From:
sukiec@optonline.net
Date: 2006-10-26 15:40:49 UTC
Subject: [ferrethealth] closer to punctualism rather than gradualism implicated in Influenza A populations (Ah, the merger of E&E and pathology...)
To: ferrethealth@smartgroups.com
It always means a lot to me when medicine finally thinks in terms of paleon=
tology and evolution knowledge. GC Williams should have been more listened=
to by those in medicine. There are so many things which become more clear=
when the ancestry is known. Anyway, Punctuated Equilibrium is a Genetics,=
Population Genetics, Evolution, Paleontology, etc term which refers to per=
iods of time when there is very little change in the genetics of a populati=
on which are punctuated by sudden large changes. There can be a range of r=
easons for large changes surviving in greater proportion and shifting the a=
lleles of a population, some due to greater pressures, some due to better s=
uccess. When breeders decide that one variant of an animal is more profita=
ble an artificially imposed punctuation can be seen in a pet population ove=
r only mere years or decades.
Because ferrets also get influenza I figured that this would be of interest=
. Currently, with the bird flu variants that exist two changes are needed =
to wind up with an epidemic. It doesn't currently grow and propagate all t=
hat well in mammals, and it also tends to live in lower respiratory tract i=
n mammals so catching it from one mammal to another needs to involve intens=
e nursing. Now, if gradualism was the primary route for change in these in=
fluenzas then the slow changes seen so far could possibly indicate that thi=
s batch was less likely to become dangerous, but with punctuated equilibriu=
m at play all bets anyone placed should be off. (Given the size of viruses=
, the splicing, etc. I don't see something approaching punctualism as being=
a particular surprise to anyone familiar with routes of genetic change in =
a population.)
http://www.nlm.nih.gov/news/press_releases/flu_studypr06.html
BEGIN QUOTE
New Study Has Important Implications for Influenza Surveillance
Printer-friendly Version Return to Web Version
National Institutes of Health
FOR IMMEDIATE RELEASE
October 25, 2006
National Library of Medicine
Robert Mehnert
Kathy Cravedi
(301) 496-6308
publicinfo@nlm.nih.gov
Vaccine Formulation Research Provides New Insights into Evolution of Flu Vi=
rus
Researchers are reporting results of a study that substantially alters the =
existing understanding of how the influenza virus evolves and that could ha=
ve important implications for monitoring changes to the virus and predictin=
g which strains should be used for flu vaccine. The study, which will be pu=
blished in the online journal Biology Direct Oct. 26, 2006, was conducted b=
y researchers from the National Library of Medicine's National Center for B=
iotechnology Information (NCBI) and Fogarty International Center , both par=
t of the National Institutes of Health.
In an effort to better understand how seasonal influenza evolves into new s=
trains, the researchers analyzed the genomic sequences of a large and repre=
sentative collection of the two most common flu strains (called H3N2 and H1=
N1) from the 1995-2005 flu seasons in New York state and New Zealand. The s=
equence data was obtained from the Genome Sequencing Project , which recent=
ly generated over 1,000 fully sequenced influenza genomes from clinical iso=
lates; the project is funded and managed by the National Institute of Aller=
gy and Infectious Diseases .
The analysis revealed a picture of flu evolution that was surprisingly diff=
erent from the prevailing conception of how the virus changes. Evolution of=
influenza A virus is commonly viewed as a typical Darwinian process. In th=
is mode of evolution, the virus' main surface protein, hemagglutinin (HA), =
is thought to continually change to evade human immune response, resulting =
in new dominant strains that eliminate all competitors in a series of rapid=
successions. Unexpectedly, however, the study found that the periods of in=
tense Darwinian selection accounted for only a relatively small portion of =
H3N2 flu evolution during the ten-year period examined.
The study found that much of the time the H3N2 virus seemed to be "in stasi=
s"; that is, the HA gene showed no significant excess of mutations in the a=
ntigenic regions (those recognized by the immune system). During these stas=
is periods, none of the co-circulating strains is significantly more fit th=
an others, apparently because multiple mutations are required to substantia=
lly improve the virus' ability to evade the immune system. As a result, an =
increased variety of strains accumulates. Ultimately, however, one of the v=
ariants will come within one mutation of achieving higher fitness and becom=
ing dominant. Once the crucial last mutation does occur, virus evolution sh=
ifts from stasis to a brief interval of rapid Darwinian evolution, where th=
e new dominant virus rapidly sweeps through the human population and elimin=
ates most other variants.
Based on their results, the researchers conclude that "the common view of t=
he evolution of influenza virus as a rapid, positive selection-driven proce=
ss is, at best, incomplete." Because the periods of stasis allow the prolif=
eration of many small groups of related viruses, any of which could become =
the next dominant virus strain, the authors suggest that sequencing much la=
rger numbers of representative isolates could be helpful in augmenting curr=
ent surveillance methods.
The study, titled "Long Intervals of Stasis Punctuated by Bursts of Positiv=
e Selection in the Seasonal Evolution of Influenza A Virus," is authored by=
Yuri Wolf, PhD, NCBI; Cecile Viboud, PhD, Fogarty International Center; Ed=
ward Holmes, PhD, Fogarty International Center and Pennsylvania State Unive=
rsity; Eugene Koonin, PhD, NCBI; and David Lipman, MD, NCBI.
Established in 1988 as a national resource for molecular biology informatio=
n, NCBI creates public databases, conducts research in computational biolog=
y, develops software tools for analyzing molecular and genomic data, and di=
sseminates biomedical information - all for the better understanding of pro=
cesses affecting human health and disease. NCBI is a division of the Nation=
al Library of Medicine at the National Institutes of Health (NIH).
###
Located in Bethesda, Maryland, the National Library of Medicine is the worl=
d's largest library of the health sciences. For more information, visit the=
Web site at http://www.nlm.nih.gov/.
The National Institutes of Health (NIH) =97 The Nation's Medical Research A=
gency =97 includes 27 Institutes and Centers and is a component of the U. S=
. Department of Health and Human Services. It is the primary federal agency=
for conducting and supporting basic, clinical, and translational medical r=
esearch, and it investigates the causes, treatments, and cures for both com=
mon and rare diseases. For more information about NIH and its programs, vis=
it http://www.nlm.nih.gov/.
END QUOTE
-- Sukie (not a vet, and not speaking for any of the below in my private po=
sts)
Recommended health resources to help ferrets and the people who love them:
Ferret Health List
http://www.smartgroups.com/groups/ferrethealth
FHL Archives
http://ferrethealth.org/archive/
AFIP Ferret Pathology
http://www.afip.org/ferrets/index.html
Miamiferrets
http://www.miamiferret.org/fhc/
International Ferret Congress Critical References
http://www.ferretcongress.org
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