Mosquito-borne Zika virus more dangerous to newborns than ever, scientists say

The United States hasn’t seen mosquito-borne Zika cases in two years, but scientists warn that complacency could be crippling or deadly for newborns.

Fearing a comeback, the scientists are aggressively pursuing a vaccine and using special bacteria to neutralize mosquitoes that carry the disease.

Researchers also say the disease is more dangerous to newborns than previously realized, with complications that range far beyond the abnormally small heads tied to the 2016 outbreak and problems that can develop months or years into an affected child’s life.

“Though Zika has disappeared from the headlines, it still remains a major public health threat due to its ability to cause severe congenital malformations,” said Dr. Amesh Adalja, a senior scholar at the Johns Hopkins Center for Health Security.

There have been signs of progress in the fight to avoid another global panic. The World Mosquito Program this year announced it was able to eradicate 96% of a related disease — dengue — by introducing a bacteria called Wolbachia to the mosquito population in a part of Australia.

It also found success in Indonesia and parts of Brazil outside Rio de Janeiro, which saw a 70% decline in cases of dengue and chikungunya, another mosquito-borne disease.

Scientists say the Wolbachia bacteria compete with viruses in a mosquito’s system and are passed down to offspring, through the maternal line.

“It makes it harder for the viruses to reproduce inside the mosquito, meaning they are less likely to spread the virus from person to person,” said Dale Amtsberg, a spokesman for the World Mosquito Program. “As the percentage of mosquitoes carrying Wolbachia grows, the incidences of Zika and other diseases reduce. It’s novel in that it is a natural self-sustaining intervention.”

The program plans to launch another trial in the Brazilian cities of Rio de Janeiro and Niteroi while adding the cities of Belo Horizonte, Campo Grande and Petrofina in 2020.

“While the intense Zika outbreak of 2016 in Brazil has passed, there are fears it may return,” said Mr. Amtsberg. “Plans are underway to cover 1.5 million people with releases of Wolbachia-carrying mosquitoes to combat future Zika outbreaks.”

There is no licensed vaccine for Zika, but the National Institutes of Health said it is receiving good feedback from a phase-two trial involving more than 2,000 people across six Central and South American countries, Mexico, Puerto Rico, Houston and Miami. The shots appear to be safe and produce an immune response, though it will take another epidemic to prove the vaccine works.

The Zika virus exploded in the Americas in 2016, causing round-the-clock news coverage. The Obama White House rolled out color-coded maps showing the risk of spread as far north as New York City and San Francisco, as it demanded nearly $2 billion for the fight.

The entire world was shocked by photos of babies with abnormally small heads in hard-hit Latin America, and the U.S. government took the unprecedented step of urging pregnant women to stay away from Miami neighborhoods that saw a batch of locally acquired cases.

Florida ultimately recorded more than 200 mosquito-borne cases in 2016, predominately in and around Miami. Texas recorded six cases that year.

The following year, Florida saw two mosquito-borne cases, and Texas recorded five near the Mexico border.

Today, the disease is barely an afterthought on cable news shows, as the U.S. wraps up a second calendar year with no mosquito-borne cases, according to the Centers for Disease Control and Prevention.

“The ferocity of the outbreak in earlier years has created a lot of population immunity that has limited its impact in this hemisphere since them,” Dr. Adalja said.

But that is not the same as eradicating the disease.

“As population immunity wanes with time and new individuals are born, the disease may re-emerge,” he said. “There are also pockets of populations with low immunity in which the virus may find individuals to infect.”Zika also is popping up in new places. The World Health Organization in November reported a handful of cases in the French town of Hyeres along the Mediterranean coast. There also have been outbreaks in India, Singapore, Vietnam and Thailand in the period since the disease vanished from the Americas.

The stakes may be even higher than initially thought. A paper published in the New England Journal of Medicine in October found 4%-7% of newborns of infected mothers died within the first week of life, while 4%-6% risk being born with an abnormally small head, a condition known as microcephaly.

Furthermore, some babies may not show signs of congenital Zika syndrome may later develop seizures, hearing loss, visual impairment, difficulty or discomfort swallowing or developmental issues.

Among U.S. children born to infected mothers, 9% had some kind of nervous system disorder by the time they were 2 years old, the paper says.

That’s notable since scientists have been trying to determine whether babies born to infected mothers can develop problems over time, and to what extent their impairments extend beyond the familiar birth defects.

“Originally, we only thought there was microcephaly or not,” said Dr. Anthony Fauci, who leads infectious disease research at the National Institutes of Health.

While no one wants to see more Zika victims, the dearth of cases has at least one drawback — scientists are unable to road-test promising vaccines.

“The good news is there are no cases,” Dr. Fauci said. “The sobering news is it doesn’t allow you to prove your vaccine works.”