By Rebecca Bowers

EXECUTIVE SUMMARY

Information from just-released data indicate that women could be experiencing pregnancy losses because of the Zika virus without realizing they have the infection. Results from a collaborative study indicate 26% of nonhuman primates that became infected with the Zika virus early in pregnancy experienced miscarriages or stillbirths, although the animals exhibited few signs of the infection.

  • While many people who are infected with Zika may not present with symptoms, other people may exhibit fever, rash, headache, joint pain, red eyes, and muscle pain.
  • An infected pregnant woman can transmit Zika virus to her fetus, causing birth defects such as microcephaly, brain abnormalities, nervous system damage, neural tube defects, and eye abnormalities. Zika also can be passed through sex from an infected person with Zika to his or her partners.

Information from just-released data indicate that women could be experiencing pregnancy losses because of the Zika virus without realizing they have the infection. Results from a collaborative study indicate 26% of nonhuman primates that became infected with the Zika virus early in pregnancy experienced miscarriage or stillbirth, although the animals exhibited few signs of the infection.1

The paper is a pooled effort from scientists at six different primate research centers: the California National Primate Research Center at the University of California-Davis; Southwest National Primate Research Center at the Texas Biomedical Research Institute; Tulane National Primate Research Center at the Tulane University Health Sciences Center; Washington National Primate Research Center at the University of Washington-Seattle; Wisconsin National Primate Research Center at the University of Wisconsin-Madison; and Oregon National Primate Research Center at the Oregon Health & Science University. Researchers at Baylor College of Medicine, the Seattle Children’s Research Institute, and the University of California-San Francisco also participated in the project. Each research team was working with experimentally infected pregnant monkeys to determine the effect on pregnancies and explore damage to different tissues. California, Oregon, Wisconsin, and Tulane University used rhesus macaques in tests, while Southwest National Primate Research Center used common marmosets, and the Washington National Primate Research Center tested pigtail macaques.

Researchers analyzed published and unpublished data from several studies of macaques that were pregnant and infected with Zika. The pooled data indicate that miscarriages or stillbirths occurred in 26% of the study population. Macaques that were infected with the Zika virus early in pregnancy experienced much higher fetal death rates than the macaques that were infected after gestation day 55, scientists report.1

Researchers note that few monkeys showed symptoms, and when they did, they typically involved rash and conjunctivitis. Data indicate that Zika strains that were identified in recent Asian and American outbreaks damaged tissues connecting mothers to their developing fetuses. Further examination determined a type of damage to the placenta, which impaired its function. Increased placental calcification was detected through ultrasound examination.1

“This is the first time we’ve been able to categorically demonstrate that Zika-related miscarriage and stillbirth happens in nonhuman primates that experience no symptoms,” notes co-author Daniel Streblow, PhD, associate professor of molecular microbiology and immunology in the Oregon Health & Science University School of Medicine, OHSU’s Vaccine and Gene Therapy Institute, and Oregon National Primate Research Center.

By pursuing such research, scientists may be able to better understand how the Zika virus damages the placenta and prevent pregnancy loss, said Streblow in a press statement.

“Our data in monkeys indicate that more research is needed so researchers can develop intervention strategies to protect pregnant women and their fetuses from Zika virus,” says Lark Coffey, PhD, study co-author and arbovirologist at the University of California at Davis.

Focus on the Virus

Humans acquire the Zika virus from the bite of an infected Aedes aegypti mosquito or via sexual contact with a person who is infected. Although many people who are infected with Zika may not present with symptoms, other people may exhibit fever, rash, headache, joint pain, red eyes, and muscle pain. A pregnant woman can transmit the Zika virus to her fetus, causing birth defects such as microcephaly, brain abnormalities, nervous system damage, neural tube defects, and eye abnormalities.

Previous research has measured miscarriages and stillbirths in women who were symptomatic. Results of a recent study that involved women known to have the Zika virus infection indicate that 5.8% had a miscarriage and 1.6% had stillbirth during their first trimester.2 However, pregnancy studies in humans may be missing about half of the people who have Zika because they rely on infections that are symptomatic, says lead author Dawn Dudley, PhD, senior scientist in the University of Wisconsin-Madison department of pathology and laboratory medicine.

“Women get enrolled in studies because they have Zika symptoms, but we know that up to half of people who have Zika don’t show any symptoms at all,” said Dudley in a press statement. “So, the pregnancy studies are probably missing half of the people who have Zika.”

Although the largest number of U.S. Zika cases have been reported in Florida, Texas, and New York, other states also have reported cases. Currently there are not any licensed treatments or vaccines available for Zika, but scientists have research options in various stages of development. Researchers at University of California San Diego School of Medicine, who are working along with other international scientists, have published findings suggesting that the antiviral drug sofosbuvir, which is used to treat hepatitis C infections, may be a possible treatment for adults, including pregnant women, who are infected with Zika.3

REFERENCES

  1. Dudley DM, Van Rompay KK, Coffey LL, et al. Miscarriage and stillbirth following maternal Zika virus infection in nonhuman primates. Nat Med 2018; doi: 10.1038/s41591-018-0088-5. [Epub ahead of print].
  2. Hoen B, Schaub B, Funk AL, et al. Pregnancy outcomes after ZIKV infection in French territories in the Americas. N Engl J Med 2018;378:985-994.
  3. Mesci P, Macia A, Moore SM, et al. Blocking Zika virus vertical transmission. Sci Rep 2018;8:1218.