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

  • 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

  • isbornin the mosquito, though, but it’s “borne”, with an ‘e’, which

  • means carried or transported. Sometimes we call organisms like thisvectors”, 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 therere 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

  • noseor 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

  • theyve 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 weve hit thespreads quicklypart, which really matters most in places

  • with lots of mosquitoes, but what about thecauses serious harmpart? 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

  • microcephalyup to a 20-fold increaseamong 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.

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

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Zika virus - definition, symptoms & complications

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    Silvia W.   posted on 2016/03/05
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