newborns last year had
abnormally tiny heads and
potentially debilitating brain
damage. In 2015 the country
reported nearly 3,000 cases of the incurable condition, called
microcephaly—about 20 times
more than the prior year. In
the nation’s northeast, where
most of the cases occurred,
government officials have already declared a state of
emergency. Now international
researchers and Brazilian
authorities are rushing to tamp
down the problem. The trouble is they are not
sure exactly what is causing
the phenomenon or how to
address it. They do have one
strong suspect—a mosquito-
borne disease called Zika that usually causes short-term
rashes and joint aches, and is
plaguing the same areas in
Brazil. There is already
evidence the virus can cross
the placental barrier: Zika has been detected in the amniotic
fluid of two pregnant women
with microcephalic fetuses in
the state of Paraiba. What’s
more, viruses from the same
genus have the ability to replicate once they reach the
central nervous system,
providing some indication of
how the viruses could
potentially cause microcephaly
in the first place. Zika disease, however, has
never been known to cause
microcephaly before.
(Microcephaly is typically
caused by exposure to toxic
substances during pregnancy, genetic abnormalities or
diseases during pregnancy like
rubella or herpes). Then again,
scientists also know very little
about Zika. In fact, until 2007
there were only sporadic cases of people infected with the
virus (at least ones that were
laboratory confirmed), with
small outbreaks in Africa and
Southeast Asia since being
discovered in 1947 in Uganda. Now, the Zika virus is rapidly
advancing across new terrain.
In May 2015 Brazil reported its
first case of Zika and by
December 2015 the virus had
made its way into several countries in Central and South
America, such as Colombia
and Mexico, and even showed up on the island of Puerto Rico. The rapid spread
suggests a change in the Zika
virus, one which scientists are
racing against the clock to
pinpoint. Worryingly, Zika has
also been linked with the future development of Guillain–
Barré syndrome,
an autoimmune disease that could lead to paralysis. Researchers know a virus like
Zika could mutate to become
more fit, essentially allowing it
to transmit more easily from
one host to another in order to
survive. But a mutation designed specifically to help it
cross the natural placental
barrier between mother and
fetus would not necessarily be
too beneficial for the virus
because it has been successfully transmitted in
more traditional ways, says
Scott Weaver, an expert on
mosquito-borne viral diseases
at The University of Texas
Medical Branch (U.T.M.B.) at Galveston. A more likely
possibility for its rapid reach,
he says, is that the virus may
have adapted in recent years
to have a higher level of
viremia, or more virus present in any given drop of blood.
That would allow Zika to be
transmitted at a greater rate
because it would increase the
chances of a mosquito picking
up the virus and transmitting it to another person after biting
an infected human. A fringe
benefit of this viremia would
be that although the virus
would not have any innate
increase in its ability to cross the placental barrier, its high
concentration may boost its
chances of making the leap.
Weaver’s team at U.T.M.B. is
studying the virus now in the
hopes of pinning down such answers. But that work will not
determine if Zika is definitely
fueling the microcephaly
cases. For that, still other
researchers at U.T.M.B., at
the request of Brazilian authorities, are part of a larger
team attempting to shore up
the connection between Zika
and microcephaly. Two
U.T.M.B. researchers, Nikos
Vasilakis and Shannan Rossi, were in Brazil over Christmas
helping to set up diagnostic
capabilities to test umbilical
cord blood for signs of Zika at
birth. The signs they are looking for
lie in the newborns’ antibodies.
Because the antibodies for
Zika virus look so much like
those for dengue or yellow
fever, (both common in Brazil) it is hard to detect if a
pregnant woman has
contracted Zika or had one of
those other conditions in the
past. But lab testing of cord
blood antibodies that show up in response to a recent
exposure—called
immunoglobulin M antibodies,
or IgM—would allow scientists
to detect if the fetus was
infected with Zika and that it happened recently (unlike tests
that would pick up longer term
antibodies transmitted from the
mom). Theoretically, those
tests, too, may also pick up
similar-looking dengue virus and confuse the results,
Weaver says, but the chance
of such a false positive is rare
because fetal dengue infection
is so uncommon. “By trying to
diagnose more of these cases at birth by sampling cord
blood, they may learn more
about how these fetuses were
infected,” he says. Even without that data there is
already some indication the
Zika–microcephaly connection
is more than just geographical
coincidence. There have also
been reports of genetic material from Zika being
detected in the blood tissue of
a microcephalic baby from the
northern Brazilian state of
Pará. (That infant died within
five minutes of birth.) And, anecdotally, some of the
women who went on to birth
children with microcephaly
also remembered having a
rash during pregnancy—a
potential but not definitive symptom of Zika. In addition,
beyond Brazil there have been
reports in French Polynesia of
an unusual uptick in central
nervous system problems
among babies born in the past couple years in areas
associated with Zika
outbreaks. Further lab testing
of those mothers found that at
least some of them may have
had asymptomatic Zika virus. But this information, by itself,
is not yet airtight. In Brazil
further investigations continue
even as the government rolls
out public health education
and mosquito control efforts. If the new cord blood information
and other research soon firms
up the Zika–microcephaly
connection, perhaps that will
add further impetus to develop
a vaccine for Zika—possibly by adapting one already in use for Zika’s cousin, dengue.
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Vectorcy
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