Zika Around the World: A History
At the First International Zika Conference, keynote speaker Annelies Wilder-Smith, MD, PhD, DTM&H, MIH, FAMS, FACTM, discussed how Zika has evolved on a global scale.
In the opening session on February 23, 2017, the keynote speaker, Annelies Wilder-Smith, MD, PhD, DTM&H, MIH, FAMS, FACTM, professor of infectious diseases, Vaccine Preventable Diseases & Emerging Infectious Diseases Laboratory, Lee Kong Chian School of Medicine, Nanyang Technological University, in Singapore, discussed the evolution of the Zika outbreak to a full house at the First International Zika Conference in Washington, DC.
Through the exploitation of what Dr. Wilder-Smith refered to as “the triad of the modern world”—globalization, urbanization, and the ability to move easily on an international scale—diseases that are spread by Aedes mosquitoes are increasing their spread around the world, and as they do so, they are expanding the impact that they have on public health. Dr. Wilder-Smith said, “Zika virus has joined the quartet of enzootic arboviruses [yellow fever, chikungunya, Dengue virus] in West Africa with a history of urban emergence,” in that it has “now entered the human-to-human cycles” and this “human-mosquito-human transmission” is resulting in a number of unprecedented epidemics.
In her presentation, Dr. Wilder-Smith shared a brief historical timeline of Zika with conference attendees, one that spanned from 1947, when Zika virus was first discovered by Alexander Haddow, up until 2016. Dr. Wilder-Smith went on to highlight how in 1954 the first human case was reported in Nigeria, how it was described for the first time outside of Africa in 1966, how in 1977 the first case was described in Asia, and, how from the 1970s up until now, “it was really a disease between Africa and Asia.”
She then went on to discuss how the modern Zika outbreak originated in the Yap islands of Micronesia and later spread to French Polynesia in 2014, where Guillain-Barré syndrome (GBS) was first noted in Zika-infected individuals. However, GBS wasn’t recognized as a complication until August 2015. On May 7, 2015 the first epidemiological alert was issued and on the first of February of the following year, the “unusual clusters of birth defects and GBS were declared as a public health emergency of international concern,” due to “its risk of global health security.”
The Zika-related birth defect, microcephaly, has continued to make headlines throughout the past years; a telltale sign of microcephaly is when an infant’s head is much smaller than expected, and often this birth defect results in improper brain development. According to Dr. Wilder-Smith, “Microcephaly appears to be the tip of the iceberg; there’s so much more” when it comes to Zika-related complications. She went on to list: “spontaneous abortion, stillbirths, epilepsy, visual problems, hearing loss,” and even severe dysphasia. In addition, Dr. Wilder-Smith listed problems that may not be witnessed until later on, such as: "mental retardation, psychotic disorders, [and] learning difficulties,” among others.
Because of the devastating effects, scientists began dedicating their efforts to explain how Zika has evolved “from an endemic arbovirus causing sporadic mild illness across equatorial Africa and Asia” into the virus that is known today, one that can result in a number of severe complications and rapidly spread across the world. As time went on, researchers started conducting more studies in an effort to understand “the full spectrum of the disease.” One such study worked to characterize the pattern of anomalies in congenital Zika syndrome. Although the spectrum is still not fully understood, Dr. Wilder-Smith feels that there is “enough data to show a very distinctive pattern of congenital Zika syndrome that is quite unique to Zika and the first is cranial morphology,” which can present in the form of a collapsed skull, an excessive scalp with folds, or occidental bone prominence.
To bring the message home, Dr. Wilder-Smith provided the audience with a series of photos that illustrated infants with a number Zika-related complications, chief among them, microcephaly. However, she reminded the audience that microcephaly is not the only serious complication that resulted in Zika being deemed a problem of international concern: “GBS needs to be taken seriously,” Dr. Wilder-Smith warned. She then shared that she is working with Galsgow colleagues to identify biomarkers that will help predict the development of GBS in Zika infections. There are a number of additional research efforts being made that are dedicated to differentiating between complications associated with asymptomatic and symptomatic Zika in pregnant women and identifying the risk of abnormalities in asymptomatically infected women.
Dr. Wilder-Smith stressed that in order to understand how the Zika virus will evolve further, researchers must look back at the past for insight. In order to illustrate this, she provided attendees with a snapshot summary of outbreaks that have occurred in the past, the sero-prevalence at the end of each outbreak, and the prevalence of microcephaly per annual 1000 livebirths. For example, Yap has a population of 7391 and the outbreak lasted for 3 months; sporadic cases after the outbreak have not been noted and the sero-prevalence at the end of the outbreak was 73%. For French Polynesia, with a population of 268,270 individuals, they expereinced an outbreak that lasted for four months. No sporadic cases were noted after the outbreak and the sero-prevalence at the end of the outbreak was 66%; the prevalence of microcephaly per annual 1000 livebirths was 2/1000.
When it comes to what will drive the epidemic, Dr. Wilder-Smith explained, “Clearly because Aedes are climate-sensitive mosquitoes, climate and ecological factors will drive and will determine where Zika will move to." Another factor to take into consideration is that Zika can be transmitted sexually from human-to-human and viral RNA can persist in semen for a number of months. Sexual transmission of Zika contributes to only 3% of the overall number of cases. However, between this and the fact that Zika can be spread through travelers going to infected areas and bringing the virus back home with them, infections are likely to also occur in countries that do not have Aedes mosquitoes.
According to the research, there are many unanswered questions pertaining to Zika virus that need further investigation:
- What is the true attack rate of congenital Zika syndrome (CZS) by gestational week for asymptomatic and symptomatic ZIKV infections in pregnant women?
- What is the full clinical spectrum of CZSD at birth and at five years of age?
- What long-term complications will appear in those with minimal CZS, or as a result of infections late in pregnancy?
- Will population immunity in endemic countries (particularly Asia and Africa) confer protection against the epidemic strains of Zika currently circulating in Latin America and the Caribbean?
- What will be the impact through due to spill over from sylvatic cycles to human populations?
- What are potential post-invasion epidemic scenarios given that even low numbers of CZS are a tragedy?
Dr. Wilder-Smith concluded, “Zika is here to stay and the WHO’s response is here to stay. We all know that the response to the Zika epidemic is probably one of the most difficult responses ever because it requires expertise ranging from reproductive health, birth defect surveillance, contraception, communication to mothers, neurology—and neurology is more complicated than you think—vector control, best practices for vector control, diagnostics, vaccine development, and policies around travel. This is an incredibly difficult outbreak and I’m really looking forward because we need to address these problems. So, Zika is here to stay, our duty is to [provide] a robust technical response; we owe it to these patients.”
First International Conference on Zika Virus
Opening Session: Keynote Lecture
Evolution of the Zika Outbreak