Zika Virus—A Devastating Global Health Threat

In her address to the 69th World Health Assembly, Margaret Chan, MD, MPH, director-general of the World Health Organization (WHO), warned the audience of the Zika virus, noting that what was once thought of as a mild disease, has become a devastating global health threat.

Dr. Chan attributes the rise of Zika as a global health threat to government failure to adhere to mosquito control policies in the 1970s. “The rapidly evolving outbreak of Zika warns us that an old disease that slumbered for 6 decades in Africa and Asia can suddenly wake up on a new continent to cause a global health emergency… Changes in the way humanity inhabits the planet have given the volatile microbial world multiple new opportunities to exploit. There will always be surprises.”

The Zika virus has left many scientists and doctors “astonished,” according to Dr. Chan, and for good reason. Although an infection with the virus typically does not present any symptoms in most individuals, it poses a great threat to the fetuses of pregnant women, causing microcephaly, ophthalmological complications, and many more devastating conditions.

Recently, researchers from Brazil and Stanford University studying three infants born to mothers suspected of having a Zika infection during the first trimester of pregnancy discovered previously unreported eye complications that may be linked to the virus. These complications may result in visual impairment, the authors warned. The researchers discovered three ocular issues which had not been previously observed in infants born of Zika-infected mothers:

• Hemorrhagic retinopathy- retinal bleeding
• Abnormal vasculature in the retina- signs of missing blood vessels in the retina where the cells may have died
• Torpedo maculopathy- torpedo-shaped lesions in the macula

In addition, a recent study published in the New England Journal of Medicine, study authors noted that the “magnitude of risk [of Zika infection] remains uncertain.” Michael A. Johansson, PhD, and colleagues studied the Zika virus outbreak in French Polynesia that occurred between 2013 and 2014. They estimated that infection with the virus during the first trimester of pregnancy was 0.95% (95% CI, 0.34 to 1.91), based on eight cases out of a 270,000-individual sample population who had an estimated 66% rate of Zika virus infection. Risk of infection in the second or third trimesters was negligible, stated the study authors.

There has yet to be active transmission of the Zika virus in the United States, as the country’s Aedes aegypti mosquito population, a Zika vector, is not infected with the virus. However, the Centers for Disease Control and Prevention (CDC) report that there are currently 591 cases of Zika infection in the United States, which have been either imported, or transmitted through sexual intercourse. With the warm weather of the coming months, these numbers can change, as those infected with the virus can be bitten, thus transmitting the virus to the mosquito population, beginning a cycle of active transmission.

In addition, since 80% of infected individuals do not show any symptoms, the CDC recently speculated that the actual number of Zika-infected individuals could be in the thousands. Many women who are pregnant or are planning to become pregnant may carry the virus unknowingly, and infect their growing fetuses. This can be an even bigger problem once the vector population becomes infected with the virus.

Through the CDC, pregnant women who qualify can be tested for the Zika virus. The CDC has also set up two surveillance systems for pregnant women, and recently updated their Zika infection reporting criteria.

Dr. Chan stated, “For Zika, we are again taken by surprise, with no vaccines and no reliable and widely available diagnostic tests. To protect women of childbearing age, all we can offer is advice. Avoid mosquito bites. Delay pregnancy. Do not travel to areas with ongoing transmission.”