get really alarming is when a virus spreads quickly and when it causes serious harm.

Zika virus has the potential to do both of these things, which is why it’s gotten a lot of attention.

Given this, it makes sense to understand a bit about Zika virus and the disease it causes.

Zika virus is an arbovirus, meaning it’s transmitted via certain arthropods, specifically

mosquitos, so it’s a mosquito-borne virus. Mosquito-borne doesn’t mean that the virus

is “born” in the mosquito, though, but it’s “borne”, with an ‘e’, which

means carried or transported. Sometimes we call organisms like this “vectors”, what

all they do is transport the virus. So with Zika virus, just like other mosquito-borne

viruses like dengue fever, yellow fever, Japanese encephalitis, and West Nile virus, the mosquito

acts as a vector that transmits the virus from one person to the next. These viruses

are all in the genus flavivirus.

In order to mature her offspring, female mosquitoes need a blood-meal, which they get from unsuspecting hosts.

Mosquitoes find their blood-meals using chemical compounds that we and other organisms

give off, like carbon dioxide, ammonia, lactic acid, and octenol. So when a mosquito that

also happens to be carrying the virus finds her meal and digs in, the virus infects the

human host and starts to multiply or reproduce within the human. With most flaviviruses though,

the virus isn’t able to replicate enough in the human host to actually be able to reinfect

another mosquito, and so the human is considered a dead-end-host. However, the Zika virus,

along with yellow and dengue fever, is well enough adapted to human hosts such that they

can multiply to a point where it can re-infect another unsuspecting mosquito, which can then

go on to infect more people. This window lasts for the first week of infection, during which

the Zika virus can be found in the blood. So if humans with the disease can transmit

back to mosquitoes then you can imagine that areas where there’re a lot of mosquitoes,

would be a set-up for spreading the virus super quickly, right?

Now the Zika virus is transmitted via mosquitos in the Aedes genus. These blood thirsty little

guys can bite at night, but are mostly active during the daytime. Aedes mosquitoes are also

the same ones that transmit Chikungunya fever and dengue fever. When Aedes aegypti or Aedes

albopictus, both species of Aedes mosquito, lands on your skin and sticks in it’s long

nose—or proboscis, it pierces the epidermis which is the topmost layer, composed almost

entirely of keratinocytes. Keratinocytes basically serve to protect against foreign pathogens,

and it’s typically pretty good at that. That proboscis though keeps going into the

dermis, since the epidermis just gets oxygen from the air and doesn’t have its own blood

supply, whereas the dermis does, and this is what our mosquito’s after, right, the

blood meal. Since the proboscis goes through both the epidermal and dermal layers, the

cells in those layers are susceptible to infection by Zika virus. So in addition to keratinocytes,

fibroblasts, and dendritic cells have also been found to be permissive to Zika virus,

meaning they have some sort of receptor or attachment site that basically says," here

you go man, come on in."

Now we still don’t know everything about the Zika virus infection, but we do know that

when it enters the cell, it injects a single-stranded positive RNA strand. "Positive" means that this

piece of RNA’s a lot like our own mRNA; it’s basically ready to rock and get translated

into proteins. The virus’s genome is translated by our own cellular machinery into more viruses.

Eventually those cells-turned-virus-making-factories die, which actually ends up releasing more

viruses to infect more cells.

As bleak as all that sounds, our immune system’s actually pretty good at fighting off Zika

virus, and only 1 in 5 get sick from infection, and the often the others won’t even notice

they’ve been infected. Common symptoms when patients have them, are mild fever and skin

rash, but some also experience muscle and joint pain, headaches, and conjunctivitis,

or red eyes. The incubation period, or time from infection to symptoms isn’t known,

but it’s thought to be from a few days to a week.

Treatment usually just involves treating the symptoms, things like getting plenty of rest,

drinking fluids to prevent dehydration, and taking medicine like acetaminophen to help

reduce pain and fever.

Okay so we’ve hit the “spreads quickly” part, which really matters most in places

with lots of mosquitoes, but what about the “causes serious harm” part? Well, although

it causes mild symptoms in adults, there’s more to the story. In October 2015, in areas

of Brazil where Zika virus has been circulated quite a bit, public health officials noticed

a significant increase in babies born with microcephaly, which is when a child is born

with an abnormally small head and therefore abnormally small brain size; this has the

tendency to cause serious neurological and intellectual deficits, seizures, as well as

vision or hearing problems. It was noticed that there was a huge increase in babies with

microcephaly—up to a 20-fold increase—among Brazilian states with Zika virus outbreak.

As of November 2015, the European Center for Disease Control has stated that it’s plausible

the Zika virus is able to cause microcephaly in the developing fetus or newborn, as the

Zika virus can be transmitted from mother to baby during pregnancy or around the time

of birth, although it’s not yet known how often this happens or how exactly the Zika

virus is linked to microcephaly.

In addition to being spread mostly by mosquito bites, and in some cases from mother to child,

Zika virus has also been reported to spread through both blood transfusions and sexual

contact.

Currently, there’s no vaccine for Zika virus, so it’s highly advised to take precautions

when traveling to areas of outbreak, mostly limiting mosquito bites, so doing things like

wearing bug spray all day, or wearing long-sleeve shirts and pants, especially during the day

when the Aedes mosquitoes are most active. If infected, it’s especially important to

avoid mosquitoes to avoid spreading Zika virus to others, especially in that first week of

symptoms. The World Health Organization currently suggests pregnant women consult their doctor

or travel clinic for guidance and recommendations.