wilfriedsoddemann
Active member
Re: H5N1 bird flu spread by drinking water ?
http://www.cdc.gov/eid/content/13/10/pdfs/07-0323.pdf
Rice EW, Adcock NJ, Sivaganesan M, Brown JD, Stallknecht DE, Swayne DE.
Chlorine inactivation of highly pathogenic avian influenza virus (H5N1).
Emerg Infect Dis. 2007 Oct; [Epub ahead of print]:
?? Briefly, virus-infected allantoic fluid was diluted (1:1,000) into continuously stirred, chlorinated, chlorine demand?free phosphate buffer (0.05 M, pH 7.0 and 8.0). ? To slow the rate of inactivation, experiments were conducted at 5 ?C. ??
?Ct (Ct value is the chlorine concentration, C [mg/L], multiplied by the exposure time, t [min]) apply to microorganisms in suspension, not embedded in particles.? [GUIDELINES FOR DRINKING-WATER QUALITY, 7. MICROBIAL ASPECTS, 7.3.2 Treatment, Table 7.6, footnote]. http://www.who.int/water_sanitation_health/dwq/gdwq0506_7.pdf
In (drinking-) water H5N1 viruses are embedded in particles and drinking-water may be colder than 5 ?C and the pH often is > 8.0, perhaps 9.5 ?
Inactivates chlorination in practice and under all conditions avian flu strains, flu viruses embedded in particles, water pH 9.5, water temperature at 3 ?C??
True reassuring news?
Dipl.-Ing. Wilfried Soddemann
[U]soddemann-aachen@t-online.de[/U]
[U]http://www.agoravox.com/article.php3?id_article=5455[/U]
Bird flu in water. How big a problem?
One of the unanswered questions about the transmission of influenza H5N1 is the mode. We presume, probably correctly, that person to person spread is the main mode, mediated by coughing, breathing, sneezing. Whether the infective material is small enough to remain suspended in the air for long periods or whether it is primarily in large droplets that settle out quickly is a matter of importance still under debate but both possibilities pertain to person to person spread via the respiratory tract. Then there is the question of the role of inanimate objects, like door knobs, arm rests or personal physical contact, like shaking hands. There is evidence that the virus remains replicable in the environment for extended periods, although its replicable lifetime on hands may be much shorter, on the order of minutes. There is also the lingering suspicion that there may be other live reservoirs of the virus besides birds in nature we are not aware of. Even with poultry, a recognized reservoir. how the virus gets from birds to humans is a matter of debate. Is it through the bird respiratory tract or intestinal tract or feces laden dust? Finally, can a human contract H5N1 infection from water or food contaminated with the virus? If food is properly cooked it will kill the virus, although undercooked or raw food or its handling during preparation can still presumably infect someone (how, isn?t quite clear). What about water?
The issues are not just drinking water but also recreational water (lakes, streams, oceans) that might be contaminated by infected wild aquatic birds or wastewater discharges. Swimming exposes the conjunctiva of the eye (the thin tissue covering the front of the eyeball which has receptors for influenza virus), not to mention the nose and throat, both suspected sites of viral entry. Drinking water is also a concern. So it is important to have studies that try to nail down some of the unknowns.
A report out of Cornell University says neither drinking water nor wastewater containing viral discharges is likely to be a problem (the paper is published in Environmental Engineering Science and can be downloaded in .pdf format here). The Cornell researchers used the H5N2 subtype of influenza A (low pathogenic for birds and not known to be pathogenic for humans) as a surrogate for H5N1. They showed that the usual water and wastewater treatment modalities of chlorine and UV light were effective in inactivating the virus. Virus was placed into at two temperatures into water and small scale bacterial digesters (the method used in wastewater treatment plants). Each was treated with chlorine (the most common disinfectant in use in water and waste water treatment) and UV light (used primarily in wastewater treatment but also in some drinking water systems). Bacteria and viruses differ greatly in their sensitivity to treatment and no virus is thought to be indicative of the sensitivity of most other viruses. Thus the use of a relatively close avian influenza virus (H5N2) to test the sensitivity of H5N1 to treatment is a reasonable step.
We?ll skip a detailed description of the experimental protocol (you can find them in the paper and they are worth reading just to see how difficult some of these seemingly straightforward questions can be to answer). The persistence of the virus as a replicating entity in water at 4 degrees C. (about 40 degrees F.) is better and longer than at 37 degrees C. (body temperature), but in buffered water was consistently and constantly present for more than 50 hours. At 4 degrees C. in buffered water it was still there after two weeks. Thus the stuff doesn?t just disappear in the environment. It can be around for days or weeks after being deposited. In anaerobic digesters the virus was undetectable at 72 hours. The virus seemed quite sensitive to UV irradiation, although this method is used in only a small percentage of drinking water systems. We have previously discussed the use of UV lights in health care facilities as a possible prophylactic measure and these data seem to support the idea in a different context.
The data on chlorine disinfection is somewhat harder to interpret. Viruses vary widely in their sensitivity to chlorine, so it isn?t a given that chlorine disinfection will inactivate H5N1. The paper gives a Ct (contact time) value of 8 mg.min/L for the virus. Ct is the product of free available chlorine and the time it is in contact with the virus. The average free available chlorine in US drinking water systems is about 1 mg/L (1 ppm) and the paper cites average and median contact times of 237 minutes and 60 minutes, respectively, based on a literature review. This would give average and median Ct?s of 237 and 60 mg.min/L, far in excess of the inactivating levels found in this paper.
The apparent large Ct safety margin is reassuring, although these are average and median Ct?s. A median contact time of 60 minutes means half the systems had contact times less than 60, so half the systems had Cts with a safety margin less than ten fold, not quite so reassuring. Much depends on the distribution in the lower tail and the upper tail of the Ct inactivation estimate. And of course all of this only holds good for conditions similar to the bench experiments of this paper. The results do not tell us with certainty what would happen in a more natural and usual water and waste water environment. What happens when the virus is inside clumps of feces, for example, or in water of different pH or salt make-up?
There are also a number of treatment methods not tested here, among them ozone (now being used increasingly because of the resistance of parasite cysts to chlorine), chlorine dioxide, chloramines and some others. Many small water supplies (almost always groundwater sources), have no treatment at all, so none of this would apply in those cases.
This paper appears to be well done and provides good information. We need more work like it, although unfortunately this kind of work is not the road to academic stardom. It may not be elegant, but it is very, very useful.
Dipl.-Ing. Wilfried Soddemann
eMail: soddemann-aachen@t-online.de
http://www.cdc.gov/eid/content/13/10/pdfs/07-0323.pdf
Rice EW, Adcock NJ, Sivaganesan M, Brown JD, Stallknecht DE, Swayne DE.
Chlorine inactivation of highly pathogenic avian influenza virus (H5N1).
Emerg Infect Dis. 2007 Oct; [Epub ahead of print]:
?? Briefly, virus-infected allantoic fluid was diluted (1:1,000) into continuously stirred, chlorinated, chlorine demand?free phosphate buffer (0.05 M, pH 7.0 and 8.0). ? To slow the rate of inactivation, experiments were conducted at 5 ?C. ??
?Ct (Ct value is the chlorine concentration, C [mg/L], multiplied by the exposure time, t [min]) apply to microorganisms in suspension, not embedded in particles.? [GUIDELINES FOR DRINKING-WATER QUALITY, 7. MICROBIAL ASPECTS, 7.3.2 Treatment, Table 7.6, footnote]. http://www.who.int/water_sanitation_health/dwq/gdwq0506_7.pdf
In (drinking-) water H5N1 viruses are embedded in particles and drinking-water may be colder than 5 ?C and the pH often is > 8.0, perhaps 9.5 ?
Inactivates chlorination in practice and under all conditions avian flu strains, flu viruses embedded in particles, water pH 9.5, water temperature at 3 ?C??
True reassuring news?
Dipl.-Ing. Wilfried Soddemann
[U]soddemann-aachen@t-online.de[/U]
[U]http://www.agoravox.com/article.php3?id_article=5455[/U]
Bird flu in water. How big a problem?
One of the unanswered questions about the transmission of influenza H5N1 is the mode. We presume, probably correctly, that person to person spread is the main mode, mediated by coughing, breathing, sneezing. Whether the infective material is small enough to remain suspended in the air for long periods or whether it is primarily in large droplets that settle out quickly is a matter of importance still under debate but both possibilities pertain to person to person spread via the respiratory tract. Then there is the question of the role of inanimate objects, like door knobs, arm rests or personal physical contact, like shaking hands. There is evidence that the virus remains replicable in the environment for extended periods, although its replicable lifetime on hands may be much shorter, on the order of minutes. There is also the lingering suspicion that there may be other live reservoirs of the virus besides birds in nature we are not aware of. Even with poultry, a recognized reservoir. how the virus gets from birds to humans is a matter of debate. Is it through the bird respiratory tract or intestinal tract or feces laden dust? Finally, can a human contract H5N1 infection from water or food contaminated with the virus? If food is properly cooked it will kill the virus, although undercooked or raw food or its handling during preparation can still presumably infect someone (how, isn?t quite clear). What about water?
The issues are not just drinking water but also recreational water (lakes, streams, oceans) that might be contaminated by infected wild aquatic birds or wastewater discharges. Swimming exposes the conjunctiva of the eye (the thin tissue covering the front of the eyeball which has receptors for influenza virus), not to mention the nose and throat, both suspected sites of viral entry. Drinking water is also a concern. So it is important to have studies that try to nail down some of the unknowns.
A report out of Cornell University says neither drinking water nor wastewater containing viral discharges is likely to be a problem (the paper is published in Environmental Engineering Science and can be downloaded in .pdf format here). The Cornell researchers used the H5N2 subtype of influenza A (low pathogenic for birds and not known to be pathogenic for humans) as a surrogate for H5N1. They showed that the usual water and wastewater treatment modalities of chlorine and UV light were effective in inactivating the virus. Virus was placed into at two temperatures into water and small scale bacterial digesters (the method used in wastewater treatment plants). Each was treated with chlorine (the most common disinfectant in use in water and waste water treatment) and UV light (used primarily in wastewater treatment but also in some drinking water systems). Bacteria and viruses differ greatly in their sensitivity to treatment and no virus is thought to be indicative of the sensitivity of most other viruses. Thus the use of a relatively close avian influenza virus (H5N2) to test the sensitivity of H5N1 to treatment is a reasonable step.
We?ll skip a detailed description of the experimental protocol (you can find them in the paper and they are worth reading just to see how difficult some of these seemingly straightforward questions can be to answer). The persistence of the virus as a replicating entity in water at 4 degrees C. (about 40 degrees F.) is better and longer than at 37 degrees C. (body temperature), but in buffered water was consistently and constantly present for more than 50 hours. At 4 degrees C. in buffered water it was still there after two weeks. Thus the stuff doesn?t just disappear in the environment. It can be around for days or weeks after being deposited. In anaerobic digesters the virus was undetectable at 72 hours. The virus seemed quite sensitive to UV irradiation, although this method is used in only a small percentage of drinking water systems. We have previously discussed the use of UV lights in health care facilities as a possible prophylactic measure and these data seem to support the idea in a different context.
The data on chlorine disinfection is somewhat harder to interpret. Viruses vary widely in their sensitivity to chlorine, so it isn?t a given that chlorine disinfection will inactivate H5N1. The paper gives a Ct (contact time) value of 8 mg.min/L for the virus. Ct is the product of free available chlorine and the time it is in contact with the virus. The average free available chlorine in US drinking water systems is about 1 mg/L (1 ppm) and the paper cites average and median contact times of 237 minutes and 60 minutes, respectively, based on a literature review. This would give average and median Ct?s of 237 and 60 mg.min/L, far in excess of the inactivating levels found in this paper.
The apparent large Ct safety margin is reassuring, although these are average and median Ct?s. A median contact time of 60 minutes means half the systems had contact times less than 60, so half the systems had Cts with a safety margin less than ten fold, not quite so reassuring. Much depends on the distribution in the lower tail and the upper tail of the Ct inactivation estimate. And of course all of this only holds good for conditions similar to the bench experiments of this paper. The results do not tell us with certainty what would happen in a more natural and usual water and waste water environment. What happens when the virus is inside clumps of feces, for example, or in water of different pH or salt make-up?
There are also a number of treatment methods not tested here, among them ozone (now being used increasingly because of the resistance of parasite cysts to chlorine), chlorine dioxide, chloramines and some others. Many small water supplies (almost always groundwater sources), have no treatment at all, so none of this would apply in those cases.
This paper appears to be well done and provides good information. We need more work like it, although unfortunately this kind of work is not the road to academic stardom. It may not be elegant, but it is very, very useful.
Dipl.-Ing. Wilfried Soddemann
eMail: soddemann-aachen@t-online.de