Sounding The Alarm

"The Aedes aegypti is today one of the main threats for public health in Brazil. This little, tiny mosquito."
"There was a very rapid and disorganized expansion of cities [historical development]. It was a very good situation for the mosquitoes. And now, today, we believe it's impossible to eradicate the mosquito. It's spread everywhere [from its ancient origins in sub-Saharan Africa]."
"It's like a pet. Eighty percent of mosquitoes we capture are inside houses."
Ademir Martins, mosquito researcher, Instituto Oswaldo Cruz, Rio de Janeiro

"So many people are literally travelling halfway around the world in a matter of hours. Any Aedes aegypti that bites you has the potential to start the cycle [of viral transmission] off and running."
"Human travel was probably the single most important factor [fuelling the emergence of exotic new viruses in countries like Brazil]."
Scott Weaver, director, Institute for Human Infections and Immunity, University of Texas Medical Branch

Aedes aegypti is now found in over 100 countries worldwide

"It [resistant gene] went from literally undetectable levels [of the gene] to close to 100 percent. We're now looking at opportunities to come up with new insecticides, but that's going to be slow and there's no guarantee they won't become resistant as well. That's why the situation is so dire."
"I think we're just starting to see the tip of the iceberg. I think you're going to start to see more and more diseases."
William Black, A.aegpti researcher, Colorado State University

"The level of social disruption that this [transmission of the Zika virus] can cause is really absolutely massive."
Dr. Kamran Khan, infectious disease scientist, clinician, St.Michael's Hospital, Toronto

About one and a half million Brazilians were infected by dengue fever last year, and over 800 were killed by the disease. Chikungunya began spreading in the country in 2014, a horribly painful disease. And now there is Zika, a virus that began appearing in the spring of 2015, recognized to be the cause of microcephaly, a birth defect once rare, where babies are born with abnormally small heads and undeveloped brains. All spread by the now-ubiquitous mosquito, Aedes aegypti.

Mind, it is not only Brazil that is challenged to cope with this disastrous situation. Cases are increasing of all three viruses world-wide. Dengue infections alone have risen 30 times in the last half-century, costing the Americas an estimated $2.1-billion annually. Since Chikungunya's late 2013 appearance in the Western Hemisphere it has spread widely and even Florida has not been spared. As for Zika, it has spread to some fourteen countries and territories, causing an "explosive pandemic re-emergency [that is] truly remarkable", according to an editorial in the New England Journal of Medicine.

Both the U.S. Centres for Disease Control and Prevention, and Health Canada have taken the step of advising pregnant women to bypass travel to those areas where Zika is known now to be in circulation. Brazil had fewer than 200 cases of microcephaly annually before the arrival of Zika but since October, over 3,500 cases have been identified where babies face death or severe mental disability.  The CDC this week announced the virus had been discovered in the brains of two babies with microcephaly who had died after birth.

The ancestors of A.aegypti, where they first surfaced in sub-Saharan Africa laid larvae in tree holes and then the mosquitoes adapted to human environments with the formation of the Sahara desert, depriving mosquitoes of a water source required for females to breed. "The most reliable water source at that time would've been in human habitats", explained Jeff Powell of Yale University who studies mosquito populations through their genetics. "It became what we call domesticated." It's his belief that in the 15th century the mosquito travelled aboard slave ships from West Africa to the New World.

With the use of DDT, an eradication campaign managed to wipe out the A.aegypti species in parts of South America and the United States in the early 20th century, even as a vaccine for yellow fever, which was what the mosquitoes spread at that time, was developed. But as so often happens just when science believes it has solved a natural threat through manipulating nature, the mosquitoes rebounded. The species in its egg form can survive months of dryness and their favourite mode of travel was inside rubber tires where moisture pools.

Because mosquitoes feed on human blood they are hugely reliant on the presence of human populations and have become accustomed to spending their time with humans in indoor environments. And since there are no truly effective drugs or vaccines to kill the mosquitoes, the killing strategy presents a conundrum. Not so readily accomplished, with mosquitoes developing natural defences against insecticides. And then there is the complicating factor of not only globalization but global warming, with mosquitoes now surviving cooler temperatures.

In the space of a year almost ten million people left Brazil for international destinations, flying to other countries in the Americas and elsewhere in the world. Dr. Khan's St. Michael's Hospital study discovered 22.7 million Americans are susceptible to Zika transmission in states prepared to welcome the mosquitoes, notably Florida. Brazilian travellers in significant numbers of tens of thousands landed in Toronto, with 30,000 of them going on to British Columbia.

There is nowhere to hide. And unless a powerful new technology named CRISPR which appears truly promising in the field of genetic engineering demonstrates that its potential can be realized, the world has a struggle on its hands. CRISPR manages specific genes by editing and swapping them out. It is now being looked at as a tool to engineer mosquitoes' genes through sterilization, or by making them resistant to pathogen infection. So there is hope, although the experts also call for caution.

"It's way, way too early. I don't want to sound like an old fogey but I've been doing this for 35 years and I've seen a lot of ideas come and go. It's [CRISPR] the newest silver bullet in a long line of silver bullets", cautioned Colorado State University's William Black.