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In the constant evolutionary battle between mankind and disease, some humans have developed a partial resistance to malaria.

In Africa, some of Asia, and northern Greece, where the disease is endemic, some people carry genes which lead to modifications to the shape of the red blood cells (those carrying oxygen around the body).

Rather than being doughnut-shaped, as is the haemoglobin of the population elsewhere, the cells of carriers of this genetic mutation are sickle-shaped. These cells cannot be colonised by the parasites causing malaria.

However, when both parents of a child carry this adaptation, their offspring is prone to the debilitating (and often fatal) sickle-cell anaemia disease.

The high mortality rate associated with this outcome limits the breeding success of such individuals, and prevents the adaptation spreading through the entire population in malarial areas.





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The Impact of Disease   

Disease was the single largest obstacle to the emergence of substantial agglomerations of people in the Lowveld, irrespective of their origins. Human concentrations, with the necessary attendant cattle and crops, were together an ideal reservoir for the storage and transmission of disease.

The biggest biological killer of mankind in Africa was, and continues to this day to be, the genus Anopheles, the mosquito. The females of certain mosquito species carry the parasites causing malaria. This disease still accounts for three million deaths across the continent each year. Around the turn of the twentieth century, is made the Lowveld impossible for the colonists to settle in substantial populations.

Amongst the colonial settlers, the introduction of quinine as a prophylactic against malaria from South America in the 1850s did enable a reduction in morbidity of four-fifths amongst these populations, even in the most infested areas.

The indigenous African populations had evolved some immunity to malaria through a modification in the structure of their blood cell structure deforming it from plate-like in shape to something resembling a sickle.

Tragically this resistance was a double-edged sword as the children of two adults carrying the recessive gene for this modification also inherit the fatal condition sickle cell anaemia. Either way, it was not until much later that the colonists shared their medicines with the local population.

Locally, Dr Siegfried Annecke pioneered the control of the dreaded mosquito. He set out to put an end to malaria in the Lowveld, and by virtue of sheer determination eradicated the disease in an industrialised area radiating out from Tzaneen. It remains a problem in many of Africa's national parks to this day.

A less auspicious introduction from foreign climes into Africa was that of rinderpest- cattle plague. An extremely contagious airborne virus, it spreads rapidly.

From its first emergence from bovine stock introduced by Italian troops from Russia into Somaliland in 1889, it spread to infect the entire continent by 1897, impeded only briefly by the Sahara desert and South Africa's erection of 1,600km of barbed wire from Bechuanaland to the Cape-Natal coastline.

Between ninety and ninety-five percent of all cattle in Africa developed fever, listlessness, bleeding from all orifices, and died over this period.

The consequences for native society where cattle were not only a vital source of foodstuffs and building materials, but a sign of status, authority, and a store of wealth, were no less terrible.

Expanses of the continent which were formerly grassland well-cropped by cattle and game returned rapidly to woods and thickets providing ideal conditions for the reproduction of the tsetse fly.

Wild game, no longer out-competed for resources by managed herds of cattle, increased rapidly in number. These animals carry trypanosomes (parasites) in their blood to which they have evolved immunity.

To those who have not co-evolved with these animals (colonists and introduced cattle), these parasites cause sleeping sickness (trypanosomiasis) which is frequently fatal. The blood-sucking tsetse fly transfers them between hosts.

The combination of the growth in tsetse fly populations and the increase in the wild game population, rendered large swathes of formerly inhabited Africa uninhabitable once again due to endemnicity of sleeping sickness.

Many such areas were declared game reserves early in the twentieth century as nature's equilibrium was shifted in favour of the wild game populations. South Africa's Kruger National Park was one of these, along with Hwange in Zimbabwe, Selous in Tanzania, the Okavango Delta in Botswana, and Luangwa and Kafue in Zambia.



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