Epidemiological map of global Zika

Revealing Data: Learning About Zika

By Erika Mills and Tannaz Motevalli~

In June of 2019, a series of two blog posts entitled “Data Science in Politics of Yellow Fever” examined collection items featured in the NLM special display, The Politics of Yellow Fever in Alexander Hamilton’s America, to better understand how and when scientists began using data to inform their knowledge and control of yellow fever. As a complement to that exploration of yellow fever and data’s place in the public health response to it, today, we shift focus to another mosquito-borne disease: Zika. This post examines NLM collection items revealing how data has informed scientists’ understanding of Zika and how scientists have shared their data to learn more about Zika and assess its impact on the health of individuals and communities around the world.

What is Zika?

In recent years, Zika has emerged as a global public health threat. Once confined to remote parts of equatorial Africa and Asia, and rare in those areas, Zika outbreaks have proliferated elsewhere in Africa and Asia, as well as in the Americas, Europe, and Oceania. These outbreaks have been accompanied by an alarming rise in birth defects and neurological issues that we now associate with Zika infection.

The Zika virus is transmitted by the Aedes genus of mosquito, which also carries yellow fever, and through sexual contact. In humans, infection can cause Zika virus disease, a constellation of symptoms including fever, rash, joint pain, and conjunctivitis (pinkeye). One in five people infected will develop Zika virus disease. In some rare cases, infection triggers Guillain-Barré Syndrome (GBS), an autoimmune condition causing muscle weakness and sometimes paralysis. Outside of acute illness, Zika can cause microcephaly, a condition in which babies are born with small heads due to abnormal brain development and other severe fetal brain defects in the children of mothers infected during pregnancy.

The Emergence of Zika

Scientists first encountered the Zika virus in the late 1940s. Studying yellow fever in Uganda’s Zika Forest, G. W. A. Dick, S. F. Kitchen, and A.J. Haddow isolated a novel virus from the blood serum of rhesus macaques they’d monitored for yellow fever infection. The group presented their findings to the Royal Society of Tropical Medicine and Hygiene in a report titled “Zika Virus: Isolations and Serological Specificity” in 1952. In it, they provide data on the virus strains isolated, the condition of the animals involved in the study, and climate through graphs and charts.

Journal article describing first encounters with Zika in 1952
“Zika Virus: Isolations and Serological Specificity,” Dick, Kitchen, and Haddow, Transactions of the Royal Society of Tropical Medicine and Hygiene, 46(5): 509-520, September 1952

Zika virus disease was considered an obscure tropical illness before cases began to appear across the globe in the 2000s. In 2007, the first reported Zika outbreak happened on Yap Island in Micronesia with around 100 probable cases. The outbreak on Yap Island was the first confirmed transmission of Zika outside of Africa and Asia.

Evidence Suggests Sexual Transmission

As researchers and epidemiologists began to learn more from the Yap Island outbreak, three Zika cases appeared in Colorado. In August 2008, scientists Brian D. Foy and Kevin C. Kobylinski were living and working in Senegal as a part of a mosquito-sampling project. Foy and Kobylinski became ill with Zika virus disease roughly a week after returning to their homes in northern Colorado. Eventually, Foy’s wife developed Zika virus disease, as well. Foy deduced that his wife, who hadn’t traveled outside of the U.S. recently, most likely contracted Zika through sexual transmission. Later evidence would confirm that Zika is sexually transmissible.

Foy, Kobylinski, and colleagues published a report of this novel case of Zika infection by sexual transmission. In “Probably Non-Vector-borne Transmission of Zika Virus, Colorado, USA,” they provide serology data to confirm Zika infection in the three patients and give a detailed account of the symptoms and progression of the illness. A unique element of the Colorado cases was that the patients were also the medical professionals that later would publish the clinical findings. In this case, both first-hand experience and notes served as data alongside the diagnostic results.

Journal article describing sexual transmission of Zika
“Probable Non-Vector-borne Transmission of Zika Virus, Colorado, USA,” Foy et al., Emerging Infectious Diseases, 17(5): 880-882, May 2011

Brazil Experiences an Epidemic and New Connections are Made

By 2014, other places where Zika hadn’t been endemic reported cases, including Japan, Norway, Easter Island, and France. Cases of Zika in Brazil reached epidemic levels by the end of 2015. During the epidemic in Brazil, physicians reported an alarming increase in cases of microcephaly. In “Physician Alert: Zika virus intrauterine infection causes fetal brain abnormality and microcephaly: tip of the iceberg?” Brazilian physicians provide statistics on cases of microcephaly in 2016 and present two case studies of fetal brain defects with ultrasound imaging.

Journal article about Zika's effects from in utero exposure
“Physician Alert: Zika virus intrauterine infection causes fetal brain abnormality and microcephaly: tip of the iceberg?,” Melo et al., Ultrasound in Obstetrics & Gynecology, 47(1): 6-7, 2016

In March 2016, the World Health Organization (WHO) confirmed there was a scientific consensus that Zika infection in pregnant mothers could cause microcephaly and other congenital brain abnormalities in infants. The WHO statement also confirmed the link between Zika virus infection and GBS. WHO scientists and researchers at other institutions performed a meta-analysis of Zika studies, examining data using a system of criteria they developed to help them establish causality. This group presented their meta-analysis in “Zika Virus Infection as a Cause of Congenital Brain Abnormalities and Guillain- Barré Syndrome: Systematic Review.” Through data, public health organizations such as the WHO have been able to more clearly identify the multi-layered risks posed by Zika, including those particular to select communities such as pregnant women, infants, and children.

Article about brain abnormalities caused by in utero Zika exposure
“Zika Virus Infection as a Cause of Congenital Brain Abnormalities and Guillain-Barré Syndrome: Systematic Review,” Krauer et al., PLoS Medicine, 14(1): e1002203, 2017

Brazil’s epidemic gave researchers a unique opportunity to collect data and better understand Zika transmission, which would eventually lead to larger public health discussions on how to protect Brazil’s vulnerable populations—pregnant mothers and their children.

A diagram of epidemiological features of Zika
Diagram of known epidemiological features of ZIKV from “The Zika Virus Epidemic in Brazil: From Discovery to Future Implications,” Lowe et al., International Journal of Environmental Research and Public Health, 15(1): 96, 2018

Using Data to Predict and Understand Global Transmission

Figure showing Zika's spread
Figure of the geographic spread of Zika across Africa and Asia, from “Molecular Evolution of Zika Virus during Its Emergence in the 20th Century,” Faye et al., PLoS Neglected Tropical Diseases, 8(1): e2636, 2014

In 2014, researchers traced the movement of the Zika virus across Africa and Asia through the 20th century. The findings presented evidence that the Zika virus had likely undergone genomic changes known as “recombination,” which can cause a virus to split into separate strains. Scientists have continued studying recombinant Zika virus to better understand how host and virus interact, means of transmission, and the pathogenesis of the virus itself.

Journal article on mosquitoes that carry Zika
“The global distribution of the arbovirus vectors Aedes aegypti and Ae. albopictus,” Kraemer et al, eLife, 4: e08347, 2015

In addition to studying the global distribution of Zika virus, insect surveillance has played a vital role in the fight against Zika and mosquito-borne disease, in general. Researchers compiled the largest contemporary database of Aedes mosquitoes alongside relevant environmental variables to predict the global distribution of the species, reporting out on their efforts in the journal article “The global distribution of the arbovirus vectors Aedes aegypti and Ae. albopictus.” This dataset has been made publicly available for other public health researchers and scientists.

Map of predicted distribution of Zika
Global map of the predicted distribution of Ae. aegypti, from eLife 4: e08347, 2015

Researchers took the resulting data from their 2015 study of the global distribution of insect vectors and refined it by overlaying travel data to more accurately anticipate how Zika could spread. Information like this helped scientists develop mosquito control efforts, in addition to public health measures.

Map tracking numbers of travelers through Zika-endemic regions and the seasonal and year round risk of transmission. High risk high travel number areas include Orland, Miami, Cuba, Asuncion, Buenos Aires, and Monevideo.
Figure of final destinations of travelers departing Brazil by potential for autochthonous Zika transmission, from “Anticipating the international spread of Zika virus from Brazil,” Bogoch et al, Lancet, 387(10016): 335-336, 2016

Since 2016, Zika has largely retreated from the U.S. and many other countries, while equatorial areas like the north of Brazil continue to grapple with the disease. Data-driven research yields information and insights that will hopefully lead to a successful containment strategy and make Zika a concern of the past everywhere.

Erika Mills is outreach coordinator for the Exhibition Program in the History of Medicine Division at the National Library of Medicine.

Tannaz Motevalli is a researcher and exhibition coordinator for the Exhibition Program in the History of Medicine Division at the National Library of Medicine.

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