Scientists have confirmed that the Zika virus, which has infected upwards of one million people in Latin America, can severely damage the brains of unborn children. Now a new study suggests the virus may also trigger brain infections in adults that can cause the brain and spinal cord to swell, causing intense damage to the nervous system.

A study published in the medical journal The Lancet argues that new research indicates a link between the contracting of the Zika virus and an infection known as myelitis, which causes inflammation in the spinal cord. Targeting such a central part of the nervous system often leads to patients experiencing difficulty moving and paralysis.

While the news that Zika can cause other related infections is not new, the link between the virus and infections that can cause severe neurological problems has yet to be conclusively proven. This study, based on a case in Guadeloupe island in the Caribbean, is the first to stake such a claim. It notes that a patient on the island, a 15-year-old girl, was diagnosed with myelitis and later found to be carrying high amounts of Zika virus in her blood.

Dr. Bruce Aylward of the World Health Organization has called the study “the strongest evidence so far that this may be a causal relationship,” and has called for more research on this front. While it is being called “the first published case to offer proof of a link” between Zika and neurological disorders, it is not conclusive, and scientists hope to expand on the study by researching the effects of Zika on other patients.

Other cases linking Zika and paralysis may offer more evidence that the virus specifically targets the human nervous system. The Agence-France Presse cites a case of an octogenarian Zika patient in France, who had contracted the virus while traveling on a tropical cruise. The man was ultimately diagnosed with a similar inflammatory infection: meningoencephalitis, which causes the brain to swell. Doctors found no evidence that any other health complications separate from the Zika infection had caused the inflammation. It is also the first such case, however, leading doctors to call for more research on this front.

In most patients – a full 80 percent – contracting the Zika virus does not trigger any symptoms, and most carry the virus without knowing it. In the majority of the 20 percent who do experience symptoms, it causes milder variants of symptoms typical of dengue fever: rashes, fever, joint pain, and conjunctivitis.

The outbreak of Zika virus in Latin America has caused panic because doctors in Brazil discovered a causal connection between Zika living in the bloodstream of pregnant women and unborn children developing severe neurological disorders. The number of cases of microcephaly, a condition in which children develop a skull too small to hold their brains, has skyrocketed in Brazil, where 1.5 million people have been confirmed to carry the virus.

In addition to microcephaly fears, there is growing evidence that Zika may cause Guillain-Barré syndrome, a condition causing intense joint pain, paralysis, and death. At least eleven Zika patients have died following a diagnosis of Guillain-Barré in Venezuela, where hospitals and pharmacies are facing severe shortages of medication. Guillain-Barré is typically treated with injections of either immunoglobulin or albumin, neither of them commercially available in most Venezuelan pharmacies.

The growing body of study suggesting Zika may trigger more significant nervous system damage may also shed light on the death of Bruno Rodrigues de Almeida, a Brazilian law professor who died after being diagnosed with Zika. Doctors announced that his death was the product of Zika “complications,” but never elaborated on what occurred following his infection.

Zika is spread through mosquito bites from the Aedes aegypti species, common throughout the Western Hemisphere. Recently, scientists have found that the virus can also be sexually transmitted. “Reports and investigations in several countries strongly suggest that sexual transmission of the virus is more common than previously assumed,” WHO Director-General Margaret Chan said this week.

The United States has registered dozens of cases of Zika, though more are expected as the winter months end and the weather turns more favorable for mosquito reproduction. The U.S. Centers for Disease Control have expressed particular concern for Puerto Rico, which has already seen a rise in the number of cases of Zika. “Puerto Rico is on the front lines of the battle against Zika and it is an uphill battle,” CDC director Tom Frieden told reporters this week, adding that he was “very concerned” that the number of Zika cases in the island territory could reach “hundreds of thousands.”