South Korea issued a nationwide warning for the Japanese encephalitis virus Thursday, advising the public to pay attention to personal hygiene and get vaccinated if necessary.

The Korea Centers for Disease Control and Prevention issued the warning after the massive presence of mosquitoes capable of carrying the virus was confirmed in the southeastern port city of Busan between Tuesday and Wednesday.

The agency issued an advisory for the virus on March 26.

Most Japanese encephalitis virus infections result in a mild fever and headache or have no apparent symptoms, but approximately 1 in 250 infections results in severe clinical illness, according to the World Health Organization.

A severe form of the disease is characterized by the rapid onset of a high fever, headaches, neck stiffness, disorientation, coma, seizures, spastic paralysis and, in severe cases, death.

The case fatality rate can be as high as 30 percent among those with symptoms of the disease, according to the WHO.

Last year, six people died of the illness in South Korea, according to health authorities. (Yonhap)