Zika virus: reason behind microcephalic fetuses

Zika Virus causes microcephaly. The presence of the virus in the brain and retinas of microcephalic fetuses can also serve as a sign of the infection. Rarely, it also causes Guillain-Barre Syndrome. It is a sporadic disease. The potential vector of Zika Virus is Aedes mosquito. It is the same mosquito that causes Dengue. A mosquito bite during day or night can make a person prone to Zika virus diseases.

The transmission can be possible from mother to fetus resulting in various congenital disabilities. Sexual transmission is also possible. The virus is present in the body fluids of infected people. 

What is the role of Zika in the human host system?

Zika destroys the human system gradually. The pathophysiology of Zika involves

  • Zika infects human cortical progenitor cells leading to cell death.
  • It efficiently attacks organoids and decreases its size by TLR (Toll-like receptors) mediated response.
  • AXL is the candidate receptor of Zika Virus. It reaches the developing brain and invades the radial glial cells with the highest AXL expression.

Various evolutionary changes and recombinant events increase the risk. Evidence also suggests that there may be recombination between Zika virus species, which could result in the non-structural proteins of Zika. These proteins were the primary reason for the outbreak in recent years.

Moreover, Zika and Dengue have many antigenic similarities. A person infected with Dengue increases the risk of Zika virus infection. Antibodies released against Dengue can bind to the antigens of Zika Virus but cannot neutralize it. As a result, they promote antibody-dependent enhancement. It is a phenomenon in which the body’s clinical symptoms are worse and increases the risk of the disease. 

Can the Zika virus cause Guillain-Barre syndrome? 

Zika and humans share a peptide in common. Hence, the immune response to Zika can cause damage to host tissue and is responsible for all neurological defects. One such complication is Guillain-Barre syndrome.

How the Zika virus causes microcephaly?

AXL is a receptor that transduces signals from the extracellular matrix to the cytoplasm. Its principal role is cell proliferation and survival. It is present in healthy tissues, especially bone marrow stroma and myeloid cells, and in cancer cells. AXL is also a cancer driver. In addition, AXL is an inhibitor of innate immunity and enhances the activity of TLR. As a result, when AXL is under attack, the TLR mediated innate immune response is activated.

AXL is the target receptor of Zika. Hence, Zika can reach the radial glial cells in the developing brain, with the highest expression. It gradually decreases the number of cells to the developing brain resulting in microcephaly. It kills the cells in the developing brain by ER stress-mediated apoptosis

How can TLR mediated immune response cause damage? 

TLR receptors can identify antigens based on patterns. They can recognize the cell walls, peptidoglycan, lipopolysaccharides, genetic material of viruses, etc. TLR mediated immune response can also lead to sepsis. Hence, targeting TLRs is vital for the treatment of several diseases. The goal of TLR inhibition is to limit excessive inflammation by the over activation of a particular TLR.

Symptoms and treatment

Very few individuals exhibit symptoms of the virus, and the vast majority have no symptoms at all. The common symptoms include fever, headache, rashes, joint pain, redness in the whites of the eye (pinkeye). Most people don’t know they have it. These symptoms can appear anywhere between 2-15 days of infection. 

The treatment includes

  • Drinking fluids to avoid dehydration
  • Fever and pain medications
  • Aspirin or other non-inflammatory drugs to avoid bleeding (if any) 

However, there is no vaccine discovered yet. 

How long Zika remains in body fluids? 

Zika can be present in body fluids like semen, urine, sweat, and tears. In a study of Zika positive participants, 50% still had detectable particles in blood serum for 14 days, and in a few, it was present for 54 days, and in urine, it was detectable for 39 days. 

Semen was also examined to see how long the infected individual can pass on the virus to their sex partners. In men, it varied from 1-3 months. However, there was no sign of the infection in the vaginal fluid.

Related: Ebola virus: What actually happens in the infected system

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