Zika virus continues to rampage through South and
Central America and the Caribbean, and new data is clarifying its link to severe
birth defects in the children of women infected during pregnancy.
Zika, born in Africa, has spread through the Pacific,
and in the last few years into South America. Most recently the Centers for Disease Control and Prevention placed travel restrictions on two small
Caribbean islands, Aruba, Bonaire. With those, Zika is now known to have
affected 28 areas through the continent.
There has been considerable discussion about birth
defects like malformed brains and tiny heads having been caused by something
other than Zika—including some of the mosquito control technologies that have
been used to attempt to control the mosquito-borne virus.
This blog previously discussed Zika six weeks ago here.
As we wrote then, “And there are all sorts of conspiracy
theories running around already, as there were about AIDS and Ebola. One of
them is that genetically modified mosquitoes are somehow involved in
transmission.”
Most of the latest data is discounting other causes and
more and more clearly targeting Zika as the direct cause of the birth defects.
Indeed, the correlation between Zika and microcephaly dates back to before the South American
outbreak.
The journal The Lancet today (March 19, 2016) reports
that microcephaly is quite clearly linked to a 2013 to 2014 outbreak of Zika in
French Polynesia—the biggest outbreak in the world before the current South
American panic.
The study found a spike in microcephaly cases among the
children of women who had been infected with Zika during the first trimester of
their pregnancies.
“Our analysis strongly supports the hypothesis that
infection in the first trimester of pregnancy is associated with an increased
risk of microcephaly,” wrote Dr. Simon Cauchemez, of the Pasteur Institute in
Paris, and co-authors.
The data could not prove a link among women who were infected
after the first trimester: “We could not rule out an increased risk of
microcephaly from infection in other trimesters, but models that excluded the
first trimester were not supported by the data.”
The French Polynesian study found that the actual risk
of having a child with microcephaly is comparatively low—about 1 percent—among mothers
in the first trimester. However, since the percentage of people who get
infected by Zika can be very high—in French Polynesia, two-thirds of the people
were infected—it can still be a significant public health hazard.
“Our findings support the need for a strong and prompt
response to protect, inform, and monitor pregnant women and to provide strong
research agendas to clarify the causal link between Zika virus and microcephaly
and develop effective treatments and vaccines,” the authors wrote.
Zika virus has been found in the amniotic fluid of two
pregnant women who had been infected with Zika, according to a Feb. 11, 2016
paper in the journal of the Center for Infectious Disease Research and Policy.
A March 10, 2016, paper in the New England Journal of Medicine, said researchers had recovered Zika virus DNA from the brain of a
microcephalic fetus. The mother was living in Brazil, and she reported Zika-like symptoms during that
period.
A number of conspiracy theories have suggested
microcephaly might be caused by genetically modified mosquitoes that were
released to control Zika, or by a pesticide, pyriproxifen, released to control
the mosquitoes, or that it was caused by vaccines.
A study published March 8, 2016, by the New England
Complex Systems Institute, downplayed either possibility.
The study said the argument for any other causes than Zika
is weakened by the presence of increased microcephaly in French Polynesia,
where genetically engineered mosquitoes, pyriroxifen and the implicated vaccine
were not widely used.
© Jan TenBruggencate 2016
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