By Val Fong, Volunteer
Last month, the UCLA Center for World Health teamed with Brazilian Student Association at UCLA to host a public forum featuring a panel of experts and researchers who discussed the current status of Zika virus research, prevention, and treatment. In the midst of the flurry of headlines presenting new information on this poorly understood virus, this moderated discussion provided a comprehensive overview of the facts and most up-to-date Zika studies. The panelists addressed topics ranging from vector control to risk factors for pregnant women, and offered thorough insight on Zika’s implications for global public health as this virus continues to spread around the world.
Despite Zika’s recent presence in the media, the virus has been circulating in the human population for decades, virtually undetected throughout Africa and Southeast Asia. However, it was not until the 2015 Zika outbreak in Brazil that a major public response developed. Growing populations with no previous exposure to the virus and a widespread presence of a competent Aedes egypti mosquito vector, created the perfect conditions for rapid viral spread. In 2015 alone, 42 countries reported mosquito borne Zika outbreaks.
As researchers continue to study this previously underestimated virus, the severity of its infection has been heavily reconsidered. Zika was initially overlooked due to its mild and short-lived symptoms but the neurological disorders associated with infection have prompted significant concern. Soon after the Zika outbreak in Brazil, authorities also reported a significant rise in the prevalence of babies born with microcephaly. Typically characterized by the unusually small head size of the newborn, microcephaly is now thought to be the end product of a spectrum of neurological and developmental disorders that are related to Zika infection of the mother.
“We have found a strong link between Zika and adverse pregnancy outcomes, which haven’t been documented before,” says Dr. Karen Nielsen, clinical professor of pediatric infectious diseases and director of the UCLA Center for Brazilian Studies. Her recent cohort study detected fetal abnormalities in a third of the Zika-positive tested mothers. This included several cases of microcephaly, and more commonly, other severe developmental and neurological defects such as intrauterine growth restriction and cerebral calcifications. While the exact cause of the surge in microcephaly is still being studied, there is clear evidence that the Zika virus plays a major role. Zika has now been found in the amniotic fluid of microcephaly babies of Zika infected mothers, as well as in aborted fetuses of mothers who either had a previous or current infection.
With so much attention spotlighting the correlation between Zika and microcephaly, it is no surprise that many pregnant women have been concerned about the risks of infection. The best recommendation is that pregnant women, or women expecting to become pregnant, avoid travelling to Zika-risk areas altogether. If they have been to active Zika areas, women should wait at least eight weeks before attempting pregnancy. Since some cases of non-mosquito transmission—including sexual transmission—have been reported, doctors also recommend that pregnant women should abstain or use condoms during sexual intercourse if their partner has been to active Zika areas.
For pregnant women who have had Zika exposure or infection, ultrasound surveillance is the primary means of monitoring for fetal abnormalities. Microcephaly is difficult to detect before 22 weeks of gestation, so it is more common to look for other signs of developmental abnormalities before possibly doing amniocentesis for viral analysis. Fetal risk is reported to be anywhere from 1-30% if the mother had been infected. However, if the mother just had Zika exposure but her blood tests for Zika antibodies are negative and she has surpassed a reasonable length of gestation without any signs of fetal abnormality, “current recommendations are that no more additional surveillance is really warranted,” says Dr. Neil Silverman, obstetrician and gynecologist at the UCLA Center for Fetal Medicine and Women’s Ultrasound.
The risk of getting a locally acquired Zika infection in the U.S. is also a growing concern. So far, all Zika cases in the U.S. have been travel related, but the possibility of a native outbreak within the US has prompted public health officials to prepare for a potential local epidemic. “Whether imported cases of Zika may result in virus introduction and local spread is the most concerning to us here,” says Dr. Laurene Mascola, chief of the acute communicable disease control program for the Los Angeles County Department of Public Health. The Aedes egypti mosquito is the most efficient Zika vector, and fortunately is not very common in the US. On the other hand, the Aedes albopictus mosquito– which is prevalent in many states in the Southeast as well as New York and Hawaii– is also a competent vector. Public health officials fear that this makes the US susceptible to an epidemic. Timely diagnosis and reporting of Zika cases is important for monitoring its spread, however detecting clusters of the disease is difficult. Since Zika’s symptoms, serological antigenic response, and region of activity is very similar to other flaviviruses, Zika is difficult to accurately distinguish.
Efforts to understand and control the spread of Zika have been followed by increased trials to develop viral therapies; however, approval for potential vaccines and treatments is not anticipated for several more years. Until then, prevention is the primary solution. “Viruses will continue to spread in areas with competent vectors, and the US is one of those areas with competent vectors,” says Dr. Mascola. By eliminating sources of standing water– where mosquitoes breed– mosquito abatement districts play an increasingly important role in controlling the spread of infectious disease, and vector control agencies are essential in preventing a potential Zika outbreak in the US. Using personal protection, habitat control, and even mosquito manipulation, the transmission of Zika can be effectively slowed.
The magnitude of alarm that the Zika virus has caused reminds the world– once again– that the human presence on our planet does not go without consequence. Many infectious diseases can remain hidden, and their emergence must be responded to with international collaboration and cooperation. Scientists, politicians, and public health experts continue to work together to combat the Zika virus—just like they have in the past for dengue, West Nile, and yellow fever—and are making progress towards controlling its transmission. Dr. Brewer concludes, “We need to respond with everybody, we need to engage society, and we have to actually put in those public health systems that weren’t there.”