Zika disease: the facts

Aedes Aegypti mosquito. Photo Credit: James Gathany. Licensed under CC BY 2.0

Aedes Aegypti mosquito. Photo Credit: James Gathany. Licensed under CC BY 2.0

By now, you’ve probably heard about Zika disease, a mosquito-borne illness causing quite a stir in the news. So what’s really going on here? Let’s get straight to it.

Zika (rhymes with “eureka”) disease is caused by Zika virus, first identified in 1947, that is spread by the bite of an infected Aedes species mosquito. These Aedes mosquitoes are what we call vectors, agents that carry and transmit an infectious pathogen. It turns out that female Aedes mosquitoes require a blood meal to produce eggs, so disease transmission is an unfortunate byproduct of the mosquito procreation process.

Now, let’s talk disease. The symptoms that Zika disease cause are a little nondescript – fever, joint pain, red eyes and a rash. These symptoms are similar to those of Dengue, West Nile, and Chikungunya, which are diseases caused by related viruses and spread by the same type of mosquitoes. Only around one in five people infected with the disease actually get sick, and for those that do get sick, the illness is quite mild.

So what’s the cause for such concern?

There’s evidence to suggest that Zika disease is linked to birth defects. [UPDATE: as of the 14th April, 2016, the Centers for Disease Control and Prevention have concluded that Zika does indeed cause birth defects.]

In Brazil, the site of the largest known outbreak of Zika, there’s been an alarming increase in cases of babies being born with microcephaly, a birth defect characterised by abnormally small heads and partially developed brains. This prompted an official press release in November of 2015, announcing the potential link between microcephaly and Zika, urging for national support to contain Aedes mosquitoes.

As it stands now, we cannot definitively prove that Zika is causing this surge in microcephaly, though there is some evidence that suggests the link is valid. We do, however, know that the virus can be transmitted from a pregnant mother to her baby during pregnancy or around the time of birth. The World Health Organization has deemed the spread of Zika a public health emergency of international concern, and public health officials and scientists alike are currently conducting studies to understand the potential microcephaly-Zika link. UPDATE: as of the 14th April, 2016, the Centers for Disease Control and Prevention have concluded that Zika does indeed cause birth defects.

Centers for Disease Control and Prevention

Comparison of a baby with microcephaly and a baby with a typical head size. Image is in the public domain and is supplied by the Centers for Disease Control and Prevention

Diagnosis and tracking are difficult.

With the symptoms being so vague and mild, many Zika-infected individuals likely don’t realise and so don’t seek medical attention. For those that do, the laboratory tests we have available can’t always definitively confirm Zika is causing the disease, so reporting cases and keeping a comprehensive record of when and where the disease is present is tricky.

Travel exacerbates dissemination of Zika.

The mosquitoes that transmit Zika disease originated in Africa but are now widespread in tropical and subtropical regions all over the world. This means that travellers visiting tropical locations could potentially bring the virus home or along with them to other travel destinations. The Pan American Health Organization reports that Zika has now spread to 30 nations and territories.

Though ever-growing, our knowledge about the intricacies of Zika virus pathogenesis is limited.

In early October 2015, fears surfaced that Zika infection could potentially induce Guillain-Barre syndrome, an autoimmune disorder characterized by paralysis and nerve damage. Brazilian health authorities confirmed in early February 2016 that Zika transmission occurred through blood transfusion of a Zika-infected donor. The Dallas County Health and Human Services department confirmed a case of sexual transmission of Zika in Texas earlier this month, though sexual transmission of Zika has been reported (and sensationalised) before.

So, now what?

As we learn more about Zika disease, the best thing we can do to prevent the spread of infection is protect yourself and your family from mosquito bites. Additionally, the CDC has issued travel warnings for people, especially pregnant women, traveling to countries with Zika. Currently, there’s no vaccine or specific treatment for Zika infection.

In addition to mosquito control programs, several companies have been working on developing genetically modified mosquitoes designed to reduce the Aedes population by releasing wild male mosquitoes that don’t produce viable offspring. Scientists have also been working toward developing a Zika vaccine, an intricate process that will take some time.

As public health officials and scientists work tirelessly to learn more about Zika and develop solutions, it will be important to minimise sensationalism and maximise collaboration. Members of the general public should stay vigilant, reporting any symptoms or suspected cases of Zika to healthcare providers, and stay informed about travel warnings. The CDC has a helpful Zika Q & A on their website for the general public that is updated as new information is confirmed.

– Kellie Vinal is a PhD student at Emory University studying the biochemistry of antibiotic resistance. When she’s not sciencing, she’s riding bikes, crafting, or perfecting her sweet dance moves.

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