Expected Rise in Zika Virus and Microcephaly a ‘Huge Concern’

Lynne Friedmann (left) moderates a panel of public health experts, Christopher Dye, Marcos Espinal, and Anthony Fauci, who provided potential Zika virus infection numbers. | Boston Atlantic Photography

Cases of both Zika virus and microcephaly—the potentially related occurrence of babies born with small-sized heads and associated neurological complications—will continue to increase across the Americas, said a panel of public health experts at a 12 February news briefing at the AAAS Annual Meeting in Washington, D.C.

Currently about 100,000 cases of the mosquito-borne Zika virus have been reported in 26 countries and territories throughout the western hemisphere, experts said, though Marcos Espinal, director of the Department of Communicable Diseases and Health Analysis at the World Health Organization/Pan American Health Organization, said these numbers are likely underreported, as Zika virus is generally a mild infection for which affected people may not seek treatment.

“I wouldn’t be surprised if we have 2 or 3 million cases of Zika virus,” said Espinal, based on recent outbreaks of similar viruses in the Americas such as dengue fever and chikungunya.

Christopher Dye, director of strategy in the World Health Organization’s Office of the Director General, meanwhile, estimated that “hundreds and hundreds of thousands” of cases of Zika virus are expected.

More than 50 cases have been found in the United States, including about 30 in Puerto Rico and several in the U.S. Virgin Islands, said Anthony Fauci, director of the U.S. Institute of Allergy and Infectious Diseases. Most cases are known as “imported cases,” which occur when the victim—one of the 30 million people who travel annually between the United States and the rest of the Americas, a half of million of whom are pregnant women—became infected elsewhere and then traveled to the United States where they became sick with no further spread, Fauci said.

Although all cases in the continental United States are imported cases, “it would not be surprising at all if, just like chikungunya and just like dengue, we do see clusters of locally transmitted Zika” in the United States, said Fauci. He referred to mini-outbreaks of dengue in the United States along the Gulf Coast, which were contained with no further spread due to an aggressive response to mosquito control.

However, Fauci said it is “highly unlikely” that any locally transmitted instances of Zika virus would balloon into a broad explosion of Zika in the United States, but he said the United States would be prepared.

Zika was known for 60 years as a mild virus that appeared sporadically, but since 2007, two troubling shifts have taken place, Dye said: Zika virus now results in widespread outbreaks of hundreds or thousands of cases, and it is associated with neurological disorders like microcephaly and Guillain-Barre syndrome, a disorder in which the body’s immune system attacks the nerves. Increasing outbreaks over the last year and a half and concern over neurological complications led to the 1 February announcement by the World Health Organization of a public health emergency of international concern, Dye said.

Microcephaly has been found in Brazil in more than 4,000 babies, the panelists said, a number they said would increase.

Of microcephaly, Dye said, “This number of cases is going to rise, both in Brazil and across the Americas. How big it will get, we’re not clear yet, but this clearly is a case for huge concern.”

Espinal said Guillain-Barre syndrome has also seen an increase of cases in five countries in Central and South America: Venezuela, Suriname, Colombia, Brazil, and El Salvador.

Response efforts for Zika virus and its associated diseases are taking place in parallel with efforts to better understand the virus’ many unknowns, including the length of the Zika infectious period and the efficacy of control methods.

Also unknown is the nature of the link between Zika infection and neurological diseases. While it may be difficult to prove causation, “the evidence for a causal link is becoming stronger and stronger,” Dye said. Treating the link between Zika virus and diseases like microcephaly as “guilty unless proven innocent” may help to aid public health responses.

Espinal detailed several studies underway, including a study in Brazil that will reveal information in April about children with microcephaly in the state of Pernambuco and cohort studies in Colombia are currently following 2,000 pregnant women infected with Zika virus.

Vaccine development has also begun, said Fauci.

To support this and other efforts by the Centers for Disease Control and the National Institutes of Health, Fauci noted that President Obama last week asked Congress for $1.8 billion budget supplement to respond to the threat of Zika, including funding to support the NIH involvement in vaccine development.