Influenza and the weather
It is well known that influenza hits hardest in winter--November to March in the Northern Hemisphere, and May to September in the Southern Hemisphere. In fact, the name influenza comes from the Italian word influenza, meaning "influence"--referring to the "influence of the season" (winter) in causing the illness. In the tropics, where there is little change in seasons, influenza occurs year-round (though increased incidence has been noted in rainy seasons--Viboud et al., 2006). Do the cold temperatures and lower humidities of winter cause increased transmission of the flu virus? If so, why is the current H1N1 swine flu outbreak doing so well, now that it is May, traditionally the end of flu season in the Northern Hemisphere? Or could it be that indoor crowding, lack of sunlight lowering vitamin D levels, and a more depressed immune system in winter are largely responsible, as some researchers have suggested?
Flu infections increase under cold or dry conditions
To test these hypotheses, researchers at the Mount Sinai School of Medicine in New York did a study in 2007 that looked at flu transmission among guinea pigs, which are highly susceptible to human influenza and easily transmit the virus to other guinea pigs (Lowen et al., 2007). The animals were placed in adjacent cages, so that infections could occur by airborne transmission, but not by direct contact (guinea pig lovers will be happy to know that the influenza virus-infected guinea pigs did not display detectable symptoms of disease--weight loss, fever, sneezing, and coughing--during the experiments). By carefully controlling temperature and humidity, the scientists were able to study the effects of each. They found that the animals shed much more of the virus--and over a longer period of time--at cold temperatures, which led to increased infection rates. The animals' immune system showed no signs of stress from the cold weather, arguing against the idea that cold conditions lead to increased infections by lowering the immune system. Lower humidities were also found to increase flu transmission rate, though the variation of infection rate with humidity was more complicated. The scientists built a model (Figure 1) to fit the data, and proposed that lower humidity increased infection rates through two mechanisms:
1) The stability of influenza virons in the suspended aerosol particles infected creatures cough out is dependent upon the humidity. Viruses are most stable at low RH (20%-40%), least stable at intermediate RH (50%), and stable again at high RH (60%-80%) (Schaffer et al., 1976). Thus, the virus has better staying power at the low moisture levels typical of winter.
2) At high RH (80%), exhaled respiratory droplets grow quite large as water vapor condenses around them, and these drops quickly settle to the ground under the force of gravity. Thus, even though the virus is stable at high humidities, it settles out of the atmosphere quickly, and cannot contribute to influenza virus spread.
Figure 1. A model of influenza transmission rates at 68°F (20°C) (dashed line) and 41°F (5°C) (solid line), as a function of relative humidity. Transmission efficiency is highest at low relative humidity, when influenza virions in an aerosol are relatively stable, and exhaled respiratory droplets stay small and don't settle out under the force of gravity. Transmission is diminished at intermediate humidity when virus particles are relatively unstable, but improves in parallel with influenza virus stability at higher humidities. At high humidity, evaporation from exhaled particles is limited, respiratory droplets settle out of the air, and transmission is blocked. At cold temperatures (solid line), transmission is more efficient than at warm temperatures (dashed line), but is reduced to a rate of 50% at higher humidities. Image credit: Lowen, A.C., S. Mubareka, J. Steel, and P. Palese, 2007, "Influenza Virus Transmission Is Dependent on Relative Humidity and Temperature", PLos Pathogons, October 2007.
The researchers found no guinea pig infections at 86°F (30°C), which implies that in tropical climates, people may transmit the virus by direct contact rather than by coughing and sneezing. A second study Lowen et al., 2009) confirmed this idea--at least among guinea pigs. The authors concluded, "To our knowledge, we demonstrate for the first time that cold temperatures and low relative humidity are favorable to the spread of influenza virus. Although other factors likely contribute to the periodicity of influenza epidemics, it is clear that air temperature and RH could play an important role. Influenza virus transmission indoors could potentially be curtailed by simply maintaining room air at warm temperatures (>20 °C) and either intermediate (50%) or high (80%) RHs".
Climate change and influenza
The results of this study imply that global warming may significantly reduce influenza world-wide, since a warmer climate will also be more humid. Typically, there are between three and five million cases of severe flu and up to 500,000 deaths worldwide each year. In the United States alone, an average of 41,400 deaths and 1.68 million hospitalizations are attributed to influenza each year. A warmer world should reduce these numbers, if the current research is correct. However, these gains must be balanced against the possibility that malaria will become more widespread in a warmer world, since malaria kills about one million people per year.
Figure 2. Combined flu and pneumonia deaths in the United Kingdom during the great 1918 flu pandemic showed that the flu had three distinct peaks: one in June - July (a relatively mild form of the disease), followed by an extremely deadly outbreak in October, then another during the winter of 1918 - 1919. The 1918 flu pandemic infected 1/3 of the world's population, killing 50 - 100 million people. Strangely, the October peak occurred almost world-wide, with Bombay, India and Boston, Massachusetts peaking the same week. Image credit: Jordan, E., "Epidemic influenza: a survey", Chicago: American Medical Association, 1927.
Flu pandemics show little seasonality
The current Mexican H1N1 swine flu outbreak is seemingly unusual, since it is hitting at the end of the traditional flu season, in April - May. However, when a new flu strain develops that humans have no immunity to, the new strain is less constrained by seasonality. According to Dr. Jeffery Taubenberger, the virologist who helped isolate the genetic code of the virus responsible for the great 1918 flu pandemic, "Historical records since the 16th century suggest that new influenza pandemics may appear at any time of year, not necessarily in the familiar annual winter patterns of inter-pandemic years, presumably because newly shifted influenza viruses behave differently when they find a universal or highly susceptible human population." Indeed, the 1918 flu pandemic reached its peak in September - October (Figure 2), and the most recent flu pandemic, the 1968 Hong Kong flu, began in July. It wouldn't surprise me if the current flu outbreak dies down in the Northern Hemisphere over the summer months, as the combined effects of high temperatures, higher humidities, less indoor crowding, and increased sunlight interfere with its spread. However, we need to be ready for the virus to reappear in the Fall--potentially in a mutated, more virulent form--such as occurred during the 1918 flu pandemic.
References
Lowen, A.C., S. Mubareka, J. Steel, and P. Palese, 2007, "Influenza Virus Transmission Is Dependent on Relative Humidity and Temperature", PLos Pathogons, October 2007.
Lowen, A.C., S. Mubareka, J. Steel, and P. Palese, 2009, "High Temperature (30°C) Blocks Aerosol but Not Contact Transmission of Influenza Virus", Journal of Virology, June 2008, p. 5650-5652, Vol. 82, No. 11 0022-538X/08/$08.00+0 doi:10.1128/JVI.00325-08
Schaffer, F.L., M.E. Soergel, and D.C. Straube, 1976, "Survival of airborne influenza virus: effects of propagating host, relative humidity, and composition of spray fluids", Arch Virol 51: 263-273.
Viboud, C, W.J. Alonso, and L. Simonsen, 2006, "Influenza in tropical regions", PLoS Med 3: e89 doi:10.1371/journal.pmed.0030089.
Vitamin D and influenza links:
http://www.medicalnewstoday.com/articles/51913.ph p
http://www.sciencedaily.com/releases/2008/08/0808 11195629.htm
http://www.vitamindcouncil.org/science/research/v itamin-d-and-influenza.shtml
Jeff Masters
Reader Comments
Page: 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 — Blog Index
TCNA21 RJTD 050000 CCA
CCAA 05000 47644 KUJIRA(0901) 01176 11327 11144 260// 90716=
CHAN-HOM(0902) 03116 11120 13234 235// 90404=
0:00 AM UTC 05MAY
17.6N 132.7E
TY KUJIRA
Dvorak Intensity: T6.0
11.6N 112.0E
STS CHAN-HOM
Dvorak Intensity T3.5
They do not have to have any sense as long as we are collectively happy that once every few hours they have a meteorologist on at all, which their polls apparently told them was just fine.
nice break down! Thanks!
Nice update. Thanks.
Did anyone guess Southern Hemisphere?
Nope
...psssst, no one wishcasts in here! ;P
go ahead... u can have the first shot at it... though presslord did say over water so that might include the southern hemisphere..lol
(rolls over and falls out of bed laughing hysterically) aka ROFOBLH!
Your right... i wouldn't want to wake those people and bring them in... I will whisper really quite next time i mention the "W" word... ;-)
Lol! love the answer KEH... sounds good to me!
Like everything else you need to take that with a grain of salt. But I'm not holding my breath either. We've been preparing by deciding where to go when we have to evac again. ( All the Ifs have become Whens.Sigh.) We even had some trees taken down. :( Not that I wanted to. At least this time they went to the mill. It broke my heart when all of the trees from Rita were burned. I'm a big fan of building things out of recycled wood. As the wise man likes to say..." Be prepared." Its all we can do.
Tropical Cyclone Advisory #14
SEVERE TROPICAL STORM CHAN-HOM (CAT 2)
09:00 AM JST May 5 2009
================================
Subject: Category Two Cyclone In The South China Sea
At 0:00 AM UTC, Severe Tropical Storm Chan-Hom (985 hPa) located at 11.5N 112.0E has 10 minute sustained winds of 50 knots with gusts of 70 knots. The storm is reported as almost stationary.
Dvorak Intensity: T3.5
Gale-Force Winds
===============
180 NM from the center in northwest quadrant
120 NM from the center in southeast quadrant
Forecast and Intensity
=======================
24 HRS: 13.2N 113.4E - 60 knots (CAT 2/Severe Tropical Storm)
48 HRS: 15.2N 116.8E - 60 knots (CAT 2/Severe Tropical Storm)
72 HRS: 16.3N 119.4E - 55 knots (CAT 2/Severe Tropical Storm)
12N 81W
You must be from my neck of the woods... Rita took 36 of our fully matured massive Pines and broke them in half like match sticks... We have taken a few trees out but prob need to take more... it seems like you are correct.. not if we evac but when... sigh
Jan. 27, 2009
Domenic Makes Landfall in Northwestern Australia
ADDED: Atlantic Basin? Will get back to you on that one!
We get remnants from Gulf 'canes often... they're usually just rainy days, not very stormy... in '05 we got Dennis, Arlene and Katrina's remnants....
On those coordinates... We shall see! This could be a fun little game to give us something to do while slow... :)
Quoting homelesswanderer:
Lol. I hope so. Although Ike did visit as far inland as Ohio.
We get remnants from Gulf 'canes often... they're usually just rainy days, not very stormy... in '05 we got Dennis, Arlene and Katrina's remnants....
--
last year here my area had Ike and Lowell
I want to say yes because there is a wind shift at the 700 mb level and a vort max at 500 mb (mid-level). I don't quite see the westward propagation yet. I am actually waiting for 2mr morning to confirm it.
Thank you :)
I figure the models have been hinting on and off that spot all week.. just hints.. nothing even close to firm.
I figure its going to be one of the first of the year.. (it might actually be one that crosses over to the pacific)
Not uncommon. Look at the 2006 Pacific Typhoon Season.
Interesting view at the start. I canot seem to find a good one.
Edit-- from the last 24 hrs or so.
South China Sea
WP012009 - Typhoon 01 KUJIRA Multiplatform Satellite Surface Wind Analysis
WP012009 - Typhoon 01 KUJIRA, RAAMB site
nope Bay of Bengal, FTW! (for the win)
That hurt. ouch.
The post earlier today had a loop of the rapid developement of Kujira and it had some distictive circulation in a dual manner. I thought that was a very unique portrayal of how things work.
At least it it something to look at ! :)
I know...
A new avatar?
The comment was referring to the one near Vietnam
Not far enough back Aussie, another 12 hrs or more would show it. This was something Skyepony saw also. I simply cannot find a longer loop. :(
Weather in Sydney there past few days....
'Mini-tornado' dumps caravan in lagoon
Saturday May 2, 2009
Police say three women have been injured when a water funnel or mini-tornado lifted a caravan on the New South Wales central coast on Saturday afternoon.
Officers say the mini-tornado tore through a caravan park at The Entrance about 3:00pm and dumped one of the caravans in a nearby lagoon.
Three women staying at the park have been taken to Gosford Hospital, one with a broken arm and the others with cuts and bruises.
And
Storms flirt with the Sydney coastline
Martin Palmer, Sunday May 3, 2009
On Saturday storms battered parts of eastern Sydney whilst much of the rest of the city remained almost bone dry.
The bright sunny skies of Saturday morning lulled many into leaving their umbrellas at home, indeed there was little evidence of the upper trough lingering ominously offshore. As things warmed up however and the trough moved landward, clouds began to build signaling that something may be afoot.
By 2.30pm clusters of storms began sparking offshore, one south of Wollongong and another just out from The Entrance. By 3pm rain was falling along parts of the coast and a tornado had struck The Entrance.
It wasn't until about 7.30pm that the storms really began to move inshore. Over the next few hours most Sydneysiders were treated to an impressive lightning show, although those in the eastern suburbs would have been diving for shelter as heavy rain moved in.
In the subsequent hours to 9am on Sunday Randwick collected 77mm, their highest May total in 35 years. Mona Vale hit 57mm, Avalon 44mm, Bondi 41mm, yet the city only saw 13mm. The storms made little progress inland and anywhere west of Canterbury saw no rain whatsoever.
- Weatherzone
KEH yes a cobbler made with dewberries... which are very similar to blackberries... dewberries just become ripe before blackberries and grow on small cluster plants instead of extensive thorny vines..
utterly delightful tasting
http://www.nrlmry.navy.mil/tc-bin/tc_home2.cgi?ACTIVES=09-WPAC-01W.KUJIRA,09-WPAC-02W.CHAN-HOM,09-W PAC-95W.INVEST&PHOT=yes&ATCF_BASIN=wp&SUB_PROD=1km&SIZE=Thumb&NAV=tc&YR=09&ATCF_YR=2009&YEAR=2009&AT CF_FILE=/SATPRODUCTS/kauai_data/www/atcf_web/public_html/image_archives/2009/wp022009.09050418.gif&C URRENT=20090505.0130.gms6.x.ir1km.02WCHAN-HOM.55kts-982mb-116N-1120E.100pc.jpg&AGE=Latest&CURRENT_AT CF=wp022009.09050418.gif&ATCF_NAME=wp022009&ATCF_DIR=/SATPRODUCTS/kauai_data/www/atcf_web/public_htm l/image_archives/2009&ARCHIVE=active&MO=MAY&BASIN=WPAC&AREA=pacific/southern_hemisphere&STORM_NAME=0 2W.CHAN-HOM&STYLE=tables&PROD=ir&TYPE=ssmi&DIR=/SATPRODUCTS/TC/tc09/WPAC/02W.CHAN-HOM/ir/geo/1km&USE _THIS_DIR=/SATPRODUCTS/TC/tc09/WPAC/02W.CHAN-HOM/ssmi/scat&ANIM_TYPE=Instant
wasn't able to post as a link
Viewing: 301 - 351
Page: 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 — Blog Index