Researchers want to know how Zika affects mothers with HIV

The National Institutes of Health will study women who are infected with both Zika and HIV to see how one virus affects the other. Doctors are eager to learn more about how Zika affects the treatment of HIV.

NIH will examine about 1,800 pregnant mothers over a period of four to six years. They're looking for women infected with both HIV and Zika, just one virus, and those not infected at all.

Researchers are looking for subjects in Puerto Rico, where an estimated 10,000 pregnant women are infected. According to a study published last year in JAMA Pediatrics, 270 of them gave birth to babies with microcephaly, one of the biggest health concerns linked to the Zika virus.

The Centers for Disease Control and Prevention report that since last year, 4,175 Zika cases involving pregnant mothers have been reported in U.S. territories. Another 1,997 cases have come from U.S. states and the District of Columbia during the same time period.

There are no reported cases of an HIV-infected pregnant woman contracting Zika. But the NIH expects such cases to rise along with the number of Zika infections.

Researchers hope examining how these two viruses interact within a pregnant woman will determine whether having HIV makes a patient susceptible to contracting Zika and vice versa. They also hope to learn whether being infected by the two viruses increases the risk of damage to the fetal brain.

Dr. Christopher Zahn, vice president of Practice Activities for the American College of Obstetricians and Gynecologists said there's little guidance for physicians regarding the overlap between these two viruses.

"So, while both Zika and HIV in pregnancy affects a relatively small population of women, this study will add to a body of research that will ultimately help us successfully combat this epidemic."

He and others worry Zika could reduce the effectiveness of antiretroviral drugs that prevent HIV from passing from a pregnant woman to her fetus. The risk of a mother transmitting HIV to her child increases if the viral load is high, but with the use of antiretrovirals, it can bring down the risk to as low as 1% or less, according to Dr. Igor Koralnik, chairperson of the Department of Neurological Sciences and chief of the Section of Neuroinfectious Diseases at Rush University Medical Center.

An estimated 8,500 women living with HIV give birth annually, according to the CDC. One in 10 of the 250 pregnant women who contracted Zika in 2015 had a fetus with birth defects related to the virus, according to an April report by the agency.