Mystery of the Zika Virus

THIS OUTBREAK OF Zika fever in Rajasthan makes me wonder if the last three years were lived in a different dimension. During September-October 2015, Zika fever emerged in Brazil and two months later its horrendous aftermath left the world thunderstruck. Pregnant women who had suffered no more than a casual fever with rash gave birth to babies with microcephaly and damaged brains.

By early 2016, surmise and denial had given way to a sullen recognition that a previously innocuous virus, kissing cousin to Dengue and Chikungunya Viruses, could cross the placenta and infect the developing embryo. This was happening in Brazil, but like most Indian doctors who deal with babies, I was familiar with such skull malformations—reason enough to worry. India had suffered a decade of Dengue at its worst, and Chikungunya at its most debilitating. I hadn’t heard of Zika Virus before, so naturally, I spent all that year finding out.

From its 1947 discovery in Uganda’s Zika Forest to the 2015 outbreak in Brazil, this virus had kept a low profile. True, it had caused a fever epidemic in Micronesia in 2007. Then, eight years later in 2013, another Zika epidemic had swept French Polynesia. This time with a complication: Guillain-Barré Syndrome, an acute paralysis associated with many infections.

This change in profile from a casual sporadic fever to outbreak to epidemic suggested the virus had grown in virulence. Nothing prepared us for the disastrous damage it would inflict in 2015. But we should have been prepared. The effects of Zika Virus on laboratory animals were elucidated as far back as 1950. The destruction of brain tissue in foetal and infant mice, so carefully documented in 1950, closely resembled what we were to encounter in affected human babies in 2015.

At the time of its discovery, Zika Virus seemed restricted to its forest of origin, abuzz in the canopies of tall trees. The sylvan host for the virus was probably a monkey. The vector, keeping the virus in circulation, was a tree-hole dwelling, night-feeding mosquito: Aédes aegypti africanus. When human outbreaks of Zika Fever were noticed in the early 1970s, several changes had occurred. Trees had been cut down to make room for human encroachments. Evicted Aédes mosquitoes had taken up residence in water cans and had changed hosts. They now swarmed lower and closer to human activity. They now bit humans, and fed by day.

The pandemic of 2016-17 had a newer profile: the innocuous virus had transformed itself into a lethal pathogen capable of crossing the placenta to target and destroy developing nervous tissue. Its defining human manifestation was in infants: damaged brains, microcephaly, blindness—all part of what we today call Congenital Zika Virus Syndrome (CZVS). Strangely, this was restricted to certain geographic areas. By January 2017, CZVS was reported in 2,618 babies from the Americas: 2,366 from Brazil, 74 from the Caribbean, 96 from the Andes, 42 from the US. Of the 50-odd countries that have reported outbreaks since, only 20 have reported CZVS. What about the mother country, Africa? Cabo Verde, off the mainland, had an epidemic in 2016. Out of 7,000 suspected cases, three babies were affected.

Zika Virus has been known to circulate in Asia since the 1950s when its presence was recorded on the Subcontinent. Since the 2016 pandemic, many Asian countries have reported Zika infections that were clearly not imported, further proof that Zika Virus has a very wide natural geographic presence.

Like the large outbreak in Singapore, Asian countries probably have sporadic bouts of Zika fever. Without the outfall of horrific complications, they pass unnoticed. Till mid-2017, there were only three reported cases of CZVS: two in Thailand and one in Vietnam. We know that Zika Virus is sexually transmitted, and can be retained in body secretions beyond the period of illness. Recent recommendations are that men who have Zika Fever should abstain from unprotected sex for at least three months. Infected women should wait eight weeks before planning a baby. These are precautions, not guarantees.

Crippled by Dengue and Chikungunya, we cough our way through clouds of insecticide, while the mosquito with its load of viruses simply laughs itself into another biting frenzy. If we remain oblivious to all the illnesses stealthily fostered by Persistent Organic Pollutants, it is from apathy alone, not ignorance.

Consider this. Brazil has had immense tree cover loss in the last decade. So have all Zika-infected islands in the Americas. Between 2010-15, Brazil lost 984,000 hectares of forest, over 42 per cent of its ‘protected’ area. South America and Southeast Asia compete for the kind of deforestation termed Partial Canopy Cover Loss. You and I see this every day in our madly expanding cities. The primary forests of Asia have all but disappeared. Knock down but a single tree, and the disturbed virus will seek out a new habitat—ours. The story of Zika Fever and CZVS always begins with a mosquito bite. Meanwhile, the conspiracy of silence about human destructiveness continues unchallenged.

(Kalpish Ratna is the author of The Secret Life of Zika Virus | 2017 | Speaking Tiger)

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