(NaturalNews) A genetically modified (GM) mosquito intended to eradicate dengue fever may have actually contributed to an epidemic of the disease in Brazil, civil society organizations have warned.
"It is extraordinary that experiments with Oxitec's GM mosquitoes continue and commercial releases have even been approved without any monitoring of the effect on dengue," said Dr. Helen Wallace, Director of GeneWatch UK. "The declaration of a dengue emergency in Jacobina should be a wake-up call for the authorities."
Critics predicted "rebound effect"
The GM mosquitoes were developed by British company Oxitec and commercialized in Brazil in partnership with Moscamed Brazil and the University of Sao Paulo. They are all males of the species Aedes aegypti, the only variety of mosquito that transmits the disease dengue fever. Oxitec claims that, when the GM mosquitoes are released into the wild, they will mate with females. Because the males carry a gene that leads to the death of all their offspring, this should lead to a drop in mosquito numbers in regions where the GM insects are released.
Oxitec claims that this, in turn, will reduce rates of dengue fever.
Convinced by Oxitec's claims that field trials had shown an 81 to 100 percent reduction in Aedes aegypti numbers, the Brazilian regulatory agency Comissao Tecnica Nacional de Biosseguranca (CTNBio) recently approved weekly releases of the GM mosquitoes in the city of Jacobina, where the trials took place. The company plans to release 10 million mosquitoes each week for every 50 thousand inhabitants.
But civil society groups and even one member of CTNBio have warned that this biological experiment could have unintended consequences, perhaps even causing increases in the incidence or virulence of dengue fever. This may occur through several different mechanisms.
Of people who are exposed to dengue fever, few actually develop any disease symptoms, because their immune systems successfully fight off the infection. This, in turn, boosts their immune systems against future exposure to the disease. But a dramatic reduction in mosquito numbers, such as that caused by the GM mosquitoes, could actually lead people to lose this acquired immunity. When they are later exposed to the virus, they might be more likely to become ill, in what is known as a "rebound effect."
Similarly, the most severe form of the disease -- dengue hemorrhagic fever -- is most likely to occur in people who have previously been infected with dengue fever. When people suffer two dengue infections in rapid succession, they are much less likely to develop hemorrhagic fever due to the persistence of antibodies in their blood. When there is a longer gap between infections -- as is likely to be caused by a dramatic reduction in mosquito numbers -- hemorrhagic fever is much more likely to result.
These problems are more likely to be serious if the population-suppressing effects of the GM mosquito releases are short-lived, Dr. Wallace warned.
This could occur if the technology fails, or if the wild mosquitoes evolve to avoid the GM males or somehow counter the killer gene.
Dengue emergency underway
Some of these nightmarish predictions may already be coming to pass. Despite Oxitec's dramatic claims about reductions in mosquito numbers around Jacobina, the city is in the midst of a dengue epidemic that has led the mayor to declare a state of emergency.
"CTNBio should review its decision to approve commercialization in light of the reality seen in Jacobina and ask for further serious studies on the full implications of releasing the GM mosquito over the local population," said Gabriel Fernandes of AS-PTA, Brazil.
"[W]ith no concrete proof that this technology is able to reduce dengue incidence, any approval of the GM mosquitoes would be grossly premature," said Lim Li Ching of Third World Network.