The health ministry will begin comprehensive research on West Nile fever, which experts believe could enter Japan from the United States or Siberia at any time, officials said Tuesday.

The ministry will work to develop a vaccine and a way to detect the disease faster, build a database on West Nile fever viruses found elsewhere in the world, and conduct other related research, the officials said.

West Nile fever, whose virus is transmitted via mosquitoes, has in recent years been observed in the United States every summer and killed about 100 of at least 2,500 people stricken with the disease there last year. The disease has also been found in Siberia in recent years, which means migrating birds could carry the virus to Japan, according to the officials.

The ministry plans to continue the research for three years, as it thinks the virus could enter Japan at any time and it needs to be prepared as soon as possible, they said.

The ministry said it wants to come up with faster and more accurate examination methods, because it took about three weeks last year to examine a Japanese woman from Okinawa to conclude she did not have the virus, after she had returned from the U.S.

Also, the examining method Japan currently employs was developed using the virus found in the U.S., and it is unknown if the method works in cases involving viruses originating in Africa or Europe, or a genetically mutated virus found more recently in the U.S., the officials said.

The Institute of Tropical Medicine at Nagasaki University and other medical institutions are developing vaccines for the disease, but they have yet to be tested on people.