NARRATOR: Brazil late 2014.
Doctors noticed a disturbing trend.
An increasing number of babies who
were born with abnormally small heads, a condition
known as microcephaly.
The spike in microcephaly was linked
to a virus called Zika that is spread by mosquitoes.
CELINA MARIA TURCHI MARTELLI: I just
never dreamt, as an epidemiologist
of infectious disease, that I would
see a congenital transmission by a virus that
will do such a great damage and would
be transmitted by mosquitoes.
NARRATOR: Throughout the Americas,
mosquito bites are tied to many viral outbreaks.
In the months before Zika spread in Brazil,
chikungunya, a tropical virus that
causes terrible joint pain, invaded the Western hemisphere,
infecting almost a million people.
And West Nile virus sickened more than 2,000 victims
in the US with symptoms ranging from fever to paralysis.
To stop these outbreaks, scientists
have turned their attention to fighting the mosquitoes that
carry these diseases.
And one of the weapons they are using is genetic engineering.
In South America, the Zika virus is
spread by a mosquito called Aedes aegypti.
Other diseases, including dengue, chikungunya,
and yellow fever, are also spread
by this persistent insect.
TOM FRIEDEN: Aedes aegypti is the cockroach of mosquitoes.
It lives indoors and outdoors.
It bites daytime and nighttime.
It develops resistance to insecticides easily.
The eggs can over winter for a year.
To control it, we have to kill the adult mosquitoes,
the larval mosquitoes, both inside and outside.
NARRATOR: Health officials have used sprays and screens
to protect people from diseases spread by mosquitoes.
But since 2002, scientists at a biotech company
called Oxitec have been investigating
a more direct approach, a line of genetically modified Aedes
aegypti mosquitoes called OX513A.
SOFIA BASTOS PINTO: The goal of this procedure here at Oxitec
is to use our mosquito, OX513A to reduce the population
numbers of the Aedes aegypti mosquito in the wild.
NARRATOR: When released, these mosquitoes
reproduce with wild mosquitoes and cause their offspring
today.
Although there are concerns about this technology,
authorities have allowed limited releases
to study its efficacy and safety.
So how were these genetically modified mosquitoes produced?
The process involved engineering mosquitoes with two new genes.
SOFIA BASTOS PINTO: What you do first is create or synthesize
the DNA you want to insert.
So in our case, we used the two genes
that we inserted, the lethality gene
and the fluorescent marker.
NARRATOR: The genes were inserted in the genomes
of mosquito eggs.
The lethality gene makes the developing mosquitoes
dependent on the antibiotic, tetracycline, which
is fed to them in the lab, but is not available in the wild.
The fluorescent marker gene produces a protein
that glows red when exposed to light of a certain wavelength.
It tells scientists which mosquitoes
have the lethality gene.
After the first genetically modified mosquitoes
grew into adults, scientists bred them in the lab.
These mosquitoes passed on the genetic modification
to each new generation, giving rise
to a colony of genetically modified mosquitoes, all
dependent on tetracycline.
SOFIA BASTOS PINTO: So this is our female room.
You can walk in.
In these big cages, what we have is our egg-producing colony,
in total about 12,000 females per cage.
And they're here to produce the egg.
So our genetic modification has been done in 2002.
[INAUDIBLE] inserted in the genome
of every single of these mosquitoes, which
are here in this room.
They lay their eggs in these pieces of paper.
All the black little dots are eggs that have been laid.
NARRATOR: When scientists plan to release genetically modified
mosquitoes into the wild, they collect eggs from this colony.
They place the eggs in water, where they hatch into larvae
and then grow into pupae.
At this stage, technicians separate the males
from the females by size.
SOFIA BASTOS PINTO: These are a separate female
and that's a male pot.
The male pupae are significantly smaller than the females.
Feeding them tetracycline, the antidote to the lethality gene,
keeps the mosquitoes alive as they grow into adults.
So we'd give an antidote in the lab to the mosquito
so that they don't die.
And then we go release our male into the field.
NARRATOR: Male mosquitoes don't bite people,
so they will not spread disease, but they live long enough
to meet with female mosquitoes.
SOFIA BASTOS PINTO: And then life becomes exciting for them.
They get to do what they're best at doing,
which is searching females, copulating with those females.
And our males will deliver the lethality gene
to their children.
And in the wild, the babies do not come in contact
with the antidote.
And there they die.
GUILHERME TRIVELLATO: Well, here in this van
you can fit almost 800,000 of male mosquitoes.
As we go driving through the area,
every time the app beeps, we just
open one of the spots in here, and the mosquitoes
will fly around and do their job.
NARRATOR: Once released, the genetically modified male
mosquitoes mate with wild females.
The male carries two copies of the genetic modification,
so all the offspring inherit a copy of the lethality gene.
The wild offspring will not feed on tetracycline, the antidote
to the gene, and they will die before reaching maturity.
Scientists monitor how the technique
is working by capturing larvae and determining
what percentage have the telltale red fluorescence.
Studies have shown that with repeated distribution
the wild mosquito population of a village or neighborhood
can be cut by 95%.
If the technique continues to prove effective and safe
to humans and wildlife, it could be
applied to other species of mosquitoes
and help stem the spread of many dangerous diseases.
[BABY CRYING]
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