Zika Outbreak in Puerto Rico Poised to Reach Dangerous Proportions

Residents and visitors in Puerto Rico, consider yourselves warned: get pregnant at your own risk.

That’s essentially the advice coming out of a recent report by the Centers for Disease Control and Prevention (CDC) regarding the ongoing Zika outbreak on the Caribbean island and its potential to cause birth defects should women become infected during pregnancy. On June 17, the CDC announced that 1% of all blood donations analyzed in the American territory had tested positive for Zika, and that this could be an indication that the outbreak is poised to reach dangerous proportions.

“In coming months, it is possible that thousands of pregnant women in Puerto Rico will catch Zika,” CDC director Thomas Frieden, MD, MPH, said at a briefing for reporters. “This could lead to dozens or hundreds of infants being born with microcephaly in the coming year.”

Microcephaly, a birth defect that causes infants to be born with abnormally small brains and, thus, in many cases, cognitive impairment, has been linked with Zika in numerous studies of the mosquito-borne virus in Brazil, ground zero for the current epidemic, and elsewhere. To date, Zika cases have been reported in the Caribbean as well as in several countries in Central and South America; however, research suggests the virus may surface in localized cases here in the US, primarily in the southern part of the country.

“The virus in circulation in the New World is different from the older, African strains,” John Lednicky, PhD, associate professor, College of Public Health and Health Professions, University of Florida, told Contagion recently. “The new viruses seem to be more neurotropic, for example, and this may explain why brain defects are seen in some of the fetuses or newborns of mothers that had been infected with Zika virus.”

Although the CDC was quick to emphasize that while blood donors hardly represent the entire population of Puerto Rico, the presence of Zika in such a relatively large segment of collected samples is cause for concern. Similar tests were performed on collected blood donations in 2014, during an outbreak of Chikungunya on the island, and though only a relatively small percentage tested positive for that virus (which, like Zika, is transmitted via the Aedes aegypti mosquito), nearly 25% of the island’s total population was infected in less than a year, according to Dr. Frieden.

In its latest analysis, the CDC tested 12,777 blood donations collected between April 3 and June 11 of this year. The incidence of Zika within collected samples increased steadily throughout the study period, with the highest (1.1%) being reported during the final week of testing. Dr. Frieden explained that this could mean that as many as 2% of all residents on the island may have been infected with Zika during the eight-week study period.

“We must be cautious in our thinking,” said Dr. Lednicky, who was not involved in the CDC assessment. “Our public health policies and guidelines should reflect the new realities. We should pay attention to all the good research work coming out of Brazil and learn from it.”

In the midst of the CDC’s report, Inovio Pharmaceuticals and GeneOne Life Science announced today that they have received approval from the Food and Drug Administration (FDA) to initiate a phase I human trial to evaluate Inovio’s Zika DNA vaccine (GLS-5700) to prevent Zika infection. According to a press release on the company’s website, “In preclinical testing this synthetic vaccine induced robust antibody and T cell responses in small and large animal models, demonstrating the product’s potential to prevent infection from this harmful pathogen in humans.” The company plans to dose their first subjects in the next few weeks and report the phase I interim results later this year.

Brian P. Dunleavy is a medical writer and editor based in New York. His work has appeared in numerous healthcare-related publications. He is the former editor of Infectious Disease Special Edition.