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Editorial Today – Zika Virus and How it Infects the Placenta

What is Zika Virus? Zika virus was first discovered in 1947 and is named after the Zika Forest in Uganda.

Issue Researchers have discovered how the virus is able to cross the placental barrier and infect the foetus.

To understand what is a virus and how does it work at the molecular level we need to understand how cells functionsAs long as the enzymes in a cell are active and all of the necessary enzymes are available, the cell is alive.

So where do all of these enzymes come from? And how does the cell produce them when it needs them? DNA guides the cell in its production of new enzymes.

How virus attacks Regardless of the type of host cell, all viruses follow the same basic steps.

How Zika virus transmit the infection to the fetus The Zika virus infects and replicates in immune cells of the placenta.

Way forward As Hofbauer cells have been found to be the target cell within the placenta, antiviral therapies should be developed.

 

What is Zika Virus?

  • Zika virus was first discovered in 1947 and is named after the Zika Forest in Uganda.
  • Zika virus disease (Zika) is a disease caused by the Zika virus, which is spread to people primarily through the bite of an infected Aedes species mosquito. The most common symptoms of Zika are fever, rash, joint pain, and conjunctivitis (red eyes).
  • However, Zika virus infection during pregnancy can cause a serious birth defect called microcephaly, as well as other severe fetal brain defects.
  • Microcephaly– abnormal smallness of the head, a congenital condition associated with incomplete brain development.

 

Issue

  • Researchers have discovered how the virus is able to cross the placental barrier and infect the fetus.
  • Placenta– It is an organ that connects the developing fetus to the uterine wall to allow nutrient uptake, provide thermo-regulation to the fetus, waste elimination, and gas exchange via the mother’s blood supply, fight against internal infection and produce hormones to support pregnancy.

 

To understand what is a virus and how does it work at the molecular level we need to understand how cells functions

  • Our body is made of about 10 trillion cells. The largest human cells are about the diameter of a human hair, but most human cells are smaller;perhaps one-tenth of the diameter of a human hair.
  • Bacteria are about the simplest cells that exist today. A bacteria is a single, self-contained, living cell.
  • Bacteria are a lot simpler than human cells. A bacterium consists of an outer wrapper called the cell membrane, and inside the membrane is a watery fluid called the cytoplasm. Cytoplasm might be 70-percent water. The other 30 percent is filled with proteins called enzymes that the cell has manufactured, along with smaller molecules like amino acids, glucose molecules and ATP. At the center of the cell is a ball of DNA (similar to a wadded-up ball of string). If we were to stretch out this DNA into a single long strand, it would be incredibly long compared to the bacteria, about 1000 times longer.
  • Human cells are much more complex than bacteria. They contain a special nuclear membrane to protect the DNA, additional membranes and structures like mitochondria and Golgi bodies, and a variety of other advanced features. However, the fundamental processes are the same in bacteria and human cells.
  • A cell really is nothing but a set of chemical reactions, and enzymes make those reactions happen properly. As long as a cell’s membrane is intact and it is making all of the enzymes it needs to function properly, the cell is alive.
  • These enzymes do everything from breaking glucose down for energy to building cell walls, constructing new enzymes and allowing the cell to reproduce. Enzymes do all of the work inside cells. As long as the enzymes in a cell are active and all of the necessary enzymes are available, the cell is alive.

 

So where do all of these enzymes come from? And how does the cell produce them when it needs them?

  • The answer to these questions lies in the DNA, or deoxyribonucleic acid.  DNA guides the cell in its production of new enzymes.
  • The amazing thing about DNA is this: DNA is nothing more than a pattern that tells the cell how to make its proteins.

 

How virus attacks

  • Viruses are tiny organisms that may lead to mild to severe illnesses in humans, animals and plants. Viruses by themselves are not alive. They cannot grow or multiply on their own and need to enter a human or animal cell and take over the cell to help them multiply.
  • Viruses lie around our environment all of the time just waiting for a host cell to come along. They can enter us through the nose, mouth or breaks in the skin. Once inside, they find a host cell to infect. For example, cold and flu viruses will attack cells that line the respiratory or digestive tracts.
  • Regardless of the type of host cell, all viruses follow the same basic steps.
  1. A virus particle attaches to a host cell.
  2. The particle releases its genetic instructions into the host cell.
  3. The injected genetic material recruits the host cell’s enzymes.
  4. The enzymes make parts for more new virus particles.
  5. The new particles assemble the parts into new viruses.
  6. The new particles break free from the host cell.
  • Those viruses that do not enter the cell must inject their contents (genetic instructions, enzymes) into the host cell. Those viruses that dissolve into a cell simply release their contents once inside the host. In either case, the results are the same.
  • Once inside the cell, the viral enzymes take over those enzymes of the host cell and begin making copies of the viral genetic instructions and new viral proteins using the virus’s genetic instructions and the cell’s enzyme machinery. The new copies of the viral genetic instructions are packaged inside the new protein coats to make new viruses.
  • Once the new viruses are made, they leave the host cell.
  • Once free from the host cell, the new viruses can attack other cells. Because one virus can reproduce thousands of new viruses, viral infections can spread quickly throughout the body.

 

How Zika virus transmit the infection to the fetus

  • The Zika virus infects and replicates in immune cells of the placenta (Hofbauer cells).
  • The infected cells, which are not killed, allow the virus to pass through the placenta of pregnant women and infect the brain cells of the foetus.
  • Since Hofbauer cells have direct access to foetal blood vessels, transmission of the virus to the foetus becomes easy when these cells are infected with Zika virus.
  • The placental cells from the five donors showed different levels of viral replication, inflammation and antiviral gene expression, likely reflecting differences in genetics in these individuals.
  • Hence, some women may have the capacity to restrict Zika virus at different stages of the viral replication cycle. Such differences in pregnant women may be the reason why some women end up transmitting the virus to the fetus while some others don’t.

 

Way forward

  • Since infection during the first trimester (a period of three months, especially as a division of the duration of pregnancy) or early second trimester has been associated with the observed increase in infants born with microcephaly, future studies should be directed at finding out when the Hofbauer and Cytotrophoblasts cells are most susceptible to Zika virus infection (first, second or third trimester).
  • As Hofbauer cells have been found to be the target cell within the placenta, antiviral therapies should be developed to prevent virus replication within these cells.
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  • kingka2

    Thank you, Nice article.