Erstellt am: 20. 2. 2016 - 12:54 Uhr
Zika: Irradication through Irradiation
There is a sickly sweet pungent smell in the warm Insect Pest Control research laboratories in Seiberdorf in Lower Austrian, run jointly by the IAEA and the FAO. The smell comes from the bags of ox blood and feed used to rear what I can only describe as a mutant army; or perhaps a mutant air force.
"Global health emergency"
Here the scientists are breeding and then sterilizing thousands of mosquitoes, a technique that could help fight the terrible disease burden of malaria, dengue fever and the sickness that the World Health Organisation recently called a “global health emergency”, the Zika virus – another horror that spreads to the sound of a whining buzz.
Chris Cummins
Here, when they are still in the pupa stage, male mosquitoes are subjected to a radiation dose of 120 Gray. Marc Vreysen, the head of the research facility, says this dose would be enough to kill a human but in a mosquito it merely alters the DNA sufficiently to render them sterile.
The technique is being developed here in Lower Austria and then the know-how is exported to tropical regions vulnerable to mosquito-borne disease. In these areas, the sterilized male insects can then be released in huge numbers into the wild where they are supposed to mate with healthy females and thus thwart the breeding cycles.
The releases are truly vast – once set free there will be perhaps a thousand sterile males for every healthy male in the target area.
Vreysen says that the females usually only mate once or perhaps twice (more likely due to time constraint and instinct rather than any idealistic romantic sensibilities) meaning that if you flood the dating market with sexual duds, then you can effectively control mosquito numbers without reliance on pesticides, and thereby fight disease in a relatively environmentally friendly way.
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The World Health Organisation says that Zika virus, which is named after the Zika forest near Entebbe in Uganda, where it was first identified in a monkey back in 1947, is now “spreading explosively” across the Americas and could affect four million people by 2017. Its effects on adult humans are relatively harmless; if you were to even notice that you had been infected then it would feel like a mild cold.
Dramatic surge in birth defects
But in October Zika made global headlines when doctors in northern Brazil warned that the arrival of the virus had coincided with a dramatic surge in microcephaly, a condition that leaves babies with smaller than usual heads and in most cases under-developed brains. Since September 3,700 babies have been born to Brazilian mothers with this condition. In the whole of 2014 the figure was just 150.
The link has not yet been confirmed beyond doubt. But virologist Derek Gatherer told FM4 that, having looked at other suspects, including use of pesticide, Zika “remains the most likely suspect.” It’s spread by the bite of mosquitoes of the Aedes genus, an insect also known to transmit yellow fever and dengue and so controlling these blood suckers is seen as vital.
Chris Cummins
Aedes mosquitoes are so hard to control, explains IAEA expert researcher Rosemary Lees, because they lay their eggs in the smallest pools of water. “I’ve known them breeding in a footprint that has been filled with rainwater.” That means that any standing water is likely to become a dangerous base for the mosquitoes, even a half empty coke can. Scientists think it is no coincidence that Zika has hit North-eastern Brazil, a poor area that has been suffering from drought. In times of water shortage, families often store water in their homes.
In another laboratory we see an African scientist separating the female and male mosquito pupa by hand. It seems painstaking work but Rosemary says it is necessary. If both males and females were irradiated then firstly, the sterile males would simply mate with the sterile females and wouldn’t go out searching for the healthy females. Secondly, it is only the females who bite – they need the blood to produce eggs. Even if they were sterile they could still bite, so effectively the men and women in white coats would be releasing thousands of laboratory-bred biting mosquitoes into vulnerable villages. That sort of thing doesn’t generally go down well!
The traditional response to mosquito control has been to spray everything with a thick cloud of insecticide and we have already seen that happening in Brazil. The problem is that this insecticide is basically a poison. If a cattle trough, for example is sprayed, then the cattle can absorb the dangerous chemicals and pass it down the food chain to humans. Authorities do try to insist on animals’ water being regularly changed but the science of control is hardly exact.
Plus, say Seiberdorf based molecular biologist Konstantinos Bourtzis, the mosquitoes have over generations developed an increasing resistance to known insecticides meaning that greater and greater doses are required for less and less effect. He describes the sterilisation programme developed and championed at Seibersdorf as the most “environmentally friendly method of insect control” and points to its success in ridding the Tanzanian island of Zanzibar of the sleeping-sickness carrying Tsetse flies.
Chris Cummins
I’m a non-scientist, who shamefully spent much of school science lessons staring out of the windows at distant cricket matches, so I won the prize for asking perhaps the scientifically most naïve question at Seibersdorf. If you irradiate thousands of mosquitoes, aren’t they then radioactive? No, Konstantinos Bourtzis, reassures me, patiently, likening the process to going for an X-ray at the dentist or a chest X-ray at the doctors.
Still the irradiated males have to convince the healthy females that they are capable of producing the goods, a perceived difficulty that proponents of other insect control techniques use to attack the sterilisation program. But Rosemary Lees says that these doubts are not backed up by any evidence, pointing the historical successes over many decades in Guatemala and Panama and Mexico for fly sterilisation programmes. To test their health the irradiated male mosquitoes are released in large beige netted domes along a gravel path at Seibersdorf where they buzz around delicious smelling orange trees.
Chris Cummins
Nuclear scientists experimenting in white coats might evoke an instinctive mistrust among those of us who grew up on Spiderman stories, but it seems to me that this work to tackle the burden of mosquito-borne disease is vitally important.
As well as the horror that Zika poses to pregnant women, there is the economic and health stasis brought about by our inability to tackle malaria effectively.
Although infection rates and death rates have fallen dramatically in recent years, the latest WHO estimates, released in December 2015, there were 214 million cases of malaria in 2015 and 438,000 deaths. I worked as a journalist in West Africa, I have seen what malaria can do, and I have been terrorised by aggressive tsetse flies in central African Uganda
The sterilisation process is just one weapon in the global fight against these diseases, but if it helps fight them whilst also reducing our need to spray everything with insecticide, it is worthy of our attention.