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Zika virus is a global public health emergency, declares WHO

BMJ 2016; 352 doi: https://doi.org/10.1136/bmj.i657 (Published 02 February 2016) Cite this as: BMJ 2016;352:i657

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Re: Zika virus is a global public health emergency, declares WHO

Might it be worthwhile to reconsider releasing GM male Aedes aegypti (AA) mosquitoes into the environment as a means of vector control of dengue? This question has become relevant in the coincidence of the release of the GM AA mosquitoes into the environment with the Zika outbreak in Brazil.

Because of their high rate of turnover, mosquitoes are capable of random genetic changes within a very short time. Not only would you get several generations in a year (20+ generations per year) but they also produce several eggs per batch – about 200 eggs per batch by AA female mosquitoes.

Let us put aside the genetic modification of the AA mosquitoes and say that the only thing done was to rear normal AA mosquitoes in the lab and release the 20th generation AA mosquitoes into the environment. If you rear ordinary mosquitoes in a lab, you would end up in a short time with generations of mosquitoes with profoundly different genetic make up from the mosquitoes you started with. When we release the lab-bred mosquitoes into the environment, we say we are releasing them into the wild. But mosquitoes in the environment are the normal mosquitoes because they live in the normal environment. So rather the lab-bred mosquitoes may well be the WILD type.

What genetic changes would male lab-bred non-GM mosquitoes bring to the normal mosquito population when released into the environment? Here we can think of several possibilities

- Female AA mosquito lives 2 to 3 weeks. Indoors - warm and moist, the female mosquito can live up to 2 months. So we know that environment determines how long the female mosquito would hang around to transmit whatever it is transmitting. Can we say that the lab-bred mosquitoes would over 20 generations assume a longer adult life to be passed on to female offspring on mating with mosquitoes not bred in the lab? And would that not increase the infection period?

- Normal AA eggs can withstand desiccation and dry conditions for very long times awaiting rains or wet conditions to advance to the next stage. Considering the 5-star hotel conditions in which generations of lab mosquitoes are bred, would it be far fetched to assume that resulting eggs in the environment would have different resistance or tolerance to the weather?

- Normal AA mosquitoes are mostly daytime mosquitoes. Would the lab-bred conditions alter day-night activity cycles of the mosquitoes in the environment?

- Male AA mosquitoes don’t bite, don’t transmit disease. Would the feeding habits and diet in lab conditions alter this?

We cannot rule out with certainty these possibilities that would alter the efficiency of AA mosquitoes in infecting humans nor the infectiousness and pathogenicity of the viruses – Dengue, chikungunya and Zika, in absolute and relative terms, carried by the AA mosquitoes

Particularly when we consider that:

- Tetracycline in chicken derived feed given to male AA mosquitoes in the lab is responsible for the failure to achieve 100% sterilization rates in any cohort of mosquitoes

- Tetracycline in the environment, into which the genetically modified mosquitoes are released, reverses the sterility of some (15% reported once) of the male GM AA mosquitoes.

These considerations become important under the current circumstances and release of male GM AA mosquitoes, where the Zika virus - the least infectious and pathogenic of the three viruses carried by AA mosquitoes - has assumed the most important status.

Competing interests: No competing interests

09 February 2016
Dr George Kweifio-Okai
Physiologist
Mental Health Foundation of Ghana
P. O. Box 5080