moving into a new area and settling there

Out of Africa malaria paper

24-Sep-2011

Out of Africa malaria paper

Here's a taste of Lisa's recent research in an extract from one of her scientific papers - called Plasmodium falciparum Accompanied the Human Expansion out of Africa.

We've provided pop-up definitions for this, since we'll be using it in a class activity.

Summary of paper

Plasmodium falciparum is distributed throughout the tropics and is responsible for an estimated 230 million cases of malaria every year, with a further 1.4 billion people at risk of infection.

Little is known about the genetic makeup of P. falciparum populations, despite variation in genetic diversity being a key factor in morbidity, mortality, and the success of malaria control initiatives.

Here we analyze a worldwide sample of 519 P. falciparum isolates sequenced for two housekeeping genes (63 single nucleotide polymorphisms from around 5000 nucleotides per isolate).

We observe a strong negative correlation between within-population genetic diversity and geographic distance from sub-Saharan Africa (R² = 0.95) over Africa, Asia, and Oceania. In contrast, regional variation in transmission intensity seems to have had a negligible impact on the distribution of genetic diversity.

The striking geographic patterns of isolation by distance observed in P. falciparum mirror the ones previously documented in humans and point to a joint sub-Saharan African origin between the parasite and its host. Age estimates for the expansion of P. falciparum further support that anatomically modern humans were infected prior to their exit out of Africa and carried the parasite along during their colonization of the world.

Extract from Discussion section of paper

Below we've provided, for information, another short extract from the same paper. We won't look at this in detail, so no pop-ups, but it does explain more than the summary - which is helpful in trying to grasp what the paper is all about.

The age of P. falciparum is also highly disputed, with previous estimates for the time to the most recent common ancestor (TMRCA) spanning more than an order of magnitude with values ranging from about 10,000 years to over 300,000 years. With P. falciparum being an exclusively human parasite with no known animal reservoir, we hypothesized that if P. falciparum had been associated with humans for over 50,000 to 60,000 years (the estimated date for the out-of-Africa migration of anatomically modern humans), its current population structure could still carry a signal of human settlement history.

Within-population genetic diversity of native human populations decreases smoothly with geographic distance measured through landmasses from a sub-Saharan African origin, and genetic differentiation between populations also increases steadily with physical distance along landmasses.

These smooth patterns in the distribution of human genetic diversity have been ascribed to sequential bottlenecks of small amplitude during the colonization of the world by our ancestors from an African cradle. In contrast, the parasite population structure may primarily depend on variation in epidemiological settings between populations. In particular, P. falciparum populations are characterized by high variability in variation in transmission intensity, which could have affected local genetic diversity. Selective pressure imposed by antimalaria interventions that used drugs and insecticides might, likewise, have locally reduced genetic diversity.

Words used in pop-ups

Alveolata	algae	breed	cell	chromosomes	DNA	evolution
exposed	fertile	flagella	flagellate	gene	genome	host
infectivity	ingest	inherit	membrane	molecule	mutation	nucleotide
nucleus	organelle	organism	protein	protist	protoplasm	protozoan
sequence	species	structure	symbiotic	template

For other websites and resources relevant to this science story try the

Out of Africa malaria paper

Out of Africa malaria paper

Summary of paper

Extract from Discussion section of paper

Further reading

Words used in pop-ups