Friday, March 18, 2016

Zika: forget conspiracies, birth defects clearly linked to the virus

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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