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Ague peak

Ross McKitrick has a new paper in the Journal of the Royal Statistical Society A, examining reasons for the eradication of malaria in some countries but not in others. You'll never guess what isn't a factor.

Malaria has disappeared in some countries but not others, and an explanation for the eradication pattern has been elusive. We show that the probability of malaria eradication jumps sharply when average household size in a country drops below four persons. Part of the effect commonly attributed to income growth is likely due to declining household size. The effect of DDT usage is difficult to isolate but we only identify a weak role for it. Warmer temperatures are not associated with increased malaria prevalence. We propose that household size matters because malaria is transmitted indoors at night, so the fewer people are sleeping in the same room, the lower the probability of transmission of the parasite to a new victim. We test this hypothesis by contrasting malaria incidence with dengue fever, another mosquito-borne illness spread mainly by daytime outdoor contact.

There's a discussion of the new paper here and the full paper can be seen here.

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Reader Comments (19)

Larger household sizes might result in the mosquito finding it easier to detect the higher amounts of respired carbon dioxide.

Nov 7, 2013 at 4:25 PM | Unregistered CommenterConfusedPhoton

Hmm... The paper isolates countries where 'DDT is used aggressively' - I assume this means external spraying of pools, etc. AFAIK, the mosquito preferentially bites sleepers, and DDT-soaked sleeping nets are a major defence.

I would guess that higher income enables people to afford such luxuries as DDT-impregnated sleeping quarters (or, of course, the use of any other insecticide), and small households equally correlates with higher income - if you have little income you need a big family to help you survive.

So I suspect that preventing insect bites by insecticides killing or repelling mosquitoes is still the primary defence - it's just that enabling people to have their own money and provide their own shelter works better than indiscriminate spraying - which is not a surprising conclusion...

Nov 7, 2013 at 4:36 PM | Unregistered CommenterDodgy Geezer

Dodgy Geezer

Wealthier people might be able to afford good cooling fans producing a strong downdraught and since mosquitoes are poor fliers,this in itself would reduce the night attacks

Nov 7, 2013 at 4:44 PM | Unregistered CommenterConfusedPhoton

The largest outbreak of malaria in modern times was in the 1920s and 1930s in Northern Siberia.

Nov 7, 2013 at 4:48 PM | Unregistered Commenterkim

Malaria disappeared from many countries spontaneusly before DDT was used as an insecticide. In countries with a high household size the level of malaria could be kept down with DDT but it returned when the spraying stopped. Everything comes down to the number of uninfected people an infective Anopheles female can bite. She is manipulated by the parasite, which affects the mathematics. Read the paper, it is explained there.

Nov 7, 2013 at 4:52 PM | Unregistered CommenterLena Hulden

- Peak Ague ..surely ?
...peak oil, peak coal, peak eco-insanity, Peak BBCbias etc ..

- PeakGreen = peak electricity prices
.... =trough economy (in both senses of the word)

Nov 7, 2013 at 5:11 PM | Registered Commenterstewgreen

It seems a bit counter-intuitive, but since Ross McKitrick is associated with it, it's well worth a long hard look.

AFAIK, the thing to remember is not that it is transmitted by mosquitoes, but that it is transmitted from one infected person to another. There are zillions of anopheles in places where their presence is no more than annoying for humans.

While relating it to people's sleeping arrangements might be a bit of a stretch, they may well be on the right track.

Nov 7, 2013 at 5:14 PM | Registered Commenterjohanna

I've just read the free summary document. From past reading I don't find it counter-intuitive but intriguing and potentially highly explanatory. Well done Ross for teaming up with the Huldéns and giving legs to their rediscovery of the neglected thesis of Sidney Price James in the 1930s. Having said which, the DDT part of the malaria reduction story is, they admit, hard to tease out statistically, unlike the other factors. But here's the key (and world-changing) background:

With regard to DDT, for instance, while about 75% of the world used it, with an average application interval of over 15 years, malaria only disappeared in 43% of the world’s countries.

In the immediate aftermath of World War II DDT was given the credit for the eradication of malaria in such countries but I've long been aware of the failures too. It's very important indeed to tease out the true facts of the matter. I hope that this work helps the experts do exactly that. The news on malaria in the last ten years or so has been very good but it's a far more deadly thing for the poor, especially children, than I for one think that AGW will ever be.

Nov 7, 2013 at 6:41 PM | Registered CommenterRichard Drake

Check out BBC 2 tonight 9 PM

Documentary about World Population Growth not such a major problem and eradicating disease and poverty in the Developing world

Got a recommend from the Daily Mail and The Sun

Unusual output for the Beeb might put a few Malthusian backs up.

Nov 7, 2013 at 7:43 PM | Unregistered Commenterjamspid

jamspid: The five questions by presenter Hans Rosling are also very encouraging.

Nov 7, 2013 at 8:08 PM | Registered CommenterRichard Drake

As a very subjective observation, I have noticed that here in Hong Kong, the prevalence of mosquitoes drops when the temperature goes above about 30C. Come the cooler weather and the buggers return with a vengeance. Another unexpected benefit of global warming?

Nov 7, 2013 at 8:24 PM | Unregistered CommenterDavid Chappell

Will the malaria parasite now be added to the list of species endangered by global warming?

Nov 7, 2013 at 8:47 PM | Unregistered Commenterkellydown

Hes a bit to Deterministic for me.

The example of the Bangladeshi woman working for the government dishing out condoms.Etc

Should be free market Industrialization and voluntary contraception leading the way.

Stable 11 billion by 2100 seems about right

Nov 7, 2013 at 9:38 PM | Unregistered Commenterjamspid

Oh god he finally got on his climate Change soap box ."Climate Change the biggest threat to mankind blah blah".

So what happens when we get to 2100 and 11 billion and still no warming can we finally let India and Africa dig up up their Coal and Frack for their Gas.

First rule of Climate Change Bullshit Bingo should be make sure you ,re right about it.

He loves his Graphs this bloke so what about the Graph for parts per million and degrees centigrade

Nov 7, 2013 at 10:09 PM | Unregistered Commenterjamspid

[N.B. Cross-posted at WUWT. Comment is based on the discussion paper, since the publication itself seems to be pay-walled.]

I am not sure that looking at current data – the text says, “Data for the year 2000 or the closest year thereto were obtained” – tells us much about the historical importance of DDT (or draining of swamps or whatever). If you looked at current data for the U.S., for example, you would conclude that TB and water-borne diseases have little or no impact on life expectancy. And that would be correct today, but it wasn’t always so. In fact, they were among the top killers in the first part of the last century.

For a variety of reasons, death rates from malaria were on the decline in the U.S. since the 1930s, if not earlier (see Fig 13 here). They continued to decline through the 1940s and were virtually zero by 1950. DDT was the coup de grace. I doubt that family sizes increased in the US through the 1930s. And we know there was a baby boom in the post-war years.

Note also that in several countries (in Latin America and Africa, for instance), “malaria has retreated, advanced, and in some places, retreated once again as levels of in-home DDT spraying have been increased, decreased and, occasionally, increased again” (pp. 179-181, Fig 6.19, in the book The Improving State of the World ).

Nov 8, 2013 at 3:03 AM | Unregistered CommenterIndur M. Goklany

Indur, I agree. This study grossly over-simplifies a very complex issue. In particular, as you point out, it does not seem to encompass the historical record of factors which reduce malaria prevalence - and where have we come across that before?

As far as I can tell, it doesn't capture the long term history of malaria control measures. Examples include drainage and public sanitation, improved treatment of patients in places where it was available, the difference between spraying DDT inside houses and widespread spraying on vegetation and waterways, other control measures such as putting a film of kerosine or oil on stagnant water (such as in water tanks and ponds) to inhibit Anopheles breeding - over many decades.

As I mentioned at WUWT, my father caught malaria as a soldier during the Korean War, and nearly died. Luckily, he was shipped to a hospital in Japan where he recovered. I called him yesterday and asked him about it. He says he spent two days and nights lying in a paddy field, being dive bombed by mosquitoes. He also says that there were no barracks in any of the places where he served - there was simply no such infrastructure. The study itself admits that Korean family groups were mostly small - maybe 3-4 people on average.

I am not saying that providing large numbers of juicy targets for Anopheles in a confined space is not going to increase the prevalence of malaria, where an infection pool already exists. But suggesting that this is the critical factor across the board seems to me to be a bridge too far.

Nov 8, 2013 at 5:56 PM | Registered Commenterjohanna

Indur Goklany said: Comment is based on the discussion paper, since the publication itself seems to be pay-walled.]

Please look at the pre-print version:

Nov 9, 2013 at 5:39 AM | Unregistered CommenterLarry Hulden

There seem to be large misconceptions about how data have been analyzed. We used both historical data AND data for the year 2000 which where crosschecked for nearly 100 parameters. In the discussion paper we have more detailed information which could not be used in the published paper.
We also showed that malaria practically never (except Palestine and Maledives; in the latter Anopheles occurred occasionally) disappeared by vector elimination simply because the vector was not eliminated. Vectors are still present in all countries from which malaria disappeared. If Mosquito Magnet traps were used you would get a lot of Anopheles mosquitoes in any country in Europe. In the 2000's in Finland we got 300 per night in the subarctic zone where malaria reached 70 degree N latitude in the 18th century. Malaria disappeared in Finland in 1954.
In countries where no counter measures were used the decline had a long tail but with counter measures it became short.
Although some malaria researchers don't agree the fact is that the vector is a constant parameter in the long term historical malaria. When Europeans sailed to South America in about 1500 the local Anopheles mosquitoes (subgenera Kertezia and Nyssorhynchus) were from day one able to transmit Plasmodium species among humans in despite of 90 million years of isolation from Africa (continental drift). The evolution of Primate Plasmodium started some 20 million years ago. The Anophelinae line separated from the Culicinae 120 million years ago. That means that the Anopheles innovation used by the Plasmodium has remained unchanged for 120 million years.

For those interested in some recent malaria research please check the following:

Endemic malaria: an 'indoor' disease in northern Europe. Historical data analysed
Lena Huldén, Larry Huldén, Kari Heliövaara 2005

Natural relapses in vivax malaria induced by Anopheles mosquitoes
Lena Huldén, Larry Huldén, Kari Heliövaara 2008

Dynamics of positional warfare malaria: Finland and Korea compared
Lena Hulden, Larry Hulden 2008

The decline of malaria in Finland – the impact of the vector and social variables
Lena Hulden, Larry Hulden 2009

Activation of the hypnozoite: a part of Plasmodium vivax life cycle and survival
Lena Hulden, Larry Hulden 2011

Nov 9, 2013 at 6:35 AM | Unregistered CommenterLarry Hulden

Larry, many thanks for the links to your papers - great stuff!

Nov 9, 2013 at 10:18 AM | Registered Commenterflaxdoctor

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