A man in Arizona who recently became infected with the West Nile virus is now paralyzed from the waist down, CBS Los Angeles reported.

Infections with the mosquito-borne West Nile virus have been known to lead to neurological problems, including paralysis, though these results are rare.

According to the Centers for Disease Control and Prevention (CDC), less than 1 percent of people who are infected with West Nile develop neurological symptoms. These cases are called "neuroinvasive" cases of infection. [5 Things You Need to Know About West Nile Virus]

Indeed, these cases are extremely rare, said Dr. Amesh Adalja, an infectious-disease specialist and a senior associate at the University of Pittsburgh Medical Center's Center for Health Security. Adalja was not involved in the Arizona man's case.

In fact, the majority of people who get West Nile virus have no symptoms at all, Adalja told Live Science. Only about 20 percent of people develop what's known as West Nile fever, which is a flu-like illness, he said.

Neurological symptoms occur when the virus crosses the blood-brain barrier, a defense system in the body that keeps many germs in the bloodstream from entering the brain, Adalja said. Once across the barrier, the virus can infect cells of the brain and nervous system, he said. Some cells may become inflamed and others may die, he said.

Only certain viruses, including the polio, rabies and Zika viruses, have the capacity to cross into the brain, he added.

People with neuroinvasive West Nile virus can develop conditions such as encephalitis (inflammation of the brain) or meningitis (inflammation of the tissue surrounding the brain), Adalja said. Symptoms can include headaches, fever, neck stiffness, disorientation, coma, tremors, seizures and paralysis, according to the CDC. About 10 percent of patients who develop a neuroinvasive infection from West Nile die, the CDC said.

There are currently no treatments or vaccines for the West Nile virus. Once a person becomes paralyzed from the virus, it's unlikely that he or she will get better in the long term, Adalja said.

Originally published on Live Science.