Measles and Zika: The Known and Unknown
Measles and Zika: The Known and Unknown
Zika and rubella infections have some striking similarities. Both are RNA viruses that cause a lot of mild and subclinical disease. Rubella is subclinical between 25% and 50% of the time. Zika is thought to be subclinical in up to 80% of infections. In adults showing clinical symptoms, rash, fever, and arthralgias are common in both zika and measles.
The most significant similarity: these illnesses that are benign and self-limited in children and adults are both devastating to a fetus.
Of course we know much more about congenital rubella. Maternal fetal transmission is essentially 100% in the first trimester and rarely causes problems in the 3rd trimester. Multiple organ systems are involved in the congenital rubella syndrome: brain, heart, hearing, vision.
As of right now, a lot of questions need to be answered about Zika infections in pregnant women. What is the maternal-fetal transmission rate in the different trimesters? Are there any other CNS consequences besides microcephaly? I personally fear that microcephaly is just the tip of an iceberg of CNS damage. Will we see increased rates of mental retardation, learning disabilities, and so on in children with normal head sizes? We won't know the answer for years. While the Zika virus can be cultured from amniotic fluid, specificity and sensitivity are unknown.
A few things are sadly obvious. We have no antiviral treatment. There is no way to completely eliminate the threat of mosquito bites. Avoidance of mosquito bites is currently the only recommendation to prevent Zika that is offered by the CDC on its Zika Virus Web page. News stories pop up frequently about the potential for a vaccine, with estimates ranging from no sooner than 3 to 5 years to perhaps something in 2017. Glaxo and Sanofi are both rumored to be working on it. But a small biotech company, Inovio Pharmaceuticals, appears to be in the lead with an innovative approach not being used in any currently licensed vaccine: a DNA vaccine. Inovio currently has a DNA vaccine against Ebola in human testing in a project begun just 18 months ago.
DNA coding for a protein from the infectious virus that can induce immunity is loaded onto a plasmid and then injected into a living host. The host cells then produce the viral protein that cannot cause infection, but can cause an immunologic response. The antigenic proteins produced this way presumably more closely resemble the wild virus epitopes as compared to both live and inactivated vaccines since the attenuation or inactivation of the wild virus is much more likely to distort the protein structure. Importantly, the time it takes to develop a vaccine with this method is much shorter (we're talking years) than the traditional approaches. Inovio is currently testing its Zika vaccine in primates with plans for human phase one testing before the end of the year.
I'm hoping someone is successful with the production of a safe and effective Zika vaccine—and soon. Many experts feel it is inevitable that there will be congenital Zika outbreaks in the southern US until we can stop the virus with a vaccine, just like we did with congenital rubella.
Centers for Disease Control Zika information page
CDC. Zika virus. Accessed March 4, 2016 and available at http://www.cdc.gov/zika. Last updated March 3, 2016.
A report on the race for a Zika vaccine
Lorenzetti L. Here's the company that’s the closest to developing a Zika vaccine. Fortune Magazine. January 26, 2016. Accessed March 1, 2016 and available at: http://fortune.com/2016/01/28/zika-virus-vaccine/
Primers on DNA vaccine technology
World Health Organization. Biologicals. Vaccines. Accessed March 2, 2016 and availble at: http://www.who.int/biologicals/areas/vaccines/dna/en/
Scuderi J. What are DNA vaccines? Kenyon.edu. Accessed March 2, 2016 and availble at: http://biology.kenyon.edu/slonc/bio38/scuderi/partii.html