Is there any new information on the link between Zika virus and birth defects?

DEAR DOCTOR K:

In a recent column, you said that doctors were still conducting research to see if the Zika virus does, as feared, cause birth defects — particularly, babies born with small heads and brains. Has there been any new information on that?

DEAR READER:

There has, and it’s important. The new information was summarized in articles in the New England Journal of Medicine in April.

First, a brief refresher. Zika virus is carried by a particular kind of mosquito known as the Aedes mosquito. When it bites a person, the virus can enter the person’s body. Most people who catch the Zika virus have only mild and temporary symptoms. However, early evidence indicated that birth defects might occur in the fetuses of some pregnant women who were infected in the first four to five months of pregnancy.

The most dramatic such birth defect in babies was very small heads and brains, called “microcephaly.” Microcephaly is rare, and can be caused by other viral infections, including rubella (“German measles”).

The Zika virus has lived in Africa and Asia for 70 years. Last year, it moved to South America, and has been spreading north, into the Caribbean, and toward Mexico, the United States and Canada. Will it reach the U.S. and Canada? No one can predict the future, but we know that the mosquito that carries the virus already is present in about 30 states of the U.S.

The World Health Organization and the U.S. Centers for Disease Control and Prevention (CDC) announced in early April that it is likely that the Zika virus is a cause of microcephaly. New studies have led them to this conclusion. Let’s look at those studies, and the reason they have convinced some skeptics:

  • MICROCEPHALY HAS OCCURRED OUTSIDE OF BRAZIL. Even though the Zika virus has existed in other countries for decades, no link to microcephaly had been previously seen until it was reported in Brazil in 2015. However, many of the countries where the virus has lived have very poor or non-existent public health systems for recognizing and reporting birth defects. Now scientists report that a surge in microcephaly also occurred in French Polynesia following a Zika outbreak in 2013-14. It also has occurred in some U.S. women who traveled briefly to South America.
  • FETAL ULTRASOUND STUDY FOUND DEFECTS: In a relatively small study in Brazil, ultrasound studies of the fetus revealed brain birth defects in 29 percent of women with a rash caused by Zika virus infection, but in none (0 percent) of a group of women with a rash not due to Zika virus infection.
  • ZIKA VIRUS CAN INFECT THE BRAIN. New studies find that the virus can infect the brain of various animals, and human brain cells in a laboratory dish. Thus, it is plausible that the virus could cause brain disorders.

In tomorrow’s column, I’ll discuss what all this means, and what we all need to think about, as the virus appears to be heading in our direction.