Zika virus (ZIKV), an arbovirus transmitted by mosquitoes of the Aedes genus, was first isolated in 1947 in the Zika forest of Uganda from a sentinel monkey. It has always been considered a minor pathogen. From its discovery until 2007 only 14 sporadic cases – all from Africa and Southeast Asia – had been detected. In 2007, however, a major outbreak occurred in Yap Island, Micronesia, with 73% of residents being infected.
The major breakthrough in the ZIKV story occurred in 2016 when it became clear that Brazil was facing the biggest epidemic ever of the virus. With a population of 210 million inhabitants and heavily infested by Aedes mosquitoes, the arrival of ZIKV in Brazil gave rise to a perfect storm.
Between October 2015 and 20 July 2016, Brazil reported 8,703 suspected cases of microcephaly and other nervous system disorders suggestive of congenital infection. Of these, 1,749 are confirmed cases of microcephaly, 277 of which are laboratory-confirmed for ZIKV infection. Now the problem seems to spread to other countries. As of 28 July 2016, 14 countries or territories have reported microcephaly and other central nervous system malformations associated with ZIKV infection.
As a possible related agent to the rise of microcephaly cases, ZIKV is now becoming associated to an even more complex congenital syndrome. It has been known for many years that some congenitally acquired viruses such as Cytomegalovirus (CMV) can cause microcephaly. Now it is becoming clear that ZIKV once acquired by pregnant mothers can give rise not only to microcephaly but also to a unique “ZIKV congenital syndrome”. This syndrome includes not only microcephaly but also a peculiar brain-imaging pattern, along with complex ocular abnormalities and arthrogryposis (congenital joint contractures).
Since its original description in 1916 by French neurologists, Guillain-Barré Syndrome (GBS) has been associated with previous infections by a number of bacterial and viral agents. In GBS the body’s immune system attacks part of the peripheral nervous system by an autoimmune mechanism. GBS is clinically characterized by a rapidly evolving flaccid paralysis of legs and arms, sometimes associated with facial palsy, swallowing difficulties and respiratory arrest. This usually follows in days or weeks an acute infectious or, less frequently, non-infectious systemic event. GBS is considered a medical emergency due to the potential risk of respiratory insufficiency and generalized paralysis. Now, growing scientific evidences have linked previous ZIKV infection to GBS.
Since the emergence of the Brazilian epidemic, ZIKV has grown in status and has brought serious concerns about its capacity of rapid spread and to give rise to ominous neurological consequences. Many non-medical issues are involved in the present situation. For many years, ZIKV has been considered a vector-transmitted agent only. This view has been recently challenged by the possibility of human-to-human transmission (transplacental and sexual contact). This could allow the rapid spread of the infection even in places where Aedes mosquitoes are not endemic.
Brazil, the epicentre of ZIKV problem, is facing an unparalleled political, economical and social crisis. Besides, it is hosting the 2016 Olympic games. The published scientific literature is still growing but most information started to become available and rose in the lay press, which can sometimes be misleading and bring panic to the population.
The uncertainties about ZIKV and its neurological complications open a vast field for research in which only well performed clinical and epidemiological studies will demolish biased, hastened opinions. In a recent review scientists, critically assessed the current literature, trying to summarize what is scientifically known about the neurological complications of ZIKV.
Futures studies need to assess the efficacy of new proposed methods of vector control as well as the effectiveness of the routine use of condoms to prevent sexual transmission. In addition, better and rapid diagnostic tools should be pursued. Because there is no proven treatment for ZIKV, the development of new therapeutic approaches should be one of the priorities for future research. Any of the potential drugs to be tested must be safe for pregnant women. In addition, more knowledge is needed to understand how to best address newborn babies with severe and disabling congenital malformations, and maybe prevent the devastating congenital infection.
The public health and economic implications of the ZIKV outbreak cannot be minimized. The emergency of an epidemic of microcephaly is of great concern for countries with relatively high birth rates. Medical, economic, and psychological burdens suffered by families are worsened by the whole health system, which cannot adequately deal with all the short and long term requirements of the current situation. Also, ethical and social implications have to be taken into account, particularly in countries in which abortion is restricted to very specific situations or even totally prohibited. The consequences of a GBS outbreak are also worrying because it brings along an unbearable overload of both public and private health systems, which may not be able to respond quickly and efficiently to an increased population of patients needing continued hospitalization support and specific and expensive treatments.
In the heat of events one must be very careful to avoid hasty conclusions based solely on crude indications. The lack of solid and scientifically indisputable evidences may easily lead to wrong decisions.
Featured image credit: Mutirão de combate ao mosquito Aedes Aegypti no Grupamento de Fuzileiros Navais de Brasília (Joint effort to combat the Aedes Aegypti mosquito in Reverse Split Marine Brasilia) by Ministério da Defesa. CC BY 2.0 via Flickr.