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Mosquitoes, dengue, Zika, …

Zica virus aedes aegypti mosquito on human skin - Dengue, Chikungunya, Mayaro, Yellow fever

A Graph a Day… 7th June 2024

I am afraid I have been too busy to post here regularly. It has been an incredibly busy period, with several projects ending or nearing end, and several trips abroad. But, I am hoping to get back into regular posting and so I am very grateful to my regular readers.

This brief post is about mosquitoes, climate change, and dengue. As the temperatures rise globally, insects – and diseases for which the insects are vectors – that so far have been confined to tropics are moving north.

As seen in the map below, cases of both dengue and Zika have been found in the European South.

Since January 1, 2024, more than 1,679 cases of dengue have been imported into mainland France, compared to 131 cases over the same period in 2023. Although most cases are mild and do not result in further transmission, there is considerable concern that it will get worse with the continuing climate change.

The mosquitoes – the potential vectors of these diseases – are certainly present there. The map below shows the distribution of tiger mosquitoes, Aedes albopictus. An even more dangerous species of mosquito, Aedes aegypti, is already present in Cyprus and Madeira.

Continuing with the theme of mosquitoes, the link below is to a new paper on how infection changes the behaviour of insects. Such a change is not unique to mosquitoes and has been seen in many species – possibly including humans. But this is a potential topic for another A Graph a Day…

A Graph a Day… 27 March 2024

From the Pearls Of Raw Nerdism. However, maths education is actually not as bad as this graph suggests. We gain these skills through Elementary, School and College, and they give us the ability to think critically to formulate and answer questions properly as part of general education. Of course, one can ask whether we all need to climb up this “mountain of mathematical knowledge”.

A graph a day… 25 March 2024

Source: Simon shows you maps, Deccan Herald, Bloomberg, OWID

There appears to be an inverse relationship between a country’s wealth measured in terms of GDP and its fertility rate—the number of children per woman. A rate of around 2.1 is needed to keep the population at a constant level (ignoring inward migration). Broadly speaking, the population in any country with a rate below 2.1 is shrinking.

As the graph above is highly skewed, it is better to use a logarithmic scale for the GDP, reflecting the large differences in wealth between the countries. The relationship is even clearer, showing differences between continents, with Africa in the low-GDP-high-fertility area, as compared with Europe and some Asian and American countries in the high-GDP-low-fertility area.

Economic factors could influence fertility directly – poorer countries rely on agriculture and low-tech industries requiring a larger workforce. GDP is also a proxy for other factors, which are known to influence the fertility rate, like lliteracy among women or public health status.

If you can, play the time-lapse of the graph on OWID, and select some country trajectories, like China:

But, on a closer look, this picture is a bit more complicated. European countries are not showing the same type of relationship, possibly because factors other than economics dominate. One such factor could be the share of men helping in the household:

This is an important factor for countries which are now struggling with a rapid population decline, like South Korea, Japan, or some East European countries.