By Elke Weesjes

Aedes Aegypti Mosquito

© Marcos Teixeira de Freitas - Aedes Aegypti Mosquito.

The mosquito-borne Zika virus has been around for nearly 70 years, yet until recently almost no one had heard of it. Outbreaks of the virus were sporadic, affecting only small groups of people, and the symptoms seemed mild, especially compared with its close relatives, dengue and yellow fever. As a result, clinical interest in Zika was almost nonexistent. Before 2015, only a dozen confirmed cases were discussed in medical literature.

All of this changed last year. Following a massive outbreak of the virus in Brazil, where more than 1.5 million people have been infected, scientists learned that Zika isn’t as benign as previously thought. That's when they discovered a link between the virus and the incidence of central nervous system (CNS) malformation, including microcephaly, a potentially deadly birth defect in which babies are born with abnormally small heads and underdeveloped brains. There is also strong evidence that Zika triggers Guillain-Barré, a neurological disorder in which the body’s immune system attacks part of the peripheral nervous system. Guillain-Barré can lead to muscle weakness, paralysis and even death. Significant clusters of microcephaly and Guillain-Barré—both otherwise rare conditions—have been reported in Brazil and French Polynesia, two countries that were hit first during the Zika epidemic.

In light of this, the World Health Organization declared Zika and associated neurological disorders an international public health emergency on February 1. During a press conference on that day, WHO Director General Margaret Chan called for international response to combat the spread of the virus.

Since April 2015, Zika has been spreading rapidly in more than 50 countries, territories and areas in the Americas, Africa and Asia. In other countries the number of travel-related Zika infections have been rising steadily. In the United States, according to the most recent data released by the Centers for Disease Control and Prevention, a total of 147 cases of Zika have surfaced in 24 states and the District of Columbia. Roughly 107 individuals have been infected outside of the continental United States, while 40 have been infected in American territories, including Puerto Rico, where mosquitoes now carry the virus.

Because the virus is linked to fetal CNS malformation, research has focused especially on women who become infected while pregnant. As of February 17, the CDC had received reports of nine pregnant U.S. women with confirmed Zika infections after traveling to countries affected by the virus. CDC researchers issued a preliminary report with their findings last Friday. Of the nine women, two chose to terminate their pregnancies, two women miscarried, while three delivered babies. Of these infants, one has severe microcephaly; the other two are healthy. The remaining two women are still pregnant, so far without any complications.

Although the sample is limited, the report’s findings are significant, according to CDC Director Tom Frieden. Many questions remain, however, according to Denise J. Jamieson, co-author of the report.

“Microcephaly can be hard to detect on ultrasound early on,” she said during a press conference last week. “The later in pregnancy, the easier it is to see the abnormalities of the skull and brain. However, it's not clear whether these abnormalities developed later on, and that's why you don't see them at 18 to 20 weeks […] when many women receive a routine screening ultrasound, or whether we're just not very good at picking them up earlier on.”

Last week an epidemiology team from the CDC arrived in Brazil to further investigate the link between Zika and microcephaly. In Brazil, between October 22, 2015, and February 20, 2016, there were 5,640 reported cases of microcephaly and/or CNS malformation, including 120 deaths, according to the WHO. Prior to the Zika outbreak, 163 cases, on average, were reported each year.

Brazilian scientists from the Federal University of Rio de Janeiro (UFRI) have made a breakthrough. They analyzed the virus found in the amniotic fluid of pregnant women and obtained the virus’ genetic data. This finding marks a significant step towards understanding how Zika behaves in the human body and how to develop a vaccine as well as new tests.

“What we know now may help us understand why the virus has chosen children’s brain cells over those of adults—the pregnant women,” said Renato Santana one of the researchers involved with the project to Agência Brasil, the country’s official news agency.

Unfortunately, the road to a vaccine is typically long and expensive. In the meantime, the primary focus is on prevention. Health officials in the United States and Europe have urged pregnant women to delay travel to Latin America and the Caribbean. In these Zika-affected countries the war on mosquitoes is well underway. In Brazil, for instance, President Dilma Roussef decided to deploy 222,000 troops to fight this unusual and vexing war. She called for the removal of stagnant water spots where Zika-carrying mosquitos live and reproduce.

“While we do not have a vaccine against the Zika virus, the war must be concentrated on the elimination of breeding grounds for the mosquito,” Rousseff said on Twitter. “Getting rid of Zika is the responsibility of all of us.”