Mosquitoes, the Zika virus and the threat for pregnant women: the buzz continues

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Over the past months, the Zika virus has been spreading across Middle and South America. Zika has long been considered relatively harmless, but recently it was discovered that the virus could cause a serious congenital malformation, microcephaly, in unborn children. Now that Guillain-Barré syndrome has also been linked to the virus and suspected cases of sexual transmission have been reported, worries have only been rising.

Edit (15/03): The final association

After multiple episodes of confusion and doubt regarding their association, the zika virus has been officially linked to birth defects in pregnant women infected with the virus. A research paper published in the New England Journal of Medicine has finally come to this conclusion after monitoring 88 women from September 2015 to February 2016. Not only is the virus responsible for congenital malformations such as microcephaly, the Zika virus apparently can cause multiple complications. Shortage of amniotic fluid, miscarriages in women infected in their first trimester, growth retardation, impaired blood supply to the brain and placental defects have all been attributed to the mosquito-borne virus.

According to experts, the fact that women infected in later stages of their pregnancy are still at risk is concerning, since many infections during pregnancy only cause complications for the fetus when occurring in the first trimester. The WHO also officially stated that the association between Zika virus and neurological disorders is of global concern.

Since April 2015, many South American countries have had to cope with an outbreak of the Zika virus. Originating in Brazil, the recent outbreak has already spread to 21 nations, from Mexico to Bolivia. The Zika virus has been known since the 1950s, when it was discovered in the Ugandan Zika forest, but before the South American outbreak, only about 70 human cases were recorded. Why the virus is causing an outbreak right now remains unclear.

Zika is transmitted by mosquito bites, which means the number of infections will likely continue to rise: the insects are most active during the rainy season, which lasts until March. The mosquito spreading the Zika virus, Aedes aegypti, is a known transmitter of disease; it is also responsible for spreading the dengue and yellow fever viruses. This mosquito’s range has expanded around the globe by human hand, with mosquito eggs becoming accidental passengers on international transports. The species is endemic to some African countries but is invasive throughout the Americas and Asia. The WHO expects Zika to spread across the entire American continent, with the exception of Canada and Chile. KU Leuven Professor of Virology Marc Van Ranst offers some nuances to the statements:

“The WHO is overreacting and, regrettably, their overreaction is causing panic. Basically, you just need to look at the areas where the A. aegypti mosquito and dengue fever are present. That’s mainly Central and South America, except for Chile and the Argentinean border. These are the areas with a higher altitude, where the mosquito doesn’t live. A. aegypti is also present in the southern states of the U.S., but we see very little dengue fever in that area. Zika will most likely follow the dengue pattern.”

Brazil has started a large campaign for the eradication of mosquitos and the prevention of bites. The Brazilian government fears any further spread of the disease during the Olympic Games in Rio, coming in August. Fortunately, however, the games take place during the South American winter, when mosquitos are less active.

Take precautions, pregnant women!

At first sight, the virus seemed relatively harmless, with infected individuals experiencing flu-like symptoms, fever and occasional skin rash. However, in October 2015, physicians observed a spectacular rise of microcephaly cases in newborn infants occurring in parallel with the spread of Zika. All tested infants showed an infection with the virus, passed on from the infected mother. Zika appears to cause problems with neuronal development, resulting in infants with small skulls and/or brains.

The governments of Brazil, Colombia, El Salvador, Jamaica and Ecuador have explicitly advised women to postpone pregnancies. These official statements have caused some controversy, since there is little access to contraceptives in those countries. Due to the deeply religious nature of many Latin-American states, abortion is also taboo or downright illegal. The American Center for Disease Control (CDC), in conjunction with other nations throughout the globe, has issued a negative travel advice for pregnant women to countries where there is currently a Zika outbreak.

On top of that, Zika has recently been linked to Guillain-Barré syndrome, a muscle disorder that causes acute paralysis. The causal association between the virus and the disease still requires scientific confirmation, and would only concern a small percentage of Zika infections. Also, rumors of the virus being sexually transmissible are starting to pop up, but there is only one case to back up this claim. “If Zika was truly sexually transmissible, we would’ve probably seen a lot more cases by now,” says Van Ranst. “This single case is very exceptional.”

Mutant mosquitos

No vaccine or treatment for Zika infection exists, and research on the subject is still in its infancy. “Research into a vaccine against Zika virus started the day before yesterday [January 24th]” says Van Ranst. “That’s how it goes; now that it has become a concrete issue, a lot of funding will be going to whatever research that mentions the virus.”

Currently, the only way to avoid Zika infection is to avoid mosquito bites. This task isn’t as difficult as it once was, because new technologies are available to control mosquito populations. Scientists have genetically engineered mosquitos to carry a lethal gene. Male specimens are then released in the environment, and all progeny of these GMO mosquitos inherit this lethal gene and die. Hence, mosquito populations can quickly be reduced or eradicated. The UK-based company Oxitec produces such “infertile” mosquitos and has performed successful field trials in Brazil, reducing populations by 87% in 4 months.

Many of us might frown at the thought of releasing genetically engineered insects into the environment. However, the fact that these mosquitos cannot reproduce ensures that they don’t persist. Also, because these mosquitos are invasive in the regions where Zika is currently wreaking havoc, their eradication should not be considered as unnatural. Future interventions will reveal whether the public is supportive of this new insect-control method.

Image courtesy of AFPMB