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Re: Canadian Govt: Large Saskatchewan Chicken Farm - Highly pathogenic H7N3
Click on the complete report; it's almost 60 pages pdf. Here are some excerpts:
The persistent survival of influenza virus in ambient air under common environmental conditions suggests that long-range inhalation transmission of influenza is possible. However, direct evidence of its contribution to influenza transmission is sparse. The panel considered a number of studies that bear on the question of long-range transmission of influenza (including all of the most widely-cited), but was unable to draw any conclusions from them as to the presence, absence or relative importance of a long-range mode of transmission of influenza. Previous reviews and reports have focussed discussion of short-range transmission on the concept of ?droplet transmission?. This, however, does not take into account the full range of particle sizes that are expelled from a potentially infectious individual. All particles of inhalable size, whether nasopharyngeal, tracheobronchial or alveolar, can contribute to short-range transmission of influenza. The panel concluded that there is evidence that influenza is transmitted primarily at short range.
Contact Transmission
Contact transmission involves transfer of virus from an infected individual to a potential host either by direct, physical contact (e.g., by kissing) or by indirect contact (e.g., by touching contaminated surfaces). Direct contact with the upper respiratory tract is not sufficient for influenza transmission to occur. Once present on mucous membranes, viral particles must migrate to a region that contains appropriate receptors, such as the nasopharynx where human influenza virus alpha-2,6-linked sialic acid receptors are present. There are no such receptors in the eye (Olofsson, 2005). Only alpha-2,3-
linked sialic acid receptors (the avian type) are present in conjunctivae which may explain why avian H7 influenza infections in humans frequently manifest as conjunctivitis. Although human influenza viruses may not be able to infect conjunctival cells, they could migrate to the nasopharynx via the lacrimal duct and infect cells there. Orally deposited virus could reach the nasopharynx through swallowing. The panel concludes that while it was unable to find evidence of experimental or natural infection of humans with human influenza virus via the mouth or eyes, there is a theoretical possibility that this could occur.
Indirect contact transmission can only occur if the influenza virus remains viable outside of the body. Influenza virus has been shown to persist on external surfaces for upwards of 24 hours depending on the surface type, and on hands for up to five minutes after transfer from the environmental surfaces (Bean, 1982). It is thus reasonable to assume that mucous membrane inoculation of influenza virus via contaminated hands could subsequently occur. Given the large amount of virus contained in ballistic particles that would survive for prolonged periods of time in the environment (that could cause infection only by direct deposition onto mucous membranes or by surface contact followed by self-inoculation), it is reasonable to postulate that contact transmission might occur. In fact, preliminary data from a guinea pig model of influenza demonstrates that contact transmission of influenza occurs, but is less efficient than transmission via inhalation (Palese, 2007; Mubareka, 2007). However, no evidence has been found that hand hygiene or other interventions that might prevent contact transmission (e.g., glove use in healthcare facilities) prevent the transmission of influenza.
The panel concludes that although the occurrence and relative importance of the contact route for influenza transmission have not been demonstrated, or indeed studied in humans, contact transmission likely occurs. (The only study they cited for this is a study on guinea pigs)
The following summarizes the consensus opinion reached by the panel.
1. Ballistic, nasopharyngeal, tracheobronchial and alveolar-sized particles are all emitted from the human respiratory tract.
2. Evidence about the relative contribution of the different modes of transmission to the spread of influenza is sparse and inconclusive.
3. There is evidence that influenza is transmitted primarily at short range.
4. There is evidence that influenza can be transmitted via inhalation of tracheobronchial and alveolar-sized particles at short range.
5. There is evidence that deposition of nasopharyngeal-sized particles in the upper respiratory tract can cause infection.
6. There is evidence that contact transmission can occur. The current weight of evidence suggests that transmission of influenza by inhalation is more probable than by indirect contact.
7. The evidence is lacking to determine whether long-range transmission of influenza occurs, but it cannot be ruled out.
Click on the complete report; it's almost 60 pages pdf. Here are some excerpts:
The persistent survival of influenza virus in ambient air under common environmental conditions suggests that long-range inhalation transmission of influenza is possible. However, direct evidence of its contribution to influenza transmission is sparse. The panel considered a number of studies that bear on the question of long-range transmission of influenza (including all of the most widely-cited), but was unable to draw any conclusions from them as to the presence, absence or relative importance of a long-range mode of transmission of influenza. Previous reviews and reports have focussed discussion of short-range transmission on the concept of ?droplet transmission?. This, however, does not take into account the full range of particle sizes that are expelled from a potentially infectious individual. All particles of inhalable size, whether nasopharyngeal, tracheobronchial or alveolar, can contribute to short-range transmission of influenza. The panel concluded that there is evidence that influenza is transmitted primarily at short range.
Contact Transmission
Contact transmission involves transfer of virus from an infected individual to a potential host either by direct, physical contact (e.g., by kissing) or by indirect contact (e.g., by touching contaminated surfaces). Direct contact with the upper respiratory tract is not sufficient for influenza transmission to occur. Once present on mucous membranes, viral particles must migrate to a region that contains appropriate receptors, such as the nasopharynx where human influenza virus alpha-2,6-linked sialic acid receptors are present. There are no such receptors in the eye (Olofsson, 2005). Only alpha-2,3-
linked sialic acid receptors (the avian type) are present in conjunctivae which may explain why avian H7 influenza infections in humans frequently manifest as conjunctivitis. Although human influenza viruses may not be able to infect conjunctival cells, they could migrate to the nasopharynx via the lacrimal duct and infect cells there. Orally deposited virus could reach the nasopharynx through swallowing. The panel concludes that while it was unable to find evidence of experimental or natural infection of humans with human influenza virus via the mouth or eyes, there is a theoretical possibility that this could occur.
Indirect contact transmission can only occur if the influenza virus remains viable outside of the body. Influenza virus has been shown to persist on external surfaces for upwards of 24 hours depending on the surface type, and on hands for up to five minutes after transfer from the environmental surfaces (Bean, 1982). It is thus reasonable to assume that mucous membrane inoculation of influenza virus via contaminated hands could subsequently occur. Given the large amount of virus contained in ballistic particles that would survive for prolonged periods of time in the environment (that could cause infection only by direct deposition onto mucous membranes or by surface contact followed by self-inoculation), it is reasonable to postulate that contact transmission might occur. In fact, preliminary data from a guinea pig model of influenza demonstrates that contact transmission of influenza occurs, but is less efficient than transmission via inhalation (Palese, 2007; Mubareka, 2007). However, no evidence has been found that hand hygiene or other interventions that might prevent contact transmission (e.g., glove use in healthcare facilities) prevent the transmission of influenza.
The panel concludes that although the occurrence and relative importance of the contact route for influenza transmission have not been demonstrated, or indeed studied in humans, contact transmission likely occurs. (The only study they cited for this is a study on guinea pigs)
The following summarizes the consensus opinion reached by the panel.
1. Ballistic, nasopharyngeal, tracheobronchial and alveolar-sized particles are all emitted from the human respiratory tract.
2. Evidence about the relative contribution of the different modes of transmission to the spread of influenza is sparse and inconclusive.
3. There is evidence that influenza is transmitted primarily at short range.
4. There is evidence that influenza can be transmitted via inhalation of tracheobronchial and alveolar-sized particles at short range.
5. There is evidence that deposition of nasopharyngeal-sized particles in the upper respiratory tract can cause infection.
6. There is evidence that contact transmission can occur. The current weight of evidence suggests that transmission of influenza by inhalation is more probable than by indirect contact.
7. The evidence is lacking to determine whether long-range transmission of influenza occurs, but it cannot be ruled out.
If you find more hand studies, maybe we can pursue them in their own thread. I'd be interested in seeing them.
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