First discovered in Uganda in 1947 as a mosquito-borne virus that caused a brief, mild illness, the Zika virus’s notoriety has expanded significantly as it continues to live up to its recent designation by the World Health Organization as a global public health emergency.

The number of confirmed cases of Zika is growing, locally and globally. The Centers for Disease Control and Prevention (CDC) reports that as of Feb. 3 there have been 35 travel-associated Zika virus cases reported in the United States.

In a study published in the latest issue of the New England Journal of Medicine, Jernel Mlaker and his colleagues have confirmed a case of Zika virus, causing microcephaly, that was obtained through vertical transmission, which is the passage of a disease-causing agent from mother to fetus. Microcephaly causes infants to be born with undersized heads, which can lead to problems with a child’s cognitive abilities and neurological functions.

“To me, that just confirms what I think many of us thought was just a matter of time before we could confirm,” Marjorie Treadwell, a specialist in high-risk pregnancies at the University of Michigan, who was not involved in the study, told NBC News. “I think the actual isolation of the virus in the brains strengthens the thought that the Zika virus is causing these cases of microcephaly.”

The case involved a 25-year-old woman who had been working in Natal, Brazil. According to the researchers, the woman became pregnant at the end of February 2015. During the 13th week of gestation, however, she had become ill and experienced severe muscle aches, a high fever and itchy rashes.

Her first fetal ultrasound appeared normal. She then returned home to Europe when she was seven months pregnant and another ultrasound showed evidence of microcephaly.

An ultrasound at 32 weeks revealed that the fetus was clearly smaller than it should have been. The fetus also had a very small head and evidence of extensive brain damage.

According to the researchers, she requested that the pregnancy be terminated. The abortion procedure was approved by national and hospital ethics committees after they concluded that the fetus was almost certainly not going to survive.

“It sounds like a pretty clear case of extreme microcephaly,” Aubree Gordon, an epidemiologist at the University of Michigan who is studying the effects of viruses on pregnancy in central America, told NBC news.

After performing an autopsy on the fetus, the researchers found Zika virus in the fetus’s brain — and not just traces, but the entire genome of the virus.

According to Taijana Avsic, one of the researchers involved in the study, the Zika virus exhibits “neurotrophism,” or a tendency to live in brain tissue. She speculates that the virus may be able to reside in the brain for longer periods of time than it resides in other types of body tissue because the immune system is less likely to reach it in the brain.

According to the researchers, the fetus did not seem to be infected by any other virus that could have caused the damage. Also, the mother did not seem to have any of the known genetic causes of microcephaly.

There is also growing evidence that the Zika virus may cause other birth defects, particularly in the fetus’s eyes.

Experts believe that the Zika virus is most dangerous when contracted during the early stages of pregnancy. Other viruses that are known to cause birth defects, such as rubella and cytomegalovirus, do the most damage to a developing fetus if the mother is infected in the early stages of her pregnancy, but researchers are still not entirely sure about the Zika virus.

“The hard part is we don’t know,” Avsic said. “A lot of viruses cause scarring or they can cause destruction of brain tissue. There are a lot of different possibilities.”

In the past, the Zika virus and its relatives had never been observed to cross the placenta and affect a growing fetus, which is why doctors had so many doubts about whether it was doing so in cases in Brazil.

Scientists are trying to figure out if the virus has mutated or if some other factors are allowing it to cross the placenta.

On Feb. 8, President Obama asked Congress for $1.8 billion in emergency funding to be spent on Zika virus research.

At best, a vaccine may be years away. In the meantime, though awareness and precautionary behavior on the part of those who are particularly susceptible to infection may be the best approach.