January 27, 2016 —The mosquito-borne Zika virus has been linked to a surge in cases of birth defects in Brazil, and is spreading in other countries in the southern hemisphere. Flaminia Catteruccia, associate professor of immunology and infectious diseases at Harvard T.H. Chan School of Public Health, says the virus may have adapted to the human environment and mutated.
What do we know about the Zika virus?
Zika is very similar to other viruses that are transmitted by the Aedes mosquitoes, including dengue and chikungunya. It was first discovered in 1947 in monkeys in Africa, and there have been several outbreaks since then. But it has not been studied much because, normally, the symptoms are quite mild—fever, headaches, joint pain. People get over it in a few days.
It seems like there is something different about the virus in the current outbreak in Brazil. It has coincided with a dramatic rise in cases of microcephaly, a birth defect that results in babies born with unusually small heads. The increase in babies born with this condition has been more than 20-fold compared with previous years—from maybe 150 cases to more than 3,000 cases in a few months.
What are the major research questions around Zika?
If Zika is the causative agent behind the surge in microcephaly—and possibly also Guillain-Barré syndrome, an autoimmune disease of the nervous system now on the rise among adults in Brazil—this may demonstrate that the virus has adapted to the human environment and may have mutated to become more pathogenic to humans. A correlation between Zika and these conditions has not been confirmed, but previous studies have shown that it can be passed from mothers to babies in utero and also that it can infect the nervous system. What is worrying is that we don’t know what may have changed, and why.
There need to be genetic studies to understand the origin of this virus. It appears that there are two different strains, one originating in Africa and one from Asia. The outbreak in Brazil seems to be from the Asian strain, which may have evolved to be better at invading nerve cells or at evading the immune system.
Should pregnant women in the U.S. be concerned about Zika?
Other viruses in the same family, like dengue and chikungunya, have not proven to be a major problem in the U.S. Most of the cases of these diseases have been imported by travelers. There have only been a few cases of direct transmission of those two diseases from one person to another through a mosquito. These examples are reassuring. For Zika, it should be the same. The only warning from the Centers for Disease Control has been to advise pregnant women not to travel to affected countries. The situation here is quite different from Brazil and Colombia, where the governments recently advised women to delay getting pregnant until the summer when the outbreak is predicted to wane.
The chart below shows the sharp increase in microcephaly cases in Brazil
In Zika response, WHO should learn from Ebola mistakes (Harvard Chan School News)
Zika ‘unknowns’ hampering public health response (Harvard Chan School News)