Is a Larvicide to Blame for the Zika Virus and Microcephaly Outbreak?

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What's the Real Deal with Zika Virus and Microcephaly? The Definitive Guide to What We Know

When the news first emerged linking Zika virus and microcephaly, it seemed that travel for pregnant women was going to become pretty scary. But it turns out that all is not what it seems.

The Zika virus is a single-stranded RNA virus transmitted to humans when they are bit by infected Aedes species mosquitoes; no other species of mosquito can transmit the virus.

When people are infected, common symptoms include fever, rash, joint pain, conjunctivitis, muscle pain, and headaches. The illness is usually mild, though it can last from several days to a week and may be similar to those of Dengue and Chikingunya diseases (both of which are spread by the same mosquitoes).

There are a few reasons that Zika is a bit scary; most have to do with how little we know about the virus.

While Zika was first discovered in 1947, there have been no developments as far as cures or preventative measures, other than avoiding mosquito bites. However, this has more to do with the relative mildness of the virus than anything else.

Infections are also difficult to diagnose.

“The incubation period (the time from exposure to symptoms) for Zika virus disease is not known, but is likely to be a few days to a week,” explains Dr. Gabrielle Francis. This means that some people will be infected for up to seven days without knowing that they are ill, meaning that they can transmit the disease to others, either by being bit by an infected mosquito or via sexual contact, which some are saying can transmit the disease.

But that's not the only time that it's possible to not know when people are infected. Only about 1 in 5 people who are infected with the virus will develop symptoms.

And then, of course, there is the possibility that Zika virus and microcephaly may be linked, something that the CDC sill does not agree is necessarily true.

At this point, the association remains fairly tenuous. As Dr. Francis explains, “Brazil has been having a significant outbreak of Zika virus since May 2015. Officials in Brazil have also noted an increase in the number of babies with congenital microcephaly during that time. Congenital microcephaly is often a sign of the brain not developing normally during pregnancy.”

So why link Zika virus and microcephaly? Because Zika, while its symptoms are usually not serious, has been linked to some neurological conditions in the past, like Guillain-Barré syndrome, causing Brazilian doctors and the Brazilian federal government to suggest this link as a possible -- but not the definite -- source of this problem.

This said, the increase in microcephaly cases may not in fact be linked to Zika, which has been present in South America for some time.

One possibility is that Zika has mutated into a form that causes microcephaly. “While Zika always existed, there are now currently different strains than what was previously around,” explains Dr. Serena Goldstein. “So if there’s different strains, that could be a contributor.”

But another frightening possibility is that this may not be due to Zika at all, as a February 10 article on GM Watch explored.

According to the story, Argentine and Brazilian doctors believe that it is not Zika, but rather the chemical larvicide pyriproxyfen, that is to blame for the microcephaly cases. In 2014 pyriproxyfen was introduced into the drinking water supply of the areas where many of the infected people live. The larvicide, which is a growth inhibitor of mosquito larvae that produces malformations in mosquitoes, is manufactured by Sumitomo Chemical.

Dr. Goldstein says that it is very likely that this chemical "could be contributing to microcephaly, as hormones and other chemicals in food are contributing to females, for example, having menses as early as 8 or 9 years old (versus what used to be an average age of 12-14 years old)."

This seems even more likely given the fact that in Colombia, Zika is just as common but no microcephaly has been reported. Even in Brazil, in areas where Zika affects 75 percent of the population, microcephaly has not been an issue until now.

The problem is that it’s too early to tell.

While the local government in the southern Brazilian state of Rio Grande do Sul has suspended the use of pyriproxyfen, the federal government of Brazil dismissed this theory, saying, “Unlike the relationship between Zika virus and microcephaly, which has had its confirmation shown in tests that indicated the presence of the virus in samples of blood, tissue, and amniotic fluid, the association between the use of pyriproxyfen and microcephaly has no scientific basis,” the Telegraph reported. However, although Brazil has registered a total of 3,852 suspected cases, only 41 of the affected babies have presented evidence of Zika infection.

For now, the CDC is recommending that pregnant women and women who plan to become pregnant steer clear of affected areas, and a 16-member American team has already been dispatched to Paraiba, a Brazilian state that has seen a large outbreak of Zika and several cases of babies born with microcephaly, to attempt to get to the bottom of the problem.

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Mosquito image via Shutterstock

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