The world health organization (WHO, to those in the know) considers malaria as one of the last of the "great plagues" that still stalk the earth. 660,000 men, women and children were struck down in 2010, dying due to a preventable and curable disease.
Malaria is disease caused by a microscopic parasite, of the Plasmodium genus. There are five species known to infect humans, with P. falciparum and P. vivax being far and away the most responsible for deaths. It is transmitted via the female Anopheles mosquito and upon transfer to a human host, travels to the liver where it reproduces a-sexually. It is at this stage where it's effects begin to be felt. Victims quickly become incapacitated with fever, headaches and vomiting. Patients may also develop severe respiratory distress and in the unlucky, cerebral malaria, which can result in seizures, coma and sadly death.
The reason why malaria remains as one of the great pathological bug-bears of our generation is the predominance of its vector, the humble mosquito. Any still body of water can breed thousands of mosquitos, and mosquitos have been shown to be frustratingly tenacious to control. Each infected person also serves as a new disease reservoir, hastening and spreading the burden of this horrible disease. Governments and national bodies spend hundreds of thousands of dollars each year in order to curtail the breeding of the blood sucking pests, using harsh chemical larvicides such as methoprene and the infamous DDT. Alarmingly, there are now DDT resistant mosquito populations emerging, calling into question the efficacy of chemical control methods.
This is where innovative science comes into play. An enterprising Michigan laboratory has managed to turn the tables, infecting mosquitos with a unique strain of bacteria in order to prevent them transmitting the deadly plasmodium.
With careful cultivation, researcher Zhiyong Xi and his team have been able to isolate a strain of bacteria called Wolbachia that infects the female Anopheles mosquito. Once infected, these mosquitos were shown to have resistance to P. falciparum, and thus, reducing the likely hood of human transmission.
What makes this particularly successful is that this strain of bacteria has been shown to be maternally heritable. In the study, an infected female was able to "pass down" the infection to her offspring. In fact, the infected females could only breed with males also infected with the bacterium. Miss-matched pairs, with only one of the mosquitoes infected with the bacteria, were unable to produce any viable young. The infected populations also "overtook" the non-infected population. A few infected males and females were placed within a non-infected population and within 8 generations, were able to replace the original non-infected mosquitoes, leaving only mosquitoes carrying the Wolbachia bacterium. So, theoretically, an infected population in the wild could potentially replace "normal" populations, reducing overall transmission of malaria.
The exact mechanism the bacterium use to prevent co-infection with P. falciparum is currently unknown. It is thought that Wolbachia creates a hostile environment inside the mosquito, possibly something to do with the immune response. Infected mosquitos contained more reactive oxygen species than the non-infected mosquitos. Such reactive oxygen species inhibit the growth and development of P. falciparum.
While promising, these results were obtained within the confines of a carefully controlled laboratory setting. The next step is field trials, to see if these results can be replicated in the wild. Similar experiments using Wolbachia to control the spread of dengue fever virus in A. aegypti mosquitos have shown promising results and it is hoped that there will be a repeated success story with these very special mosquitos.
The imaginative usage of naturally occurring phenomena is one of the core ideals of Biotechnology. With this step, we may be able to control the scourge that is malaria, in a way that has minimal ecological impact while still maintaining a broad scope of control. This ground up, or rather, mosquito up, approach also has the obvious financial benefits over a large medication based health control measure. It will be able to protect larger amounts of a population, with minimal financial outlay. The financial conundrum of malaria control is critical, due to the socio-economic situation of countries where malaria runs rife, such as sub-saharan Africa, where malaria is an too real occurrence. This form biological control is also blessedly free from potential political machinations, which are tragically all too common in the areas of concern within Africa.
With further research into this field it is hoped that within a life-time, malaria can finally be relegated to the history books, where it can join the ranks of small pox and bubonic plague, a hazy memory only used as a cautionary tale.
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