Trypanosomes, climate change and evolution; past and present

By: Charles Ebikeme

“Trypanosomiasis has kept Africa green”

The quote above comes from a book I can’t remember by an author whose name escapes me. In essence, it alludes to the inextricable relationship and balance that exists between all things on our planet, particularly the relationship between man and his environment. For a long time, we have known about the influence diseases can have on us, but we are only now beginning to realise its full extent.

The delicate relationship and inter-connected influence between human populations, climate, and the ecology of disease (vector-borne or otherwise) has unfolded over evolutionary time.

Photo credit: Britannica Encyclopedia

Genetically, some populations are predisposed to particular diseases. A Science last year, showed  African-Americans have higher rates of kidney disease than European-Americans. The reason, as postulated by the researchers, was due to variants of a gene (APOL1), common in African chromosomes but absent from European chromosomes. The gene codes for a serum factor that lyses (or harms) trypanosomes. It seems the evolution of a critical survival factor in Africa now contributes to the high rates of kidney disease in African-Americans.

Changes in African climate in the last 5-6 million years are thought to have mediated important modifications in the African environment and in the animals that live there. As the rivers changed, and as plant and animal species adapted to a changing climate, disease was brought to areas where it wasnt before. These phenomena have marked important milestones in the evolution of humans and their predecessors.

The expansion of savannah grasslands influenced the evolution and behaviour of early humans, as well as representing a turning point in the relation between apes and primate-infective trypanosomes. The two diseases of trypanosomiasis (rhodesiense and gambiense) perhaps drove early man ‘out of Africa’ in an attempt to avoid tsetse infested areas of the Rift Valley.

Then came colonisation disrupting the balance between parasite, fly, people, flora and fauna. Which, for the sake of brevity, leads us to where we are today.  After witnessing the fall and rise of trypanosomiasis, we are now witnessing the fall. The question is if a rise will follow a rise due to anthropogenic climate change. With the record, as shown by the International Energy Agency and without increased action, the cost of a 2-4°C rise in temperature will no longer be measured in dollars and cents, and instead in human lives.

The next decades are crucial to climate change, as we approach, closer and closer, the point of no return. Major environmental and human modifications are occurring in an Africa already ripe with neglected diseases.

Furthermore, the ongoing environmental changes as well as changes in human population will have drastic repercussions on the epidemiology and the spatial distribution of sleeping sickness in the region.

The question for the now and for the future in particular relating to health and disease is how to mitigate for an ever changing climate. And to understand how climate, human population dynamics and environmental changes will continue to influence not just trypanosomiasis, but other neglected diseases over time.

Charles Ebikeme has worked for many years as a research scientist on African Sleeping Sickness. Possessing a MSc from the London School of Hygiene & Tropical Medicine, and a PhD in Parasitology from the University of Glasgow, Charles currently blogs and writes for the All Results Journals – a new publication system focusing on negative results – covering topics on the hidden side of the scientific publication process.

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