2009 virus will become established in pet animal populations as it has done in human populations. The most likely route of infection for cats and dogs is through contact with owners infected with the virus.
What about ‘cat flu’? Is it related?
No, ‘cat flu’ in its common usage refers to a disease that is not caused by an influenza A virus. It is most commonly caused by two viruses (Feline Herpes Virus or Feline Calicivirus) that do not belong to the family of influenza virus. The name of ‘cat flu’ can be confusing as it refers to the flu-like clinical signs of the disease rather than to the name of the infectious agent.
Does OIE recommend specific measures when interacting with pet animals?
Basic hygiene measures should always be practiced when interacting with pet animals – including the hand washing, practising personal hygiene, keeping the environment clean, and on and around farms applying good biosecurity measures. Pandemic H1N1 2009 has not meant that these recommendations are any less relevant.
Can I get infected from eating pork?
Foodborne illness in humans can sometimes occur after eating food products contaminated with bacteria, viruses, parasites, or toxins. Influenza infection in humans is a respiratory disease – people are exposed to the virus by breathing it in or carrying it to nose or eyes after being in contact with virus. Because of this, influenza is not a foodborne disease. There are no documented cases of human infection associated with eating foods carrying swine influenza virus or pandemic influenza virus, and the risk of being infected with swine influenza viruses through consuming pork or pork products is negligible. According to international food hygiene standards, only healthy animals should be slaughtered for food. Even if these rules are broken the risk is still extremely low because influenza viruses are generally restricted to the respiratory tract (e.g. airways and lungs) of pigs and are not detected in the muscle (meat) of pigs, even when pigs are ill.
Are influenzas in animals OIE listed diseases?
All highly pathogenic avian influenza (HPAI) viruses are OIE listed diseases and thus notifiable to the OIE because they have the potential for rapid international spread and have a severe impact on animal health, and in the case of H5N1 HPAI have severe consequences for infected humans. Low pathogenic avian influenza viruses of subtypes H5 and H7 in domestic poultry are also notifiable to the OIE because they have the potential to mutate readily into HPAI viruses.
What is current OIE requirement for export of animals susceptible to pandemic H1N1 2009 virus?
Neither swine influenza nor pandemic H1N1 2009 are OIE listed diseases, the OIE recommends against imposing trade measures such as testing herds from which animals or meat are sourced for export from countries that have experienced outbreaks of swine influenza or pandemic H1N1 infection in pigs or humans. There is no scientific justification to do so because the diseases are mild and transient in infected pigs and pigs that have recovered from infection are not infectious for other pigs or humans.
What would be the consequences for an importing country of importing pigs carrying pandemic H1N1 2009 virus?
There would be little consequence of importing pigs carrying pandemic H1N1 2009 virus. Clinical infection of pigs with pandemic H1N1 2009 is generally rather uneventful and infected pigs make a full recovery. In large groups of pigs the virus may circulate for some time but the impact on health and productivity is not significant.
Why has there been surveillance for certain types of influenzas in some animals for many years?
Owing to their impact on animal health and more recently the impact of H5N1 Highly Pathogenic Avian Influenza (HPAI) on human health, there has been extensive surveillance for influenza viruses in domestic and wild birds, particularly of avian influenza viruses of subtypes H5 and H7, but also other subtypes. HPAI viruses and low pathogenic avian influenza viruses (LPAI) of subtypes H5 and H7 in domestic poultry, and influenza in horses are OIE listed diseases, and OIE Members must have surveillance in place and report occurrences of these diseases.
Why is pandemic H1N1 2009 surveillance among animals so important?
Surveillance for pandemic H1N1 2009 and other influenza viruses in animal populations has benefits for animal and human health. For animal health, epidemiological and virological surveillance provides useful information for animal production management and operations, leads to the development of better diagnostic tests, improves our understanding of the local, regional, and global animal health situation related to pandemic H1N1 2009 and other influenza viruses, and can benefit animal vaccine development. Perhaps the larger benefits of surveillance for pandemic H1N1 2009 relate to public health needs. The major international desire expressed by public health relating to the occurrence of influenza viruses in animals, particularly in pigs, concerns the potential for the pandemic virus to mutate or exchange genes with circulating swine influenza or other influenza viruses – and that the result of these reassortments and mutations might be able to cause more severe disease in humans in the future. Mutations and reassortments can result in significant changes to the characteristics of the virus such as the ability to cause more severe disease, to more easily spread among humans or animals, or to exhibit resistance to the common antiviral medicines used to treat influenza in humans. The OIE/FAO network of expertise on animal influenza (OFFLU) continues to work on sharing data and information among the world’s leading laboratories to advance our knowledge and build preparedness in this area. One of the primary objectives of OFFLU is to share key information with the human health network, providing an early warning to significant changes in viral characteristics, and providing biological material and information for early preparation of human influenza vaccines that may protect against emerging virus strains.
Are there any testing methods for pandemic H1N1 2009 in animals, and in pigs in particular?
Yes. OFFLU - the joint OIE-FAO network of expertise on animal influenza - has developed a laboratory testing algorithm for detection of pandemic H1N1 2009 in pigs. This provides advice on the tests that should be used to confirm an occurrence of pandemic H1N1 2009 in pigs and how to differentiate the pandemic virus from other H1N1 influenza viruses known to circulate in pigs.
What is the likely origin of pandemic H1N1 2009?
Although the pandemic H1N1 2009 virus contains genetic material from influenza viruses known to have been circulating in pigs, birds, and humans, we still do not know in which animal species this genetic material combined; we may never know the definitive answer to this.
What do we know about the genetic make-up of the pandemic H1N1 virus?
Analyses of available genetic sequence data from the current pandemic virus and influenza viruses previously isolated in animals and humans show that pandemic H1N1 2009 is a triple reassortant virus with a combination of genes that are most likely to have originated from influenza A viruses circulating in pigs, birds, and humans. The pandemic virus contains genes that are very similar to those found in influenza viruses of swine, some of which are known to have been circulating in pigs approximately ten years ago and others currently circulating in pigs. Notably, six genes are closely related to genes from a triple reassortant virus circulating in North America and two are closely related to genes from a virus circulating in pigs in Eurasia.
If influenza viruses have been known to cause disease in animals and humans for more than a century, why are there still so many unanswered questions?
Influenza viruses have an impressive ability to change rapidly, adapting themselves to any situation to try to overcome a body’s natural defences to prevent the infection. The science that allows us to investigate and understand viruses like influenza has undergone dramatic advances in the last 10 years. Recent technological advances led to the practice of molecular epidemiology – the ability to analyse the genetic code material of viruses. This allows us to understand the genetic differences between viruses, and in combination with laboratory studies and classic epidemiology, answer questions like “Why do some animals get influenza more than others?” and “Why do humans sometimes catch influenza from an animal, or vice versa, but most of the time this does not happen?” The emergence of H5N1 HPAI further advanced research into avian influenza viruses, because it caused such severe, frequently fatal, disease in poultry and the consequences of human infection, although infrequent, were usually very severe – but much remains to be learned about other influenza viruses, and the factors that lead to transmission between different kinds of animal species (including humans).
What does current experimental evidence tell us about the susceptibility of different animals to pandemic H1N1 2009?
A limited number of preliminary experiments have provided useful information about infection in pigs. Pigs experimentally infected with pandemic H1N1 2009 (originally isolated from human cases) develop a mild respiratory illness that quickly resolves. The illness is very similar to the disease pigs experience when they have swine influenza caused by other strains of influenza. Sick pigs infected with pandemic H1N1 2009 are able to infect other pigs. These experimental findings were supported by infections later seen on pig farms in multiple countries. Based on experimental evidence and experiences on the farm, we expect the disease in pigs caused by this strain to continue to be very similar to swine influenza.
Why are pigs considered so important in relation to the evolution of influenza A viruses?
In general - although not always the case - pigs can be susceptible to influenza A viruses established in avian, human, and pig populations; therefore they have the potential to become co-infected with human, avian, and swine influenza viruses. A co-infection with several different influenza A viruses can lead – through exchange of genetic material between the viruses (reassortment) – to the emergence of a new antigenically distinct virus (a reassortant strain) with pandemic potential.
How are pandemic H1N1 2009 infections in pigs different than swine influenza? Will infection with pandemic H1N1 2009 eventually be considered just another swine influenza?
Currently, “classical” swine influenza is characterised as a respiratory illness caused by influenza viruses circulating in pig populations and is capable of routinely spreading within and among pig populations. Pandemic H1N1 2009, however, is still occurring as a sporadic disease in swine. It is not yet clear if pig infections with pandemic H1N1 2009 will become routine, and whether this influenza strain will become established in the swine populations. So far, pandemic H1N1 2009 has not manifested itself differently from swine influenzas in pigs. The OIE continues to work with Members to better understand the occurrences of this new pandemic virus in pigs, and with influenza experts to understand the disease epidemiology associated with these occurrences.