What happens in Zika fever, exactly?

What is it?

Zika fever is an infectious disease caused by the Zika virus. Despite the extensive media coverage the disease is mostly harmless – in the majority of cases there are no symptoms at all, and when there are, they are usually mild and resolve within a week. The most common symptoms include fever, red eyes, a rash, and headache.

A couple of years ago the Zika virus caused an epidemic in South and Central America. The CDC has estimated that as much as 20% of the population of Puerto Rico, 700 000 people, could be infected before 2017. Several authorities have expressed concern about the spread of the disease, because it has been linked to life-threatening neurological problems in fetuses whose mothers have been infected as well as in adults who have themselves been infected.

What causes it?

The Zika virus causes the Zika fever. Some mosquitoes act as a host to the virus, and the virus can spread to humans in the saliva of the mosquito when they are bitten. Sexual transmission is also common: for some reason there are over 100 000 times more viruses in the semen than in other bodily fluids like blood and urine. This is why the Zika virus is only known to be transmitted from men to their partners and not from women to theirs. In addition to this, transmission can occur during blood transfusions and from a mother to their fetus.

What happens during it?

Viruses, like the Zika virus, are essentially protein cells with genetic information inside them. They invade living cells and make them produce new viruses according to that genetic information. The cell dies once it has produced enough viruses.

There is a lot left to find out about the progression of the Zika fever. It is known that the virus invades the body through the skin and proceeds to the lymph nodes and the bloodstream. The symptoms associated with infection occur mostly because the body tries to fight off the virus.  For example, when cells realize there is a pathogen trying to invade the body they start releasing substances called pyrogens to the bloodstream, and when the pyrogens reach our brain, our brain increases our body temperature and produces a fever. Fever and other symptoms associated with bacterial and viral infections might help the body fight off the pathogen, but they might also be useless “side-effects” of some other processes.

Zika fever can in rare cases lead to Guillain-Barre syndrome. It is a life-threatening condition in which the body’s own immune system attacks the nerves that are supposed to transmit signals to and from muscles. Symptoms include muscle weakness as well as changes in sensation. It is particularly dangerous if the muscle weakness spreads to the muscles we  need for breathing. Even in optimum care where medication is used to suppress the immune attack and breathing aids are available, Guillain-Barre syndrome leads to death in about 5% of cases.  The reason why Zika fever can cause this syndrome is probably that some proteins that are on the surface of the Zika virus resemble those that are on our nerves. When the virus invades our body and our body fights it off, it classifies those proteins as something to destroy. When our immune system then encounters similar proteins on our nerves, it sees the nerves as something to destroy too and starts an attack.

If a mother is infected with Zika virus during the first stages of her pregnancy, her baby might develop a condition called microcephaly in which the head of the baby is smaller than normal because his brain is not fully developed. It is yet to be established why this happens, but it has been suggested that the virus kills the stem cells that are supposed to divide until the wanted amount of brain cells exist. Normal brain cells cannot start dividing to compensate for this loss, so if these stem cells die, it is very unlikely that the brain would ever be able to develop as it should.

How can it be treated?

There is currently no vaccine or established treatment for Zika fever. It is recommended to avoid traveling to places where the disease is prevalent,  and if this isn’t possible, protecting oneself from mosquitoes and either abstaining from sex or using condoms. Treatment during the disease focuses on alleviating the symptoms like fever.

 

 

 

Sources: en.wikipedia.org/wiki/Zika_fever, en.wikipedia.org/wiki/Zika_virus, http://bestpractice.bmj.com/best-practice/monograph/1302/basics/pathophysiology.html, https://en.wikipedia.org/wiki/Guillain–Barré_syndrome, https://en.wikipedia.org/wiki/Microcephaly, https://www.scientificamerican.com/article/what-causes-a-fever/

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