Earlier this year, it was confirmed that Zika virus infection during pregnancy can have devastating implications for the developing fetus, causing babies to be born with a smaller-than-normal head – a condition known as microcephaly. Now, researchers say they have identified a human antibody that could stop the infection in its tracks.
Zika is a virus most commonly spread by the bite of an infected Aedes mosquito.
Symptoms often last no longer than 1 week, and they are often not severe enough to warrant a hospital visit. For pregnant women, however, Zika infection can have severe consequences.
In February of this year, the World Health Organization (WHO) concluded that Zika virus infection during pregnancy is a cause of microcephaly and should be considered a Public Health Emergency of International Concern.
The conclusion came after a significant increase in reports of microcephaly following Zika virus outbreaks in French Polynesia in 2014 and Brazil in 2015.
At present, there is no vaccine against Zika; the only way for expectant mothers to protect themselves against the virus is to avoid mosquito bites.
Now, researchers from Washington University School of Medicine in St. Louis and Vanderbilt University School of Medicine in Nashville, TN, say they have uncovered a naturally occurring antibody called ZIKV-177 that could protect the developing fetus from Zika virus, bring us closer to a Zika vaccine.
Their findings were recently published in the journal Nature.
For the study, co-senior author Dr. Michael Diamond, the Herbert S. Gasser professor of medicine at Washington, and colleagues took blood samples from adults who had been infected with Zika virus.
- Microcephaly is a birth defect where a baby’s head is much smaller than other babies of the same sex and age
- In the United States, microcephaly is estimated to affect 2-12 babies per 10,000 live births
- Rubella, toxoplasmosis, and cytomegalovirus are some infections during pregnancy known to cause microcephaly
The researchers isolated 29 anti-Zika antibodies from the blood samples and tested each one on different strains of Zika in a laboratory. They identified one antibody – ZIKV-177 – that effectively neutralized five Zika strains.
Next, Dr. Diamond and team set out to investigate whether ZIKV-177 might be effective against Zika virus in animal models.
The researchers administered the antibody to pregnant mice, either 1 day before or 1 day after they were infected with Zika virus.
In both cases, researchers found that ZIKV-177 reduced levels of Zika virus in pregnant mice and their fetuses, compared with pregnant mice that were not given the antibody.
“We did not see any damage to the fetal blood vessels, thinning of the placenta or any growth restriction in the fetuses of the antibody-treated mice,” notes study co-author Indira Mysorekar, Ph.D., an associate professor of obstetrics and gynecology and pathology and immunology at Washington.
“The anti-Zika antibodies are able to keep the fetus safe from harm by blocking the virus from crossing the placenta,” she adds.
Additionally, when the researchers gave ZIKV-177 to male mice infected with a lethal strain of Zika, they found it reduced levels of the virus, even when administered 5 days after initial infection.
“We stacked the deck against ourselves by using a highly pathogenic strain of Zika, and even in that case, the antibody protected the mice,” notes Dr. Diamond.
The researchers say their findings indicate that antibodies alone can offer effective protection against Zika among adults and fetuses.
What is more, the results suggest that a vaccine that evokes protective antibodies – such as ZIKV-177 – has the potential to prevent Zika infection in expectant mothers and their fetuses, as well as treat fetuses that have already been infected.
“These naturally occurring human antibodies isolated from humans represent the first medical intervention that prevents Zika infection and damage to fetuses. We’re excited because the data suggests we may have antibody treatments in hand that could be developed for use in pregnant women.”
Study co-author James Crowe Jr., Vanderbilt Vaccine Center
While further studies are required to determine whether their results can be translated to humans, the researchers are hopeful that their findings can lead to effective prevention and treatment strategies for Zika.
As well as preparing ZIKV-177 for testing in humans, the team plans to investigate whether antibodies might be effective for eliminating persistent Zika infection.
“We know that Zika can persist in certain parts of the body, such as the eyes and the testes, where it can cause long-term damage, at least in mice,” says Dr. Diamond. “We showed that the antibody can prevent disease, and now we want to know whether it can clear persistent infection from those parts of the body.”