Zika Virus: One Year Later

This article has been published in Spanish in El País- Planeta Futuro by Pablo Martínez de Salazar, ISGlobal coordinator of the response to Zika virus and other arboviruses and Adelaida Sarukhan, PhD in immunology and scientific writer in ISGlobal

February 1st, 2017, marks one year since the World Health Organisation (WHO) declared the Zika virus epidemic a Public Health Emergency of International Concern

February 1st, 2017, marks one year since the World Health Organisation (WHO) declared the Zika virus epidemic a Public Health Emergency of International Concern (PEIC). The WHO had declared this kind of emergency only in three previous occasions: the swine flu epidemic (2009), the threat of polio re-emergence (2014) and the Ebola epidemic in West Africa (2014). Since November 2016, the emergency status has started a transition whereby the temporary emergency management and recommendations are to be substituted by measures that guarantee a long-term response. However, the WHO has emphasized that the global risk assessment of Zika virus has not changed and that it will continue to spread geographically. 

The global risk assessment of Zika virus has not changed and it will continue to spread geographically

Since the beginning, the Zika virus outbreak in Brazil was associated with a surge in serious neurological malformations among babies born to mothers potentially exposed to the virus. Although the number of new reported cases has declined in the last months, the virus has spread throughout the Americas and all the countries of the continent, except three (Chile, Paraguay and Canada) have reported local transmission of the virus. In the Pacific region, Zika continues to circulate and small outbreaks have been reported in Africa and Southeast Asia, where the virus is likely to spread. The real impact of the virus is still unknown, and more than 2,000 million people live in areas at risk of infection. Although the virus can be transmitted through sexual intercourse, the major transmission route is via the bite of infected Aedes mosquitoes. In regions where the vector is absent, the risk of outbreaks is minimal and efforts should be concentrated on identifying pregnant women potentially exposed to the virus due to travel or sexual intercourse with an infected person. 

Despite the impressive scientific progress achieved in the last year, there are still a number of open questions on Zika virus disease. We know, for example, that infection during pregnancy may lead to microcephaly and other neurological defects in the foetus, but we still cannot quantify the risk or predict how the pregnancy will evolve. Neither do we know the entire range of congenital defects, or whether apparently healthy babies born to infected mothers will evolve, walk or talk normally.  

The real impact of the virus is still unknown, and more than 2,000 million people live in areas at risk of infection

Laboratory diagnosis of Zika virus infection is still limited to specialized centres, which constitutes a considerable challenge in low-resource settings. Although several promising assays have been described, we still do not have a rapid, sensitive and specific point of care test. 

To date, two Zika virus strains- the African and the Asiatic- have been described, with the latter responsible for the outbreaks in the Americas and the Pacific.  Serious complications such as birth defects and neurological disorders have only been observed with the Asiatic strain. There is evidence that immunity acquired upon infection by one of the lineages can confer protection against the other one, something that does not occur with dengue virus for example. However, we do not know how long the immunity lasts after infection with any of the strains. This is a key issue for the development and success of an effective Zika virus vaccine. To date, a couple of vaccine candidates have entered clinical phases, although we will have to wait at least two to four years before the vaccine is made available to the public. Similarly, a handful of drugs have displayed antiviral activity in the laboratory, but there is still a long way to go before being able to treat pregnant women, who are the most vulnerable group to the virus.  

The Zika virus has joined the already complex “ecology” of arboviruses (arthropod-transmitted viruses). In the last decades, we have witnessed the emergence and global spread of infections by such viruses, including dengue, chikungunya, West Nile virus, and yellow fever. These diseases share the same predisposition factors related to the modern world: urbanization, globalization and international mobility. Thus, arboviral diseases have become a priority within all Public Health agendas. This prioritisation should be accompanied by a strong support to research and public health interventions that improve their prevention, control and response. The combination of interventions that have proved effective against multiple arboviruses will guarantee the best cost-effectiveness and sustainability. Importantly, resources should not be “redirected” from other programs, at the cost of decreasing funding for major diseases such as malaria, HIV or TB. Another key aspect is ensuring an adequate flow of communication between the scientific community, the Public Health authorities and the general population. A correct flow and handling of information is critical for guiding prevention and response measures, as well as avoiding unnecessary alarm or fear.   

Arboviral diseases have become a priority within all Public Health agendas

Humanity is under the constant risk of new infectious agents. It is crucial to establish new international alliances that favour the combination of multidisciplinary efforts and resources to guarantee more rapid and effective responses against emerging and re-emerging diseases.