Science Explained: The Zika Virus

The Zika Virus

Earlier this month, the World Health Organization declared the Zika virus a global health threat, stating that microcephaly and neurological disorder incidence in newborns in Brazil “constitutes a Public Health Emergency of International Concern.”

When considered against other prominent mosquito-borne viruses, such as dengue and West Nile, the Zika virus has been a fairly low priority. According to the WHO, there are approximately 50- to 100-million cases of dengue annually, with 22,000 of those resulting in death, most of which are children. As a result, Zika hasn’t been a widespread threat and this virus is still uncharted territory for vaccines and treatment.

Everyday more information is learned about this virus. Currently, we know it is travelling quickly via mosquitoes as well as being transmitted sexually, and through blood transfusions. The virus has been found in saliva and urine, but it is unknown if it can be contracted through these bodily fluids.

The Zika virus is a Flavavirus, and is further classified as an arbovirus. Most Flaviviruses cannot replicate enough in a human host to reinfect the next mosquito that comes by, making humans a “dead-end host.” However, the Zika virus is fairly well adapted to humans, and can transmit the disease very effectively.

Zika is very effective because once the mosquito remits infected blood, the virus injects single-stranded positive RNA into its human host. This RNA is called “positive RNA” because it is very similar to our mRNA, which is an intermediate molecule between our own genome and the proteins our cells produce. Once this virus injects its genetic material, it uses its host’s cellular machinery to manufacture clones of itself. When our cell dies, the colony of new viruses is released, and this cycle continues.

The two primary mosquito species that act as vectors for the Zika virus are Aedes aegypti and Aedes albopictus. These mosquitoes are most active during the day, and are also known to transmit Chikungunya and Dengue virus.

If infected with the Zika virus, only 20 per cent of adults will experience symptoms similar to a mild flu, such as fever, skin rash, and joint pain.

The major concern with the Zika virus is the health risk it poses to the fetuses of pregnant women. The virus is thought to be linked to a rare-neurological condition known as microcephaly, a condition where babies are born with abnormally small heads, thus small, underdeveloped brains. The complications of microcephaly include development problems, vision and hearing problems, short stature, mental retardation, and seizures.

When the incidence of microcephaly increased 20-fold in Brazil, doctors starting running tests, and found the Zika virus in the brains of these newborns with microcephaly. Although the virus’s exact mechanism in the fetus is unknown, scientists are hypothesizing that the virus is able to cross the placenta and cause brain damage, but the link between them has not officially been confirmed.

There are two reported cases so far in British Columbia but it is still unknown whether Canadian mosquitoes could pick up the virus from an infected traveller and spread the virus. There is a lot of money funding a vaccine for Zika, with potential of having one by the end of the year.