New study shows Malaria has little to do with temperature or climate, but more with household size

Malaria room

Malaria room (Photo credit: YoHandy)

For General Release – Summary of: Average Household Size and the Eradication of Malaria

By Lena Huldén, Ross McKitrick and Larry Huldén

Journal of the Royal Statistical Society Series A, October 2013 Online at http://onlinelibrary.wiley.com/doi/10.1111/rssa.12036/abstract  Document identifier: DOI: 10.1111/rssa.12036;

Abstract

Malaria has disappeared in some countries but not others, and an explanation for the pattern remains elusive. We show that the probability of malaria eradication jumps sharply when average household size drops below four persons. Part of the effect commonly attributed to income growth is likely due to declining household size. DDT usage plays only a weak role. Warmer temperatures are not associated with increased malaria prevalence. We propose that household size matters because malaria is transmitted indoors at night. We test this hypothesis by contrasting malaria with dengue fever, another mosquito-borne illness spread mainly by daytime outdoor contact.

Background

Malaria is a parasitic disease that is transmitted to humans by infected Anopheles mosquitoes. It infects red blood cells, causing anemia, nausea, fever and sometimes death. There are about 225 million cases annually leading to 800 000 fatalities, of which 90 percent are in Africa, and most of whom are children.

It is a common misconception that malaria is a tropical disease. Although that is where it remains prevalent, it used to occur throughout the world, in all climate zones, from the tropics to the coast of the Arctic Sea (up to 70° N latitude). Malaria was endemic in Europe and North America during the 20th century, but has largely disappeared and has been unable to re-establish itself there in spite of frequent annual importation of cases.

An interesting aspect of this history is that the disease disappeared in many countries that made no special efforts to eradicate it, while remaining prevalent in other countries that tried. Numerous explanations for the global pattern of eradication have been suggested, such as a change in the feeding pattern of the insects, draining of wetlands, or intensive use of the insecticide DDT (dichlorodiphenyltrichloroethane). Despite superficial plausibility, such explanations begin to fail upon close examination. 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.

This study looks at the connection between declining average household size and the disappearance of malaria. The ongoing prevalence of malaria in tropical countries suggests a connection with socioeconomic conditions, but explanations have been lacking as to specific mechanisms by which the disease is affected by poverty. Back in the 1930s, Sidney Price James observed that the number of malaria cases was always higher in cottages in which big families slept together in one room, which was especially the case among the poor. This received little attention subsequently and research efforts focused on other factors.

In a 2009 analysis of the malaria trend in Finland over the interval 1750–2006, Lena and Larry Huldén noted that while many standard theories of malaria disappearance had little explanatory power, mean household size appeared to correlate very closely over a long interval with the decline in malaria cases, which led them to ask whether this pattern might hold true globally. Together with economist Ross McKitrick, they have now developed and analyzed a large international data base and found that James’ early conjecture appears to have been correct.

Study details

Data on malaria, insect vectors, demographic factors, sociological factors, and environmental factors for 232 countries or corresponding administrative units were compiled. Data for the year 2000 or the closest year thereto were obtained. Of these 220 countries, malaria was never endemic in 32, remains prevalent in 106 and has been eradicated from 82. Mongolia is the only country with an indigenous vector species but no historical or recent malaria. Thus indigenous malaria vectors (Anopheles species) are known from 188 countries, which is the sample for the analysis.

Explanatory variables include Gross Domestic Product (GDP) per capita, household size, female literacy, urbanization and slums, latitude, mean temperature, forest coverage, Muslim population, national DDT usage, population density and national mean temperature (over the 1980-2008 interval).

The authors used regression analysis to determine which factors affect the probability that malaria will have been eradicated from a country, and, among those countries where it is still present, what affects the disease incidence in the population.

The authors included the Muslim fraction in society as an explanatory variable because households in Muslim countries are characterized by a gender-segregated sleeping arrangements which, in varying degree, divides the household into smaller units depending on how strictly the practice is applied. Hence these are countries that may have relatively large households on average, but effective household sizes below four persons as regards sleeping arrangements.

Note: DDT Usage

The only countries that use DDT for malaria vector control are those that have malaria, so the presence of malaria strongly predicts the use of DDT. Naively putting a DDT usage measure into the model would give results that apparently suggest DDT causes malaria.

The remedy for this problem is to obtain a statistical instrument that measures the the effect of DDT usage on malaria frequency and eradication probability, independent of a country’s decision to use it in response to the presence of malaria. One aspect of the usage decision that was outside the control of most countries was the move by the United States to ban the production and use of DDT in 1971, which marked the start of worldwide efforts to withdraw the product from usage due to environmental concerns.

Figure 1 (below) shows the fraction of countries in our sample with malaria, the fraction using DDT, and the ratio of the two, by year, from 1951 to 2005. In 1951, 81% of the countries in our sample experienced malaria and 63% used DDT, a usage ratio of 0.78. This declined relatively steadily until the 1990s. As of 1971, 55% experienced malaria and 33% were using DDT, yielding a usage ratio of 0.60. In the 1990s the usage ratio began falling more rapidly, such that by 2005, 48% still experience malaria but only 4% use DDT, a ratio of 0.08.

Conditional on a country already having experienced malaria, an aggressive malaria control stance would be indicated by a willingness to use DDT right up to the year in which malaria was eradicated, despite the international pressure not to do so. The authors therefore defined a variable indicating if the year in which a country ceased using DDT was the same as the year malaria disappeared, or one or two years after that. This describes 18% of the sample, and was interpreted as an indication of aggressive DDT usage.

clip_image002 Figure 1. By year: fraction of countries in our sample in which malaria is still present (mal_still, dashed line), DDT is still used (ddt_still, solid line) and the ratio of the two (dotted line). Vertical dash line: 1971, year US banned DDT.

Results

What increases the probability of malaria eradication?

The table below presents some key results regarding factors affecting the probability of success in malaria eradication.

Explanatory variable Effect on the probability of malaria eradication
Higher income positive significant
Avg household size under 4 persons positive significant
Higher population density positive significant
Higher population growth rate negative weakly significant
% living in urban area positive significant
% Muslim positive significant
Mean national temperature positive significant
DDT used aggressively positive insignificant
Sample size 188
Fraction of variance explained by model 78.3%

clip_image004Household Size Effect

The household size effect shows up strongly when measured as a binary indicator of whether a country’s average household size is below a certain number of persons or not. The largest effects arise when the threshold is set to 4.0 or 4.5 persons: in these cases the threshold effect is larger than that associated with a one-standard deviation increase in real income.

In the Figure, filled circles show the effect when household size drops below the indicated threshold, with clip_image006 uncertainty ranges shown. The solid line shows the effect associated with a one standard deviation increase in average income, and the dotted lines show the corresponding clip_image006[1] ranges shown.

clip_image008 TemperatureIf one looks at annual mean temperature in isolation, it could easily yield the mistaken view that higher temperature results in a higher likelihood of malaria occurring in a country. For instance, a simple comparison of histograms showing the fraction of countries by temperature, dividing the sample into places where malaria has been eradicated (top panel) versus where it is still present (bottom panel), could lead to the inference that the higher the mean annual temperature, the greater the number of countries with malaria.

But this is incorrect because it fails to control for the influences of income, household size and other socioeconomic characteristics. The multivariate analysis shows that when these factors are controlled, higher temperatures are actually associated with a small but significant increase in the probability of malaria eradication.

What factors decrease malaria incidence?

The table below presents some key results regarding factors affecting the number of cases per 100,000 each year in countries where malaria is still present.

Explanatory Variable Effect on rates of malaria infection
Higher income negative significant
Avg household size under 4 persons negative significant
Higher population density negative insignificant
Higher population growth rate negative insignificant
% living in urban area negative insignificant
% Muslim negative significant
Mean national temperature negative insignificant
DDT used aggressively negative insignificant
Sample Size 188
Fraction of variance explained by model 0.306

The regression results show that when household size drops below a four-person threshold, about one-third of the effect that would otherwise be attributed to income disappears and instead is attributable to small household size.

clip_image010

Regarding temperature, the analysis of disease incidence again shows that higher temperatures, if anything, are associated with lower disease incidence, but the effect is statistically insignificant.

An Explanatory Mechanism

The mosquitoes responsible for malaria pick up the parasite from humans. At the local level, practically all Anopheles species feed at night. The female mosquito gets the infection from a human blood meal. After egg laying it returns to the same approximate location for another blood meal. The parasite multiplies sexually in the mosquito. The process takes ~10–16 days and is completed when the infective form of the parasite reaches the salivary glands of the mosquito, which allows it to be transferred to another human through the bite.. Early experiments with Plasmodium vivax showed that an infective mosquito will bite 30–40 times (James 1926). For a new person to be infected, a mosquito carrying the mature parasite back to its feeding location must find a victim who is not already infected. Therefore the more people who are sleeping together in the same room, the higher the probability of spreading the infection to a new person. Reinfection is thus a stochastic process, and below a certain threshold number of persons sleeping together, Plasmodium infection success rates drop below the replacement rate and it begins to disappear from the human population, even without other control measures. This study indicates that the threshold is likely crossed when average household size drops below somewhere between 4.0 and 4.5 persons.

The hypothesis was tested by re-doing the analysis using data on the incidence of dengue fever, which, like malaria, is mosquito-borne and has wide geographic distribution, but is spread by different species that are active during the day in shaded places and only occasionally at night. Thus its transmission mechanism is not expected to be sensitive to household size, but to factors affecting outdoor exposure. In the dengue re-analysis, the household size effect disappeared, as did the Muslim effect, and the income effect became much smaller and less significant. The measure of aggressive DDT usage became marginally significant (p=0.073).

Conclusions

These findings suggest that as average household sizes continue to decline around the world, malaria will also gradually disappear. The authors did not differentiate between adult and children household members. There is evidence that the threshold is not affected by the fraction of children, since the effect has been observed in populations of soldiers where children are not present. The result raise the possibility that in regions with large households (or large populations sharing sleeping quarters, such as lumber camps or military barracks), the eradication of malaria will require segmenting sleeping quarters into smaller units, such as with mosquito nets. The average number of bed nets per person in 35 African countries is 0.21. In Vanuatu (average household size 5.6) a high provision of individual bed nets has, in combination with effective drug distribution and surveillance, been credited with the disappearance of malaria since 1996. Use of individual bed nets emulates a house with several bedrooms, making it more difficult for an infective vector to transmit the parasite to new household members.

Corresponding author contact: Ross McKitrick

Professor of Economics

University of Guelph

ross.mckitrick@uoguelph.ca

Tel 519-824-4120 x52532

About these ads

71 thoughts on “New study shows Malaria has little to do with temperature or climate, but more with household size

  1. Well, we know all this is irrelevant as global temps are rapidly declining. Less sun, therefore more cosmic rays, therefore more clouds. Even though real climate scientist Rasmus Benestad is trying to muddy the waters with so-called research and data, even asserting that “I found little evidence of the cosmic rays having a discernible affect on a range of common meteorological elements”.

    That’s because the ‘data’ used at has been adjusted by his chums. Yes, even barometric pressure and precipitation. Remember you heard it first on WWUT.

    http://environmentalresearchweb.org/cws/article/news/55200

  2. My immediate response is: what about screens on windows and doors? That is often credited with helping eradicate malaria in the US. However, one does not find malaria in the UK any longer, and the citizens of that fair isle have yet to learn how to screen windows (hence major problems with hungry moth larvae) so that cannot be held accountable – nor do they tend to use mosquito netting.

    Richer nations do tend to do more infilling of marshes for development and in the past, disease control, reducing the prevalence of mosquito vectors. Tren and Bates maintain that malaria only disappeared in Italy after 1970 once the government conceded that socialism alone was not doing the job (the previous, social-improvement policy), and surrendered to the necessity of using DDT.

    I agree with M Courtney, correlation is not causation.

  3. I have traveled to the Congo several times and Malaria is a bigger problem in the cities than it is in the countryside (you are most likely to contract it staying in the city rather than in a village) So I would guess population density in general and and population density per household in particular are contributing factors as the article suggests. But correlation is not causation and there are at least a couple other correlating conditions to consider: The near universal use of window screens and air conditioning has been adopted in the same countries that saw household size fall over the last several decades. People in the United States are intolerant of inscets inside their homes and they take positive measures to keep them out or to kill them if they get in. Mosquitos are high on the list of undesirable insects. I suspect it is very similar in Europe.

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

  5. Malaria is just a thing of the past…………..in some areas.

    Abstract
    From Shakespeare to Defoe: malaria in England in the Little Ice Age.
    “Until the second half of the 20th century, malaria was endemic and widespread in many temperate regions, with major epidemics as far north as the Arctic Circle. From 1564 to the 1730s the coldest period of the Little Ice Age malaria was an important cause of illness and death in several parts of England.”

    http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2627969/

    Abstract
    Global warming and malaria: knowing the horse before hitching the cart
    “….from Poland to eastern Siberia, major epidemics occurred throughout the 19th century and the disease remained one of the principal public health problems for the entire first half of the 20th century…..Tens of thousands of infections, many caused by P. falciparum, occurred as far north as the Arctic seaport of Arkhangelsk (61° 30’N)….”
    doi:10.1186/1475-2875-7-S1-S3

    Abstract – [1999]
    The return of swamp fever: malaria in Canadians
    Malaria is an old Canadian disease. It was an important cause of illness and death in the past century in Upper and Lower Canada and outinto the Prairies. 1,2 During the period 1826–1832, malaria epidemics halted the construction of the Rideau Canal be-tween Ottawa and Kingston, Ont., during several consecu-tive summers, with infection rates of up to 60% and death rates of 4% among the labourers.
    ncbi.nlm.nih.gov/pmc/articles/PMC1229992/

    Abstract
    Endemic malaria: an ‘indoor’ disease in northern Europe. Historical data analysed
    “A total of 1,803 persons died of malaria in the western parts of Finland and in the south-western archipelago during the years 1751–1773 [23]. Haartman [21] reports severe epidemics in the region of Turku in the years 1774–1777 and the physician F.W. Radloff mentioned that malaria was very common in the Aland Islands in 1795 [39].”
    Huldén et al – 2005 Malaria Journal

    http://dx.doi.org/10.1186/1475-2875-4-19

    Abstract
    Anopheles (Diptera: Culicidae) and malaria in northern Europe, with special reference to Sweden
    ….An. messeae was probably the principal vector during the malaria epidemics in Sweden….
    ingentaconnect.com/content/esa/jme/1986/00000023/00000001/art00009

    Abstract
    Insect Pests in northern Norway. The Mosquito Nuisance.
    …Brief reference is made to insect-borne diseases, and it is pointed out that malaria was widespread in Sweden and Finland early in the nineteenth century, and though no records have been found from Norway, species of Anopheles occur there….
    cabdirect.org/abstracts/19412900788.html

    Abstract
    Malaria in Norway–a tropical disease off the track?
    …efforts to find the reasons for the appearance and disappearance of a disease. It is well known that malaria was common on the European continent, but it is less well known that malaria also existed in Norway during the 19th century…
    ncbi.nlm.nih.gov/pubmed/7825149

    Abstract
    Malaria Around the North Sea: A Survey
    Malaria may have been introduced into the North Sea Basin in late Antiquity. It has been endemic at least since the 7th century, but its high-days were the Little Ice Age…. The rise and fall of malaria took place largely independent of long-term climatic change.

    Abstract [1916]
    Malaria as a public health and economic problem in the United States
    Malaria constitutes one of the big national health problems, and because it is a common disease, it receives less consideration than many other diseases less destructive…
    doi: 10.2105/AJPH.6.12.1290

    Abstract
    Malaria in Poland
    Abstract
    Malaria epidemiological situation in Poland since nineteenth century to 1995 has been described. The changes observed during this period are enormous. Poland has been transformed from endemic country with huge epidemics into the country with sporadic imported malaria cases.

    Abstract [1977]
    Malaria eradication in Portugal
    Research on malaria, which was endemic in several parts of Portugal at the beginning of this century, was intensified in the 1940’s and led to the development of better control methods, especially in the rice-growing areas of the country. In the 1950’s residual DDT spraying was introduced…….The country was placed in the maintenance phase of malaria eradication and the certification of malaria eradication was confirmed by the WHO in 1973.
    [Transactions of the Royal Society of Tropical Medicine and Hygiene - Volume 71, Issue 3, 1977, Pages 232–240]
    doi: dx.doi.org/10.1016/0035-9203(77)90014-1

    ———————
    Review article
    Global Warming and Infectious Disease
    In modern times, we tend to think of malaria as a tropical disease. However, malaria has existed in many temperate areas of the world (30). Outbreaks have occurred as far north as the Arctic Circle and the disease has flourished in much of Europe and North America….. In Europe, cases of malaria persisted throughout the Little Ice Age, a period of intensely cold winters and cool summers that began in 1564…..

    Archives of Medical Research – Volume 36, Issue 6, November–December 2005, Pages 689–696
    Infectious Diseases: Revisiting Past Problems and Addressing Future Challenges

  6. But……but…..it’s getting worse! We must tackle global warming, we must act now!

    Abstract – 2010
    Climate change and the global malaria recession
    “…observed decreasing global trends in both its endemicity and geographic extent. Second, the proposed future effects of rising temperatures on endemicity are at least one order of magnitude smaller than changes observed since about 1900 and up to two orders of magnitude smaller than those that can be achieved by the effective scale-up of key control measures. Predictions of an intensification of malaria in a warmer world, based on extrapolated empirical relationships or biological mechanisms, must be set against a context of a century of warming that has seen marked global declines in the disease and a substantial weakening of the global correlation between malaria endemicity and climate.”

    http://dx.doi.org/10.1038/nature09098

    Abstract – 2001
    Climate change and mosquito-borne disease.
    …Elementary models suggest that higher global temperatures will enhance their transmission rates and extend their geographic ranges. However, the histories of three such diseases–malaria, yellow fever, and dengue–reveal that climate has rarely been the principal determinant of their prevalence or range; human activities and their impact on local ecology have generally been much more significant….
    ncbi.nlm.nih.gov/pmc/articles/PMC1240549/

  7. About one hundred parameters including all here discussed was crosschecked leading to one single parameter as the only one affecting the ultimate fate of malaria.

  8. vigilantfish says:

    … one does not find malaria in the UK any longer, and the citizens of that fair isle have yet to learn how to screen windows …

    I wondered about that. They don’t really need to learn that because there are no mosquitoes to speak of, and those you do see on occasion don’t bite.

    I live in the fenland and swim in local rivers. I see lots of places that would be prolific mosquito breeding grounds elsewhere. But I have not been bitten by anything during more that three years that I’ve lived here. I have never seen a place like this before. You can’t live without mosquito screens in Illinois, for example, and the infilling of marshes does not seem to be a factor. There is more open, stagnant, and potentially mosquito-friendly water everywhere on the Island (including Scotland) than in most places I’ve been to before, but something makes this environment mosquito-free. I even wonder if this situation is artificial in any way.

    I’d love to hear from the locals whether it has always been like this and what might have changed if not.

  9. John B., M.D. says: Not sure why use of mosquito netting was not accounted for in the study.
    Not sure why you did not read our results of use of mosquito netting

  10. Excellent analysis by Ross McKittrick and co authors.

    A slight caveat, however. Malaria was eradicated in the US between 1905 (in Ithica, NY, the first place it was eradicated) and the early 1950s, in the TVA area in Tennessee. A lot of specific actions were taken in order to do so. The story is found in detail in Robert Desowitz’s excellent book, Who Gave Pinta to the Santa Maria?

    Since this was back in the day when families were quite large, other measures were the ones that worked. Mainly, covering breeding waters with mineral oil when mosquitos were breeding, draining of swamps where mosquitos bred, standard stuff, that is what happened in Ithica The last place where the anopheles mosquitos bred in high enough numbers to still spread the disease was in some TVA lakes, behind dams. They hatched in the shallow waters near shore of these lakes. So TVA was instructed to lower, then raise water levels in these lakes at the crucial times in the mosquito breeding cycle, exposing the eggs when lowering the water level. Certainly screens were involved.

    Once there were no longer people infected, because of the combination of fewer mosquitos along with screening, the mosquitos no longer had sources from which they could spread the disease. The actions outlined above did not exterminate the vector mosquitos, but eliminated enough of them at the right time so that the disease gradually winked out. Anopheles mosquitos are still around, but they don’t carry malaria anymore in the US and western Europe.

  11. Larry Hulden – I see the remarks about bed netting at the end of the conclusions section now. Thanks.

  12. 1. Use lots of DDT
    2. Kill all misquitos
    3. Apply ice cube to misquito bite – no itch no swelling no lump
    4. repeat steps 1 and 2 and 3

  13. chris y says: Should Mann return the unspent portion of his grant on malaria and global warming now?
    Yes, I agree.

  14. Maybe it’s a combination of factors. Middle class people tend to have smaller families, they are also more likely to be able to afford and seek earlier testing and treatment. There are some poor people who have to make a choice between testing, treatment and the next meal. Many seek treatment when it’s too late. I know this because I live in a heavy duty malaria zone.

  15. Read “Path Between The Seas” about the construction of the Panama Canal. It goes into depth about the malaria and yellow fever problem and how they solved it. Simple things like how the mosquito would only fly a certain distance and removing trees and shrubs kept them away. Once the vector was acknowledged and methods to control were introduced yellow fever and malaria was no longer a problem with the supervision and skilled trades. The laborers still suffered as not much effort was directed their way.

    I wonder how much of the continuing malaria problem is due to people not knowing/believing mosquitoes are the cause?

  16. Ralph B says: I wonder how much of the continuing malaria problem is due to people not knowing/believing mosquitoes are the cause?
    I am sure this is one important obstacle in many regions.

  17. M Courtney says: November 7, 2013 at 8:00 am
    “Correlation is not Causation.”

    The cause of malaria is the transfer of Plasmodium sp. from an Anopheles mosquito to a susceptible human. The correlation to rates is what it is; the CAUSE of the correlation is physical difficulty infected mosquitoes have during a multi-victim evening feed habit of finding multiple victims.

    At times we correctly dismiss correlation as a sign of causation – like the rise of pirate numbers with global warming. Other times we quibble: when the “thing” of a correlation is very tightly tied to the causation – like sunspots with GCR with cloud cover with global temperatures (perhaps) – the correlation is, in itself, hard-connected enough to be loosely said to be the “cause”.

    Correlations are not indicative of cause, no. But correlations can be USED as substitutes for causes for both predictive and preventative actions if two conditions are met: 1) the chain of connections from observed aspect to final result is very hard, and 2) the prevalence of the “links” is not subject to some non-related factor. It might be wise to say the value of correlation to causation is always in question, but as long as the conditions that create the correlation do not substantially change, a good correlation does have predictive usage.

    Note that I say “predictive usage”. A trend is not a prediction, but a trend tied closely to an outcome can have extremely useful predictive usage. In a preventative manner, reducing household group sleeping densities – by providing mosquito nets – does solve the problem.

    In climatology and in the pages of WUWT, there is much derision about confusing and using trends, predictions and curve-matching. Academically, the derision is valid. Pragmatically, it is sometimes absolutely invalid. And pragmatism is, after all, THE determinant in Darwinian evolutionary theory: things develop because they work, not because they are right (morally or energetically, as seen in the peacock’s fabulous tail).

    We live in a world of uncertainty. Warmists love models/modeles-with-the-French-accent. Nail-
    ‘er-down with an algorithm, dispense with uncertainties by building them OUT of your thinking. The real world of living, breathing and paying taxes has uncertainties. Any person with investments knows the certainty of human thought and effort does not extend beyond about 18 months – perhaps even 6 months is a stretch. Our understanding of how things interrelate is just not good enough.

    As a social set, we have far more informative correlations than we have causations. Even if we do confuse or conflate the things that are connected with the things that cause, trends and patterns are materially useful – until, of course, they are not. The trick is to recognize those that are hard-wired to causative factors and when that hard-wiring has come apart.

  18. A quick note on how DDT is presently used in rural areas of places like South Africa.

    It isn’t spread far and wide as a way of killing mosquitos. Instead, it is used only inside the thatched rural homes. The insects hate the small, so they don’t enter the dwelling.

    Very different that how DDT was used in the US in the 1940s and 1950s, liberally used on many farms.

  19. “Naively putting a DDT usage measure into the model would give results that apparently suggest DDT causes malaria.”
    We all know that correlation is not causation, but this statement reveals a superlative degree of ignorance.

  20. @ tadchem: Not ignorance. Sometimes people must state the obvious, because to some others, the obvious is never obvious. Unfortunately, we seem to have an increasing proportion of people in the world who would have make that linkage.

  21. tadchem says: We all know that correlation is not causation, but this statement reveals a superlative degree of ignorance.
    Sorry, we also lnow that !!!

  22. M Courtney says:
    November 7, 2013 at 8:00 am

    Didn’t actually read the paper did you? Smaller household size also correlates to wealth. More importantly, wealth correlates with how many people you share the bedroom with. Fewer people -> less chance of malaria. Of course, if you are heavily invested in DDT production, the results are not helpful.

  23. highflight56433 says:
    November 7, 2013 at 9:04 am

    1. Don’t share bedroom with more than spouse.
    End process
    There, it’s fixed.

  24. AFAIK malaria recrudescence relates directly with bad or non-existent public health policy. It’s so much cheaper to do nothing and blame it on something else.

  25. Duster says: Don’t share bedroom with more than spouse. End process . There, it’s fixed.

    Exactly !! 10 billion dollars without 100 billion dollars to vaccines will be the result !!

  26. Just think what could be achieved in the world if money spent on trying to avoid cagw was instead spent on mosquito nets, fresh water and clean burning stoves. If only we had the technology.
    By the way, did you know Oliver Cromwell died of malaria?

  27. Bloke down the pub says: Just think what could be achieved in the world if money spent on trying to avoid cagw was instead spent on mosquito nets, fresh water and clean burning stoves. If only we had the technology. — By the way, did you know Oliver Cromwell died of malaria?
    That is the main point. 10 B Dollars is enough!

  28. Wow, I reread my first comment and boy, was I sarcastic. Not very polite, sorry.

    Look the point I was making was that all of these parameters are related and the root cause of the factors is poverty and its alleviation. So the clearest signal comes from household size? Don’t you think household size is related to wealth? All of these parameters are related to wealth.

    And do you think household size is the cause of the poverty or the result?

  29. Larry,
    Thank You for a very interesting article on malarial epidemiology! I only had a half hour to ‘read and partially digest’ your report on my lunch break but will return to this as more time allows.
    MtK

  30. Most of the alternative ”explanations” touted above won’t hold water. Malaria was quite common in Sweden up to c. 1850 and then gradually disappeared and was practically extinct by 1900.
    This was long before DDT was invented and mosquito nets have never been used in Sweden
    There were certainly never any shortage of mosquitos, and no eradication campaigns. They would be utterly hopeless in any case, Sweden is recently deglaciated land, there is literally hundreds of thousands of lakes and marshes of all sizes, and yes, mosquitos (including Anopheles) are often very bad, particularly in the northern part of the country, but there is no malaria, since about a century or so.

  31. Larry Hulden says:
    November 7, 2013 at 8:47 am

    About one hundred parameters including all here discussed was crosschecked leading to one single parameter as the only one affecting the ultimate fate of malaria.

    Was early testing and treatment of malaria an input? I only ask because as poor people in developing countries get wealthier they tend to have fewer children. They also have the means to send their kids and themselves for lab tests and if positive, take meds the same day. This behavior is less frequent among the poor as I have seen it many times myself.

  32. The Tiwi people of the Bathurst and Melville Islands off the north coast of Australia didn’t know where babies come from half way through the 20th century. One can imagine a bad anthropologist (who disobeys the prime directive) trying to tell them that sex makes babies, while they hoot and holler as they carry him off to the asylum, explaining to him that correlation is not causation, especially if delayed by nine moons.

    In non-Tiwi houses the first thing the babies experiment with when they can stand up in their cribs is the light switch. They delude themselves into thinking there is some causal correlation between flipping the switch and the room lighting up. Now maybe the rooster doesn’t make the sun come up, but the correlation does suggest some sort of causation–we only have to sort out the mechanistic trail, like maybe the predawn light wakes the rooster; or the long night makes him hungry and anxious for daylight to feed by.

    Of course what the authors are tying to do is control for false causation and get down to the real causes, which of course they are doing admirably. –AGF

  33. M Courtney: ” So the clearest signal comes from household size? Don’t you think household size is related to wealth?”

    Depends on the culture, really. But this topic simply reiterates that transmittable issues are a factor of effective human density in general; and time sensitive effective human density in specific. eg. The greater effective density for a given duration, the higher the odds of transmission.

  34. agfosterjr said @ November 7, 2013 at 12:22 pm

    The Tiwi people of the Bathurst and Melville Islands off the north coast of Australia didn’t know where babies come from half way through the 20th century. One can imagine a bad anthropologist (who disobeys the prime directive) trying to tell them that sex makes babies, while they hoot and holler as they carry him off to the asylum, explaining to him that correlation is not causation, especially if delayed by nine moons.
    I’m a tad sceptical of this claim. A close friend and descendant of Cromwell as it happens) was on Cape Barren Island when it was visited by an anthropologist. The local aborigines to their and my friend’s amusement spun many wild tales for consumption by the gullible anthropologist.

    Interesting to see Sidney Price James’ speultion receiving some confirmation. Thanks for an informative read Lena, Ross and Larry.

  35. The Pompous Git says:
    November 7, 2013 at 2:12 pm

    Ignoring for the moment the well documented widespread ignorance of the procreative mechanism among primitive societies, when do you suppose humans figured it out, and how? –AGF

  36. As a DDT kinda guy I have to say that this paper does make a good point.

    On a bit of a sad note I remember around 10 years ago sitting by my daughter’s hospital bedside as she was being treated for cerebral malaria. She made it through – unlike the new born baby next to her bed who passed away in front of my eyes. The doctor and nurses did their best but to no avail. I too had a bad bout of malaria back in 1981. This is why I get so angry when Warmists try to alarm the populace with their horseshit.

  37. Since Larry Hulden is actively responding to this thread. . . I’ve been a DDT fan for a while now, but this study is compelling me to rethink. It sounds like the solution for places where poverty and family size precludes 4 or fewer sleeping in a room is to use sleeping nets to segregate into smaller sleeping units AND make medication available to deal with infections. I know the nets are inexpensive. How costly is the medication? And what to do about dengue fever? Or is that your next study?

  38. Great analysis!

    It’ll be nice to have something to point to when someone starts shrieking over increased malaria due to global warming.

    Of course, as with any disease transmitted from individual to individual any interruption in the sequence of infection would have similar outcomes. “Herd Immunity” works in a similar way, if a contagion can’t spread from one individual to another it eventually dies out. While I agree with many commenters here that correlation does not prove causation; I think the case as presented for lower household size being a significant if not dominant cause for the decline in malaria is at the very least reasonable to believe, but more importantly reduces the case for causal temperature linkages to malaria to unreasonable to believe.

  39. I liked “Warmer temperatures are not associated with increased malaria prevalence”. So much for the IPCC’s conclusions.

    I work in the tropics were malaria is rampant. The main factors appears to be poverty and density of population, as well as the abundance of water for breeding. In the dry season there are no mosquitoes and therefore no malaria.

    I also note that many of the areas where there are lots of people and poverty there are also a lot of colds, even though we are in the tropics. I suspect colds (that’s sneezing and coughing etc) are also more prevalent where there are bigger household sizes and poverty. Even though malaria tapers off in the dry season, colds do not. Colds spread more easily amongst bigger households, and amongst markets etc. I wonder if anyone has done a study on this also.

  40. Slightly O/T, but can anyone here clarify how long malaria is infectious (via the mosquito vector)?

    My father got malaria in Korea during the war there in the early 1950s. He continued to have sporadic attacks for decades afterwards. Was he a potential source of further infection after the acute phase passed? We had plenty of anopheles, and their bites, in the places that we lived in. Nobody else contracted malaria – in particular my mother, who slept in the same bed every night and got bitten by mozzies (as he did) all the time.

    In his case, he wasn’t sleeping in barracks when he contracted it. He was sleeping in a small tent (4 -6 guys) out in the field. From what he tells me, it was a major health problem for the soldiers there. Presumably it was transmitted from the local population to the troops.

  41. Very interesting. It makes intuitive sense that larger families/groups sleeping together should lead increased incidence of mosquito-mediated diseases.

    But 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 ).

  42. We have crosschecked the same parameters with dengue fever and shown that household size has no effect on dengue. It is because Aedes bites from dawn to dusk and Anopheles from dusk to dawn.
    When we look at the world statistics on household size and malaria the threshold value of four members becomes very evident. During the last phase of malaria there are still occasional epidemics because of stochastical reasons. Malaria in the 1930’s in USA appeared was caused by warm weather because the activity of insects are higher during increased temperature. Vivax malaria can remain dormant in humans for at least about 10 yaers. This behaviour of the plasmodium cause irregularities in the extinction process but historically we see malaria disappearing quite soon when household size decreases below four members. Household size decreased finally below four in the southeastern states of USA in about 1940’s. So, the use of DDT was like kicking a dying dog (the words of Margaret Humphries).
    Malaria returned in Korea although household size was about three members in the south and about four in the nort. Military troup concentrations on both side of DMZ between 400000 and 600000 thousend soldiers living in barracks of more than four soldiers in each building cause a situation with increased “household” size. We have described this in a separate article in Malaria Journal.
    The key result of the new article is that individual bed nets are necessary for malaria eradication. The price of one bed net (using chinese products) is about five dollars including transport and other logistics. The total price of malaria eradication within ten years in risk regions would be about 5-10 billion dollars. This is definitely lower cost than the ongoing development of a malaria vaccine.

  43. Somebody may have already observed that malaria has disappeared from about ten mouslim countries in the Near East although average houshold size is about 6-7. The reason for this is gender related segregation of the family. This family is divided in smaller units than four members.

  44. We have looked at both historical malaria and a cross-section of malaria situation in the year 2000. All detailed country studies and global statistics confirm the threshold value of household size as the only single parameter explaining the historical epidemiology of malaria.
    Still a comment on US malaria history. Margaret Humphries and many other have observed that none of the previous explanations for the decline of malaria in USA are valid because they do not correlate either in time or in space. Also for USA the household size decline is the best explanation of the decline of malaria, both in time and space.

  45. Larry Hulden says:

    Malaria returned in Korea although household size was about three members in the south and about four in the nort. Military troup concentrations on both side of DMZ between 400000 and 600000 thousend soldiers living in barracks of more than four soldiers in each building cause a situation with increased “household” size. We have described this in a separate article in Malaria Journal.
    ——————————————————–
    Well, I just phoned my old man and he tells me that he got malaria (in Korea) while lying in a paddy field. In keeping with the warnings – which he said were ubiquitous – he was covered from head to foot, except for his ears and face, for obvious reasons. He was dive-bombed by Anopheles for two nights.

    Then, he collapsed and was shipped to a hospital in Japan. Luckily, he made it.

    According to him, almost no soldiers in the Korean War lived in barracks, or anything like it. The infrastructure simply wasn’t there.

    It is indefensible that in this day and age people still die from malaria. Oh, and I read the other day that polio has re-emerged somewhere (one of the ezekstans maybe?) Polio? Most readers wouldn’t even know what that means. As someone who lived through the end of the polio era, where many died and the rest were crippled for life, that is another indefensible thing.

  46. If you sleep outside you will also be attacked by Anopheles mosquitoes because of nocturnal behaviour. You can get malaria from mosquitoes independently of from where the mosquito got it in the first place. The main point is that most people in the world sleep indoors and the bulk of malaria cases arise among indoor sleeping people. This fact will have a fundamental impact on the relationship of malaria and family size. The Plasmodium is actually dependant on a certain minimum number of humans available to the infective mosquito. When the mosquito is infective it has difficulties in sucking blood (the Plasmodium in the salivary glands actually decrease the production of anticoagulants), leading to numerous biting trials on all available humans during the same night. This process will insure that subsequent occasional uninfective mosquitoes (which have no difficulties with blood sucking) also will become infective although they only suck blood from one participant in the household. We have not yet produced a formula for this relationship.

  47. All details we have presented concerning the Plasmodium and the mosquitoes have been described in previous literature. Our new article, however, is the first to combine them all in one synthesis of the malaria epidemiology.

  48. Larry, you said:

    “Malaria returned in Korea although household size was about three members in the south and about four in the nort. Military troup concentrations on both side of DMZ between 400000 and 600000 thousend soldiers living in barracks of more than four soldiers in each building cause a situation with increased “household” size. We have described this in a separate article in Malaria Journal.”
    ———————————————————————–
    A citation would be useful. Meanwhile, you do not address the point I made (via my Dad who is a Korea vet) that “barracks” in the conventional sense did not exist. If you are redefining military “barracks” to any space where more than three soldiers sleep, you really are stretching the definition to the point of meaninglessness.

    You admit that Korean family groups were small; there is no evidence of “barracks” in the conventional meaning during the Korean War. So what happened there?

  49. During the Korean war in 1950’s malaria occurred everywhere in Korea but after 1993 it returned to DMZ originating from activation of dormant stage in humans. It is mostly concentrated within 50 km from DMZ and along fortified wetern coast of North Korea. It may well have started from civilians. We have compared with Continuation War in Finland 1941-44.

  50. And so… science has finally found something positive about islam. The fact that households have gender-segregated sleeping arrangements, makes new malaria infections less likely.
    The question remains: which of the two diseases is worse?

  51. Something that appears to be missing from the study is the effect of the existing background infection rate. For example, if 25% of the population have malaria, the odds of getting the disease would appear to much higher than if 1% of the population have malaria.

    If the infection rate is 25%, would you want to sleep in the same room as 4 other people? So, perhaps the critical factor is a public health program that keeps the incidence of malaria low enough that the odds of contracting the disease are essentially zero.

  52. johanna says:
    November 7, 2013 at 9:18 pm
    “It is indefensible that in this day and age people still die from malaria. Oh, and I read the other day that polio has re-emerged somewhere (one of the ezekstans maybe?)”

    Syria, thanks to Obama’s terror war.

  53. Love articles like this that make me rethink my previous misconceptions : ) I had never considered that DDT wasn’t the answer.

    Now I am thinking that simply understanding the problem is half the cure, (don’t let the buggers bite).

  54. johanna says:
    November 7, 2013 at 9:18 pm

    ….It is indefensible that in this day and age people still die from malaria. Oh, and I read the other day that polio has re-emerged somewhere (one of the ezekstans maybe?) Polio? Most readers wouldn’t even know what that means. As someone who lived through the end of the polio era, where many died and the rest were crippled for life, that is another indefensible thing.
    >>>>>>>>>>>>>
    Agreed, I knew several kids in school that had it or had sibs die of it.

  55. There is probably no greater expert in the epidemiology of Malaria, than Paul Reiter is professor at the Institut Pasteur in Paris, chief of its Insects and Infectious Disease Unit, and a specialist in the natural history and biology of mosquitoes, the epidemiology of the diseases they transmit, and strategies for their control. He has served as chairman of the American Committee of Medical Entomology of the American Society for Tropical Medicine and Hygiene, and of several committees of other professional societies. He has worked for the World Health Organization, the Pan American Health Organization, and other agencies in investigations of outbreaks of mosquito-borne diseases.

    See his video presentation at the Eighth International Conference on Climate Change in
    Munich, Germany. Recorded in 2012. Please find this video among the many others at the website of The Fraudulent Climate (linked to author name).

    Find the Paul Reiter video this way.
    1. Go to Fraudulent Climate website main page.
    2. Click the link – * Recent Media *
    3. Scroll down and click on the link –
    CLICK HERE TO OPEN THE ICCC-8 VIDEO SELECTOR / PLAYER IN A NEW WINDOW
    4. Click on the small thumbnail image of Paul Reiter.

    Sorry that’s such a rigmarole, but we have hundreds of videos on the website, and there are a few cubbyholes where some real gems can be found. Paul Reiter video is one such Gem.

  56. Larry, you have not responded substantively to my questions. Referring to other work you have done (without citations or links) doesn’t cut it.

    I don’t doubt that the availability of large groups of people sleeping in the same room, where there is already an infection pool, helps the spread of malaria by Anopheles. But, rather like those who claim that CO2 controls the climate, it seems to me that your study grossly over-simplifies a complex issue.

    To quote my post at Bishop Hill about this:

    “This study grossly over-simplifies a very complex issue. In particular, as you [Indur Golkany] 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.”
    ————————————————
    One of your responses seems to address my question upthread about whether people who have recurrences of malaria are still capable of passing on the disease – your reference to “dormant” infected populations. Can you confirm whether this is the case?

  57. It has been convincingly demonstrated that P. falciparum originated in gorillas from where it spread to humans:

    http://www.nature.com/nature/journal/v467/n7314/full/nature09442.html

    “In phylogenetic analyses of full-length mitochondrial sequences, human P. falciparum formed a monophyletic lineage within the gorilla parasite radiation. These findings indicate that P. falciparum is of gorilla origin and not of chimpanzee, bonobo or ancient human origin”.

    It’s also helpful to remember that mosquitos catch malaria from humans. A vast swarm of mosquitos rising above a tropical swamp can be almost parasite-free, while unhygienic urban humans can rapidly infect each other using relatively few mosquitos breeding in discarded tin cans and puddles around their shacks. This seems to apply even if they use nets:

    http://www.ncbi.nlm.nih.gov/pubmed/22647493

    A large local bat population can be a great help, according to this old study:

    http://www.whale.to/a/camppref.html

  58. After egg laying it returns to the same approximate location for another blood meal. [...] For a new person to be infected, a mosquito carrying the mature parasite back to its feeding location must find a victim who is not already infected. Therefore the more people who are sleeping together in the same room, the higher the probability of spreading the infection to a new person.

    While this is clever, it depends on the mosquito only returning to the same approximate location, and what is approximate to the mosquito? I’ve never found them that fussy, but they certainly are persistent. If there is a way in they will find it. The more people there are sleeping in a room, the higher the chances that someone will leave a door or window or tent flap open.

  59. Gene Selkov says:
    November 7, 2013 at 8:53 am
    … UK … I live in the fenland ,,, but something makes this environment mosquito-free.

    The British taste really, really bad. Prob’ly the diet.

  60. It’s CO2, again. Mosquitoes track it, and the denser the body count, the more CO2. Mixed sleeping multiplies the effect, for obvious reasons.

Comments are closed.