MEDICAL

Influenza viruses exist in three “types,” designated A, B and C. Of these, only influenza A viruses are significant concerns for the health of pigs. However, there are a large number of different “subtypes” of influenza A viruses. These subtypes are defined by the hemagglutinin (H or HA) and neuraminidase (N or NA) proteins of the virus. The HA is also the protein against which the host directs antibodies that can neutralize the virus. Of practical significance, there is no cross-protective immunity mediated by antibodies from one HA subtype to another.

There are 15 different subtypes of hemagglutinin and 9 different subtypes of neuraminidase among influenza A viruses. Subtypes are distinguished by differences in their genetic sequences, which translate into differences in their antigenic structure. The combination of HA and NA subtypes present in a virus are depicted by H and N designations, such as H1N1, H3N2, and so on. In the course of history, relatively few hemagglutinin and neuraminidase combinations have consistently circulated among pigs or people (predominantly H1N1, H1N2 and H3N2 in pigs, and H1N1, H1N2, H2N2 and H3N2 in people). In contrast, virtually all of the possible influenza A virus subtypes exist among wild waterfowl. In these birds, influenza viruses infect the gastrointestinal tract rather than the respiratory tract, which is the target organ in pigs, people, horses and other mammalian hosts of influenza viruses. The infections generally do not make the birds sick. In waterfowl, the viruses are shed in the bird’s feces, and ultimately into the water of lakes and ponds that the birds visit during migrations, but also potentially onto the ground of barnyards and farm fields.

Influenza viruses carry their genes on 8 separate pieces (”segments”) of nucleic acid (RNA), rather than on one long single molecule. This structural feature has very important implications for virus evolution, because if two (or more) influenza viruses simultaneously infect cells in the same individual, then during replication, these viruses can exchange RNA segments with one another, thereby creating viruses with entirely new combinations of genes. This process of reassortment was the basis for the appearance of the pandemic viruses of 1957 (the “Asian” flu) and 1968 (the “Hong Kong” flu) in the human population. These pandemic viruses were responsible for millions of cases of human illness and tens of thousands of human deaths. In both cases, influenza viruses from waterfowl reassorted with the previously circulating human influenza viruses to create viruses with different hemagglutinin subtypes (from H1 to H2 in 1957 and from H2 to H3 in 1968). It is the change to a hemagglutinin subtype against which the population has no immunity (”antigenic shift”) that causes these periodic global disease outbreaks of human disease.

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Tags: Asian flu | H1n1 | H1N2 | H2N2 | H3N2 | hemagglutinin | Hong Kong flu | influenza viruses | neuraminidase | nucleic acid | RNA | Swine Flu | virus

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<h2>Pigs, People and Public Health Swine Influenza</h2> <p style="text-align: justify;">Influenza viruses exist in three ”types,” designated A, B and C. Of these, only influenza A viruses are significant concerns for the health of pigs. However, there are a large number of different ”subtypes” of influenza A viruses. These subtypes are defined by the <a title="hemagglutinin" href="http://911medicalcare.com/medicalcare/hemagglutinin/">hemagglutinin</a> (H or HA) and <a title="neuraminidase" href="http://911medicalcare.com/medicalcare/neuraminidase/">neuraminidase</a> (N or NA) proteins of the virus. The HA is also the protein against which the host directs antibodies that can neutralize the virus. Of practical significance, there is no cross-protective immunity mediated by antibodies from one HA subtype to another.</p> <p style="text-align: justify;">There are 15 different subtypes of hemagglutinin and 9 different subtypes of neuraminidase among influenza A viruses. Subtypes are distinguished by differences in their genetic sequences, which translate into differences in their antigenic structure. The combination of HA and NA subtypes present in a virus are depicted by H and N designations, such as H1N1, H3N2, and so on. In the course of history, relatively few hemagglutinin and neuraminidase combinations have consistently circulated among pigs or people (predominantly H1N1, H1N2 and H3N2 in pigs, and H1N1, H1N2, H2N2 and H3N2 in people). In contrast, virtually all of the possible influenza A virus subtypes exist among wild waterfowl. In these birds, influenza viruses infect the gastrointestinal tract rather than the respiratory tract, which is the target organ in pigs, people, horses and other mammalian hosts of influenza viruses. The infections generally do not make the birds sick. In waterfowl, the viruses are shed in the bird’s feces, and ultimately into the water of lakes and ponds that the birds visit during migrations, but also potentially onto the ground of barnyards and farm fields.</p> <p style="text-align: justify;">Influenza viruses carry their genes on 8 separate pieces (”segments”) of nucleic acid (RNA), rather than on one long single molecule. This structural feature has very important implications for virus evolution, because if two (or more) influenza viruses simultaneously infect cells in the same individual, then during replication, these viruses can exchange RNA segments with one another, thereby creating viruses with entirely new combinations of genes. This process of reassortment was the basis for the appearance of the pandemic viruses of 1957 (the ”Asian” flu) and 1968 (the ”Hong Kong” flu) in the human <a title="population" href="http://911medicalcare.com/medicalcare/population/">population</a>. These pandemic viruses were responsible for millions of cases of human illness and tens of thousands of human deaths. In both cases, influenza viruses from waterfowl reassorted with the previously circulating human influenza viruses to create viruses with different hemagglutinin subtypes (from H1 to H2 in 1957 and from H2 to H3 in 1968). It is the change to a hemagglutinin subtype against which the population has no immunity (”antigenic shift”) that causes these periodic global disease outbreaks of human disease.</p> <p style="text-align: justify;">(Read More on Free Ebook at PDF Format)</p> <p style="text-align: justify;"><a href="http://911medicalcare.com/pdf/public-health-swine-influenza" target="_blank">Download</a> Pigs, People and Public Health Swine Influenza.pdf</p> <p style="text-align: justify;"><a href="http://911medicalcare.com/wp-content/uploads/2009/06/public-health-swine-influenza-image.jpg"><img class="alignnone size-full wp-image-880" title="public health swine influenza image" src="http://911medicalcare.com/wp-content/uploads/2009/06/public-health-swine-influenza-image.jpg" alt="public health swine influenza image" width="350" height="350" /></a></p><br/><a href="http://www.socialmarker.com/?link=http://911medicalcare.com/swine-flu/pigs-people-and-public-health-swine-influenza/&title=Pigs%2C+People+and+Public+Health+Swine+Influenza&text=...&tags=" target="_blank"><img src= "http://www.socialmarker.com/bookmark.gif" border="0" /></a><noscript><a href="http://www.socialmarker.com" >Social Bookmarking</a></noscript> <p>The article <a href="http://911medicalcare.com/swine-flu/pigs-people-and-public-health-swine-influenza/">Pigs, People and Public Health Swine Influenza</a> is provided by <a href="http://911medicalcare.com" title="Manual Nurse and health Guidelines"> Manual Nurse and Health Guidelines</a>. The article from<a href="http://911medicalcare.com" title="Medical"> Medical</a> site is freely distributed for non-commercial purposes to include the source for the article and does not alter the content.</p>

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