A leading pediatric neurologist who has studied the brains of babies stricken with the Zika virus says the damage is far more severe than global health officials are telling the public.

Dr. William Dobyns was emailed the images by a specialist in Brazil and told The Daily Beast the cases are some of the worst he’s seen in more than 30 years of study. Dobyns says images also share telltale signs of viral infection, though a definitive link from the birth defects to the Zika virus has not yet been established.

The iconic image of the Zika outbreak are babies born with abnormally small heads, a condition called microcephaly. The microcephaly diagnosis is made when a baby’s head is at least two standard deviations below the mean for age and sex.

These heads are six deviations below the mean, Dobyns estimates.

“In these kids with Zika you see really severe microcephaly,” he said. “The heads are probably minus five to six standard deviations below the norm, and that’s really small. If the appearance of the head seems problematic, the brain is worse.”

Dobyns said, based on the pictures, that some of the infants may have brains that are 10 standard deviations below the mean for age and sex.

An estimated 15 percent of children born with microcephaly have normal intelligence, but in Brazil, that percentage may be zero.

“The idea that these children are mildly handicapped is a fantasy,” Dobyns said. “OK, so they’re awake and feeding, but how much does it take to be awake and be feeding?”

Microcephaly afflicts 25,000 children in the United States annually and has been linked to a number of factors like chromosomal abnormalities, malnutrition, and exposure to drugs or other toxins.

It is only infections that cause cases of microcephaly like this, though.

“When a baby’s brain is growing and a severe viral infection happens, it shrinks,” Dobyns said. Brain scans show an abundance of damaged white matter, Dobyns said, indicating that trauma was incurred during development, not prescribed genetically.

Not only was development interrupted, the Zika babies’ brains look like those of children whose mothers were infected with the Cytomegalovirus. Like Zika, CMV leaves people with a mild cold but can cause severe cases of microcephaly.

Not only are CMV-ravaged brains shrunken, they don’t have ridges and wrinkles like normal brains. The condition is known as polymicrogyria and was also seen in the Zika brains. (Polymicrogyria, can produce stroke-like symptoms, seizures, and extreme muscle impairment.)

The final sign that a virus caused microcephaly in the Zika babies are calcium salts found in a critical part of the brain, Dobyns said.

The vast majority of calcium in the body goes to bones, but in this case it is deposited where it does not belong: the brain’s cerebral cortex. Once there, the deposits harden and interfere with functions ranging from memory to motor control.

It’s this “rare” combination of symptoms that Dobyns believes makes the strongest case for Zika being the cause.

“This is a well-known pattern with documentation in the literature going back decades—if not a century—and it’s proven to be viral,” Dobyns said. “The media has not picked up second line of evidence. There is a consistent pattern, a severe one.”

Dobyns’s theory is not proven, though.

At the time that Dobyns viewed the five scans, scientists had yet to discover Zika in the brain tissue of infants with microcephaly (only their mothers had tested positive). Since then, both the Center for Disease Control and Brazilian health officials have confirmed the Zika virus was active in the brains of at least two babies with microcephaly who died shortly after birth.

Despite this mounting evidence of a Zika-microcephaly connection, large questions remain.Chief among them: If the virus has been around since 1947, why is microcephaly just being seen in today's outbreak? After all, a spike in microcephaly cases was not recorded during the largest previous Zika outbreak in French Polynesia in 2013. Even today in Colombia, where more than 3,000 pregnant women are infected, medical authorities said they have yet to see a single case of microcephaly.

Dobyns suggests that the French Polynesia outbreak was not large enough to show a statistically significant rise in microcephaly cases. Dobyns also said the medical infrastructure in Colombia may be hindering the country’s ability to accurately report whether or not there is an microcephaly spike with the Zika outbreak.

Dobyns said he hopes to get dozens more scans in the next few weeks, but while he waits, Zika marches north. The World Health Organization declared the outbreak a global health emergency in early February as it began “explosively” spreading through the Americas and Europe. Today, 39 countries have reported cases of Zika, with 52 travel-associated cases confirmed in the U.S.

While pregnant women in the U.S. are not in immediate danger, Dobyns gives urgency to the need for studies that can quickly nail down the cause of these severe birth defects—whether Zika or not.

“It’s coming,” Dobyns says of Zika outbreak. “The preponderance of evidence suggests it’s real and it’s a significant risk, so do you sit on your butt or do you do something? You do something.”