Unlike malaria, tuberculosis (TB) is found across the whole world. Why and explain? I mean why are people affected with TB more than malaria and some say that in cold and developed countries malaria is less but TB cases are more.
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1$\begingroup$ Malaria is no longer found around the world because it has been eradicated from developed countries. It was common in the USA until mid-20th century. $\endgroup$– iayorkMay 4, 2016 at 18:08
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1$\begingroup$ Both diseases have totally different dynamics. Why compare them? $\endgroup$– WYSIWYGMay 5, 2016 at 7:08
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$\begingroup$ @WYSIWYG Please tell me why this is not a 'good' answer? $\endgroup$– ABcDexterMay 7, 2016 at 19:19
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1 Answer
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The statement in the question about the current distribution of these diseases is not strictly accurate, as shown by the graphic below.
[Malaria graphic: Wikipedia user, Percherie (2006); TB graphic: Corbett et al. (2003)]
However there is no disputing that the contemporary and historical geographical distribution of these diseases differ. Why?
The crux of the answer is that this is because of the different agents that cause these diseases. Malaria is transmitted by certain mosquitoes and is therefore restricted to places in which these mosquitoes are found. TB is a bacterial disease, the geographical range of which is determined by human contact under conditions which favour its transmission.
To expand:
Malaria is transmitted by Anopheles mosquitoes, especially in Africa by Anopheles gambia together with the Plasmodium falciparum parasite. One of the factors determining the mosquito habitat is standing water and the elimination of malaria from Southern Europe followed drainage of the marches and swamps in which it breeds.
That is not to say that this is the only factor in the elimination of the malarial mosquitos from certain parts of the world in recent historic times. For example malaria has not been eliminated from Africa partly because of the cost and logistic problems of implementing programmes of eradication using drugs etc.
Tuberculosis (TB) in humans is caused by the bacterium, Mycobacterium tuberculosis. Its airborne spread was favoured by the crowded conditions in cities following the industrial revolution, and its elimination fostered by improved living conditions and the development of antibiotics in the twentieth century.
Footnote: Some Factors affecting Malarial Outbreaks in Africa
A section from an article by Tarekegn A. Abeku, entitled Response to Malaria Epidemics in Africa, is relevant:
In highlands, transmission is unstable due to fluctuations in temperatures that are normally low. Temperature affects duration of the sporogonic cycle of the Plasmodium parasite within the Anopheles vector, survival and feeding frequency of the adult female, and duration of the aquatic stages.
and
Semi-arid areas, on the other hand, have mostly warm climates, and epidemics are associated with anomalous rainfall, which causes increases in vector breeding and survival.
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$\begingroup$ This is flat wrong. Malaria was common in the USA before the 1940s. It was transmitted by Anopheles quadrimaculatus in the east, An. freeborni in the west, and An. pseudopunctipennis along the U.S./Mexico border. All three are still prevalent; thus there is a constant risk that malaria could be reintroduced in the United States. $\endgroup$– iayorkMay 4, 2016 at 18:47
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$\begingroup$ @iayork I was talking about Africa and Europe, where I believe malaria originated. That is why sickle cell anaemia and the thalasaemias arose. Malaria was wiped out in Europe by draining marches. I think your comment and down vote unjustified. $\endgroup$– DavidMay 4, 2016 at 19:07
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1$\begingroup$ @iayork I have modified my answer. Biology SE exists to provide answers to biology questions. I have therefore tried to provide an answer to the question, which was about the restricted geographical distributiion of malaria. Is my first paragraph a correct answer to that question? If you think my amplification of that can be improved, please make constructive suggestions to that end and I will consider incorporating them. The risk of the recurrence of malaria in various parts of the world may be a global health concern, but it is not the subject of the question. $\endgroup$– DavidMay 4, 2016 at 20:54
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$\begingroup$ @iayork I have further modified my entry by adding some maps. This means that the one-line answer is no longer the first paragraph, as stated in my last comment, but the italicized sentence starting "The crux of the answer..." $\endgroup$– DavidMay 5, 2016 at 11:32