Scientists in China may have just discovered why the Zika virus causes small heads in babies. The relevant study was published in Science magazine in September by a team of scientists from the Beijing Institute of Microbiology and Epidemiology. It reports that tests on animals has shown that the ZIKV, as the Zika virus is called, directly attacks NPCs (neuronal progenitor cells) and leads to conditions including microcephaly or small heads. NPCs are cells that can divide and differentiate into neuronal cells and connective tissues of the nervous system in all animals.

This is an important discovery as it will help scientists better understand how the virus evolved from the Aedes-borne virus into a pathogen that is causing congenital birth defects around the world. It will also help scientists in researching vaccines and treatments.

Zika Virus Has Become More Deadly Over the Years

Bear with me for some technical details. In order to understand what gives ZIKV its characteristics, scientists compared different strains of the virus. Samples were taken from ZIKV strains from the 2015-2016 epidemic in South America. These were compared with the Asian ZIKV strain that affected Cambodia in 2010. The number of infants born with small heads has gone up since the epidemic in Brazil in 2015. The appearance of Zika virus in Cambodia was limited to seven between 2007 and 2010. Since then, the virus seems to have undergone mutations to its present form.

Zika Fact Card
Zika Fact Card

The scientists found one particular mutation, the S139N, to be critical in the cause of small heads at birth. This mutation has taken place over the period between 2010 and 2016. This mutation has killed more newborn mice and caused more severe cases of small heads in mice than the others. The Asian Zika virus is the ancestor of this deadly mutated strain. The strain’s lethality is partly because of the replacement of one amino acid with another, to dangerous ends. In this mutated strain, an amino acid called serine is replaced with an amino acid called arparagine, which may be responsible for microcephaly.

The History of the Zika Virus

The Zika virus was first spotted in monkeys in Uganda as early as 1947. Three years later the first human infection of the Zika virus was reported. The virus had existed in Asia for years before this. Blood tests in South and Southeast Asia found Zika antibodies in the local population, suggesting that these regions had been exposed to the virus. But not many cases of the virus were reported.

Zika Virus Risk
Zika Virus Risk

The first outbreak in a large scale was in 2007. The virus appeared in the Western Pacific island of Yap and affected fifty people. Doctors were baffled by the symptoms of joint pain, inflamed eyes and rashes. Still something of a medical curiosity, the virus then spread across Africa and Asia.

But the incidence of symptoms was low – only one in five infected people would develop symptoms, and most were mild symptoms. Today, 1.5 million people in Brazil are affected by the virus. Scientists are anxious to find out what made it worse. There are speculations that more symptoms of Zika may already have existed but been mistaken for similar illnesses like dengue. Some experts believe that the Zika did less damage in Asia possibly because of aggressive vaccination for Japanese encephalitis, which may have had some effect on the Zika.

Zika and Birth Defects

Brazilian research into the Zika virus has only recently confirmed that women infected by the Zika virus were highly likely to give birth to babies with an underdeveloped brain and an unusually small head. Not all babies infected by the Zika virus at birth will display the symptoms of the virus, but they may experience slower head growth after birth. Not all women infected by the Zika virus give birth to babies with abnormally small heads either.

Meanwhile, if you’re visiting an area affected by Zika, you should be very careful in using condoms, which is good advice in the best of times.