A thin-film Giemsa stained micrograph of ring-forms, and gametocytes of Plasmodium falciparum. Photo: Wikipedia
With climate change spreading insect-borne diseases into new areas already, and increasing rates of resistance to current anti-malarial drugs, two stories today seem to resonate: Scientists say they are closer to developing genetically modified mosquitos to combat malaria; and, some new research shows that anti-malarial trees in East Africa that have been used for generations as herbal medicine, and possibly could be sources of new anti-malarial drugs, are threatened with extinction. We Can Learn From Communities Using Plants To Treat Malaria
Scientists from the World Agroforestry Centre and the Kenya Medical Research Institute have identified 22 anti-malarial trees and shrubs from East Africa which are effective in treating malaria's symptoms and deserve further study. Unfortunately, like many trees in East Africa, these are at risk of extinction due to deforestation and over-harvesting for medicinal use.
One species given as example and which is critically endangered is Zanthoxylum chalybeum, knobwood. It grows in dry woodlands and grasslands and has been used to treat malaria by local people. Extractions of its leaves, bark and roots have promising anti-malarial properties.
Lead author Dr Najma Dharani says,
We're not saying these medicinal plants is a replacement for common prevention treatments like bed nets or effective medicines like ACT, but we believe that it's worth learning from communities that have been treating malaria symptoms with plants for hundreds of years. We need to do more research because of one of these plants could prove to be the next Artemesia, and we need to do our best to preserve the plants that are going extinct.
What's Artemesia and Why Do We Need a 'Next'?
Originally from South America, Artemesia annua is the shrub from which quinine comes, which has been used historically to treat malaria (it's the bitter taste, much much diluted from medicinal levels, in tonic water) and from from which the most effective modern anti-malarial drugs have been derived. The trouble is that in Southeast Asia the malarial parasite is becoming resistant to these drugs.
If the plants used traditionally in this part of the world go extinct, so also goes the possibility to treat malarial either with the plant itself as herbal medicine or by deriving more concentrated pharmaceuticals from them.
Anti-Malarial GM Mosquitos Still A Long Way Off
Taking an opposite track from finding anti-malarial drugs from nature is the work from scientists attempting to manipulate the DNA of wild mosquitos so that the malaria parasite cannot develop in them and therefore can't be transmitted to humans.
They inserted a gene into the mosquito DNA which is very good at looking after its own interests - a homing endonuclease called I-SceI. The gene makes an enzyme which cuts the DNA in two. The cell's repair machinery then uses the gene as a template when repairing the cut. As a result the homing endonuclease gene is copied. It does this in such a way that all the sperm produced by a male mosquito carry the gene. So all its offspring have the gene. The process is then repeated so the offspring's offspring have the gene and so on. In the laboratory experiments, the gene was spread to half the caged mosquitoes in 12 generations.
The idea is to develop a way that the anti-malarial properties of the GM mosquitos is reproduced across generations--no small feat.
The scientists involved in this research say that though this is a long way off from being used on wild mosquito populations, it is a strong step forward.