Introduction to the Zika collection

A new page in the history of Public Health in the 21st century was turned when the world realised, during one of the new outbreaks of ZIKA virus, that infection in a pregnant women could be transmitted to the foetus, causing  microcephaly and – we now know – other manifestations of Congenital Zika Syndrome (CZS). This flavivirus, transmitted by mosquitoes, mostly A. aegypti, was identified more than 60 years ago, and was not considered to be of public health importance until it started to cause outbreaks in 2007. It was only in 2015 that an epidemic of microcephaly was identified in Brazil. Investigation of space and time correlations to the epidemic of Zika indicated the possibility of a Congenital Zika Syndrome; there has never been an epidemic of congenital infections with a newly discovered virus, or by a mosquito-transmitted virus, and the few organisms known to cause congenital infections did not include flavivirus. Zika continued to spread, with 70 countries or territories reporting mosquito transmitted Zika since 2015. The World Health Organization (WHO) declared the epidemic a Public Health Emergency of International concern. The process of establishing causality followed with great speed.

It is not clear why the virus is causing outbreaks and congenital syndrome now. It may be that it was circulating in Africa and Asia at sporadic levels causing high levels of population immunity, and the outbreaks were triggered by the introduction of the virus on totally susceptible populations in the Americas islands in the Pacific Ocean and the coast of Africa. If this is the case, the world will suffer epidemics for a few years, and transmission will settle in sporadic, low levels, like rubella before the introduction of vaccines. It is possible that the virus circulating in the outbreak areas is different biologically from the virus circulating in Africa and Asia; the virus in the outbreak areas can spread more rapidly and cause CZS. Whatever the reason, given the current expansion, the potential is for a major increase in the numbers of Zika congenital infections.

Because we monitored microcephaly as the marker of the epidemic, this is the manifestation we know most about. Features include neurological damage to the brain, mostly visible at radiological image, mostly to cortical subcortical areas of the brain, to the brain stem; and visual and hearing abnormalities. Follow up will identify anomalies in children apparently normal at birth as well as evolution; marked development delays, dysphagia and epilepsy seem frequent. Studies of the impact on families, society and health services are ongoing and will provide information necessary to provide needed support for affected children and families as well as for planning for health and other services. Given the number of the outbreaks – Zika has now been identified in 60 countries – other manifestations of post-natal Zika became apparent, and these include rare but severe neurological complications, including Guillan-Barre.

Zika is different from Ebola: in Ebola, most of the deaths and the outbreaks themselves could have been avoided by tools we have and know work, but lacked the political will to do so: provision of sufficient infrastructure, more and better health facilities, with capacity for diagnosis and isolation, access to water (in homes and health facilities). Zika is different; mosquitoes are hard to control: for decades, the world has tried to reduce A. aegypti populations to control dengue without much success and right now we have neither good tests, nor treatments, nor vaccines. A major effort is leading to progress towards vaccines, treatments and better diagnostic tests and methods for mosquito control. Reproductive rights of women are back on the agenda, with recognition of the need for free, local, efficient access to contraception for women wishing to postpone pregnancy until the worst of the epidemic is over or a vaccine is developed and implemented, and for women infected with Zika during pregnancy, the right to legal, safe termination of pregnancy when this is their choice.

Author Laura C Rodrigues is the Professor of Infectious Disease Epidemiology, Faculty  of Epidemiology and Population Health, London School of Hygiene and Tropical Medicine, London, UK.

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