Certainly, there are so many virus that can infect humans around. Virus becomes dangerous and alarming when it starts spreading from people to people and starts creating a serious harm. Zika Virus, has a potential characteristic in doing both of this thing. Due to this, it can come to lot of worldwide attention. This spread widely across the Central and South America. It posses characteristic of "Virus" , "Emergency" and "Explosively". The major cases happens from this infection is the microcephaly and Guillain-Barre Syndrome. Previous studies has shown that the cause for the born child developing neurological condition was from transfer of virus from mother to fetus. Virus remains in long-term in the fetus but what it does to the placenta is not known by people. "Lets find out now ! "

So, What is Zika virus ?

Zika virus is an arbovirus. Arbovirus means those virus that gets trasferred from arthropods. Generally Aedes mosquitoes does this so it is also called as mosquito-borne virus. When I say mosquito-borne virus, I don't want to mean it is "born" in mosquito. But, it carries and transports this virus ("borne"). In this case,mosquitoes is considered as "vectors" because it do all the transportation works of virus. Zika virus is just like Malaria, Dengue, Japanese Encephalitis virus where mosquitoes transfer the virus from person to person. Commonly, these all lies in same family of virus; flavivirus. From this process, we can say that is a stable relationship between the Virus, Mosquito and Human. [1]

Sturucture of Zika Particle Credit - Left - Modified from "Zika virus: Virion" by ViralZone. Swiss Institute of Bioinformatics Right- Zika Virus by C.Goldsmith, CDC Public Health Image Library

Tiny structure made up of protein molecules , RNA and a lipid membrane. Each viral particle has a single-stranded RNA genome lying inside a shell of protein called Capsid. This is again surrounded by a spherical membrane called as Envelope. Microscopic figure can be seen above. [2]

Female mosquitoes need blood as meals to mature her offspring. They get the meal from the host. They use certain kind of chemical compounds in detecting the host who happens to give out certain odors of carbon-dioxide, ammonia, octenol and lactic acids. -"Hunting blood capillaries". Basically, when the mosquitoes carrying the virus happens to find and digs the blood-meals in a definitive host, the virus then spreads and infects the host. They start to reproduce and multiply within the human.

Infection and multiplying process :

Most of the families of flavivirus, it does not replicate in the human host but can infect the another mosquito who tries to find the blood meal in the infected host. We can say that "Human acts as a dead end host". But in case of Zika Virus infection, there acts no dead end host. The virus multiply within the host and even transmit to the mosquito who tries to get their blood meals. Thereby, mosquitoes can go further and infect more people .

Mosquito hunting capillaries (credit)

"Window period refers to the time period between the onset of symptoms and detection of virus antibodies in the blood sample ". For the Zika virus, the window period is the first week of infection. If the environment which has plenty of mosquitoes, there will be a kind of set-up for spreading the virus in quick.

Aedes aegypti and Aedes albopictus are the two species of Aedes. These generally bite during the night but are mostly active during the day time. These are also responsible in transferring the Dengue fever and Chikunguniya fever. When these species of mosquito having the Zika virus lies on the skin surface, it inserts it's proboscis inside the epithelium. Epithelium is the topmost part of skin which has plenty of keratinocytes. These protect from the foreign particles and pathogens. The capillaries lies in the dermis layer where the mosquito is actually finding for. Proboscis goes through the epidermis and dermis layer. The cells around them are prone to infection starts suspecting the Zika virus . Not only the keratinocyte cells around but fibroblasts and dendritic cells also gets the trigger. These cells have a certain kind of receptors that attaches the Zika virus.

Cycle of Zika virus by Ted Pierson (credit)

Zika virus has a special kind of protein in its out cell which comes and interact with the cell receptors. It tricks them and enter the viral particle into the cell. It inject the single-strabded positive RNA strand into the cytoplasm. This RNA is broken into pieces and then is translated by enzymes into protein . Many of these proteins are made into structural component like envelop protein or capsid for the new viral particle. Cellular machinery works and process more viruses.

The virus then merges with the Endoplasmic reticulum which is the component of export system of cell. Virus takes a piece of the Endoplasmic reticulum which helps in making a envelop for them . The virus then goes to the Golgi apparatus which udergoes more processing before budding off the cell. This release viral particle can infect more cells and starts the infection process.

" Our immune System is so well in fighting back the Zika Virus . Only 1 in 5 gets sick with the infection. "

Credit |- WHO fact sheet

How will the patients know if they are suffering from Zika virus Infection ?

Common symptoms seen in the patients are

Mild fever with skin rashes
Headaches
Muscle and Joint pain
Conjunctivitis or red eyes

"Incubation period is the time period between infection and arise of symptoms". Incubation period is thought to be some days from infection to weeks .

There is more to the story in causing serious harms to the humans !

In Brazil, October 2015, Zika Virus spread so quickly that Public Health Individual noticed a significant rise in the babies born with the micro-cephaly about 20-fold increase with decrease in brain size. This has been causing a serious neurological defects and intellectual deficient condition. This has caused even a hearing as well as vision problems in children.

How did this occur eventually ?

It is able to cause the sign of microcephaly in the developing fetus or newborn. This virus is transmitted from mother to baby during the pregnancy or during the time of birth. It can also be spread from blood trasfusion and sexual intercourse.

Functions of placenta (credit)

In the pregnant women , the placenta has various functions:

Transporting the Nutrietns and oxygen from the mother to embryo during pregancy
Removing the waste materials from fetus to mother via blood-stream
Producing hormones like Human Chorionic Gonardotrophin (HCG), Estrogen and Progesterone. These hormones helps in maintaining the activities of pregancy. Not only this, this helps in promoting a normal fetal development. [3]

In the 3rd week after conception, placenta has almost 20% of the area covered in the uterus. All of the major exchanges takes place between the mother and the embryo. Food and oxygen like molecules are transported for the fetus along with the blood stream.

When virus enter the placenta of mother, it gets harmed. Damage tissue response with Inflammatory reactions . Placental tissue becomes thickened and inflammed.

Inflammed tissue of placenta (credit) Oregon Health & Science University

Maternal Blood vessels feed into the placenta. In spot. A, maternal vessels become narrower and restrictions of blood flow to the fetus. spot. B less blood flow and less perfusion of maternal blood flow ,spot.C decrease in the blood which has oxygen-rich substances, nutrients, waste products and gets damaged. spot.D. when infected with the Zika virus, cells making the pregnant mother 's placenta fetal villi also gets damaged.

Conclusively, When Zika virus goes into fetus, it remain long-term which can lead to chronic infections in the utero. Evaluating the oxygen levels inside the placenta and oxygen flow between mother and baby, decrease of oxygen transport through the placenta decrease upto 10-fold !

Reference :

Mentioned along with the post, further reference I took :

(1) https://vitalrecord.tamhsc.edu/zika360/transmission/

(2)https://www.cfr.org/backgrounder/zika-virus

(3)http://www.who.int/mediacentre/factsheets/zika/en/

(4)https://www.sciencedaily.com/releases/2018/01/180118142608.htm

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