The Mosquitos-Men Foe: the story of Malaria

The Mosquitos-Men Foe: the story of Malaria

Mayleen Lee

To many humans, Mosquitos seem harmless in any possible way: tiny, soft, and squishable.

The reality, however, is unfortunately very ironic.

Mosquitoes have caused more human suffering than any other organism in the human history – more than one million people die from mosquito-transmitted diseases worldwide every year since ancient time.

Malaria perfect demonstrates this formidable foe between mosquitos and men.  Malaria, caused by infection from Plasmodium parasites, is transmitted to people through the bites of infected mosquitoes.  The stings, particularly from Anopheles mosquitoes, would normally lead to seemly mild symptoms such as fever and headache, making them difficult to be recognized as Malaria.  According to the World Health Organization (WHO), untreated Malaria can progress in 24 hours and lead to death.  This makes Malaria the deadliest infectious disease in history, taking 1.2 million lives per year.

The medical world has put lots of efforts into creating effective vaccine for Malaria.  It turns out that, despite our advanced scientific knowledge and technology, we failed at outfoxing evolution - when we attack Malaria germs with drugs, the germs fight back.  Scientists have discovered that the Plasmodium parasites have repeatedly evolved to resist the front-line treatments. The mosquitoes that carry the parasites have rapidly evolved to resist the insecticides we poison them with.  And now, scientist has found that some malaria parasite can cause disease severe enough to cause evolutionary selection pressures in human populations!

Dr. Anna Rosana-Urgell and her collegues from PNG Institute In Medical Research found that Plasmodium vivax malaria is the reason behind the abnormally high rates of Southeast Asian Ovalovytosis (SAO), a hereditary erythrocytes (red blood cell) disorder, in the Asian and Oceanic region.    

In SAO, the red blood cells are a different shape (elliptical) from the usual biconcave disc shape.  This genetic defect is carried by up to 35% of people living on the coasts of Papua New Guinea, an area happened to have high malaria endemic.  The researchers performed genetic tests in 1,975 children and found that nearly 50% of children in Papua New Guinea aged 0-14 years are SAO-positive and immune to P. vivax.  This means that SAO genetic defect may have protective effect against malaria caused by P.vivax by altering the ability of the parasite to develop within the red blood cell.  These findings indicated that P.vivax have caused enough evolutionary pressure that it has influence genetic adaption of the human population.

As Professor Andrew Read, a biologies and entomologist from Penn State University, presented at TEDMED: disease superbugs have the ability to mutate faster than treatments are developed, and understanding natural selection can help scientists fight back and control antibiotic resistance.

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 Phyo, A.P. et al. Emergence of artemisinin-resistant malaria on the western border of Thailand: a longitudinal study, The Lancet, Volume 379, Issue 9830, 26 May–1 June 2012, Pages 1960-1966,(http://www.sciencedirect.com/science/article/pii/S014067361260484X)
 

Rosanas-Urgell A, Lin E, Manning L, Rarau P, Laman M, et al. (2012) Reduced Risk of Plasmodium vivax Malaria in Papua New Guinean Children with Southeast Asian Ovalocytosis in Two Cohorts and a Case-Control Study. PLoS Med 9(9): e1001305. doi:10.1371/journal.pmed.1001305