The Zika virus , already linked to brain damage in babies, can also cause a serious brain infection in  adult victims, French researchers warned Thursday. The Zika virus was found in the spinal fluid of an 81-year-old man who was admitted in January to a hospital near Paris shortly after returning from a month-long cruise. The man - semi-comatose, with a high fever and partial paralysis — was diagnosed with meningoencephalitis, an inflammation of the brain and its membrane, the team wrote in New England Journal of Medicine. “It is the first case of its kind to be reported, to our knowledge,” Guillaume Carteaux, co-author of the paper and specialist at the hospital which treated him, told AFP. The mere presence of the virus does not prove it is what caused the disease. But Carteaux said that “other infectious causes, either viral or bacterial, have been ruled out” in this case. The patient, who was reported to have been in good health during his cruise around New Caledonia, Vanuato, the Solomon Islands and New Zealand, has since partially recovered. “Clinicians should be aware that (Zika virus) may be associated with meningoencephalitis,” the team wrote. On Wednesday, a different French team linked the virus sweeping Latin America and the Caribbean to paralysis-causing myelitis. They reported that a 15-year-old girl diagnosed on the French Caribbean island of Guadeloupe with acute myelitis in January had high levels of Zika in her cerebrospinal fluid, blood and urine.

Myelitis is an inflammation of the spinal cord. It can affect limb movement and cause paralysis by interrupting communication between the spinal cord and the rest of the body. The mosquito-borne Zika virus usually causes mild symptoms in adults, with a low fever, headaches and joint pain.

Its quick spread has caused alarm due to an observed association with microcephaly, which deforms the brains of unborn babies, and Guillain-Barre, a rare condition in which the body’s immune system attacks a part of the nervous system that controls muscle strength. Brazil has been hardest hit by the Zika outbreak, with some 1.5 million people infected and 745 confirmed cases of microcephaly in children born to women infected with the virus while pregnant.

Two US soldiers serving in South America contracted Zika but have fully recovered and returned to duty, while a third, pregnant service member left the region early for fear of contracting the virus, a top U.S. commander said on Thursday.

Zika infections have been linked to thousands of birth defects as the mosquito-borne virus spreads rapidly in Brazil and other countries in Latin America and the Caribbean. Two US servicemembers stationed in Brazil and Colombia, both men, were confirmed to have contracted Zika, said Navy Admiral Kurt Tidd, commander of U.S. Southern Command.

“Both cases were confirmed. The cases have (been) resolved,” Tidd said in a news briefing. “They both returned to duty.” A third, pregnant servicemember in the region sped up her scheduled return to the United States as a result of the Zika scare, Tidd said. The US military has discussed mosquito eradication with partner militaries in the region and has provided small amounts of supplies, including mosquito netting, Tidd said.

Much remains unknown about Zika, including whether the virus actually causes microcephaly in babies, a condition defined by unusually small heads that can result in developmental problems. On March 9, Brazil said confirmed microcephaly cases rose to 745 and considers most of them to be related to Zika infections in the mothers. Brazil is investigating an additional 4,231 suspected cases of microcephaly. Traces of Zika virus have been found in the bodily fluids and tissue of mothers and babies affected by microcephaly.