English subtitles for clip: File:Zika virus video osmosis.webm

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There are a lot of viruses out there that
can infect humans, but two things that can

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

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

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

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causes.

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

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

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

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

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

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

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

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are all in the genus flavivirus.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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you go man, come on in.

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

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

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

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

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

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viruses to infect more cells.

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

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

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

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

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

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

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

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

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reduce pain and fever.

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

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

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

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

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

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

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

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

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

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

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

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

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

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virus is linked to microcephaly.

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

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

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contact.

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

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

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

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

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

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

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or travel clinic for guidance and recommendations.